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| 2000 Part 2 |
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Front Cover (2000 - Part
2)
No author information
available
Summary: Not
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Table
of Contents (2000 - Part 2)
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author information available
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Superconductivity,
an enabling technology for 21st century power
systems?
W.V.
Hassenzahl
Summary: Several technologies
based on superconductivity are moving to practical use on
electric power systems. The next decade will see operational
prototypes of superconducting cables, transformers, SMES, and
motors installed on electric utilities in sizes that are
appropriate for power distribution applications. Will these
installations lead to a change in the power system of the
future? Will that power system (or parts of it) look different
from what we see today? Two independent and very different
issues will determine the answers to these questions. The
first is the future demand for electric power, both locally
and worldwide. The second is the progress in superconducting
materials and the subsequent development of the applications
mentioned above. Several very different scenarios have been
proposed for the growth and evolution of electric power in the
21/sup st/ century. These scenarios will be described briefly
and their implication for superconductivity will be discussed.
Finally, the author predicts the likely penetration of
superconducting technologies into electric power
systems. |
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Analysis
of the behaviour of superconducting windings with
short-circuited turns
V.E. Keilin
and L.B. Lugansky
Summary: Though it is
widely known that short-circuited turns can considerably spoil
the performance of superconducting windings, this problem (to
our knowledge) was not properly discussed in the literature.
We performed an analysis of the consequences of the presence
of shorted turns inside superconducting windings. The main
conclusions are as follows: such windings can undergo
premature quenches during their charging, therefore the
acceptable charging rates should be very low; such windings
can also quench during their planned discharge; and a
considerable amount of the stored magnetic energy cannot be
effectively evacuated out of a short-circuited winding in the
case of its quench. |
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Study
on designing high current density rotor windings of
superconducting generator and relation of the stabilities in
static and rotating conditions
M.
Furuse, O. Tsukamoto, S. Torii, S. Akita and M.
Shibuya
Summary: It is critically important
to realize high current density superconducting rotor windings
to make the superconducting generator economically competitive
to a conventional one. High current density rotor windings
inevitably suffer from instability problems. Therefore, the
rotor windings should be designed for the quench currents to
surely exceed the maximum operational currents in the rotating
condition. In the next step of the Super-GM project, the
current density required is 30% higher than that of the rotor
winding developed in the former Super-GM project. To test the
stability of the rotor windings, usually quench tests are
conducted in a static and pool-cooled condition for the
simplicity of the test but presently the relation between the
stabilities in the static and rotating conditions is not
clear. In the paper, we study what information can be obtained
and how the stability in the rotating condition can be
estimated from the static test. Based on this study, we
investigate a method to design quench currents of high current
density rotor windings to exceed a required value and discuss
what level for the quench current to exceed in the static
condition to satisfy the requirement in the rotating
condition. |
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Monte
Carlo calculation of strand position in CIC conductor to
analyze mechanical loss
S.
Nishijima, T. Sasaki, K. Takahata and T.
Satow
Summary: Strand position in a
cable-in-conduit (CIC) conductor has been calculated by means
of Monte Carlo method in order to analyze the stability of the
CIC conductor which was employed in the Large Helical Device.
The calculated data were compared with the experimental
results. It is found that the strands move due to the
electromagnetic force and do not return to the original
position even when the current becomes zero. The pressure drop
changes with the number of excitation time. The mechanical
loss originated from the frictional motion between strands is
induced during the charging-discharging process. The contact
stress between strands changes with the transport current and
the number of excitation time. |
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Relation
between impedance distribution and current imbalance in an
insulated multi-strand superconducting cable
conductor
A. Ninomiya, T.
Ishigohka, S. Yamaguchi, K. Nakamura, T. Sato, S. Hanai, Y.
Hasegawa, H. Okumura, S. Takayama and R.
Shimada
Summary: We have been investigating
the current imbalance problem comparing the calculated result
obtained by the measurement of inductance distribution in
multi-strand superconducting cable conductor using high
accuracy LCR meter and the measured actual current
distribution in it. So far, the measurement of inductance and
that of actual current had been carried out at 1 kHz and at
few Hz, respectively. As a result, the experimental result did
not agree well with the calculated one. It was estimated that
the discrepancy between both results was due to the error in
the inductance measurement. So, this time, we have carried out
inductance measurement more precisely at 100 Hz, and, we have
also measured actual current at wider frequency range. From
these results, it is concluded that the current distribution
is very sensitive to the inductance distribution.
Particularly, in multi-stranded conductors with higher
magnetic coupling among the strands, such as a large scale and
multi twisted cable conductor, the current distribution shows
a very dynamic change with the frequency. |
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Analysis
of wire motion in a superconducting magnet by Monte Carlo
method
H. Ogata and S.
Nishijima
Summary: The wire motion in a
superconducting magnet has been analyzed by means of Monte
Carlo and finite element method (FEM). A sufficient analysis
about the instability originated from wire motion has not been
made because the wire motion is not clarified in the irregular
area in the coil. The study of the wire motion has been made
in the irregular area such as "step up" or "cross over"
position where a wire steps up at the flanges or crosses over
the wires of the lower layer. Using FEM, the stress in the
coil was calculated and the boundary conditions of the
irregular area were determined. In the area using Monte Carlo
method, the wire motion was analyzed. It was clarified that in
the irregular area the wire motion is easily generated. The
frictional heating of the magnet is discussed in connection to
the mechanical behavior of a coil. |
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Wire
dynamics simulation of impregnated superconducting
magnet
S. Ohira and S.
Nishijima
Summary: The wire dynamics
simulation has been performed to evaluate the stability of the
impregnated superconducting magnet. The relationship between
quench current and the impregnating material failure in the
magnet was studied. In the impregnated superconducting magnet
it is considered that the heating is induced by the cracking
of the impregnating material or by the friction between wires
or wires and bobbin after the cracking. The wire dynamics
simulation can clarify the behavior of a superconducting coil
by solving the equation of motion for each wire. It was found
that just after the impregnating material failure the heating
is induced in the place where the cracking of the impregnating
material was introduced and resulted in quench. The result
suggests that the impregnating material failure is closely
related to the stability of superconducting
magnet. |
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Comparison
of solenoidal and pancake model windings for a superconducting
transformer
M. Polak, P. Usak, J.
Pitel, L. Jansak, Z. Timoransky, F. Zizek and H.
Piel
Summary: We prepared 2 model windings
from multifilamentary Bi-2223/Ag tape for a small experimental
transformer and studied their electromagnetic behavior. The
first winding was a solenoid consisting from 4 helically wound
layers, the second one consisted of 3 double pancake coils.
The outer dimensions of both types of windings were identical.
We calculated the magnetic field in the space occupied by the
winding and in its vicinity neglecting the magnetic properties
of the tape. To study the influence of winding magnetization
on the magnetic field distribution we measured the field in
the vicinity of the coil and compared it with the calculated
one. The relation between the electric field and the transport
current in the turns of the windings was measured using
several potential taps. By comparing these results with those
obtained on short samples we find a way to estimate the
critical current of a tape in the inhomogeneous magnetic
field. AC loss of the coils was also measured and compared.
Recommendations for improvements of the coil performance are
presented. |
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AC
loss properties of a 1 MVA single-phase HTS power
transformer
M. Iwakuma, K.
Funaki, K. Kajikawa, H. Tanaka, T. Bohno, A. Tomioka, H.
Yamada, S. Nose, M. Konno, Y. Yagi, H. Maruyama, T. Ogata, S.
Yoshida, K. Ohashi, K. Tsutsumi and K.
Honda
Summary: We designed and built a
single-phase 1 MVA-22/6.9 kV HTS transformer with the
multi-layered cylindrical windings composed of Bi2223 parallel
conductors. In advance of the design, the AC loss induced in
the windings was estimated on the basis of the observed
results in a strand. A subcooled liquid nitrogen cryogenic
system with the corresponding cooling capacity was developed
and attached to the transformer. The actual AC loss was
measured by an electrical method. It was a great part of the
total heat load and dominated the temperature rise of
subcooled liquid nitrogen. We discussed the validity of the
present estimation procedure of the AC loss in the windings as
compared with the observed results. |
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Test
and characteristic analysis of an HTS power
transformer
Hee Joon Lee, Gueesoo
Cha, Ji-Kwang Lee, Kyeong Dal Choi, Kyung Woo Ryu and Song Yop
Hahn
Summary: This paper describes the
construction and test results of a 10 kVA single phase HTS
transformer. Double pancake windings with BSCCO-2223 HTS tape
and GFRP cryostat with room temperature bore are used in the
transformer. Two double pancake windings are connected in
series to provide 94/spl times/2 turns and two double pancake
windings are connected in parallel to conduct the secondary
current of 45.4 A. Coefficients of the constructed transformer
are obtained using fundamental tests of the transformer.
According to the test results, a slightly larger leakage
reactance than expected is observed due to the bulky core
which surrounded the cryostat. |
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Magnetic
field and electromagnetic force analysis of 3-phase air-core
superconducting power
transformer
H. Yamaguchi, T.
Kataoka, H. Matsuoka, T. Mouri, S. Nishikata and Y.
Sato
Summary: The superconducting windings of
the air-core superconducting power transformer have
possibilities of being exposed to a higher magnetic field than
those of the iron-core transformer because of no special paths
for magnetic flux. Thus, in this paper, the magnetic field and
electromagnetic force acting on the windings of an
experimental 3-phase air-core superconducting transformer are
analyzed. From the results, it has become clear that the
superconducting windings of the air-core transformer are
exposed to a 3-dimensional magnetic field containing a
rotational component. |
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The
superconducting transformer of the Samsung Superconductor Test
Facility (SSTF)
Sungkeun Baang,
Hyunjung Choi, Keeman Kim, Sangbo Kim, Yongjin Kim, Hyunki
Park, Qiuliang Wang, A.I. Boev, D.P. Ivanov, V.E. Keilin, I.A.
Kovalev, S.L. Kruglov, V.V. Lysenko, I.O. Shchegolev, V.I.
Shcherbakov, I.O. Shugaev and M.I. Surin
Summary:
In the frames of designing the SSTF (Samsung
Superconductor Test Facility) for the KSTAR (Korea
Superconducting Tokamak Advanced Research), the 50 kA
transformer charging a CICC (cable-in-conduit conductor) short
sample for one second is now under design. The primary winding
conductor consists of six NbTi and six stainless steel strands
tabled around a low RRR rectangular copper core, which was
used by Kurchatov Institute in small SMES (superconducting
magnetic energy storage) windings. The secondary winding
consists of 24 subcables wrapped around and soldered to a low
RRR copper strip. Each subcable consists of six NbTi strands
cabled around a copper strand. The strands for primary and
secondary windings are 0.85 mm diameter NbTi wires with six
micrometer 8910 filaments. Both primary and secondary
conductors have large current and temperature margins to
ensure a reliable operation of the superconducting
transformer. The primary coil is placed in a cylindrical LHe
vessel. The four secondary turns are glued to the outer
surface of the LHe vessel. The joints between the transformer
and the sample are described. |
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Considerations
about HTS superconducting
transformers
G. Donnier-Valentin,
P. Tixador and E. Vinot
Summary: A
superconducting transformer brings savings in weight, loss and
to a lesser degree, in volume. A transformer uses a magnetic
circuit in order to decrease the no-load current. The magnetic
circuit can operate either at the same temperature than the
superconducting windings or at room temperature. In the first
case the cryostat is simple and can be metallic but the iron
losses must be multiplied by the refrigeration system
coefficient of performance (about 30 W/W at 77 K). With a
magnetic circuit at 300 K, there is no multiplying coefficient
for the iron losses but the cryostat is more complicated and
requires electrical isolating materials which are problematic
in cryogenics. We have reviewed several magnetic materials and
measured their iron losses at 77 K and compared the latter to
the one obtained at 300 K. Scratched Fe-Si steel show
reasonable iron losses and could be used in a cold iron HTS
transformers. Amorphous materials offer good opportunities.
Transformers with a rating of 30 MVA were designed. With PIT
(powder in tube) conductors the AC losses are relatively high
and a cold magnetic circuit can be considered. However with Y
coated conductors a cold magnetic circuit penalises the
transformer efficiency a lot. |
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Magnet
and cryostat configurations for a multi-port quadrupole
array
M.A. Green and R.O.
Bangerter
Summary: This report describes the
results of a study of arrays of up to sixteen quadrupoles in a
single cryostat surrounded by an induction accelerator that is
used for accelerating high current heavy ion beams for fusion.
Each quadrupole in the array can have a gradient of 72 T/m,
when the quadrupole has a warm bore diameter of 90 mm. An
array of sixteen quadrupoles can be made to fit into a round
cryostat vacuum vessel with a diameter of 850 mm. If the
number of quadrupoles in the array is reduced to nine, the
outer diameter of the cryostat is 700 mm. It is proposed that
the quadrupole array be conduction cooled using either a 4 K
cryocooler or two phase liquid helium in pipes around the
magnet array. The two-phase helium can be supplied to a string
of multi-bore quadrupoles using a large
refrigerator. |
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Focusing
magnets for HIF based on
racetracks
N.N. Martovetsky and
R.R. Manahan
Summary: Heavy ion fusion (HIF)
is considered a promising path to a practical fusion reactor.
A driver for a HIF reactor will require a large number of
quadrupole arrays to focus heavy ion beams. A conceptual
design, and trade off studies of the quadrupole array based on
racetracks are presented. A comparison with a conventional
shell magnet is given and advantages and disadvantages are
discussed. A more detailed design of a single quadrupole for
the High Current Experiment (HCX) is presented and
discussed. |
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Superconducting
bending magnet for superconducting ring
cyclotron
H. Okuno, S. Fujishima,
T. Tominaka, T. Kawaguchi, K. Ikegami, J. Ohnishi, M. Okamura,
X. Jieping, B. Ikeda, K. Kuno, A. Goto and Y.
Yano
Summary: A K2500 superconducting ring
cyclotron with 6-sectors is being constructed at RIKEN as an
energy booster of the existing K540 ring cyclotron. The
bending magnet for beam injection should be superconducting.
Required fields are about 4 T and curvature of the coils is
about 1.2 m. We developed test cells for the bending magnet.
The results are very promising for the real bending magnet. In
the paper the results of the test cells and the design of the
real bending magnets are described. |
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Superconducting
magnetic system of the fast cycling intermediate energy ion
synchrotron
N.N. Agapov, H.G.
Khodzhibagiyan, A.D. Kovalenko, V.A. Mikhailov, A.A. Smirnov
and A.Yu. Starikov
Summary: A superconducting
magnetic system for the 250 to 500 MeV/Amu booster synchrotron
of the Nuclotron is discussed. The repetition rate of the
booster is 1 Hz and the circumference 84 m. There are 32
dipole and 24 quadrupole magnets with a "cold" iron yoke and a
hollow superconductor winding (NbTi) in the accelerator ring.
Basic parameters of the magnets, superconducting cable
construction, cryogenic system and cryomagnetic assembly
design are presented. |
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HERA
luminosity upgrade superconducting magnet production at
BNL
B. Parker, M. Anerella, J.
Escallier, A. Ghosh, A. Jain, A. Marone, J. Muratore, A.
Prodell, P. Thompson, P. Wanderer and K.C.
Wu
Summary: The production of two types of
superconducting multi-function magnets, needed for the HERA
Luminosity Upgrade is underway at BNL. Coil winding is now
completed and cryostat assembly is in progress. Magnet type GO
and type GG cold masses have been satisfactorily cold tested
in vertical dewars and the first fully assembled GO magnet
system has been horizontally cold tested and shipped to DESY.
Warm measurements confirm that the coils meet challenging
harmonic content targets. In this paper, the authors discuss
GO and GG magnet design and construction solutions, field
harmonic measurements and quench test results. |
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Cost
scaling analysis of large warm-bore superconducting
quadrupoles
J.A. Waynert, J.
Schultz, R.J. Thome, L. Myatt, F.M. Kimball and R.W.
Baldi
Summary: This paper presents an
approach to estimating the cost of large warm-bore
superconducting quadrupoles that are frequently used in
magnetic imaging systems in accelerators. Quadrupole magnet
radial apertures greater than about 10 cm and gradients
exceeding 10 T/m are considered. A relationship is established
so that the cost estimate may be scaled with the gradient,
aperture, and length of the magnet. |
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Experimental
verification of the temperature and strain dependence of the
critical properties in Nb/sub 3/Sn
wires
A. Godeke, H.J.G.
Krooshoop, H.G. Knoopers, B. ten Haken and H.H.J. Ten
Kate
Summary: The critical current density in
Nb/sub 3/Sn conductors is described with an improved scaling
formula for the temperature, magnetic field and strain
dependence. In an earlier study, it is concluded that the
largest uncertainties in this description arise from the
temperature dependence that is described with various slightly
different empirical relations. For the optimization of the
numerical codes, used to predict the stability of large magnet
systems, a more accurate description is required. Therefore,
two different bronze processed conductors for the ITER CS
model coil are analyzed in detail. The critical current is
measured at temperatures from 4.2 K up to the critical
temperature, in magnetic fields from 1 T to 13 T and with an
applied axial strain from -0.6% to +0.4%. The axial strain is
applied by a U-shaped bending spring and a comparison is made
between brass and Ti-6Al-4V, as substrate
material. |
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Validation
of the CEA electrical network model for the ITER
coils
D. Ciazynski and J.-L.
Duchateau
Summary: Within the framework of
the studies for the superconducting magnets of the
International Tokamak Experimental Reactor (ITER) project, the
authors have developed an electrical network model for
simulating the behavior of a full conductor length (including
the joints) under DC operation. The analysis of the tests of
three different European full-size (conductor and joint)
samples gave them the opportunity to improve and validate
their model. The adjustment of the free parameters used in the
model to fit the experimental voltage/current characteristics
led us to the effective values of the strain in the Nb/sub
3/Sn filaments. They have found that the two steel jacketed
conductors showed lower strain than expected, while the
Incoloy jacketed conductor showed higher strain than expected,
although remaining lower than the steel conductors. Similar
results have been found on the joints of these
samples. |
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Eddy
current and thermal analysis of the TF model coil during
safety discharges
P. Hertout,
J.L. Duchateau and A. Martinez
Summary: The
Toroidal Field Model Coil (TFMC) has been manufactured by
European industry since 1997 in the frame of the International
Thermonuclear Experimental Reactor (ITER) project. It is
representative of the toroidal field system of a large
tokamak. About 800 m of Nb/sub 3/Sn cable-in-conduit has been
used to build this coil which will be tested at Karlsruhe
(Germany) in the TOSKA test stand facility. The TFMC can
achieve magnetic field values between 7.8 T alone and 9 T with
the adjacent LCT coil of TOSKA. The 10 pancakes of the TFMC
are inserted between stainless steel radial plates, and the
whole winding-park is enclosed in a thick stainless steel
case. These passive conductive structures are expected to
experience severe eddy currents during the last testing phase
of the TFMC, when triggering rapid discharges to study the
electromagnetic and thermohydraulic transient behavior of the
coil. Using a finite element code, CORFOU, the safety
rapid-discharge from current levels up to 80 kA in the 98
turns (time constant 4 s), and another even faster discharge
(time constant 58 ms), aimed at loading the coil to 10 kV, are
modeled. The eddy currents induced in the passive structures
are computed with the thin shell approach and validated with a
simple analytical model. The Joule power, the total Joule
heating and the temperature increase in the radial plates are
deduced. The thermal analysis is carried out with a 1D model
(finite difference method): the heat propagation through
insulation to the cable and to the helium is studied. The
possibility of a quench of the whole magnet is
discussed. |
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Current
distribution and strain influence on the electromagnetic
performance of the CS Insert
V.
Galindo, D. Ciazynski, J.L. Duchateau, G. Nishijima, N.
Koizumi, Y. Takahashi and T. Ando
Summary:
The Central Solenoid Model Coil (CSMC) is a solenoid
consisting of 18 concentric layers, wound with Nb/sub 3/Sn
cable-in-conduit conductor, jacketed with Incoloy. The
Japanese HT and USHT were in charge of the manufacturing, and
the coil is being tested at JAERI, Naka (Japan). The European
Home Team is involved in the testing program, which includes
electromagnetic characteristics of the CSMC, and of the CS
Insert. Two effects influence strongly the electromagnetic
properties: (i) connections introduce a nonuniform current
distribution among the strands, and (ii) the performance of
the strands are dependent on the strain of the Nb/sub 3/Sn
filaments. The current distribution calculated in the CS
Insert takes into account magnetic field and strain applied on
the conductor, the joint effect and the current transfer
between strands. The model developed at CEA, uses an
equivalent electric network composed of resistive joints,
superconducting lengths and interstrand resistances and
provides the voltage-current characteristics, which ran be
directly compared to the experimental results. |
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Stability
in a long length NbTi CICC
L.
Bottura, M. Ciotti, P. Gislon, M. Spadoni, P. Bellucci, L.
Muzzi, S. Turtu, A. Catitti, S. Chiarelli, A. della Corte and
E. Di Ferdinando
Summary: A crucial issue for
a superconducting coil in order to be safely used in the
magnetic system of a fusion reactor is stability against all
foreseen disturbances. To simulate the fusion machine
conditions, including off-normal events, e.g. plasma
disruptions, the energy deposition has to be spread over a
"long length" cable in conduit conductor (CICC) and a
background magnetic field is needed. We have therefore
designed and built an experiment consisting of an instrumented
NbTi test module inserted in a pair of co-axial pulsed copper
coils. A 0.6 m diameter superconducting coil provides a
background magnetic field up to 3 T. Calibration of the energy
inductively coupled between the pulsed coils and the module
has been obtained measuring the system temperature increase
just after the pulse by means of thermometers positioned along
the conductor. Stability vs. operating current I/sub op/ has
been examined for different helium temperatures and different
background magnetic fields. The finite element code Gandalf
for the stability and quenching transients analysis in forced
flow cooled superconducting coils has been run to check the
matching with the experimental results. |
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AC
loss measurement of 46 kA-13T Nb/sub 3/Sn conductor for
ITER
Y. Takahashi, K. Matsui, K.
Nishii, N. Koizumi, Y. Nunoya, T. Isono, T. Ando, H. Tsuji, S.
Murase and S. Shimamoto
Summary: AC losses of
Nb/sub 3/Sn conductor samples with various void fractions for
the ITER Central Solenoid Model Coil (CSMC) were measured by
using calorimetric and magnetization techniques. The CSMC is
designed to generate the magnetic field of 13 T at the
operating current of 46 kA. The conductor consists of the
multi-stage cable, having 1152 Nb/sub 3/Sn strands, and
Incoloy 908 square jacket with circular hole. The strands are
coated by chrome plating with 2 /spl mu/m layer. The last
sub-cables are wrapped with Inconel tape, having high electric
resistivity, to reduce the coupling current loss. The optimum
void fraction for pulse coils is obtained from the relation
between the coupling time constant and the void fraction. It
is indicated that the sub-cable wrapping is very effective in
limiting the coupling current between the sub-cables, as
expected. The AC losses of the CS Insert were measured in
various operating modes. From these obtained results, the
validity of conductor design is demonstrated. |
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Conductors
of the ITER magnets
D. Bessette,
N. Mitchell, E. Zapretilina and H. Takigami
Summary:
Nb/sub 3/Sn and NbTi cable in conduit conductors
(CICCs) cooled by a supercritical helium forced flow are
considered in the ITER magnets. The design of the various
CICCs relies on consideration of cost and manufacture as well
as on the R&D performed on conductors for the ITER Model
Coils. The amount of superconducting strand is optimized to
satisfy operational requirements such as a minimum temperature
margin, a heat power balance for stability (Stekly parameter),
and a maximum hot spot temperature in case of quench. The
conductor design and the main results of the conductor
thermohydraulic analysis are discussed including consideration
of nonuniform current distribution among superconducting
strands. |
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Performance
of the LHC final design full scale superconducting dipole
prototypes
L. Bottura, P. Pugnat,
A. Siemko, J. Vlogaert and C. Wyss
Summary:
Within the LHC magnet program, a series of six, final
design, full-scale superconducting dipole prototypes are
presently being built in industry and tested at CERN. The main
features of these magnets are: two-in-one structure, 56 mm
aperture, six-block two layer coils wound from 15.1 mm wide
graded NbTi cables, and all-polyimide insulation. This paper
reviews the main test results of magnets tested at 4.2 K and
1.8 K. The results of the quench training, conductor
performance, magnet protection, sensitivity to ramp rate and
field quality are presented and discussed in terms of the
design parameters and the aims of the full scale dipole
prototype program. |
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Status
of the LHC inner triplet quadrupole program at
Fermilab
N. Andreev, T. Arkan, P.
Bauer, R. Bossert, J. Brandt, J. Carson, S. Caspi, D.R.
Chichili, L. Chiesa, C. Darve, J. DiMarco, S. Feher, A. Ghosh,
H. Glass, Y. Huang, J. Kerby, M. Lamm, A.A. Markarov, A.D.
McInturff, T. Nicol, A. Nobrega, I. Novitski, T. Ogitsu, D.
Orris, J.P. Ozelis, T. Page, T. Peterson, R. Rabehl, W.
Robotham, G. Sabbi, R. Scanlan, P. Schlabach, C. Sylvester, J.
Strait, M. Tartaglia, J.C. Tompkins, G. Velev, S. Yadav and
A.V. Zlobin
Summary: Fermilab, in
collaboration with LBNL and BNL, is developing a quadrupole
for installation in the interaction region inner triplets of
the LHC. This magnet is required to have an operating gradient
of 215 T/m across a 70 mm coil bore, and operates in
superfluid helium at 1.9 K. A 2 m magnet program addressing
mechanical, magnetic, quench protection, and thermal issues
associated with the design was completed earlier this year,
and production of the first full length, cryostatted prototype
magnet is underway. This paper summarizes the conclusions of
the 2 m program, and the design and status of the first
full-length prototype magnet. |
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Progress
of LHC low-/spl beta/ quadrupole magnets at
KEK
T. Shintomi, Y. Ajima, E.E.
Burkhardt, T. Haruyama, N. Higashi, M. Iida, N. Kimura, S.
Murai, T. Nakamoto, T. Ogitsu, H. Ohhata, N. Ohuchi, A.
Orikasa, O. Osaki, R.J.M.Y. Ruber, K. Sugita, K. Tanaka, A.
Terashima, K. Tsuchiya, A. Yamamoto and H.
Yamaoka
Summary: Development of the LHC
low-/spl beta/ insertion quadrupole magnet has been in
progress at KEK since 1995 as a cooperative program between
CERN and KEK. Five 1-m short model magnets have been
fabricated and three of them have been tested. From the
various test results of the first two models, the coil
configuration was further optimized to reduce the higher
magnetic field harmonic coefficients. The cold test of the
third model showed satisfactory performances of the field
harmonics. After this R&D work, the authors are at a stage
for the fabrication of two prototype magnets which have the
same scale as the production magnets. The status of the
R&D for the LHC low-beta insertion quadrupole magnet at
KEK is described. |
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Field
quality in Fermilab-built models of quadrupole magnets for the
LHC interaction region
N.
Andreev, T. Arkan, P. Bauer, R. Bossert, J. Brandt, S. Caspi,
D.R. Chichili, J. Carson, J. DiMarco, S. Feher, A. Ghosh, H.
Glass, V.V. Kashikhin, J. Kerby, M.J. Lamm, A.D. McInturff,
A.A. Makarov, A. Nobrega, I. Novitski, T. Ogitsu, D. Orris,
J.P. Ozelis, T. Peterson, R. Rabehl, W. Robotham, G. Sabbi, R.
Scanlan, P. Schlabach, C. Sylvester, J. Strait, M. Tartaglia,
J.C. Tompkins, G. Velev, S. Yadav and A.V.
Zlobin
Summary: Superconducting quadrupole
magnets for the interaction regions of the Large Hadron
Collider are being developed by the US-LHC Accelerator
Project. These 70 mm bore quadrupole magnets are intended to
operate in superfluid helium at 1.9 K with a nominal field
gradient of 215 T/m. A series of 2 m model magnets has been
built and cold tested at Fermilab to optimize their design and
construction and to study the performance of the magnets.
Field measurements of the 8 model magnets and comparisons with
the required field quality are reported in this
paper. |
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Construction
and test of a 1 MVA-class BSCCO resonator
coil
A. Godeke, O.A. Shevchenko,
J.J. Rabbers, B. ten Haken, C.J.G. Spoorenberg, P. Klein
Schiphorst, G.C. Damstra and H.H.J. Ten
Kate
Summary: A high quality factor,
superconducting resonator coil is developed in cooperation
with the Dutch companies SMIT Transformers and SMIT DRAAD. The
coil system is manufactured in industry, using industrial
tooling. It has a design reactive power rating of 1 MVA at a
frequency of 50 Hz and the operating temperature is 64 K. The
system consists of four concentric but separate coils, made of
2 km of Bi-2223 conductors from two different manufacturers.
The coils are optimized by shaping the magnetic field around
the coil edges with ferro-magnetic C-cups to reach a design
electrical quality factor of 1000. The system is operated in a
glass-epoxy cryostat at 64 K and 77 K. The resonator coil
design demonstrates all the superconducting elements that are
essential for manufacturing superconducting transformers. A
numerical model has been developed to predict the DC and AC
behavior of the system based on measurements of short samples
and test coils. A comparison is made between the experiment
and model calculations. |
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Optimization
of high-temperature superconducting power
transformers
E. Sissimatos, G.
Harms and B.R. Oswald
Summary: The discovery
of high-temperature superconductors in 1987 opened new
opportunities in the design of power supply equipment. The
advantages of a transformer with high-temperature
superconducting windings have been discussed and presented in
several papers in the past. The design of transformers depends
on the operation requirements and the installed position in
the power network. In this paper the fundamental equations for
the design of transformers are discussed and modified in such
a way that an optimization of HTS transformers can be
successfully studied. The best design in terms of low load
losses or low no-load losses is calculated for different power
transformers considering the volume of the transformer and the
impedance voltage. The resulting "growth laws" are discussed
and analyzed. |
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Development
of a 22 kV/6.9 kV single-phase model for a 3 MVA HTS power
transformer
K. Funaki, M.
Iwakuma, K. Kajikawa, M. Hara, J. Suchiro, T. Ito, Y. Takata,
T. Bohno, S.-I. Nose, M. Konno, Y. Yagi, H. Maruyama, T.
Ogata, S. Yoshida, K. Ohashi, H. Kimura and K.
Tsutsumi
Summary: We have developed a 22
kV/6.9 kV HTS single-phase transformer cooled by liquid
nitrogen for field test, which is a practical model for the
single-phase part of a 3 MVA HTS power transformer. First, we
numerically simulated electromagnetic, mechanical and thermal
conditions of the windings in accidental cases of
short-circuit and lightning impulse, and considered the
winding structure withstanding the severe loads. We
constructed a small-sized model coil of Bi-2223 Ag/Mn-sheathed
tapes and confirmed applicability of the design concept for
the overcurrent and high-withstand-voltage tests. We designed
and constructed a single-phase HTS transformer on the basis of
the model-coil-test results. The primary and secondary
windings are transposed parallel conductors of two and six
Bi-2223 Ag/Mn tapes, respectively. The same tests for the HTS
transformer as for usual oil-filled ones indicated the
reliable operation and high performance. The field test in a
distribution grid of Kyushu Electric Power Co. included
in-rush-current test and long-term operation of the
transformer cooled by a continuous supply system of subcooled
liquid nitrogen with cryocoolers. |
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The
B00 model coil in the ATLAS Magnet Test
Facility
A.V. Dudarev, E.W.
Boxman, H.H.J. Ten Kate, O.P. Anashkin, V.E. Keilin and V.V.
Lysenko
Summary: A 1-m size model coil has
been developed to investigate the transport properties of the
three aluminum-stabilized superconductors used in the ATLAS
magnets. The coil, named B00, is also used for debugging the
cryogenic, power and control systems of the ATLAS Magnet Test
Facility. The coil comprises two double pancakes made of the
barrel toroid and end-cap toroid conductors and a single
pancake made of the central solenoid conductor. The pancakes
are placed inside an aluminum coil casing. The coil
construction and cooling conditions are quite similar to the
final design of the ATLAS magnets. The B00 coil is well
equipped with various sensors to measure thermal and
electrodynamic properties of the conductor inside the coils.
Special attention has been paid to the study of the current
diffusion process and the normal zone propagation in the ATLAS
conductors and windings. Special pick-up coils have been made
to measure the diffusion at different currents and magnetic
field values. |
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Mechanical
characteristics of a coil support system for the ATLAS central
superconducting solenoid
magnet
H. Yamaoka, S. Mizumaki,
Y. Makida, A. Yamamoto, Y. Doi, K. Tanaka, S. Mine and T.
Kondo
Summary: Mechanical characteristics of
the support system for the ATLAS (A Toroidal LHC Apparatus)
central superconducting solenoid magnet have been
investigated. The coil support system was designed with a
unique triangular-shape configuration made of GFRP and with
spherical bearings at the joints. A mechanical performance
test has been carried out to simulate various operational
conditions. This paper describes the mechanical design and
test results. |
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The
chimney and superconducting bus lines for the ATLAS central
solenoid
Y. Makida, Y. Doi, A.
Yamamoto, Y. Kondo, T. Haruyama, T. Kondo, Y. Wachi, S. Mine,
S. Mizumaki, T. Kobayashi, F. Haug, N. Delruelle, J.
Tischhauser, G. Passardi and H. ten Kate
Summary:
A thin superconducting solenoid magnet for the ATLAS
detector in the CERN-LHC project is under construction as a
cooperative work between KEK and CERN. A control dewar at the
top of the detector is connected with a coil through a long
chimney placed in the gap of the outer detectors and toroidal
magnets. A set of superconducting bus lines and cooling tubes
is arranged in the chimney. The fabrication of the chimney and
the control dewar has been completed and the performance test
was carried out. The current leads in the control dewar and
the superconducting bus lines in the chimney were successfully
tested with a current of 10 kA including 2 kA contingency.
Quench characteristics of the bus was measured and also
analyzed. A superconducting quench detector worked well to
pick up quenches. |
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Superconducting
septum magnet design for Jefferson Lab Hall
A
P. Brindza, A. Gavalya, S.
Lassiter, J. LeRose, E. Cisabni, S. Frullani, F. Garibaldi, M.
Iodice, G. Urciuoli and M. Nilles
Summary: A
pair of superconducting septum magnets are required to permit
hypernuclear physics experiments at JLAB's Hall A at angles to
the incident beam as small as 6 degrees. A cold iron
superconducting "C" magnet design has been selected. This
magnet has a central field of 4.23 Tesla at a current density
of 25,000 Amp/cm2, the stored energy is 0.22 Megajoules and
the inductance is 1.0 Henries. The magnet has an effective
field length of 0.67 meters, an average gap of 0.25 meters and
an average pole width of 0.15 meters. The magnet is currently
being fabricated by BWXT Inc. under contract to
INFN. |
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Construction
of the ATLAS B0 model coil
A.
Dael, E. Acerbi, F. Alessandria, C. Berriaud, R. Berthier, F.
Broggi, C. Mayri, Y. Pabot, J.M. Rey, M. Reytier, L. Rossi, M.
Sorbi, H. Van Hille, G. Volpini and Z. Sun
Summary:
The B0 coil is a technological model for the ATLAS
Barrel Toroid coils. The major concepts and the construction
procedures are the same as those specified for the BT coils.
So the manufacturing feasibility has been extensively proved
and the technological developments have been carried out for
the industrial production of the conductor, the welding
technique of the coil casing, the prestress of the coil with
bladders, the cold to warm supports, the construction and
assembly of the cryostat. The paper illustrates all these
phases. |
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A
dual 6T persistent-mode SC solenoid ion-optical system for
radioactive nuclear beam
research
F.D. Becchetti, M.Y.
Lee, D.A. Roberts, T.W. O'Donnell, J.A. Zimmerman, J.J.
Kolata, D. Peterson, P. Santi, V. Guimaraes and L.O.
Lamm
Summary: A unique ion-optical system for
the production of high-intensity, short-lived radioactive
nuclear beams has been designed, constructed and put into
operation at the Nuclear Structure Laboratory at the
University of Notre Dame as a joint project between the
University of Michigan and NSL-UND. The system consists of a
matched in-line pair of large-bore (30 cm) 6T superconductive
solenoid magnets which act as high-acceptance collectors and
magnetic filters of secondary radioactive nuclear beam (RNB)
products. The latter are brought to a focus on a secondary
target and nuclear reactions using the RNB studied. These are
primarily reactions of interest in Big-Bang nucleosynthesis
and stellar helium burning and involve the production of /sup
6/He, /sup 7/Be, /sup 8/B and similar beams. A number of
unique features were incorporated in the magnet design to
permit use as a precise ion-optical device in the RNB mode. To
the authors' knowledge this is the only large-scale in-beam
ion-optical system to operate primarily in persistent mode. A
similar device will also be built at the University of Sao
Paulo for RNB research. |
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Measurements
of magnetic field pattern in a short LHC dipole
model
L. Bottura, M. Breschi and
M. Schneider
Summary: The magnetic field in
superconducting accelerator magnets has a fine structure with
longitudinal periodicity. This periodic pattern, with period
identical to the cable twist pitch, is originated by uneven
current distribution within the cable. Here, the authors
present results of measurements of the periodic pattern
performed in an LHC dipole model. They report in particular
the results obtained powering the magnet with simple current
steps and typical operation cycles as will be used during
accelerator operation. The main result of the analysis is the
time variation of the amplitude of the periodic pattern, from
which they infer the evolution of the current distribution in
the cable. They discuss the dependence of the pattern
amplitude on ramp and pre-cycle parameters. |
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Interaction
between current imbalance and magnetization in LHC
cables
M. Haverkamp, A. Kuijper,
A. den Ouden, B. ten Haken, L. Bottura and H.H.J. Ten
Kate
Summary: The quality of the magnetic
field in superconducting accelerator magnets is associated
with the properties of the superconducting cable. Current
imbalances due to coupling currents /spl Delta/I, as large as
100 A, are induced by spatial variations of the field sweep
rate and contact resistances. During injection at a constant
field all magnetic field components show a decay behavior. The
decay is caused by a diffusion of coupling currents into the
whole magnet. This results in a redistribution of the
transport current among the strands and causes a
demagnetization of the superconducting cable. As soon as the
field is ramped up again after the end of injection, the
magnetization rapidly recovers from the decay and follows the
course of the original hysteresis curve. In order to clarify
the interactions between the changes in current and
magnetization during injection the authors performed a number
of experiments. A magnetic field with a spatially periodic
pattern was applied to a superconducting wire in order to
simulate the coupling behavior in a magnet. This model system
was placed into a stand for magnetization measurements and the
influence of different powering conditions was
analyzed. |
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Busbar
studies for the LHC interaction region
quadrupoles
P. Bauer, L. Chiesa,
S. Feher, J. Kerby, M. Lamm, D. Orris, C. Sylvester, J.C.
Tompkins and A.V. Zlobin
Summary: Fermilab
(FNAL) and the Japanese high energy physics lab (KEK) are
developing the superconducting quadrupole magnets for the
interaction regions (IR) of the Large Hadron Collider (LHC).
These magnets have a nominal field gradient of 215 T/m in a 70
mm bore and operate in superfluid helium at 1.9 K. The IR
magnets are electrically interconnected with superconducting
busbars, which need to be protected in the event of a quench.
Experiments to determine the most suitable busbar design for
the LHC IR magnets and the analysis of the data are presented.
The main purpose of the study was to find a design that allows
the inclusion of the superconducting busbars in the magnet
quench protection scheme, thus avoiding additional quench
protection circuitry. A proposed busbar design that was tested
in these experiments consists of a superconducting cable,
which is normally used for the inner layer of the Fermilab IR
quadrupoles, soldered to similar Rutherford type cables as a
stabilizer. A series of prototypes with varying numbers and
types of stabilizers (one or two stabilizers, pure copper or
Cu/NbTi composite) were tested. These samples were
characterized with respect to their quench temperature profile
and their quench propagation velocity during normal zone
growth. From these tests, a suitable design has been
determined. |
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Quench
protection of the LHC inner triplet quadrupoles built at
Fermilab
P. Bauer, R. Bossert, L.
Chiesa, J. DiMarco, S. Feher, M.J. Lamm, A.D. McInturff, A.
Nobrega, D. Orris, M. Tartaglia, J.C. Tompkins and A.V.
Zlobin
Summary: High gradient quadrupoles are
being developed by the US-LHC Accelerator project for the LHC
interaction region inner triplets. These 5.5 m long magnets
have a single 70 mm aperture and operate in superfluid helium
at a peak gradient of 215 T/m. Through the construction and
test of eight 2 meter long model quadrupoles, strip heaters of
various geometries and insulation thicknesses have proven to
be effective in protecting the magnets from excessively high
coil temperatures and coil voltages to ground. This paper
reports on the results of the model program to optimize the
heater performance within the context of the LHC inner triplet
electrical power and quench detection scheme. |
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Quench
protection heater studies of the 3rd 1-m model magnet for the
KEK-LHC low-/spl beta/
quadrupoles
E.E. Burkhardt, A.
Yamamoto, T. Nakamoto, T. Ogitsu, T. Shintomi and K.
Tsuchiya
Summary: In superconducting magnets
with large energies, quench protection heaters (QPHs) are
necessary to prevent localized quenches. If the full energy of
a magnet is dissipated into a small volume, the magnet may
suffer irreparable damage. The QPHs are used to heat the
surface of the coil to increase the size of the normal zone so
the heat is dissipated over a larger volume. As a result, the
maximum temperature after a quench will be reduced. The KEK
low-/spl beta/ quadrupole 1-m model magnets for the Large
Hadron Collider (LHC) have four QPHs on the outer surface of
the coil. A capacitive power supply with 7.2 mF/channel and a
maximum charge of 400 V is used to fire the heaters, yielding
a maximum energy of 576 J/channel. The QPH set-up used at CERN
has an initial current of 54 A and a time-constant of 118 ms.
Because the power supply used for the KEK 1-m model is not
identical to the power supplies used at CERN for the 6-m
production magnets, a similar set-up is achieved by connecting
two power supply channels in parallel and adding an external
resistor to each circuit giving an initial current of 52.6 A
with a time-constant of 109 ms. Several aspects of the
performance of the QPHs for the third 1-m model magnet
(LHCIRQ03) have been studied: full energy dump (compared with
2nd model, LHCIRQ02), full charge on QPHs at 215 T/m,
determine the minimum magnet current at which the QPHs can
initiate a quench, and spot heater tests (both with and
without the QPHs). |
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Thermal
studies of a high gradient quadrupole magnet cooled with
pressurized, stagnant
superfluid
L. Chiesa, S. Feher,
J. Kerby, M. Lamm, I. Novitski, D. Orris, J.P. Ozelis, T.J.
Peterson, M. Tartaglia and A.V. Zlobin
Summary:
A 2-m long superconducting model of an LHC Interaction
Region quadrupole magnet was wound with stabrite coated cable.
The resulting low interstrand resistance and high AC losses
presented the opportunity to measure magnet quench performance
in superfluid as a function of helium temperature and heat
deposition in the coil. Our motivation was to duplicate the
high radiation heat loads predicted for the inner triplet
quadrupoles at LHC and study the coil cooling conditions in
the magnet. At the Magnet Test Facility in Fermilab's
Technical Division, the magnet quench performance was tested
as a function of bulk helium temperature and current ramp rate
near the planned high luminosity interaction region field
gradient of 205 T/m. AC loss measurements provided a
correlation between current ramp rate and heat deposition in
the coil. Analysis indicates that the results are consistent
with there being little participation of superfluid helium in
the small channels inside the inner layer in the heat removal
from the coil. However magnet performance will be limited by
the outer coil pole turn in LHC at a current level well above
the operating current. |
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Experimental
investigations of He II heat transfer through a short section
of LHC inner triplet quadrupole heat
exchanger
Ch. Darve, Y. Huang,
T.H. Nicol and T.J. Peterson
Summary: The LHC
inner triplet quadrupoles, cooled by pressurized He II, are
subjected to a total heat load of more than 7 W/m at nominal
luminosity. The heat absorbed in pressurized He II will be
transferred to the saturated, two-phase He II via a corrugated
copper pipe. Experimental investigations of He II heat
transfer across the corrugated pipe are reported. The test
sample of corrugated pipe is filled with pressurized He II and
with saturated He II on the outside. The maximum heat flux to
the test sample is up to 145 W/m/sup 2/. The characteristics
of the corrugated copper pipes under investigation are the
Kapitza resistance, thermal conductivity of the material and
the geometry of the pipe. The test results for a series of
bath temperatures and surface treatments are
included. |
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Quench
performance of Fermilab model magnets for the LHC inner
triplet quadrupoles
N. Andreev,
T. Arkan, P. Bauer, R. Bossert, J. Brandt, J. Carson, S.
Caspi, D.R. Chichili, L. Chiesa, J. DiMarco, S. Feher, A.
Ghosh, H. Glass, J. Kerby, M.J. Lamm, A. Makarov, A.D.
McInturff, A. Nobrega, I. Novitski, T. Ogitsu, D. Orris, J.P.
Ozelis, T. Peterson, R. Rabehl, W. Robotham, R. Scanlan, P.
Schlabach, C. Sylvester, J. Strait, M. Tartaglia, J.C.
Tompkins, G. Velev, S. Yadev and A.V.
Zlobin
Summary: As part of the US LHC program
to develop high gradient superconducting quadrupoles for the
LHC interaction regions, a series of 2 meter long model
magnets has been built and tested at Fermilab. This R&D
program was used to refine the mechanical and magnetic design,
optimize fabrication and assembly tooling and ensure adequate
quench performance. The final design, fabrication, and
assembly procedures developed in this program have produced
magnets which meet the LHC requirements of operating at 215
T/m with excellent magnetic field harmonics. This paper
summarizes the test results of the last five model magnets,
including quench tests over several thermal cycles, and
excitation current ramp rate and temperature dependence
studies. |
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Quench
performance and mechanical behavior of 1 m model magnet for
the LHC low-beta quadrupoles at
KEK
T. Nakamoto, A. Yamamoto, K.
Tsuchiya, E.E. Burkhardt, N. Higashi, N. Kimura, T. Ogitsu, N.
Ohuchi, T. Shintomi and A. Terashima
Summary:
High gradient 70 mm aperture superconducting low-beta
quadrupole magnets have been developed at KEK as part of the
collaboration between CERN and KEK for the Large Hadron
Collider (LHC). After development of two 1 m model magnets,
the third model magnet with the new coil design was built and
excitation tests were completed. The third model successfully
reached the design field gradient of 240 T/m and showed
training memory after full thermal cycles. Other quench tests
were performed and it was verified that the third model
exhibited reliable quench performance and sufficient safety
margin during operation. |
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Performance
of the 1-m model of the 70 mm bore twin-aperture
superconducting quadrupole for the LHC
insertions
G. Kirby, R. Ostojic,
Z. Ang, L. Bottura, F. Rodriguez-Mateos, S. Sanfilippo, A.
Siemko and F. Sonnemann
Summary: Individually
powered twin-aperture superconducting quadrupoles with a coil
bore of 70 mm will be installed in certain areas of the LHC
insertions where increased geometrical acceptance is required.
A 1-m twin-aperture model of the quadrupole, featuring a
four-layer coil with a nominal gradient of 160 T/m at 4.5 K,
has been built and tested. In this report we present the
quench performance of the magnet, and discuss the results of
the quench protection studies and magnetic field
measurements. |
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Performance
of the single and twin-aperture models of the 6 kA
superconducting quadrupole for the LHC
insertions
J. Lucas, R. Ostojic,
L. Bottura, R. Bussjaeger, H. Dariol, A. Hobl, D. Krischel, G.
Kirby, V. Remondino, S. Sanfilippo, M. Schillo, A. Siemko, F.
Sonnemann, D. Tommasini, I. Vanenkov and W. Venturini
Delsolaro
Summary: The LHC dispersion
suppressors and matching sections will be equipped with
individually powered superconducting quadrupoles with an
aperture of 56 mm. In order to optimise the parameters and
cost of the magnets and of their powering, the quadrupole has
been designed on the basis of an 8.2 mm wide Rutherford-type
cable for a nominal current of 5300 A, corresponding to a
gradient of 200 T/m at 1.9 K. In order to validate the design
two 1-m single-aperture quadrupoles and one twin-aperture
quadrupole have been built and tested. In this report we
describe the construction features of the magnets and present
the results of the magnet tests. |
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Study
on high temperature superconducting magnetic bearing for 10
kWh flywheel energy storage
system
S. Nagaya, N. Kashima, M.
Minami, H. Kawashima and S. Unisuga
Summary:
Flywheel energy storage systems with high temperature
superconducting magnetic bearings are expected for load
leveling use. A 1 kWh flywheel of 600 mm diameter was
developed and the maximum energy storage of 1.4 kWh at 20,000
RPM was attained. For the development of a large capacity
flywheel system, it is necessary to sophisticate the cooling
system and improve the performance of the HTS magnetic
bearing. So, an advanced cooling system of the bearing with a
cryogenic refrigerator has been developed, and also the
bearing characteristics in several cooling conditions have
been investigated. It has been confirmed that the repulsive
force of the bearing at 50 K was 1.5 times of its value at 80
K, and the rotating loss of the bearing at 50 K was one third
of its value at 80 K, but the lateral magnetic stiffness at 50
K became small in comparison to that of 80 K. On the basis of
the above results, an HTS magnetic bearing for 12.5 kWh
flywheel system is under development. |
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Numerical
analysis of rotation loss of superconducting magnetic
bearing
K. Demachi, A. Miura, T.
Uchimoto and K. Miya
Summary: The degradation
of levitation force and rotation speed is one of the most
significant problems for the practical use of superconducting
magnetic bearings (SMB) for flywheel energy storage systems.
The rotation loss is caused by the AC magnetic field due to
the inhomogeneous distribution of magnetic flux density of the
permanent magnet (PM) rotor. A simulation method has been
developed by the authors' group to simulate the rotation
losses. In this research, this method was improved so that the
eddy current flowing in the cryostat around the superconductor
was taken into account. The dependency of the rotation losses
of radial type SMB with cryostat were evaluated by this new
simulation method with respect to the levitating height, the
initial rotation speed and the amplitude of inhomogeneous
component of PM rotor's field. |
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A
new flywheel energy storage system using hybrid
superconducting magnetic
bearings
J.R. Fang, L.Z. Lin,
L.G. Yan and L.Y. Xiao
Summary: The high
temperature superconductor (HTS) YBaCuO coupled with permanent
magnets has been applied to construct the superconducting
magnetic bearings (SMB) which can be utilized in some
engineering fields such as the flywheel energy storage system
(FESS). However, there are many problems needed to be
resolved, such as low stiffness and damping, the uncertainty
of working displacement, flux creep and flux flow. In this
paper, a new FESS using hybrid SMB system which consists of
SMB, active magnetic bearings (AMB), and permanent magnetic
bearings (PMB) is presented. In this design, the authors
constructed an experimental device for the FESS with hybrid
SMB. An axial PMB is joined to provide a levitation force so
as to suspend a heavier flywheel; in addition, two AMB are
added in radial degrees to improve the stiffness by two orders
of magnitude from 10/sup 4/ N/m to 10/sup 6/ N/m and the
damping of FESS. |
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Drag
torque in high Tc superconducting magnetic bearings with
multi-piece superconductors in low speed high load
applications
H. Ye, Y.
Postrekhin, Ki Bui Ma and Wei-Kan Chu
Summary:
The design of superconductor magnet bearings for high
load applications such as flywheel kinetic energy storage
necessitates the use of large pieces of high quality high
temperature superconductors. Limitations on the size of one
continuous block of HTS materials that can be produced make it
very attractive to use contiguous pieces of high quality HTS
materials to provide the same large amount of HTS surface that
can interact with magnets to give as high a levitation force.
More often than not, the shape of such a composite piece is
not symmetric about any axis of rotation. Variations in the
drag torque are observed within each rotation cycle of the
magnet above the composite HTS piece. The authors show that
part of this drag torque variation originates from the
nonaxisymmetric shape of the composite HTS piece. Implications
of this drag torque variation on the power loss of
superconductor magnet bearings made with composite HTS pieces
are discussed. |
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Magnetic
interaction force between high-Tc superconductor-ring and
magnet
K.B. Ma, Y. Postrekhin, H.
Ye and Wei-Kan Chu
Summary: The magnetic
interaction force between superconducting ring and cylindrical
permanent magnets of different lengths, aligned coaxially, has
been investigated experimentally at zero-field-cooled and
field-cooled conditions. The force as a function of the
position of the magnet relative to the superconductor ring is
qualitatively that expected if the superconductor is regarded
as a diamagnet with nonohmic dissipation. The hysteretic
behavior of the axial force component was studied. It is shown
that the size of the hysteresis loop grows with the strength
of the magnet in general, but the shape of the loop also
undergoes complicated changes. It was found that field-cooled
conditions can yield a higher support force in this permanent
magnet and superconducting ring system, with lower hysteresis
loss. This makes this system an attractive candidate for a low
loss magnetic journal bearing. |
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Magnetic
bearings using bulk superconductors as a field shaping
material
H. Ohsaki, N. Nozawa and
Y. Kubo
Summary: Magnetic bearings have been
studied that use bulk superconductors as a field shaping
material and need only a steel component on the rotor side.
Two bearing configurations are considered: the bulk magnet
type and the mixed-/spl mu/ type. In both systems, stable
levitation of the steel rotor has been demonstrated.
Electromagnetic force measurements have shown that the
mixed-/spl mu/ type has better vertical force characteristics
and similar radial force characteristics to the bulk magnet
type. Rotation tests have been also carried out, which
indicate that eddy current loss in the steel rotor is dominant
and a larger loss was observed in the mixed-/spl mu/
type. |
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Analysis
of magnetic forces and rotational losses of high-Tc
superconducting magnetic bearings by Preisach's
diagram
S. Yokoyama, S. Nakamura,
M. Hirose and H. Nasu
Summary: A flywheel
system using a high-Tc superconducting bearing is researched
to apply for a power storage system. The authors analyzed the
magnetization of the high-Tc superconducting bulk using
Preisach's diagrams. They calculated the magnetic forces and
rotational losses of radial type high-Tc superconducting
bearings by the electromagnetic simulation using the
magnetization. In this paper, the authors calculate the
magnetic force and loss of the bearing regarding the
parameters of the bearing size and the characteristics of the
permanent magnet. It was found that the magnetic force is
affected due to the size and the characteristics of the
permanent magnet. This calculation method is considered to be
satisfactory for application to large scale
bearings. |
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Improvement
and evaluation of bearing stiffness in high T/sub c/
superconducting magnetic
bearing
M. Komori and T.
Hamasaki
Summary: This paper describes a new
method of dynamics of passive type superconducting magnetic
bearings (SMBs). In order to clarify the method, a simple
experimental setup was constructed that consists of a
superconductor attached to a mechanical x-stage and a
permanent magnet attached to a z-stage. In the experiments,
the stages were forced to move in the x and z directions to
improve bearing stiffness and repulsive forces. Moreover, a
simple theoretical model to explain the results is applied to
the experimental setup. As a result, it is found that the
improved method for SMBs is effective experimentally and
theoretically. |
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Study
of back quench in the superconducting coils of the barrel
toroid of ATLAS due to losses during a "slow" discharge of the
magnet
M.
Sorbi
Summary: An analysis of the losses in
the Al matrix of the conductor and in the casings where the
superconducting coils are located, due to a "slow discharge"
(heaters of the coils off) of the Barrel Toroid of ATLAS has
been carried out. The values of the losses have been
calculated and cross checked by means of different analytical
and FE approaches, and simple relations have been carried out
in order to correlate them with the main electrical parameters
of the magnet. With a thermal analysis, the increase of
temperature in the superconducting coils due to these extra
losses has been calculated. The temperature margin (i.e.
difference between current sharing temperature and operating
temperature) has been calculated and compared with the
temperature margin during the normal run of the
magnet. |
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Analysis
of normal zone propagation in pancake-shaped Nb/sub 3/Sn
superconducting magnet
Qiuliang
Wang, Jinliang He, Cheon Seog Yoon, Keeman Kim and Zheng
Nam
Summary: A quench phenomenon is caused by
an external disturbance in a superconducting magnet, where the
magnet is operating in a cryogenic environment. The heat
coupling between the layers and pancakes of the magnet can
induce the normal zone propagation with fast speed, in order
to analyze quench behavior in a pancake-shaped superconducting
magnet, a quasi-three-dimensional model is proposed. A moving
mesh finite volume method is employed in solving the heat
conduction equation. The quench process of the superconducting
magnet is studied under the various operating conditions and
cooling conditions. |
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Experimental
investigation to overcome the ramp-rate limitation of CICC
superconducting magnets
Sangkwon
Jeong, Seokho Kim and Tae Kuk Ko
Summary: RRL
(ramp-rate limitation) is a phenomenon in which a magnet
quenches before it reaches its apparent critical current. This
paper is an experimental investigation not about the detailed
influence of various parameters on the ramp-rate limitation,
but about the general methodology to overcome it. A CICC
(cable-in-conduit conductor) superconducting magnet has been
made of three-strand NbTi triplet. The magnet produced a
maximum 3.6 T/s ramp-rate at the inner most region. The
temperature of the supercritical helium coolant was
deliberately raised to investigate RRL-related quench. The
main purpose of the experiment was to study RRL phenomena at
the first and consecutive ramp-ups. If quench is avoided
during the first ramp-up, the consecutive ramp-ups of the
magnet have much higher resistance against the RRL. This paper
describes several experimental observations of several
interesting hysteretic characteristics of RRL. |
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Quench
modeling of the ATLAS superconducting
toroids
A.V. Gavrilin, A.V.
Dudarev and H.H.J. Ten Kate
Summary: Details
of the normal zone propagation and the temperature
distribution in the coils of ATLAS toroids under quench are
presented. A tailor-made mathematical model and corresponding
computer code enable obtainment of computational results for
the propagation process over the coils in transverse
(turn-to-turn) and longitudinal directions. The slow
electromagnetic diffusion into the pure aluminum stabilizer of
the toroid's conductor, as well as the essentially transient
heat transfer through inter-turn insulation, is appropriately
included in the model. The effect of nonuniform distribution
of the magnetic field and the thermal links to the coil casing
on the temperature gradients within the coils is analyzed in
full. |
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Analysis
of the impact of strand joints and copper location on the
current distribution and stability in cable-in-conduit
conductors
N.
Mitchell
Summary: A typical cable in conduit
conductor can contain over 1000 NbTi, Nb/sub 3/Sn or Nb/sub
3/Al strands, cabled together with a helium flow through the
interstices to provide cooling. The impacts of strand joints
within the cable, and copper, present as separate strands,
have been analysed using a time dependent model of current
diffusion and heat transfer. It is concluded that a few well
distributed strand joints in the cable are acceptable, and
that separate copper strands can contribute to cable
stability. |
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Acoustic
emission induced from alternating current superconducting
coils resulting from vibration of
windings
K. Arai, H. Yamaguchi,
K. Kaiho, A. Ninomiya, T. Ishigohka and T.
Saitoh
Summary: Acoustic emission (AE)
induced from alternating current (AC) superconducting coils
was studied in terms of the vibration of the superconducting
windings caused by the interaction between self-magnetic
fields and operating currents. The AE signals were analyzed
regarding two types of epoxy-impregnated NbTi coils having
different tension at their winding ends. The AE pulses from
vibrations appear at the time of zero-crossings of the
operating currents as well as at the time of peaks of the
currents, where the former AE signals resulted from the
electromagnetic force in the axial direction combined with
that in the radial direction. The waveforms of AE envelopes
that depended on the tension and the amplitude of operating
current were also described. Those data are considered to
contribute to understanding of AE signals, for example, for
detecting vibration that suddenly appears during operation or
for discriminating between the vibration-induced AE components
and other components. |
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Statistical
diagnosis method of conductor motions in superconducting
magnets to predict their quench
performance
P. Pugnat, B.
Khomenko, A. Rijllart, S. Sanfilippo and A.
Siemko
Summary: Premature training quenches
are usually caused by the transient energy released within the
magnet coil as it is energised. Two distinct varieties of
disturbances exist. They are thought to be electrical and
mechanical in origin. The first type of disturbance comes from
nonuniform current distribution in superconducting cables
whereas the second one usually originates from conductor
motions or micro-fractures of insulating materials under the
action of Lorentz forces. All of these mechanical events
produce in general a rapid variation of the voltages in the
so-called quench antennas and across the magnet coil, called
spikes. A statistical method to treat the spatial localisation
and the time occurrence of spikes is presented. It allows
identification of the mechanical weak points in the magnet
without need to increase the current to provoke a quench. The
prediction of the quench level from detailed analysis of the
spike statistics can be expected. |
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Status
report of the CMS superconducting coil
project
D. Campi, P.
Fabbricatore, A. Herve, I.L. Horvath and F.
Kircher
Summary: The CMS superconducting coil
is designed for one of the two large experiments of LHC at
CERN. This coil 12.5 m long, 6 m diameter and 2.7 GJ stored
energy is a common project of the CMS Collaboration. It is a
four-layer coil, equipped with a self-supporting conductor
capable of carrying 20 kA to reach the maximum potential field
of 4 T. It has been designed with a considerable contribution
from CEA-Saclay for the engineering, ETH-Zurich for the
conductor, INFN-Genova for the winding and CERN for the
general coordination and construction of the ancillaries. The
project entered the construction phase one year ago. The civil
engineering is well advanced and ready to accept part of the
yoke components already built. The coil itself has finished
the pre-industrialization phase and the construction is
beginning in industry. Most of the important contracts have
been awarded and the foreseen schedule is now based on
contractual engagements. A quick overview of the features of
the project as well as a status report of the main activities
are given. |
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The
ATLAS magnet test facility at
CERN
P. Miele, F. Cataneo, N.
Dolgetta, A. Dudarev, A. Foussat, F. Haug, H. ten Kate, E.
Sbrissa and H. Tyrvainen
Summary: The ATLAS
magnet system consists of a barrel toroid (BT), two end-cap
toroids (ECT) and a central solenoid (CS). The BT with overall
dimensions of 20 m diameter by 26 m length is made of 8 coils
placed in their individual cryostats and symmetrically
assembled around the central axis. The ATLAS magnet test
facility is being completed at CERN and will host in the next
years to come pairs of BT coils at the same time as well as
the ECT and the CS systems already fully assembled. Two model
coils will be tested in the years 2000-2001, the B00 model
coil and the B0 model coil, a 9 m short version of the BT coil
built to verify the functionality and the construction
concepts of the BT. |
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Pre-industrialization
activities related to CMS coil
winding
P. Fabbricatore, S.
Farinon, R. Musenich, C. Pirano, A. Calvo, B. Levesy, F.
Rondeaux, M. Perralla and C. D'Urzo
Summary:
The CMS coil is a large 4 layer superconducting
solenoid involving the use of a new design reinforced
conductor. In order to understand the feasibility of the coil
manufacture using the inner winding technique for this
particular conductor, the CMS Collaboration has developed a
pre-industrialization activity. The main objectives were: (1)
study of the methods for winding a coil using a stiff
conductor; (2) design, construction and testing of a prototype
winding line; and (3) construction of a model for the fine
tuning of the required operation and procedures. The
activities, carried out in cooperation with industry, were
successfully completed, giving basic information for the
necessary tool and methods to be used for the coil
winding. |
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Structural
design and analysis of a compact sweeper magnet for nuclear
physics
S. Prestemon, M.D. Bird,
D.G. Crook, J.C. DeKamp, Y.M. Eyssa, L. Morris, M. Thoennessen
and A. Zeller
Summary: A superconducting
dipole, designed for use as a sweeper magnet in nuclear
physics experiments, is being constructed by the NHMFL for
operation at the NSCL. The magnet operates at a peak field of
3.8 T in a 140 mm gap. A multi-particle beam enters the magnet
from the upstream side. The neutrons continue straight through
to a neutron detector. The charged particles are swept 40
degrees on a one-meter radius into a mass spectrometer. To
allow space for the exit of the downstream neutron beam, the
magnet iron and coil structure are built in a modified "C"
configuration. There are two coils of "D" shape, one above and
one below the beam. This configuration keeps the magnet
compact and removes the need for a negative curvature side.
The peak field in the winding is 6.5 T. The net force on the
curved leg of a single "D" is 1.6 MN. Design of the structure
to contain these forces in a superconducting magnet of such a
geometry is presented along with details of stability and
quench analysis, field profiles, etc. |
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Construction
and testing of superferric dipoles for the A1900 Fragment
Separator
A.F. Zeller, J.C.
DeKamp, J. Wagner and D. Capelli
Summary: The
A1900 Fragment Separator contains four superconducting
dipoles. The dipoles produce a field of 2 T at an operating
current of 185 A. The changes in effective length have been
measured and compared with calculations that predict a longer
field boundary than observed. The magnets ran to full field
without training. Edge angles were measured and found to be
small. All magnets have been installed in the beam line and
retested. First beam through the Separator is expected by the
end of 2000. |
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Test
results of 2-kWh flywheel using passive PM and HTS
bearings
T.M. Mulcahy, J.R. Hull,
K.L. Uherka, R.G. Abboud and J.J. Juna
Summary:
Toward demonstrating the potential of flywheel energy
storage systems that use high-temperature superconductors
(HTSs) and permanent magnets (PMs) as passive rotor bearings,
a flywheel system was developed and tested with a 165-kg
cylindrical carbon- and glass-fiber rotor to rim speeds of 400
m/s (19,000 rpm) and stored energies of >2.25 kWh. The main
bearing's internal stack of PM rings was passively stabilized
by HTS bearings at each end of the rotor. The stator portion
of the HTS bearing consisted of an array of melt-textured YBCO
pellets bathed in liquid nitrogen inside a nonconducting
cryochamber. The motor/generator (M/G) was based on an
internal-dipole Halbach array and could produce 1.5 Nm of
torque. Each bearing and the M/G included multipiece banded PM
rings secured to the rotor inside diameter with flexible
urethane rings. In a vacuum enclosure at 10/sup -4/ Pa
pressure, rotational drag on the rotor was hysteretic and at
low speeds the coefficient of friction was well below 10/sup
-6/. |
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A
prototype of flywheel energy storage system suppressed by
hybrid magnetic bearings with H/sup /spl infin//
controller
M. Komori and N.
Akinaga
Summary: This paper discusses a
prototype of miniature flywheel energy storage system. The
system consists of a rotor with a flywheel disk and a pair of
hybrid magnetic bearings (HMBs). The HMB is composed of both
superconducting magnetic bearings (SMBs) and active magnetic
bearings (AMBs). An H-infinity control method and zero bias
method are applied to the AMB. In this paper, the design and
dynamics of the flywheel energy storage system are
discussed. |
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Laser
beam deflection polygon scanner using HTS
bearings
F.N. Werfel, U.
Floegel-Delor, R. Rothfeld, D. Wippich and T.
Riedel
Summary: A light scanning device with
a rotating mirror up to 3 kHz rotational frequency for
directing and aiming a radiation beam at a surface was
developed and tested. Conventional fluid and air bearing
systems because of friction are unable to accelerate up to 60
mm rotors above 2 kHz frequency. The rationale for the
selection of the magnetic bearing configuration using YBCO,
the control of the bearing and low power motor concepts are
discussed. Radial centering and axial stabilization of the
rotor are affected by means of two superconducting radial
bearings with oppositely magnetized PM rings. The rim speed of
the polygon is close to 600 m/s, giving rise to appreciable
centrifugal forces and necessitates high quality material
selection. The extreme optical sensitivity requires a soft
suspension of the rotor coupled with a high damping
efficiency. Low consumption LN/sub 2/ cooling gives stable
cryogenic conditions in case of power failure. Features and
limitations of this novel scanning system are discussed,
especially those related to a higher line deflection
frequency. |
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Optimization
of levitation forces [in superconducting magnetic
bearings]
M. Zeisberger, T.
Habisreuther, D. Litzkendorf, O. Surzhenko, R. Muller and W.
Gawalek
Summary: In this contribution, the
authors present a systematic approach to the calculation of
levitation forces in plane-parallel (infinitely extended in
one direction) arrangements of permanent magnets and
superconductors. Starting from an extremely idealized geometry
with a very simple expression for the levitation force, they
go step by step to more realistic arrangements and present the
corrections in the force equations. In particular, magnet
configurations with an increased field gradient which allow a
higher stiffness are investigated. Finally, numerical
calculations are presented which show the dependance of the
levitation force on the size and the critical current density
of the superconductor and the effect of magnet-iron
combinations instead of magnets without iron. The calculations
show that the stiffness can be increased by using magnets
which consist of several sections with alternating polarity.
However, this improvement can only be used for reduced bearing
gaps and increased critical current density. The use of
magnet-iron combinations has only little
advantage. |
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Calculation
of magnetic levitation/suspension force of single grained
Y-Ba-Cu-O superconductors
In-Gann
Chen, Jen-Chou Hsu and Maw-Kuen Wu
Summary:
Top-seeded single-grained YBCO samples capable of
levitating or suspending over kilograms of weight have been
measured. However, the detailed relationship of the levitation
or suspension forces between permanent magnets and single
grained superconductor samples have not been fully studied,
which is required to design a large scale system. In this
report, an empirical method was used to calculate the
levitation/suspension force. First, the magnetic field of the
permanent magnet and the superconductor was measured by a Hall
probe, which was mounted on a x-y stage. The corresponding
circulating current, which results in the measured magnetic
field distribution, could therefore be calculated. The force
between these two sets of current distributions at various
distances was calculated and compared with measured
levitation/suspension forces. A good degree of agreement
between the measured and calculated suspension/levitation
force was achieved by this empirical method. |
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Superconducting
magnets for Maglifter launch assist
sleds
J.H. Schultz, A.
Radovinsky, R.J. Thome, B. Smith, J.V. Minervini, R.L. Myatt,
R. Meinke and M. Senti
Summary: The Maglifter
is an electromagnetic catapult being considered by NASA to
reduce the cost of lifting a payload into space. The system
would accelerate a vehicle of up to 590 tonnes to a final
velocity of 268 m/s at an acceleration of 2 g. Superconducting
coils are considered for levitation because they permit
track-to-vehicle clearances of more than 95 mm. The high
clearances reduce tolerances and maintenance costs, and allow
a system with permanently deployed wheels for take- off and
emergency landing. Cable-in-conduit conductors (CICC) were
selected because of their high electrical and mechanical
strength, as well as high energy margin for stability. The
selected coil shape is a pair of racetrack coils forming a
module with four modules on a sled. The superconducting
levitation modules weigh about 4% of the gross lift off weight
and are capable of achieving lift off at about 20 m/s. The
maximum magnetic drag power is negligible compared to the
power required for acceleration. |
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Power
system stabilizing control and current limiting by a SMES with
a series phase compensator
D.
Kamolyabutra, Y. Mitani and K. Tsuji
Summary:
In this paper, a combined controller of a
superconducting magnetic energy storage (SMES) with series
phase compensator for the stabilization of a power system is
proposed. By the use of a series compensator, the SMES becomes
capable of absorbing the generator accelerating power during a
short circuit fault. In addition, the fault current is limited
by the energy absorption as well as by the leakage reactance
of a series transformer. A new control scheme for damping
control of the generator swing has been proposed that is
suitable for a SMES with series configuration. Some numerical
results demonstrate significant effectiveness for the
enhancement of power system stability and fault current
limiting. |
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Feasibility
of Nb/sub 3/Sn in a /spl mu/-SMES
concept
R. Mikkonen, A. Korpela
and J. Lehtonen
Summary: Today's SMES related
efforts are mainly concentrating on a number of small-scale
devices for high value applications such as improving power
quality and providing frequency control or dynamic response.
The commercialised SMES units utilise NbTi at 4.2 K as a coil
material. In addition some demonstration concepts have been
tested with HTS materials operating at 20-30 K or even at 77
K. One approach is to utilise Nb/sub 3/Sn in the vicinity of
10 K. This kind of system has been constructed. The designed
SMES coil is compared to a NbTi coil cooled with liquid helium
and a conduction cooled BSCCO coil operating at 20 K. The
starting point is a 200 kJ magnet where the coil volume has
been optimised under electromagnetic and mechanical
constraints. The comparison of these three coil concepts is
mainly concentrated on the questions of stability and coil
protection. The benefits and disadvantages of adopting Nb/sub
3/Sn as a coil material are emphasized. |
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Study
of a high-Tc superconducting magnet made with Bi-2212/Ag
Rutherford cable
S. Nagaya, N.
Hirano, M. Minami and T. Nakano
Summary: A
high temperature superconducting magnet using newly developed
Bi-2212/Ag Rutherford cable was trial manufactured as a
partial model for a 10 T magnet. The developed magnet consists
of 4 double pancake coils constructed from a Rutherford cable
with a critical current of 3.5 kA at 4.2 K, 0 T. The magnet
has inside and outside diameters of 100 mm and 180 mm,
respectively and is 75 mm long axially. The coil successfully
operated with DC 1.25 kA and 1.5 kJ was stored stably. A
maximum magnetic field of 2 T with A current of 1.47 kA was
confirmed in liquid helium. Also, the authors performed
excitation tests under the high-speed rate of change of
magnetic field (0.54 T/S) and 300 cycles simulating
alternating operation, and estimated the value of AC losses at
5.3 W using the change of liquid helium level. |
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SMES
system for study on utility and customer power
applications
Xiaohua Jiang, Xu
Chu, Xuezhi Wu, Wei Liu, Yongchuan Lai, Zanji Wang, Yingming
Dai and Heli Lan
Summary: A grid model SMES
system was developed for study on utility and customer power
applications. The system consists of a 20 kJ NbTi magnet, a 15
kW 12-pulse IGBT current source converter and a DSP-based
controller. To reduce the heat leakage, a couple of HTS
current leads were designed and fabricated which are composed
of Bi-2223 tapes and have a maximum operating current of 150
A. The 12-pulse current source topology was chosen for the
converter not only owing to its low total harmonic distortion
(THD) but also to its high capability of injecting capacitive
reactive power into network. In the controller of the system
two very fast DSPs (TMS320C32) are used to implement the
control algorithms and perform the generation of the firing
signals, giving a high accuracy and a high speed of
response. |
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SMES
control algorithms for improving customer power
quality
Xu Chu, Xiaohua Jiang,
Yongchuan Lai, Xuezhi Wu and Wei Liu
Summary:
Control algorithms of SMES based on a 12-pulse IGBT
current source converter were developed for improving customer
power quality. The control performances include
uninterruptible power supplies (UPS) and load fluctuation
leveling. To demonstrate the control algorithms, both
simulations and experiments were carried out on a 20 kJ/15 kW
grid model SMES system. The results of the simulations and
experiments are presented and compared in this
paper. |
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The
relationship among AC surface spark-over voltage, specific
capacitance of solid insulator and bubbles in LN/sub 2/ and
LHe
T. Nitta, M. Chiba and H.
Uematsu
Summary: The characteristics of AC
surface electrical discharge on solid insulators in liquid
nitrogen (LN/sub 2/) or liquid helium (LHe) are studied. The
insulation structure used is a model of a power cable end.
Bubbles are generated due to discharge at a lower voltage than
that of spark-over. However, it was experimentally and
computationally confirmed that the bubbles do not influence
the spark-over voltage. In the structure, static capacitance
is formed on the insulator surface. The surface spark-over
voltage depends on the static capacitance. The relation
between surface spark-over voltage and the static capacitance
is experimentally considered for several insulators. The
results show that the spark-over voltage is lower for larger
static capacitance. The relation between the spark-over
voltage and the capacitance can be expressed by an equation
V=A/spl middot/C/sub sp//sup -B/. |
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Calorimetric
measurements of losses in HTS
cables
C. Traeholt, S.K. Olsen,
C. Rasmussen, E. Veje and O. Tonnesen
Summary:
A calorimetric test rig is used to investigate various
loss components in a 10 m long superconducting cable model. A
calorimetric technique, based on thermocouple measurements, is
used to measure the losses of the 10 m long superconducting
cable model. The current dependent losses are also measured
electrically and compared with the losses obtained with the
calorimetric method. The results obtained by the two methods
are consistent. Based on an I/sup 2/ (current) fitting
procedure, the loss, caused by the eddy current generated in
the stainless steel cryostat housing, and the hysteresis loss
generated in the conductor can be separated. From this result,
it appears that the two contributions are roughly equal in
size. |
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Overcurrent
experiments on HTS tape and cable
conductor
K.H. Jensen, C.
Traeholt, E. Veje, M. Daumling, C.N. Rasmussen, D.W.A. Willen
and O. Tonnesen
Summary: Overcurrents in the
power grid can have a magnitude of up to 20 times or higher
than the rated current. This may cause problems and permanent
damage to electrical equipment in the grid. High temperature
superconducting (HTS) tapes are known to be sensitive to
currents much larger than their critical current. In this
light, it is important to investigate the response of HTS
tapes and cable conductors to overcurrents several times the
critical current. A number of experiments have been performed
on HTS tapes and cable conductors, with currents up to 20
times the critical current. During overcurrent experiments,
the voltage, and the temperature were measured as functions of
time in order to investigate the dynamic behavior of the HTS
tape and cable conductor. After each experiment, damage to the
superconductors was assessed by measuring the critical
current. Preliminary results show that within seconds an HTS
tape (critical current=17 A) heats above room temperature with
an overcurrent larger than 140 A. Similar overcurrent
experiments showed that a HTS cable conductor could sustain
damage with overcurrents exceeding 10 times the critical
current of the cable conductor. |
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Fault
current tests of a 5-m HTS
cable
J.W. Lue, G.C. Barber, J.A.
Demko, M.J. Gouge, J.P. Stovall, R.L. Hughey and U.K.
Sinha
Summary: The first industrial
demonstration of a three-phase, HTS power transmission cable
at the Southwire manufacturing complex is in progress. One
crucial issue during operation of the 30-m HTS cables is
whether they can survive the fault current (which can be over
an order of magnitude higher than the operating current) in
the event of a short circuit fault and how HTS cables and the
cryogenic system would respond. Simulated fault-current tests
were performed at ORNL on a 5-m cable. This single-phase cable
was constructed in the same way as the 30-m cables and is also
rated for 1250 A at 7.2 kV AC line-to-ground voltage. Tests
were performed with fault-current pulses of up to 15 kA (for
0.5 s) with pulse lengths of up to 5 s (at 6.8 kA). Although a
large voltage drop was produced across the HTS cable during
the fault-current pulse, no significant changes in the coolant
temperature, pressure, or joint resistance were observed. The
cable survived all 15 simulated fault-current shots without
any degradation in its V-I characteristics. |
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Practical
AC loss and thermal considerations for HTS power transmission
cable systems
J.A. Demko, J.W.
Lue, M.J. Gouge, J.P. Stovall, Z. Butterworth, U. Sinha and
R.L. Hughey
Summary: The use of
high-temperature superconducting materials for
power-transmission cable applications is being realized in
prototype situations. It is well known that AC loss decreases
as the temperature of the conductor decreases. Also, thermal
losses are higher at lower temperatures, owing to the
increased temperature difference between ambient and cryogenic
operating conditions. Both counterflow and parallel-flow
cooling arrangements have been proposed in the literature and
significantly affect temperature distribution along the cable.
In this investigation, the counteracting AC loss and thermal
losses are analyzed for both cooling configurations to
determine the benefits and limits of each. The
thermal-insulation performance levels of materials versus
those of typical systems in operation are presented.
Widespread application of long-length flexible cable systems,
from the refrigeration point of view, will depend on an
energy-efficient cryogenic system that is economical to
manufacture and operate. While the counterflow arrangement
will typically have a lower heat load, it has a length limit
arising from the large pressure drop associated with the
configuration. |
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Homogenization
of the magnetic field in the air-gap of a permanent magnet
superconductor bearing
H.W.
Lorenzen, R. Zickermann and D. Schafer
Summary:
This paper presents a way to reduce the nonhomogeneity
of the magnetic field leaving a permanent magnet ring composed
of several segments with a soft iron layer. This is
particularly important for bearings consisting of permanent
magnets and superconductors. |
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Characteristics
of lift and restoring force in HTS bulk-Application to
two-dimensional maglev
transporter
Y. Sanagawa, H. Ueda,
M. Tsuda, A. Ishiyama, S. Kohayashi and S.
Haseyama
Summary: One of the advantages of
magnetic levitation using a high-temperature superconducting
(HTS) bulk is that stable levitation can be achieved without
any control systems. The authors have been investigating the
electromagnetic behaviors of an HTS bulk to realize a
two-dimensional magnetic levitating transporter without any
fixed guides. The characteristics of lift and stability are
key parameters to design and optimize such a device. They
measured the lift and the restoring force of a YBCO bulk,
displaced by a distance in lateral direction, for various
field-cooling conditions and permanent-magnet arrangements.
Both lift and restoring force are closely related to the air
gap in the field-cooling process, distance between the
permanent magnets, number of permanent magnets, and permanent
magnet arrangement, that is, external magnetic field
distribution. The most suitable arrangement of permanent
magnets depends on the required levitation height and the
weight of the levitating part. It can be considered that the
size of the levitating part and geometry are also very
important to determine the optimal arrangement in the maglev
device. |
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Levitation
force of a YBaCuO bulk high temperature superconductor over a
NdFeB guideway
J.S. Wang, S.Y.
Wang, Z.Y. Ren, M. Zhu, H. Jiang and Q.X.
Tang
Summary: One of the prospective
applications of YBaCuO bulk high temperature superconductors
(HTS) is for superconducting magnetic levitation (Maglev)
vehicles. The levitation force of a single permanent magnet
over a single superconducting YBaCuO bulk has been researched,
but this is not enough for practical Maglev vehicles. In this
paper, properties of the levitation force of a YBaCuO bulk HTS
over a NdFeB guideway are investigated. The magnetic field at
the guideway surface is up to 1.2 T. During the experiment,
bulk YBaCuO is placed in a columnar liquid nitrogen vessel,
whose bottom thickness is only 3.5 mm, and it is over the
guideway. The YBaCuO is cooled in a zero magnetic field with
liquid nitrogen and can move up and down at different
velocities. The measurement process is fully controlled by a
computer. In this case, there is a 103.4 N levitation force at
a 5 mm gap between the YBaCuO (diameter=30 mm, thickness=14
mm) sample and the NdFeB guideway. In addition, the authors
compare the levitation force over the NdFeB guideway with that
over a single cylindrical NdFeB permanent
magnet. |
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Levitation
force in YBCO/Nd-Fe-B permanent magnet
system
H. Lee and Y.
Iwasa
Summary: This paper presents an
experimental study of the levitation force on a bulk
high-temperature superconducting YBCO disk in liquid nitrogen
above a Nd-Fe-B permanent magnet disk. The force data agree
with Kordynk's "frozen-image" model that states that
levitation force is independent of YBCO disk thickness and is
greater with defective YBCO disks than with defect-free YBCO
disks. |
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Levitation
force of multi-block YBaCuO bulk high temperature
superconductors
S.Y. Wang, J.S.
Wang, Z.Y. Ren, H. Jiang, M. Zhu, X.R. Wang and Q.X.
Tang
Summary: Experimental results of
levitation force of multi-block YBaCuO hulk HTSs over a NdFeB
guideway are presented. The magnetic field in the center of
the surface of the NdFeB permanent magnet guideway is up to
1.2 T and still 0.4 T at the position of 20 mm above it.
Several YBaCuO bulk samples are fixed in a columnar liquid
nitrogen vessel with a thin bottom (3.5 mm). The experimental
results show that the levitation force is quite different for
various combinations of YBaCuO bulks. The otal combination
magnetic levitation force of seven blocks of YBaCuO bulk
superconductors is 264.1 N when the gap between the YBaCuO HTS
and the NdFeB guideway is 10 mm, and levitation force is 167.5
N at 20 mm. Levitation force is even 106.2 N at 30 mm. The
optimization of the levitation force of multi-block YBaCuO
bulk superconductors is discussed after the authors analyze
the experimental data. |
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Three
dimensional vibration of the HTSC-permanent magnet bearing
system in the mechanical resonant
state
S. Ohashi, H. Tanaka and Y.
Hirane
Summary: The three dimensional
vibration of the rotor in a HTSC-permanent magnet bearing
system is studied. We have developed the bearing system which
can revolve up to 12000 rpm, and the three dimensional
vibration of the rotor is measured with laser displacement
sensors. The shape of the rotor has been improved, and
influence of the air resistance becomes small. The vibration
of the rotor around the mechanical resonance frequency is
investigated. Both columnar and conical behavior of the rotor
are confirmed and mainly columnar motion is
observed. |
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Repeated
pulsed-field magnetization with temperature control in a
high-T/sub c/ bulk
superconductor
H. Kamijo and H.
Fujimoto
Summary: We investigated the
applicability of high-Tc superconducting bulk magnets to the
superconducting Maglev system. A bulk superconductor needs to
generate as high a magnetic field as possible to obtain a
powerful bulk magnet. The bulk magnet requires a larger
external coil and larger power supply, and has a problem that
large electromagnetic force is applied to the bulk in the
process of magnetization. Therefore, a relatively small
magnetic field is preferable to magnetize a high-Tc bulk
superconductor. In this study, we magnetized a melt-processed
YBCO bulk superconductor by repeated pulsed-magnetic field
while controlling its temperature. In this method, a
comparatively small pulsed-magnetic field was repeatedly
applied to the bulk while lowering the temperature of the bulk
from the critical level at intervals of magnetization. For
example, the TBCO bulk was magnetized by a series of seven
pulsed-magnetic fields, while temperature was lowered from 94
K to 82 K at intervals of 2 K. As a result, it is found that
the bulk superconductor can generate a higher magnetic field
by using a comparatively small magnetic field. |
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Two-dimensional
quench propagation model for a three-dimensional
high-temperature superconducting
coil
B. Haid, Y. Iwasa and J.
Bascunan
Summary: The results of an
experimental and analytical study of quench propagation in a
three-dimensional, layer-wound, high-temperature
superconducting magnet are presented. The test magnet is wound
"dry" with silver-sheathed Bi-2223/Ag tape. It operates in
zero background field under quasi-adiabatic conditions at 20 K
and above, with a transport current of 50-100 A. Quenching is
initiated by a stainless steel heater attached to one turn of
the outermost layer. The resulting thermal response was
recorded through voltage measurements across regions of the
conductor near the heater. Quench events are simulated by a
numerical code using the finite-difference method to solve the
two-dimensional transient heat conduction equation. The model
indicates that thermal contact resistance has a dominant
effect on propagation in the transverse direction (across
layers). |
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Quench
development analysis in HTSC coils by use of the universal
scaling theory
V.S. Vysotsky,
Yu.A. Ilyin, A.L. Rakhmanov and M. Takeo
Summary:
The theory, describing thermal quench in HTSC devices,
was developed. It permits evaluation of thermal quench
conditions and development dependent on materials' parameters
and cooling. Thermal quench threshold current and time
characteristics of the quench can be predicted. The theory has
been extensively verified by experiments with different
superconducting HTSC devices. Good correspondence between
theory and experiments has been observed. We use this theory
to analyze the thermal quench emergence conditions that are
dependent on cooling, sizes of the device, material
properties, etc. It was shown, that with increase of the size
of the device threshold thermal quench current may become less
than standard determined critical current. Time
characteristics of the thermal quench increase with sizes. The
analysis is supported by comparison with experiments with
different HTSC coils. |
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Fabrication
of Bi-2223 HTS magnet with a superconducting
switch
Sang-Soo Oh, Hong-Soo Ha,
Hyun-Man Jang, Dong-Woo Ha, Rock-Kil Ko, Young-Kil Kwon,
Kang-Sik Ryu, Haigun Lee, B. Haid and Y.
Iwasa
Summary: A test pancake magnet,
equipped with persistent superconducting switch, was
fabricated with Bi-2223/Ag-Mg tape. The magnet was operated in
persistent mode at 20 and 77 K. For large operating currents
that forces the magnet to operate in the flux flow range, the
field decays is exponentially with time. A simple circuit
model is used to compute field decay time constants. It was
also found that Pb-Sn solder joints are unsuitable for
persistent mode operation. |
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A
stability criterion for cryocooler-cooled HTS
coils
A. Ishiyama and H.
Asai
Summary: The magnet technology of a
high-temperature superconductor (HTS) with a conduction
cooling system by a GM cryocooler has been advanced. It is
very important to understand the thermal and electromagnetic
phenomena in HTS tapes for HTS coil design. We have measured
the quench characteristics of HTS tapes with a conduction
cooling system of a GM cryocooler and developed a computer
program based on the finite element method (FEM) to
investigate the thermal and electromagnetic behaviors within
HTS tapes. From these experimental and analytical results, the
validity of the computer program has been confirmed. In this
paper, we discuss a stability criterion for cryocooler-cooled
HTS coils by using the computer program. The current at which
"thermal runaway" occurs, which depends on the relationship
between the cooling power of the GM cryocooler and the heat
generation within HTS coils, is chosen as a stability
criterion. We also investigate the transient thermal and
electromagnetic behavior in HTS coils. |
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Analytical
studies of the thermal stability of a high temperature
superconducting tube
J. Leveque,
D. Netter, P. Masson and A. Rezzoug
Summary:
The study of the HTS tube transition, which must be
provoked for some applications or controlled for other ones,
is very important. In any case, it is necessary to protect the
superconductor from an excessive rise of temperature to avoid
its destruction. Our paper deals with the study of the
influence of the thermal conductivity and the specific heat on
the stability of a superconducting tube. Indeed, these
parameters may have an important variation due to the
different materials and technology of manufacturing. Beyond
scientific curiosity, this theoretical study and the obtained
results could help the user to design a suitable material for
a given application. |
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Limiting
length in cooling design of HTS
magnets
Y.
Lvovsky
Summary: Regular operation of HTS
windings is accompanied by a low-level heat (index loss),
generated due to the low n-value of HTS materials. The paper
shows that the index loss in conduction cooled magnets causes
thermal instability and quench, when the cooling length
exceeds certain critical value L*. This index conduction
crisis is brought by the abrupt temperature growth of the
index loss. The crisis can occur at rather small temperature
gradients (of the order of a K), and should be among the major
design considerations for a conduction cooled magnet.
Stability criterion /spl lambda/ is derived in a
one-dimensional conduction model with nonlinear index loss.
Practical formulae are suggested defining maximum allowable
current vs. cooling length. Effect of limited cryocooler
capacity is modeled. The theory is illustrated by examples of
a solenoidal coil and a solitary conductor
(bus). |
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Transport
current properties of Y-Ba-Cu-O tape above critical current
region
S. Torii, S. Akita, Y.
Iijima, K. Takeda and T. Saitoh
Summary: YBCO
tape is highly promising as a 2nd-stage HTS conductor for
power applications, and development of long tape is proceeding
worldwide. Generally, HTS tape conductors have broad
transition characteristics ranging from the superconducting
state to the normal state, so they rarely quench just above
the critical current defined for a usual electrical field or
resistivity. However, such characteristics make the stability
criteria complex when these tapes are considered for power
applications. To estimate the stability criteria of HTS tapes,
we prepared YBCO tapes with YSZ textured buffers by the IBAD
method. The thickness, width and length of the YBCO layer are
1 /spl mu/m, 10 mm and about 140 mm, respectively, and tapes
are coated with Ag of various thicknesses as a stabilizer and
protector. Transport current properties are measured in a wide
range of current above the critical current defined by 1 /spl
mu/V/cm. The establishment of criteria to define the stability
of HTS tapes will be necessary for their applications in power
apparatuses. |
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Transient
electrical and thermal responses of a 2-section BSCCO-2223
coil under overcurrent pulses
A.
Sugawara, H. Isogami, K.W. Kowallis and Y.
Iwasa
Summary: This paper presents
experimental and numerical simulation results of 2-section
coil subjected to overcurrent pulses in the temperature range
20-60 K. The experiment simulates a high-temperature
superconducting (HTS) magnet for electric devices such as
fault-current limiters, transformers, motors, and power lines
under fault-mode overcurrent pulses. Each section of the test
coil is layer-wound with Bi-2223/Ag composite tape, 3.5 mm
wide and 0.23 mm thick, with the outer section wound directly
over the inner section. A pulse current exceeds the critical
current of each conductor and may drive each section normal. A
constant current that follows the pulse current leaves each
section in three possible conditions: completely
superconducting, recovering, and quenching. Simulation agrees
reasonably well with experiment. |
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Thermal
behavior of a solid nitrogen impregnated high-temperature
superconducting pancake test coil under transient
heating
H. Isogami, B.J. Haid and
Y. Iwasa
Summary: This paper presents
experimental and analytical results on a solid nitrogen
impregnated high-temperature superconducting (HTS) test coil
under transient heating. The test coil is a 1-layer, 10-turn
single-pancake wound with Bi2223/Ag composite tape, 9-mm wide
and 0.5-mm thick, with an average winding diameter of 105 mm.
The solid nitrogen impregnating the 0.38-mm turn-to-turn
radial gaps in the winding enhances the winding's overall heat
capacity significantly in the operating temperature range
30-40 K and thereby limits the test coil's temperature rise
when it is subjected to overcurrent pulses. The presence of
solid nitrogen within the winding improves stability against
fault-mode overcurrent pulses for HTS magnets used in electric
power devices. |
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Power
converter for SMES by use of ICB energy transfer
circuit
J. Baba, T. Nitta, Y.
Shirai, S. Akita, Y. Hayashi and Y.
Kobayashi
Summary: Inverter-converter bridge
(ICB) energy transfer circuit consists of two power converters
and the capacitor bank. Two superconducting magnets are
connected to the circuit and the stored energy is transferred
by use of the circuit. The circuit has been mainly studied as
an exciter circuit for pulse superconducting magnets because
it enables excitation of the large magnet quickly without
affecting the utility. It is easy to achieve the required
capacity because the circuit can be made by a natural
commutation thyristor. The circuit, which is connected to the
power system through the converter (utility tie converter) has
attractive features for the SMES power converter, for
instance, wide control region of active and reactive power.
The relation between utility tie converter control and the ICB
circuit control is important for realizing SMES converter
system, however, it has not been studied. In this paper, the
magnet current control method concerned with the utility tie
converter has been discussed to control the energy flows. The
theoretical analysis and the experimental results are
shown. |
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A
mechanism causing an additional AC loss in a large CICC
coil
T. Hamajima, M. Yoshida, H.
Shimamura, N. Harada, M. Tsuda, S. Hanai and T.
Satow
Summary: A large superconducting coil
wound with cable-in-conduit (CIC) conductor caused an
additional AC loss which cannot be estimated from short
conductor sample test results. It was confirmed that the
additional AC loss was generated by long current loops in the
CIC conductor. Magnetic field decays of the loops with various
long time constants were observed through Hall probes. We
propose a mechanism forming the long loops. The CIC conductor
is composed of several staged sub-cables. If one strand on the
surface of a sub-cable contacts with the other strand on the
surface of the adjacent sub-cable, the two strands must
encounter each other again at LCM (least common multiplier)
distance of all staged cable pitches and thereby result in
forming a pair of a long loop. We traced each strand in the
CIC according to a method that the sub-cables at all
sub-stages rotate around a center of inertia. The long time
constants were calculated and their results can explain the
data measured in a large SMES coil. The proposed mechanism is
effective for estimating the additional AC loss in the
coil. |
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Electric
surface resistance R/sup E/(T, f, E/sup /spl perp//) of
Nb/Nb/sub 2/O/sub 5-y/-interfaces and Q-drop of
superconducting Nb cavities
J.
Halbritter, P. Kneisel, V. Palmieri and M.
Pekeler
Summary: The RF losses, especially
actual level and increase with RF fields limit most
stringently the application of superconducting RF cavities.
This is due to the needed cooling power to be supplied locally
to the high field region and due to the nonlinearities causing
harmonics and RF breakdown. The separation of RF residual
losses R/sub res/(T,f) from the intrinsic losses R/sub
BSC/(T,f) yields the quasi-exponential increases of the
electric surface resistance with the electric field E/sup l/
perpendicular to the surface /spl delta/R/sup E/(E/sup /spl
perp//)/spl prop/exp (-c/E/sup /spl perp//) and the power law
increases of the magnetic surface impedances with the magnetic
field H/sup /spl par// parallel to the surface /spl
delta/R/sup H/(H/sup /spl par//)/spl prop/(H/sup /spl
par//)/sup 2n/ (n=1, 2..). By the Nb/Nb/sub 2/O/sub 5-y/
interfaces at external and internal surfaces R/sup H//sub
res/(T,f) and R/sup E//sub res/(f,E/sup /spl perp//) can be
explained quantitatively. Especially, the drop of Q/sub
0/(E/sup /spl perp//)/spl prop/1/R/sup E//sub res/(E/sup /spl
perp//) and its reduction by EP- and BCP-smoothening and by
better interfaces by UHV anneal are well accounted for by
interface tunnel exchange. |
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Design,
fabrication and test of the react and wind, Nb/sub 3/Sn, LDX
floating coil conductor
B.A.
Smith, P.C. Michael, J.V. Minervini, M. Takayasu, J.H.
Schultz, E. Gregory, T. Pyon, W.B. Sampson, A. Ghosh and R.
Scanlan
Summary: The Levitated Dipole
Experiment (LDX) is a novel approach for studying magnetic
confinement of a fusion plasma. In this approach, a
superconducting ring coil is magnetically levitated for up to
8 hours a day in the center of a 5 meter diameter vacuum
vessel. The levitated coil, with on-board helium supply, is
called the floating coil (F-Coil). Although the maximum field
at the coil is only 5.3 tesla, a react-and-wind Nb/sub 3/Sn
conductor was selected because the relatively high critical
temperature will enable the coil to remain levitated while it
warms from 5 K to 10 K. Since prereacted Nb/sub 3/Sn tape is
no longer commercially available, a composite conductor was
designed that contains an 18 strand Nb/sub 3/Sn Rutherford
cable. The cable was reacted and then soldered into a
structural copper channel that completes the conductor and
also provides quench protection. The strain fabrication steps
such as: soldering into the copper channel, spooling, and coil
winding, to prevent degradation of the critical current.
Measurements of strand and cable critical during state of the
cable was continuously controlled currents are reported, as
well as estimates fabrication, winding and operating strains
on critical current. |
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Charging
magnet for the floating coil of
LDX
A. Zhukovsky, J. Schultz, B.
Smith, A. Radovinsky, D. Garnier, O. Filatov, V. Beljakov, S.
Egorov, V. Kuchinsky, A. Malkov, E. Bondarchouk, V. Korsunsky
and V. Sytnikov
Summary: The charging coil
(C-coil) for the joint Columbia University/MIT Levitated
Dipole Experiment (LDX) is under development jointly by MIT
and the Efremov Institute. The NbTi superconducting C-coil
serves to charge/discharge inductively the floating
superconducting magnet to/from 2277 A when it is resting in
the charging port at the bottom of the LDX vacuum vessel. The
C-coil is designed for 3200 charge-discharge cycles. The
solenoid magnet is installed in a low heat leak liquid helium
cryostat with a warm bore of more than 1 m. The magnet
protection system has an external dump resistor, which
dissipates most of the 12 MJ stored during a
quench. |
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Mechanical
preloading of the Central Solenoid Model
Coil
P.C. Michael, R. Vieira,
R.V. Jayakumar, T. Kato, H. Nakajima and M.
Sugimoto
Summary: The inner and outer modules
of the Central Solenoid Model Coil (CSMC) are mechanically
compressed by a preload structure. The necessary preload is
determined for the support of the modules' terminal leads. The
forces in the preload structure are monitored by strain gauge
bridges mounted to each of the structure's 16 inner and 16
outer tension rods during: (1) room temperature loading; (2)
cool-down to the coil's operating temperature; and (3)
electromagnetic operation. The preload structure is described
and the variations in the preload with each stage of coil
operation are presented. Analytical models are presented,
which use the observed variations in preload to deduce
equivalent mechanical properties for the coil
modules. |
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Instrumentation
of the Central Solenoid Model Coil and the CS
insert
C.Y. Gung, P.C. Michael,
N.N. Martovetsky, T. Isono, Y. Nunoya, T. Ando and K.
Okuno
Summary: The Central Solenoid Model
Coil (CSMC) was built by the US and the Japanese home teams as
part of an international collaboration which also involved the
European Union and Russian Federation. The CSMC and CS insert
coil were installed at a purpose build a test facility at the
Japan Atomic Energy Research Institute in Naka, Japan and
tested from March through August 2000. With over 500 sensors
installed on the coils, bus bars, plumbing, facility and the
structure, the CSMC and CS insert were instrumented to obtain
valuable data about their performances, and to reveal the
qualification of the large state superconducting solenoids for
the nest fusion machine. This paper describes the
instrumentation inside the vacuum chamber used in various
stages of the CSMC and the CS insert coil
operation. |
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Development
of high copper ratio Nb/sub 3/Al strands for fusion
magnets
F. Hosono, G. Iwaki, K.
Kikuchi, S. Ishida and T. Ando
Summary: A
joint project was carried out between the Japan Atomic Energy
Research institute (JAERI) and Hitachi Cable, Ltd, to develop
long length Nb/sub 3/Al strands with a Cu ratio of 4 using the
Jelly Roll process with the intention to fabricate a CICC
(cable-in-conduit-conductor). The workability of the
hydrostatically extruded multifilament rod proved to be very
good, comparable that the formerly developed Jelly Roll
processed Nb/sub 3/Al strands with Cu ratio 2. The strands
with Cu ratio 4 show the same Jc 605 A/mm/sup 2/ at 12 T as
that for the strands with Cu ratio 2. A CICC is formed through
a drawing process. The inserted cables have the pattern of
3/spl times/3/spl times/3/spl times/3/spl times/4 with a first
triplet composed of 2 Nb/sub 3/Al strands and a Cu strand. The
finished 5th stage cable is wrapped with SS304 tape, after
which it if drawn inside a 1.9 mm thick SS316L tube to a void
fraction of 38% as a demonstration of conductor fabrication
feasibility. |
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Excitation
properties and cryogenic stability of helical coils for the
LHD
S. Imagawa, N. Yanagi, T.
Mito, H. Chikaraishi, S. Hamaguchi, H. Sekiguchi, S. Yamada,
T. Satow, Y. Nakamura, S. Satoh and O.
Motojima
Summary: The helical coils for the
Large Helical Device are the world's largest pool-cooled
superconducting coils in operation. These were expected to be
cryostable up to 13.0 kA at 4.4 K on a basis of the measured
recovery currents in all the short samples. However, a
normal-zone was induced at higher than 11 kA repeatedly. It
propagated to the finite length and recovered within several
seconds except at 11.45 kA. Because of slow current diffusion
into a pure aluminum stabilizer, a normal zone can propagate
dynamically below the cold-end recovery current. The
excitation tests have been carried out, and average 11.65 kA
has been achieved by grading the current in the three blocks
of the helical coil. The disturbance during excitations and
the cryogenic stability of the coil are
presented. |
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Contact
resistance distribution at the termination of cable-in-conduit
conductors
P.
Bruzzone
Summary: For large cable-in-conduit
conductors, a current unbalance among the strands may be the
reason for reduced performance in both DC and pulsed
operation. The resistance distribution of the strands at the
conductor termination has been investigated as the key
parameter controlling the current distribution in operation. A
Nb/sub 3/Sn cable-in-conduit conductor consisting of 144 Cr
plated strands has been used to prepare two terminations, one
of them filled with low resistivity solder. The resistance
distribution results for the two layouts are compared with the
expected distribution from the count of the strand contacts,
carried out on several conductor sections. Conclusions are
drawn on the role of interstrand resistance and the degree of
current unbalance that can be expected in the conductor next
to the joint. |
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Studies
on power conditioning system for SMES in
ITER
T. Ise
Summary:
The International Thermonuclear Experimental Reactor
(ITER) draws huge power from utility power grid and it may
cause some problems in the power system. Especially, the power
required to control the movement of plasma caused by some
instabilities of the plasma is suitable for compensation by
SMES, because the time duration is a few seconds although the
required power is around 100 MW. In this system, the design of
the power conditioning system is one of the keys. As a power
conditioning system, two systems were studied; one is the
system using line commutation and light triggered thyristors,
another is the system of multi-series converters using forced
commutation and gate turn-off devices such as GTOs. Feature of
the former circuit is the inter-phase DC reactor-less
configuration. Thyristor rectifiers are directly connected in
parallel at DC side, primary side windings of rectifier
transformers are connected in series in order to ensure equal
sharing of current between rectifiers. Reactive power can be
compensated by TSC (thyristor switched capacitors). The
performances of two proposed circuits were studied by computer
simulation. |
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Using
a superconducting magnetic energy storage coil to improve
efficiency of a gas turbine powered high speed rail
locomotive
B.K. Johnson, J.D. Law
and G.P. Saw
Summary: The US Federal Railroad
Administration has been pursuing the use of locomotives with
an on-board prime mover for high speed rail. Such systems
would not require the added cost of rail electrification on
top of the rail bed modifications. The prime mover runs a
synchronous generator, with the output rectified to feed a DC
bus. Adjustable speed drives control the traction motors.
However, gas turbines run efficiently over a narrow speed
range and a relatively narrow power range. The addition of a
superconducting magnetic energy storage coil can improve
overall system performance. The SMES coil is charged whenever
the locomotive is in regenerative braking mode and whenever
the prime mover is producing more power than is needed to
maintain the desired speed down the track. The chief benefits
to such a scheme are: (1) better acceleration at high speeds,
(2) reduced prime mover power rating and weight, (3) reduced
railbed cost due to reduced weight (4) reduced trip time and
(5) improved fuel efficiency. |
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Connecting
tests of superconducting persistent-current-switch in a type
of current transformer to 1 kWh SMES
system
H. Hayashi, T. Sannomiya,
H. Kimura, K. Tsutsumi, Y. Yamashita, R. Kuboyama, S. Sato, M.
Takeo, T. Ishii, K. Asano and S. Okada
Summary:
A full system of 1 kWh/1 MW module-type SMES
(superconducting magnetic energy storage) has been completed
at a substation in Fukuoka City. There is a need for a PCS
(persistent-current-switch) with a quick response and large
current capacity for use with a SMES system. We have
investigated a superconducting PCS in a type of transformer
which works according to the principle of a current
transformer. A 900 A class PCS has already been manufactured.
This paper describes experimental results with connecting
tests of the PCS to a SMES which consists of two modules, each
comprising a converter of 500 kVA and three superconducting
pulse coils. |
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Test
results of compensation for load fluctuation under a fuzzy
control by a 1 kWh/1 MW SMES
T.
Sannomiya, H. Hayashi, T. Ishii and R.
Ikeda
Summary: A full system of 1 kWh/1 MW
SMES (superconducting magnetic energy storage) has been
completed. This SMES is the first step to the realization of
practical SMES system for power line control. In the field
tests the SMES, its function for compensating load fluctuation
of 6 kV distribution line with fuzzy control applied, was
confirmed. The fuzzy control of the SMES interprets whether
power variation in the distribution line increases or
decreases. It interprets concurrently whether the energy
capacity stored in the SMES increases or decreases. In the
tests, the calculated theoretical values almost coincident
well with experimental values under the fuzzy control. The
test results proved the effectiveness of the fuzzy control
system of SMES. These results might be useful for the design
of the next larger scale SMES. |
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Experimental
and analytical studies on mechanical behavior of
superconducting coil for SMES
K.
Shimada, S. Hanai, L. Kushida, K. Hirabayashi, T. Kobayashi,
T. Shimonosono, H. Hayashi, K. Tsutsumi, F. Irie, Y. Horiuchi
and T. Ezaki
Summary: The mechanical behavior
of a superconducting coil is important for improving the
stability and reducing the mechanical losses of SMES.
Mechanical displacements of a model coil for 1 kWh
experimental SMES (ESK) are measured and compared with
analytical results using 2D FEM. Nonlinear behaviors, such as
friction and sliding between conductors and spacers are
considered in this model. The preliminary stress condition
caused by refrigeration is also considered. The results of
this analysis show a good agreement with the experimentally
observed ones. |
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New
SMES coil configurations
O.
Vincent-Viry, A. Mailfert and D. Trassart
Summary:
This paper deals with a new approach to the problem of
energy storage by the use of SMES. A comparison method of the
performances of different SMES configurations has been
established, and some new SMES configurations are presented.
The good performances of these coils configurations have been
checked first by analytical study and then by numerical
computation. |
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Design
considerations for force-balanced coil applied to
SMES
S. Nomura, D. Ajiki, C.
Suzuki, N. Watanabe, E. Koizumi, H. Tsutsui, S. Tsuji-Iio and
R. Shimada
Summary: Strong electromagnetic
force caused by high magnetic field and large coil current is
a serious problem in superconducting magnetic energy storage
(SMES) systems. In facing this problem, we propose the concept
of force-balanced coil (FBC) which is a helical-winding
toroidal coil and can reduce the centering force of toroidal
field coil (TFC). The helical-winding of the FBC is modulated
in order to reduce the torsional force. This paper describes
the cost-related parameters of the FBC in terms of the
dimension of the coil, the ampere-meters of superconductors
and the surface area of the coil compared with the TFC and the
solenoid. Moreover, we discuss the structure requirements by
the virial theorem and improve the concept of FBC in terms of
the further optimization of SMES through the structural
analysis. |
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Experimental
study on on-line grasp of operating condition of longitudinal
power system by use of SMES
T.
Nitta, S. Mohri, Y. Shirai, H. Taniguchi, Y. Kitauchi, Y.
Morioka and K. Kawada
Summary: SMES
(superconducting magnetic energy storage) system has excellent
ability as not only an energy storage system but also a power
system stabilizer, a load fluctuation compensator and so on. A
new application of SMES in a power system has been proposed,
that is, for on-line grasp of power system operating
conditions. This paper shows the possibility and validity of
the proposed application of SMES by use of a small SMES system
and power system simulator of rotating machine type. The
experimental system is a longitudinal four machine power
system. It was confirmed the SMES can give a small power swing
of known pattern without affecting operating conditions of the
power system. On-line data of response due to the small power
disturbance of SMES were analyzed to obtain natural
frequencies and eigenvectors of the power system operated. The
power system operating condition was estimated by these data.
This application can be easily used with a SMES of small
size. |
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Design
performance of a superconducting power
link
J. Paasi, J. Lehtonen, T.
Verhaege and P.F. Herrmann
Summary:
Superconducting power links (SUPERPOLI) will offer
low-loss power transmission and fault current limitation in a
single device. In the European SUPERPOLI project, a long term
goal is to build a 200 m long, 20 kV/sub rms/ 28 kA/sub rms/
3-phase superconducting power link which will be refrigerated
by subcooled liquid nitrogen. The SUPERPOLI will have a
compact coaxial multitube structure which significantly
reduces the AC losses. As a step towards this GVA-class
application, a 2 m long, 20 kV, 2 kA/5 kA, one-phase
functional model is under construction. The conductor variants
considered are Bi-2212 bulk conductor and Y-123 coated film
conductor. They present very different behaviors in normal
operation and during the limiting phase: Bi-2212 bulk
conductor has higher AC losses and allows short transients or
moderate overcurrents without quenching, while Y-123 film has
low AC losses and immediate response for overcritical
currents. |
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Reduction
of inductance and current rating of the coil and enhancement
of fault current limiting capability of a rectifier type
superconducting fault current
limiter
T. Ise, N.H. Nguyen and
S. Kumagai
Summary: A rectifier type
superconducting fault current limiter is mainly composed of a
rectifier using diodes and/or thyristors, and a
superconducting coil. It has advantages in the following
aspects. It can control the fault current level by controlling
the coil current. AC losses can be reduced because the current
through the superconducting coil is rectified DC current. But
the longer the fault current limiting time is, the larger the
superconducting coil current becomes and the fault current
level increases due to the increase of the coil current. This
paper shows how to reduce the inductance and current rating of
the coil and how to increase the fault current limiting
capability. The idea is to put a resistor in series with the
superconducting coil for absorbing the incoming energy into
the coil and turn on and off the switching device connected in
parallel with the resistor in order to control the coil
current in a pre-set region. Simulation results assuming the
fault current limiter as an inter-connecting device between a
generator of IPP (independent power producers) and utility
grids, and some experimental results with a laboratory model
will be shown. |
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A
system study on superconducting fault current limiting
transformer (SFCLT) with the functions of fault current
suppression and system stability
improvement
N. Hayakawa, H.
Kagawa, H. Okubo, N. Kashima and S. Nagaya
Summary:
In this paper, the authors propose a "superconducting
fault current limiting transformer (SFCLT)", a superconducting
transformer equipped with the function of a superconducting
fault current limiter. They discussed the operating
characteristics of SFCLT introduced into a simplified power
transmission model system. Fault current, transient stability,
overvoltage and thermal characteristics of SFCLT were analyzed
in the model system. It was finally revealed that SFCLT could
satisfactorily bring about the functions of fault current
suppression and power system stability
improvement. |
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Nonlinear
current-voltage characteristics of HTS conductor and its
application to the operation of
SFCL
Yu Wang, Zhi Qi, Wei Wang,
Chunyi Li, Daole Yin, Liangzhen Lin, Liye Xiao and Naihao
Song
Summary: A proper description of the
nonlinear voltage-current relation of the superconductor is
necessary for accurate analysis of the superconducting fault
current limiters (SFCL). Discrepancies between the
experimental results and the prediction of Bean's critical
state model were observed. Using a recently found unified
nonlinear response function of type-II superconductors, the
authors derive the current-voltage characteristic of
metal-sheathed HTS conductor and compare it with experiments.
Its relation to the operation of SFCL is also
discussed. |
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DC
reactor effect on bridge type superconducting fault current
limiter during load increasing
T.
Hoshino, K. Mohammad Salim, M. Nishikawa, I. Muta and T.
Nakamura
Summary: In high power applications,
the fault current limiter has been discussed for many years
because of some limitations of conventional circuit breakers.
Many types of fault current limiter have already been
introduced in papers. In this work, a simple bridge-type fault
current limiter has been designed and constructed. The
performances of the limiter have been tested successfully. In
the bridge-type current limiter, a DC reactor appears in the
line when the connected load is increasing. This causes a
voltage drop across the load terminal during load changing.
The DC reactor effect of the current limiter has been studied.
Some experimental results regarding the reactor effect of the
limiter have been considered and compared with the results
obtained from computer simulation. |
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Resistance
rise in Bi2223 superconducting bulk after normal transition
due to overcurrent [fault current
limiters]
H. Shimizu, K. Kato, Y.
Yokomizu, T. Matsumura and N. Murayama
Summary:
The resistance and joule heat generating in a Bi2223
bulk for the overcurrent carrying period were measured. The
authors suddenly supplied the overcurrent having the peak
value which is about ten times as high as the critical current
of the sample conductor. The resistance slightly increased
immediately after the current exceeded the critical current
level. When the accumulative joule heat generated in the
sample reached 32 M/m/sup 3/, the quench occurred. The
resistance rise in the sample proceeds adiabatically and the
magnitude of the resistance may be estimated only by the joule
heat generated in the sample. |
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Y-Ba-Cu-O
thin films as active high power
switches
A. Heinrich, J. Muller,
A. Hiebl, K. Numssen, H. Kinder, W. Weck, A. Muller and H.
Scholderle
Summary: The authors have studied
the active switching of nonshunted YBaCuO films. Therefore
films of 10-300 nm thickness were deposited on substrates by
thermal co-evaporation. Bridges, 5 mm/spl times/26 mm and 10
mm/spl times/42 mm, were structured by standard
photolithography. No topcoat of gold was used to retain higher
switching powers. The active switching of the DC-biased YBaCuO
bridges was triggered by heat pulses or radio frequency. For
the thermal trigger, a resistive thin film heater was
evaporated on the back side of the substrate. The samples were
biased by currents up to 20A and triggered by heat pulses (up
to 500 W) at 10-70 K. A resonant circuit was used in the case
of the RF-trigger. The pancake coil of this circuit was placed
2 mm above the 10 mm wide YBaCuO bridge. At 77 K the stripes
were biased by currents up to 40A and triggered with RF-pulses
of >1 ms duration and 3-40 W (10 MHz). Active switching was
observed in both cases. In comparison to the thermal trigger,
power for RF induced switching power is very
low. |
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Design
guideline of flux-lock type HTS fault current limiter for
power system application
T.
Matsumura, H. Shimizu and Y. Yokomizu
Summary:
The authors have proposed a "flux-lock" type high T/sub
c/ superconducting (HTS) fault current limiter (FCL) composed
of a flux-lock reactor with HTS element and a magnetic field
coil circuit. In this FCL, the initial limiting current level
can be arranged by setting the inductance combination of the
flux-lock coils and an AC magnetic field is applied to the HTS
to get higher resistance only in a current limiting phase.
This paper describes design guidelines for the NTS-FCLs. The
impedances of the FCLs were expressed as a function of the
product of the normal resistance and the square of the quench
current level, which the authors have proposed to refer to as
"quench power". Supposing the FCLs are introduced into the
extra-high voltage transmission system and power distribution
system, the "quench power" necessary for the FCLs to suppress
the fault current under the required level was
discussed. |
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Investigation
of high-Tc bulk material for its use in resistive
superconducting fault current
limiters
M. Noe, K.-P. Juengst,
F. Werfel, L. Cowey, A. Wolf and S.
Elschner
Summary: Superconducting fault
current limiters (SCFCL) offer an attractive means to limit
short-circuit currents in power systems. Comparisons of
available HTS material led to the derision to investigate melt
cast processed (MCP) BSCCO and melt textured polycrystalline
YBCO for use in resistive SCFCLs. As a great length of a
superconductor per unit element is preferred, the BSCCO
samples are shaped as bifilar coils prepared from tubes and
the YBCO samples are manufactured in a meander shaped
geometry. Test results concerning contact resistances, E-J
curves, AC losses as well as the quench behaviour of the
samples are presented. The experiments reveal the requirement
of a high material homogeneity as the main
challenge. |
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Fundamental
experiments of axial-type BSCCO-bulk superconducting motor
model
I. Muta, H.J. Jung, T.
Hirata, T. Nakamura, T. Hoshino and T.
Konishi
Summary: An axial type HTS hysteresis
motor has the same structure as a conventional axial flux type
permanent magnet synchronous motor. The permanent magnet rotor
of a conventional permanent magnet synchronous motor is
replaced by a rotor made from HTS materials with the objective
of increasing power densities and reducing losses. The
behavior of a BSCCO bulk rotor has been tested in rotating
magnetic fields produced by two poles and three phase motor
coils fed by a PWM inverter at 77 K. To characterize the
torque output capability of the HTS hysteresis motor, speed
versus torque and current versus torque are tested.
Experimental results for the HTS hysteresis motor are
presented. |
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Development
and test of an HTS induction
generator
Sung-Hoon Kim, Woo-Seok
kim, Song-Yop Hahn and Gueesoo Cha
Summary: A
superconducting induction generator (SIG) with two rotors is
presented. The two rotors are called inner rotor and outer
rotor, respectively. The inner rotor is located inside of the
outer rotor and free to rotate. The inner rotor consists of an
HTS winding and iron yoke. The outer rotor is made of a copper
shell. It is driven by a mechanical power source. The outer
rotor rotates at higher angular velocity than that of the
rotating magnetic field generated by the stator current while
the inner rotor rotates at the same angular velocity with the
field made by the stator current. The HTS winding produces
enough magnetic field to compensate the reactive armature
current, which improves the power factor of the generator
close to unity. A 1.5 kVA SIG was manufactured and tested to
realize the concepts of the HTS free inner rotor. Good
electrical characteristics were shown by experiment. Due to
the simplified structure of the inner rotor cooled with LN/sub
2/, the SIG presented in this paper can be realized as a
medium-sized generator, as well as a large one and used as a
supplemental power source connected to a conventional power
system. |
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Improvement
of a magnetically levitated stepping motor using high T/sub c/
bulk superconductor
M. Komori and
S. Nomura
Summary: A magnetically levitated
stepping motor using high T/sub c/ superconductor has been
studied. The levitated stepping motor consists of a
cylindrical rotor with superconductors and a stator with eight
electromagnets. The rotor measures 10 mm in diameter, 46 mm in
length, and 18 g in mass. The superconductors of the rotor are
field-cooled in liquid nitrogen. The levitated rotor is driven
by four-phase and eight-phase excitations. The rotation angles
by each step are 90 and 35 deg, respectively. The rotor spins
as the excitation phase shifts one by one. This paper
discusses the dynamics of the motor driven by the four-phase
and eight-phase excitations. |
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Trial
production and experiments of linear actuator with HTS bulk
secondary
R. Muramatsu, S.
Sadakata, M. Tsuda and A. Ishiyama
Summary:
To investigate characteristics of a linear actuator
with high-temperature superconducting (HTS) bulk secondary, a
short secondary type linear actuator has been designed and
constructed. The actuator is comprised of an YBCO bulk
secondary (mover) and copper windings with iron core
(primary). A zero-field-cooled bulk located at the center of
the actuator plays a role of generating thrust, while four
field-cooled (trapped field) bulks are used for levitation and
guidance of the secondary. The authors measured the starting
thrust force and magnetic field distribution in the air gap.
They developed a simulation program based on the finite
element method (FEM) taking the voltage-current (E-J)
characteristics of the bulk into consideration to investigate
electromagnetic behaviors within the bulk exposed to a
time-varying magnetic field. Agreement between experiment and
simulation is good, and it validates the simulation program
and the presented assumptions in the numerical approach, using
the simulation program, they investigated the dependency of
n-value and critical current density of the bulk material on
the magnetic flux density in the air gap and the starting
thrust force. Supercurrent density within the bulk is a key
factor for the magnetic flux density and the thrust
force. |
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Flux
trapping characteristics of YBCO bulks using pulse
magnetization [superconducting
magnets]
T. Ishigohka, H.
Ichikawa, A. Ninomiya, H. Kamijo and H.
Fujimoto
Summary: The authors have studied
the magnetization characteristics of an array of high Tc
superconductor (HTS) bulks. Experiments using pulsed field
magnetization were carried out at 77 K. In the experiment, the
width of the applied pulse current was varied; i.e.: (1) the
wave-front length of the pulse magnetization current; and (2)
the wave-tail length of the pulse magnetization current were
changed independently. The authors measured the magnetization
pattern of single HTS bulks and that of arrayed HTS bulks.
Furthermore, several HTS bulks were arranged in array and
inserted into a pulse magnetization coil wound by copper wire.
The measured trapped magnetic flux distribution in this
experimental setup was compared with experimental results from
"field cooling". The experimental result shows that the
trapped magnetic flux density is lower in the pulse
magnetization than in the "field cooling". Also, the flux
density pattern of pulse magnetization shows a conspicuous sag
in the center of the bulk. As for the effect of the width of
the applied pulse wave, the wave-front length affects strongly
the trapped magnetic flux density. Meanwhile, the effect of
the wave-tail length was very mild. |
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Dynamics
and relaxation of magnetic stress between magnet and
superconductor in a levitation
system
E. Postrekhin, Ki Bui Ma,
Hong Ye and Wei-Kan Chu
Summary: The force of
levitation experienced by a magnet on top of a superconductor
depends on position and how fast the magnet was put into that
position. As a result, when the levitation force is measured
as a function of the height of the magnet above the
superconductor, a plot of the force versus height also depends
on the rate at which the magnet position was changed during
the experiment. The authors have measured this dependence of
the levitation force (as a function of position) on the
average rate of moving the magnet towards the superconductor
under zero field cooled conditions. This dependence is
appreciable only when the magnet is close to the
superconductor. After the magnet is brought to a stop at the
nearest position, they continued to observe the relaxation of
the magnetic stress between the magnet and the superconductor.
The gross characteristics of the relaxation process after the
magnet stops are similar for different speeds of approach
before the magnet stops. This study aims at determining how
the long term reliability of a superconductor magnet bearing
depend on the process of setting it up. |
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Trapped
field characteristics of Y-Ba-Cu-O bulk in time-varying
external magnetic field
T.
Ohyama, H. Shimizu, M. Tsuda and A.
Ishiyama
Summary: The trapped field
characteristics of disk-shaped YBaCuO bulk exposed to an
external AC magnetic field are investigated experimentally.
The magnetic flux density on the top surface of the disk,
defined as "trapped flux" in this paper, was measured in both
short and long terms as functions of amplitude and frequency
of the AC external magnetic field. The observed trapped flux
attenuation was obviously different from that of flux creep,
i.e., with no external magnetic field; this implies that the
trapped flux density within the YBCO disk is reduced by a
temperature rise due to AC loss. The abrupt attenuation of
trapped flux density in the first several cycles was observed
at frequencies of 0.1 and 1 Hz while not observed at 10 Hz.
The attenuation rate after seven minutes of applying AC
magnetic field, however, became almost the same regardless of
frequency. The trapped flux attenuation in one cycle of AC
magnetic field decreases with the frequency and increases with
the amplitude of AC magnetic field. These results imply that
the characteristic of trapped flux is closely related to AC
loss, especially the hysteresis loss, and the AC loss depends
on the frequency and the amplitude of the AC external magnetic
field. It ran be considered that transient electromagnetic
behavior within HTS bulk, especially supercurrent
distribution, is a key factor of the relationship between the
trapped flux attenuation and the AC loss. |
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Stress
distribution and shape factor of a disk trapped field
magnet
M. Tsuchimoto and H.
Takashima
Summary: Trapped fields and
stresses are examined through one- and two-dimensional
(axisymmetric three-dimensional) solutions when a bulk
high-T/sub c/ superconductor (HTS) is fully magnetized by
field cooling. The shape factor of the bulk magnet is
discussed analytically with ring currents, since the maximum
trapped field depends strongly on its shape. The stresses in
the bulk HTS are numerically evaluated with the
finite-difference method in the framework of the Bean model.
Differences between one- and two-dimensional solutions are
examined in terms of the maximum tension stress and shear
stress. |
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3-D
field analysis of a superconducting bulk
magnet
Seung-Yong Hahn, Ji Hoon
Kim, Chang-Seop Koh and Song-Yop Hahn
Summary:
Magnetic field can be trapped in a superconducting bulk
by using the field cooling method. In this paper, trapped
field was calculated by 3-D numerical analysis. The existing
1-D critical state model was expanded to 3-D. With this model
and iteration method, the nonlinearity of J-E constitutive
relation of a superconducting bulk was numerically modeled.
The field cooling system with a hexahedral bulk and
cylindrical magnet, which is impossible to be analyzed by 2-D
or axisymmetric numerical analysis, was analyzed by the
presented method. Being compared with experimental data, the
validity of the presented method was verified. The finite
element method was adopted for numerical
calculation. |
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Finite
element analysis of magnetic field in high temperature bulk
superconductor
Yon-Do Chun,
Youn-Hyun Kim, Ju Lee, Jung-Pyo Hong and Jong-Woo
Lee
Summary: This paper presents the analysis
of magnetic field in high temperature bulk superconductor
(HTSC). The macroscopic field equations constructed on the
basis of the critical state model and levitation forces are
simulated between permanent magnets (PM) and HTSC using a 3D
axisymmetric finite element method. The force computations are
obtained by using the Lorentz force equation. An iteration
method is used to determine the current distribution of HTSC,
because the J-E relation in HTSC is extremely nonlinear. The
numerical results show that the presented method is
comparatively accurate by comparing the measured levitation
forces and the simulation ones. |
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High
temperature superconducting levitation coil for the Levitated
Dipole Experiment (LDX)
J.H.
Schultz, G. Driscoll, D. Garnier, J. Kesner, M. Mauel, J.V.
Minervini, B. Smith, A. Radovinsky, G. Snitchler and A.
Zhukovsky
Summary: The Levitated Dipole
Experiment (LDX) is an innovative approach to explore the
magnetic confinement of fusion plasmas. A superconducting
solenoid (floating coil) is magnetically levitated for up to 8
hours in the center of a 5-meter diameter vacuum vessel. This
coil is supported by a levitating coil (L-Coil) on top of the
vacuum vessel. In the initial machine design, this levitating
coil was a water-cooled copper solenoid, and was the
experiment's single largest load on the available water
system. The main benefit of using a high temperature
superconducting coil is the ability to apply more auxiliary
heating power to the plasma. However, this coil will also be
the first high temperature superconducting coil to be used in
a US fusion program experiment. The high temperature
superconducting L-Coil is a solenoid, using a two-in-hand
winding of a commercially available 0.17 mm/spl times/3.1 mm
tape by American Superconductor Corporation with a critical
current of 62 A at 77 K and self-field. The L-Coil will be
operated at 0.9 T and 20 K. The L-Coil has a protection
circuit that not only protects it against overheating in the
event of quench, but also against F-Coil collision in the
event of a control failure. |
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Design,
fabrication and test of the react and wind, Nb3Sn, LDX
floating coil
B.A. Smith, J.H.
Schultz, A. Zhukovsky, A. Radovinsky, C. Gung, P.C. Michael,
J.V. Minervini, J. Kesner, D. Garnier, M. Mauel, G. Naumovich
and R. Kocher
Summary: The Levitated Dipole
Experiment (LDX) is an innovative approach to explore the
magnetic confinement of fusion plasma. A superconducting
solenoid (floating coil) is magnetically levitated for up to 8
hours in the center of a 5-meter diameter vacuum vessel. The
floating coil maximum field is 5.3 T, and a react-and-wind
Nb/sub 3/Sn conductor was selected to enable continued field
production as the coil warms from 5 K during the experiment up
to a final temperature of about 10 K. The coil is wound using
an 18-strand Rutherford cable soldered into a half-hard copper
channel, and is self protected during quench. The coil is
insulated during winding and then vacuum impregnated with
epoxy. The impregnated coil is tested with 2 kA operating
current at 4.2 K, and then a single, low resistance joint is
formed at the outer diameter of the coil before the coil is
enclosed in its toroidal helium vessel. This paper presents
details of the coil design and manufacturing procedures, with
special attention to the techniques used to protect the coil
from excessive strain damage throughout the manufacturing
process. |
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Production
of NbTi CICC's for SST-1 project at
IPR
F. Hosono, G. Iwaki, S.
Inaba, T. Suzuki, K. Hiroshima, K. Kikuchi, K. Chida, M.
Watahiki, K. Kamata, S. Pradhan and Y.C.
Sazena
Summary: A total of 24 pieces of NbTi
CICC with outer dimension of 14.8 mm/spl times/14.8 mm and a
piece length of 600 m each have been successfully fabricated
for building TF and PF coils. The CICC is made through the
roll forming and welding process. The insert cable with a
scheme of 3/spl times/3/spl times/3/spl times/5 is made from
0.86 mm diameter multifilamentary NbTi/Cu strand with 10 /spl
mu/m diameter NbTi filaments embedded in Cu matrix at a Cu
ratio of 4.9. No treatment is applied to the strand surface. A
0.025 mm thick SS304 tape is wrapped on the finished fourth
stage cable. A 15 mm thick SS304L strip is then roll formed
around the wrapped fourth stage cable and TIG welding 6
applied continuously at the top longitudinal seam. The welded
conduit is finished to the final square dimension, by passing
it through sizing rolls and turks head rolls set at the end of
the jacketing line. The critical current for a CICC, estimated
through multiplying an average I/sub c/ (without self-field
correction) for the 10 extracted strands by the number of
strands of 135 in a CICC, is approximately 38 kA at 5 T, 4.2
K. This means that there is: no significant degradation of
I/sub c/'s for the strands due to the cabling and jacketing
process. It is confirmed that the finished CICC pieces of 600
m each show a He leakage level well below 0.2/spl times/10/sup
-3/ Toll 1/s. |
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Test
results of SeCRETS, a stability experiment about segregated
copper in CICC
P. Bruzzone, A.M.
Fuchs, B. Stepanov, G. Vecsey and E.
Zapretilina
Summary: Two Nb/sub 3/Sn
cable-in-conduit conductors have been manufactured with
identical non-Cu cross sections and the stabilizer either
included in the Nb/sub 3/Sn composite or partly segregated as
copper wires. The two conductors are series connected and
wound as a bifilar, single layer solenoid, assembled in the
high field bore (11 T) of the SULTAN test facility. Beside the
DC and AC losses characterization, the key tests include
stability under pulsed transversal field (dB/dt up to 180
T/s), at DC operating current up to 12 kA. The results show
that strong, transverse field transients can be withstood by
both conductors with small temperature margin. Cost reduction
measures for fusion conductors are discussed. |
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Facility
status and results on ITER full-size conductor tests in
SULTAN
A.M. Fuchs, B. Blau, P.
Bruzzone, G. Vecsey and M. Vogel
Summary:
SULTAN, the world wide unique, high field, large bore
test facility, has been built as European contribution to the
development program for ITER. The facility has primarily been
devoted to the qualification of full-size
cable-in-conduit-conductors (CICC) foreseen as potential
candidates for use in the Central-Solenoid (CS) and the
Toroidal-Field (TF) coils of ITER, Fields up to 11 T can be
imposed to the vertically inserted CICC-Samples. Horizontal
insertion of coiled long conductor samples is possible as
demonstrated for the QUELL and SeCRETS experiments. The
facility has been upgraded to ITER full-size conductor and
joint testing program requirements. A new, superconducting 100
kA DC-transformer has been constructed in collaboration with
industry. New current sources have been installed for the
pulsed field coils used for AC loss measurements. A new remote
control system has been installed and the control system for
cryogenics has been replaced. Within the frame of the ITER
full size conductor test programme, three Japanese, three
European, one American and two CRPP-FT home made (conductor
and joint) samples have successfully been tested in SULTAN.
The present performance of the facility, experimental results
and a comparison of the joint samples measured up to now are
discussed. |
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Electromagnetic
evaluation of the collective behavior of 720 twisted strands
for the TF model coil
experiment
J.-L. Duchateau, D.
Ciazynski, P. Hertour, M. Spadoni and W.
Specking
Summary: The TF model coil
experiment is aimed at simulating the magnetic behavior of the
toroidal field system of ITER. This coil will operate in DC
current mode. Even in these conditions, the theoretical
critical currents of the cable, which should be the sum of the
critical current of the 720 superconducting strands, may not
be reached. The intrinsically nonperfect current distribution
in the connection area can affect the conductor performances
in the peak field region, only 1.2 m away. This has a strong
influence on the voltage-current characteristic and can
generate a quench before the theoretical critical current is
reached. The theoretical critical current chart is calculated
as a function of temperature and field. This calculation is
based on a precise characterization of the strand at different
temperatures and fields, coupled to quality assurance for each
of the billets. A redistribution process is activated by the
saturation of the overloaded strands leading to current
transfer into underloaded strands. The interstrand contact
resistance and the field pattern affect this
process. |
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ITER
CS model coil and CS insert test
results
N. Martovetsky, P.
Michael, J. Minervini, A. Radovinsky, M. Takayasu, R. Thome,
T. Ando, T. Isono, T. Kato, H. Nakajima, G. Nishijima, Y.
Nunoya, M. Sugimoto, Y. Takahashi, H. Tsuji, D. Bessette, K.
Okuno and M. Ricci
Summary: The inner and
outer modules of the central solenoid model coil (CSMC) were
built by US and Japanese home teams in collaboration with
European and Russian teams to demonstrate the feasibility of a
superconducting central solenoid for ITER and other large
tokamak reactors. The CSMC mass is about 120 t; OD is about
3.6 m and the stored energy is 640 MJ at 36 kA and peak field
of 13 T. Testing of the CSMC and the CS insert took place at
Japan Atomic Energy Research Institute (JAERI) from mid March
until mid August 2000. This paper presents the main results of
the tests performed,. |
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Current
limitation with bulk Y-Ba-Cu-O
P.
Tixador, L. Porcar, E. Floch, D. Buzon, D. Isfort, D.
Bourgault, X. Chaud and R. Tournier
Summary:
The fault current limiter is a very attractive device
for electric networks. Meander pattern conductors cut from
bulk melt textured YBCO were studied for this application. The
meanders are put in series and/or in parallel to match the
required current and voltage. The YBCO materials are
attractive because they show a very effective limitation with
a relative low volume (high engineering current density and
normal state resistivity). However, they are sensitive to hot
spots. To avoid these destructive hot spots the operating
temperature is chosen very close to the critical temperature
(above 90 K). This temperature range is reached using a
pressurised liquid nitrogen bath. Working close to Tc has two
major advantages. The first is reduced values of Jc which
limit the power dissipation. The Jc can be matched by changing
the pressure on the nitrogen bath. The second is that the
proximity of the normal state is favourable for homogeneous
quenches along the whole meander as it can be experimentally
recorded. Results obtained on single meanders and on the whole
assembly are reported under steady state operation as well as
during current limitation. Forty three meanders in series
limited the current to 740 A (11 000 A unlimited value) under
1 kV. |
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Current
limiting performance by single grained Y-Ba-Cu-O
superconducting rings
In-Gann
Chen and Jyh-Ming Lin
Summary: The
single-grained YBCO high Tc superconducting (HTS) offer
applications in the field of superconducting screening fault
current limiters (SSFCL) in electric power networks. The
current limiting mechanism is related to the magnetic
shielding effect of superconductors. Current limitation can be
accomplished by means of the nonlinear impedance of a
transformer with the primary winding carrying the power
circuit current and the short-circuited secondary winding
consisting of rings of single grained Y-Ba-Cu-O (YBCO)
material. The latter remains superconductive at normal load
level, which act as a magnetic flux shielding device to
provide low impedance. If a defined current level is exceeded,
a sufficient high magnetic flux is generated to penetrate the
HTS ring. The secondary winding turns resistive, and provides
a high impedance which limits the prospective fault current.
Ring-shaped single grained YBCO disks with different thickness
and Jc(H) were produced by the top-seeding melt-textured
(TSMT) method. The relationship between the superconducting
properties and the current limiting performance are
reported. |
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Technical
and economical impacts on a power system by introducing an HTS
FCL
M. Sjostrom and D.
Politano
Summary: Fault current limiters
(FCLs) can be considered as key elements in power systems
using high temperature superconductors. This analysis takes
into account the system benefits provided by the introduction
of FCLs in various network configurations. New meshing
possibilities, alternative grounding method and increase of
power transmission are highlighted. It is the desire of most
power system utilities to maximize transferred power and to
reduce system losses to a minimum in their systems. These
goals could be achieved if the system impedance could be
reduced. However, such measures would increase short-circuit
currents enormously and endanger equipment and safety. This
problem could be circumvented by the installation of an IFCL.
FCLs are often implemented in combination with transformers
but the transformer itself could also be designed having an
integrated current limiting functionality. |
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Properties
of YBCO films at high current densities: fault current limiter
implications
M. Decroux, L.
Antognazza, N. Musolino, E. de Chambrier, S. Reymond, J.-M.
Triscone, O. Fischer, W. Paul and M. Chen
Summary:
We have studied the properties of superconducting strip
lines, based on epitaxial YBCO thin films, at high current
densities. Experiments performed with short constant current
pulses show that a quasi spontaneous highly dissipative state
(HDS) appears at high current densities. By carefully
measuring the temperature of the YBCO line, we found that its
temperature is still below T/sub c/ when the HDS occurs,
indicating that this state does not originate from a thermal
runaway. Once initiated, this HDS starts to propagate with an
initial velocity larger than 100 m/s, which is one order of
magnitude higher than thermal velocities. We also applied
constant voltage pulses to the YBCO line, therefore simulating
a real short circuit. We found that the spatial extent of the
HDS along the line, a few microseconds after the short
circuit, depends linearly on the applied voltage. These
results allow explanation of the fast switching properties
observed in superconducting fault current limiters (SFCL) and
the fact that the peak current is limited at, typically, 3
times the critical current. |
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Fault
current limiter-predominantly resistive behavior of a
BSCCO-shielded-core reactor
M.G.
Ennis, T.J. Tobin, Y.S. Cha and J.R. Hull
Summary:
Tests were conducted to determine the electrical and
magnetic characteristics of a superconductor-shielded core
reactor (SSCR). The results show that a closed-core SSCR is
predominantly a resistive device and an open-core SSCR is a
hybrid resistive/inductive device. The open-core SSCR appears
to dissipate less energy than the closed-core SSCR. However,
the impedance of the open-core SSCR is less than that of the
closed-core SSCR. Magnetic and thermal diffusion are believed
to be the mechanisms that facilitate penetration of the
superconductor tube under fault conditions. |
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Design
and considerations on long Nb/sub 3/Sn high field magnets for
hadron colliders
R. Yamada, M.
Wake, Seog-Whan Kim and R.H. Wands
Summary:
Design studies for long high field Nb/sub 3/Sn
superconducting magnets for hadron colliders are described,
taking a 10 meter magnet with a cosine-theta type coil as an
example. The problems and complications are discussed in
comparison with short magnets of 1 meter length, using MIIT
calculations and quench simulation. As the stored energy in
the high field Nb/sub 3/Sn magnets is quite large, close
attention must be paid to all design details, and especially
the extraction of the stored energy. The extensive use of
heaters on the coil surface is simulated to dump the energy on
the coil body itself. The MIIT value of the Nb/sub 3/Sn
superconducting cable should be made large for safe operation.
This is done by increasing the copper ratio. According to the
results of this study, an 11.5 Tesla magnet might be the
limiting case for the design of a practical accelerator high
field magnet. |
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Correction
of the persistent current effect in Nb/sub 3/Sn dipole
magnets
V.V. Kashikhin and A.V.
Zlobin
Summary: The paper describes a method
and results of simulation of persistent current effect in high
field Nb/sub 3/Sn dipole magnets being developed for the
future hadron colliders. Simple and effective techniques of
passive correction of the persistent current effect in
superconducting accelerator magnets are proposed. Using of
these techniques allows a significant reduction of sextupole
and decapole field components induced by persistent currents
in a coil. |
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Helium
and current feeder systems of
KSTAR
C.H. Choi, Y.K. Oh, Y.S.
Kim, Y.M. Park, H.-C. Ri, D.L. Kim, D. Ivanov and G.S.
Lee
Summary: We have estimated the heat load
due to an operating sequence and designed a cooling scheme for
the coil, structure, and bus-line of the Korea Superconducting
Tokamak Advanced Research (KSTAR) device cooled by
supercritical helium. We have also estimated the heat load of
the current lead cooled by liquid helium. Since KSTAR will be
operated in a pulse mode, the AC loss is dominant in the heat
load. The cooling scheme of the magnet system is presented.
Discussion is given for the cooling parameters that consist of
temperature, pressure, mass flow rate, etc. |
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KSTAR
magnet structure design
Y.K. Oh,
C.H. Choi, J.W. Sa, D.K. Lee, K.-I. You, H.G. Jhang, J.Y. Kim,
N.I. Her and G.S. Lee
Summary: The Korea
Superconducting Tokamak Advanced Research (KSTAR) device is a
steady-state-capable experimental fusion device with a fully
superconducting magnet system, including toroidal field (TF)
coils, central solenoid (CS) coils, and poloidal field (PF)
coils. The major design consideration of the magnet system is
to meet the KSTAR mission with plasma current of 2 MA and
toroidal field of 3.5 T at the major radius 1.8 m and z=0. The
preliminary analyses show that the magnet structure design has
mechanical, electrical, and thermal stability during
operation. The TF magnets have a wedged structure, including
coil cases, inter-coil structures, and inter-octant joints.
The CS and PF structures are designed to support the
electromagnetic forces. To support the coil system against
gravity and lateral loads, gravity support and lateral load
structures are designed. |
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Thermohydraulic
simulation on CIC conductor with adaptive mesh finite volume
method for KSTAR tokamak superconducting
magnet
Q.L. Wang, C.S. Yoon, S.
Baang, S.B. Kim, H.K. Park, M.K. Kim, Y.J. Kim, S.L. Lee and
K. Kim
Summary: To study the quench in the
CICC, the numerical analysis code was developed. The fully
implicit time integration of upwind scheme for finite volume
method is utilized to discretize the equations on the
staggered mesh. The scheme of adaptive mesh is proposed for
the moving boundary problem and the time term is discretized
by the /spl theta/-implicit scheme. The discretized equations
are solved by the IMSL. The error analysis of this method is
performed by various step-sizes of time and space. The thermal
hydraulic behavior of the CICC used in KSTAR is
studied. |
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Induced
voltage and alternating current loss in superconducting magnet
system for SSTF
Q.L. Wang, S.
Baang, C.S. Yoon, S.B. Kim, H.K. Park, M.K. Kim, Y.J. Kim,
S.I. Lee and K. Kim
Summary: The induced
voltage in the Samsung Superconducting Test Facility (SSTF) is
analyzed according to the calculation of self-inductance and
mutual inductance. The voltage induced by blip and
compensating coils in the main coils is about 6.4 V. In order
to charge the main coils, the power supply must provide the
minimum voltage of 1.1 kV. The compensating coils have an
influence on the field distribution. The compensating coils
result in the decreasing center field about 2.67%. AC losses
that include the coupling, hysteresis and eddy losses are
calculated in the main, blip and compensating coils. It leads
to the temperature rise of about 8 K in main
coils. |
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Current
control of magneticlly coupled superconducting coils for large
helical device using H-infinity control
scheme
T. Ise, Y. Taizawa, S.
Kumagai and H. Chikaraishi
Summary: Precise
control is required for the current control of the
superconducting coils in the Large Helical Device (LHD) in
NIFS, Japan. There are strong mutual couplings between coils,
and the effect of structure materials surrounding materials of
the coils and plasma, which act like shorted coils seen from
the power source, must be considered for the design of the
current controller. The authors designed the current
controller for the LHD coil, which is composed of an
H-infinity controller and a feedforward controller. Features
of the controller are as follows. At first, it is possible to
design the controller by considering frequency domain
characteristics of the closed loop system and stability of the
designed controller is guaranteed according to the theory of
the H-infinity control. Secondly, the response characteristics
to current reference values and DC-coupled characteristics of
current control can be determined by the design of the
feedforward controller. The designed controller showed
excellent characteristics in both simulation and experimental
results. |
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The
background magnets of the Samsung Superconductor Test Facility
(SSTF)
Sungkeun Baang, Keeman
Kim, Yongjin Kim, Hyunki Park, Sangbo Kim, Qiuliang Wang, M.P.
Alexeev, O.P. Anashkin, D.P. Ivanov, V.E. Keilin, I.A.
Kovalev, S.L. Kruglov, V.V. Lysenko, S.M. Miklyaev, I.O.
Shchegolev, V.I. Shcherbakov, S. Shevchenko, I.O. Shugaev and
M.I. Surin
Summary: The background magnet
system of SSTF (Samsung Superconductor Test Facility) for
KSTAR (Korea Superconducting Tokamak Advanced Research) is now
under design. The main coil (MC) is split solenoids and the
gap can be changed from 0 to 750 mm. The ID of MC is 750 mm.
It will be wound using a CICC (cable-in-conduit conductor)
designed for the central solenoid of KSTAR. The central field
is 8 T at 22.5 kA when the gap is 250 mm. The ramp rate of MC
is 3 T/s. A pair of blip coils will simulate (during the
discharge) 1 T amplitude and 20 T/s rate electromagnetic
disturbances expected from the KSTAR operation. To compensate
the inductive interaction between MC and blip coils during the
discharge of the blip coils, a pair of cancellation coils is
foreseen. Both blip and cancellation coils (BCC) are fed in
series and generate 1 T central field at 7 kA and 250 mm gap.
The BCC are wound with CICC and cooled internally and
externally. |
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Study
on recovery time of a superconducting fault current limiter
with adjustable trigger current
level
Y. Shirai, K. Fujikawa, T.
Kitagawa, M. Shiotsu, H. Hatta, S. Muroya and T.
Nitta
Summary: The recovery time of a
transformer type SCFCL (superconducting fault current limiter)
with adjustable trigger current level, is studied
experimentally The recovery time is defined as the required
time of zero current period of SCFCL for recovery from its
current limiting mode to its waiting mode. A trial SCFCL,
which was designed and made, is tested to measure the recovery
time with various fault time. The experimental results show
that the recovery time depends on the fault time. When the
fault time is longer than 200 ms, the recovery time becomes
shorter and approaches a certain value (a few ten ms) as the
fault time is longer. |
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Single
DC reactor type fault current limiter for 6.6 kV power
system
T. Nomura, M. Yamaguchi,
S. Fukui, K. Yokoyama, T. Satoh and K. Usui
Summary:
We propose a single DC reactor type fault current
limiter. This fault current limiter is for a three-phase power
system, employing only one superconducting coil that is
connected with the secondary windings of transformers through
a diode-bridge. In this composition, a DC reactor type fault
current limiter using a high temperature superconducting coil
takes advantage of coil inductance and does not require a
superconducting coil normal transition. This paper presents
the most suitable case of a single DC reactor type fault
current limiter for a 6.6 kV power system and compares it with
a three DC reactors type fault current limiter. |
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Increase
in transient resistance of Bi2223 superconducting bulk by
applying external magnetic
field
K. Kato, T. Noda, H.
Shimizu, Y. Yokomizu, T. Matsumura and N.
Murayama
Summary: The critical current and
the transient change of resistance in a Bi2223 bulk applied DC
magnetic field were experimentally investigated. Taking
account of the decreasing rate of critical current and the
increasing rate of resistance obtained from the measurement,
we estimated the condition under which the gross resistance of
the bulk rises while maintaining the critical current and bulk
volume. Furthermore, it is discussed whether the bulk should
be used with the applied magnetic field or not from the
viewpoint of the bulk volume required to obtain the critical
current and resistance designated. |
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Stability
analysis of a power system with superconducting fault current
limiter installed
Seungje Lee,
Chanjoo Lee, Tae Kuk Ko and Okbae Hyun
Summary:
As a process of developing high temperature
superconducting fault current limiter (SFCL), the stability of
a power system in which SFCLs were installed was analyzed. For
the investigation into the effect of SFCLs to a power system,
we have proposed a simple model power system that had SFCL
circuits. The modeling parameters of SFCL are obtained by
experiment of a prototype SFCL, which is 440 V class and a
shielding type model. This electric circuit was solved for
transient performance by numerical methods. In case the SFCLs
are installed in a power system, it can effectively protect
synchronization both in a symmetrical three-phase fault and a
single-phase line to ground fault by maintaining synchronism
of the synchronous machines for a long time. By this analysis,
we found a quantitative effect of SFCLs to a power system.
Limiting fault currents means not only an improvement of
circuit breaker abilities but also a protection of
synchronism. So its synchronism protection property must be
considered for a design of superconducting fault current
limiters. |
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Design
and characteristic analysis of a rod type high-Tc
superconducting fault current limiter through electromagnetic
analysis
Chanjoo Lee, Seungje
Lee, Ok-Bae Hyun and Tae Kuk Ko
Summary: The
existence of large air gaps, between a high-Tc superconducting
(HTS) tube and an iron core, or between a primary winding and
a HTS tube, possibly causes some undesirable voltage drops
under the condition of normal operation. It makes the power
system unstable. For this reason, the optimization of air gaps
is essential in designing a high-Tc superconducting fault
current limiter (SFCL). In this paper, the optimal values of
air gaps are determined through electromagnetic analysis, and
the comparison between computational and experimental results
is provided. |
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Application
of single DC reactor type fault current limiter as a power
source
K. Yokoyama, T. Sato, T.
Nomura, S. Fukui and M. Yamaguchi
Summary:
This paper presents an application of single DC reactor
type fault current limiter (FCL) with a gate turnoff (GTO)
thyristor bridge as an emergency power source. A DC reactor
type FCL stores electrical energy in a superconducting coil at
a steady state. When a power transmission stops due to line
faults, the FCL supplies stored energy to the load. This
conception can be realized by operating the GTO thyristor
bridge as an inverter. On the other hand, the function of
fault current limitation is possible by keeping all GTO
thyristors turned-on. The proposed FCL is numerically tested
in a three-phase distribution system. |
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Study
of the quench conditions in superconducting current
limiters
V. Sokolovsky, V.
Meerovich, S. Goren and I. Vajda
Summary: A
peculiarity of the operation of superconducting current
limiters is that the resistance appearing in a superconductor
influences the current in the circuit. Using an analytical
approach, we analyze the conditions of the normal state
formation and return into the superconducting state. The
stability of equilibrium points is investigated as a function
of the parameters of the circuit. It is shown that the
superconductor stability is increased in comparison with the
stability of a superconductor in the circuit of the current
source. This allows one to use superconductors nonstabilized
by normal metal to build current limiters and switches. It is
demonstrated that using high-temperature superconductors the
current limitation can be achieved even in the flux creep
regime. |
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Thermal
design and performance tests of a current limiter with a
conduction cooled Nb/sub 3/Sn
screen
K. Sasaki, A. Yamagata, A.
Nii, T. Onishi and M. Shibuya
Summary: We
examined the possibility of the practical use of a conduction
cooled magnetic shield type fault current limiter from the
view point of a thermal design. The thermal calculation was
carried out with a small model using the Nb/sub 3/Sn wire with
low AC loss. We found that the temperature increase of the
small model was insignificant. We also confirmed the current
limiting operation in an experiment. The conceptual design and
the thermal calculation of the conduction cooled fault current
limiter for a distribution power system is also discussed in
this report. |
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Quench
development and ultimate normal zone propagation "velocity" in
superconductors under fast current
change
V.S. Vysotsky, Yu.A.
Ilyin, A.L. Rakhmanov, K. Funaki, M. Takeo, K. Shimohata, S.
Nakamura, M. Yamada and K. Hasegawa
Summary:
Normal zone evolution or quench development is a major
feature for resistive type fault current limiters design. We
studied quench development under fast current rise in several
samples of multifilament superconducting wires with a highly
resistive matrix. At very fast current rise rates simultaneous
quench of the entire sample takes place. It may be described
by a characteristic time of a quench. We found that at the
highest current rise rate this time is the same for samples
with different lengths and cooling conditions made from the
same wire. Apparent normal zone "velocity" determined by this
time is an ultimate velocity for a given length of a
superconducting wire of certain type. We present experimental
data about quench development under fast current rise and
provide the theoretical estimations of quench
parameters. |
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Application
of resistor based superconducting fault current limiter to
enhancement of power system transient
stability
M. Tsuda, Y. Mitani, K.
Tsuji and K. Kakihana
Summary: This paper
presents an application of a superconducting fault current
limiter (SFCL) to enhance the power system transient
stability. Resistance as the current limiting devices is used
for damping the generator accelerating power. A method to
evaluate an appropriate resistance is proposed. The SFCL is
combined with the superconducting magnetic energy storage
(SMES) for power system stabilization. As a result the
capacity of SMES is significantly reduced. |
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A
single DC reactor type fault current limiting interrupter for
three-phase power system
K. Usui,
T. Nomura, T. Satoh, M. Yamaguchi, S. Fukni, K. Yokoyama and
T. Nagasawa
Summary: The authors propose a
single DC reactor type fault current limiting interrupter
(FCLI) for a three-phase power system. The device uses a
single high temperature superconducting (HTS) coil that
operates in conjunction with a modified half control bridge
composed of thyristors and diodes connected to a transformer's
secondary windings. One variety is an automatic interrupter,
which automatically blocks fault current through the
application of DC bias current to the bridge. Another is a
gate interrupter, which does the same thing by locking the
thyristor's gate pulses. The authors examine the results of
various simulations on a new device that both limits and
interrupts fault current in a three-phase power
system. |
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Experimental
characterization of resistive joints for use inside ATLAS
toroids
G. Volpini, G.
Baccaglioni and M. Pojer
Summary: The authors
have investigated, both experimentally and theoretically, the
thermo-electrical behavior of the ATLAS magnets resistive
joints. These magnets exploit an Al-clad NbTi Rutherford
superconducting cable, and the splices between different
sections are performed by TIG-welding the Al matrices of the
two cables to be connected. This technique is simple from a
construction point of view, and we have shown that its
performance is adequate for a safe operation of the magnets.
The two main concerns during the design of these joints are
the temperature rise due to Joule dissipation and the eddy
currents induced under nonstationary conditions. We have
devised a reliable model of these joints, that allows
estimating their resistances and the induced eddy currents;
later we have built and measured several sample joints to give
experimental confirmation. The model requires, along with the
joint geometry, the knowledge of the Rutherford-matrix
interface resistance as well as the RRR of the aluminum
matrix. In this paper we present the latest experimental data
about the joint specific resistances, confirming the first
results, and independent measurements of the interface
resistance and Al RRR. All these quantities are characterized
as a function of an applied magnetic field between 0 and 4
T. |
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Strand
critical current degradation in Nb/sub 3/Sn Rutherford
cables
E. Barzi, M. Fratini, H.C.
Higley, R.M. Scanlan, R. Yamada and A.V.
Zlobin
Summary: Fermilab is developing 11
Tesla superconducting accelerator magnets based on Nb/sub 3/Sn
superconductor. Multifilamentary Nb/sub 3/Sn strands produced
using the modified jelly roll, internal tin, and
powder-in-tube technologies were used for the development and
test of the prototype cable. To optimize the cable geometry
with respect to the critical current, short samples of
Rutherford cable with packing factors in the 85 to 95% range
were fabricated and studied. In this paper, the results of
measurements of critical current, n-value and RRR made on the
round virgin strands and on the strands extracted from the
cable samples are presented. |
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A
continuum model for current distribution in Rutherford
cables
A. Akhmetov, L. Bottura
and M. Breschi
Summary: An analysis of eddy
currents induced in flat Rutherford-type cables by external
time dependent magnetic fields has been performed. The induced
currents generate in turn a secondary magnetic field which has
a longitudinal periodicity (periodic pattern). The dependence
of the amplitude of the pattern on the history of the cable
excitation has been investigated. The study has been carried
out with two different models for the simulation of current
distribution in Rutherford cables, namely a network model,
based on a lumped parameters circuit and a "continuum" model,
based on a distributed parameters circuit. We show the results
of simulations of the current distribution in the inner cable
of a short LHC dipole model in different powering conditions
and compare them to experimental data. |
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Fabrication
and prototype testing of a strain-tolerant Bi-2212
cable
R. Soika, N. Diaczenko, T.
Elliott, W. Henchel, E. Hill, G. Liang, P. McIntyre, L.
Motowidlo and M. Yavuz
Summary: We have
successfully manufactured and tested prototypes of a
mechanically stabilized Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub
2/O/sub 5/ (Bi-2212) 6-on-1 cable-in-conduit (CIC). The
superconducting wire in the cable is reinforced with Inconel
X-750 tubes to provide improved strain tolerance and greater
ease of handling. We provide a detailed description of the
manufacturing process. We have wound test coils from the
cable, and report on the preliminary testing of the
coils. |
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Electromagnetic
behavior of a superconducting power
cable
M.
Daumling
Summary: The electromagnetic
behavior of a superconducting power cables consisting of a
layered structure is described using a circuit model.
Ingredients for the model are the voltage current
characteristics of the tapes used to make the cable, and the
self and mutual inductances of the layers. Current and voltage
wave shapes are calculated numerically as a function of
externally applied AC. This is shown, quantitatively for a 4
layer cable with alternating pitch of +/- 0.3 m. Saturation
losses are computed simply by multiplying voltage and current.
Due to the nonlinear VI characteristics of the layers, layer
currents becomes nonsinusoidal in the vicinity of the layer
critical current. However, if the current is below the
critical current of the whole cable these nonlinearities
appear to cancel and the overall current shape remains
sinusoidal. |
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Conductor
development for high energy physics-plans and status of the US
program
R.M.
Scanlan
Summary: In order to provide a cost
effective high field magnet option for the next generation HEP
accelerator, higher performance Nb/sub 3/Sn superconductor is
required. These requirements have been recognized by the DOE,
and a conductor development program has been initiated. The
goal is to produce cost-effective conductor with a Jc
(noncopper, 12 T, 4.2 K) exceeding 3000 A/mm/sup 2/ and an
effective filament size of less than 40 micrometers. Although
the Nb/sub 3/Sn conductors manufactured at present have
produced Jc values in excess of 2200 A/mm/sup 2/, no conductor
being manufactured at present can achieve both the aggressive
Jc and effective filament size goals. The first phase of the
present program is underway, and is focused on improving the
understanding of the factors that control Jc. Samples are
being manufactured by industry and are being characterized
with respect to Jc and magnetization as a function of
composition and heat treatment condition. Using this new
knowledge as a base, the program will move into a fabrication
scale-up phase where the performance and cost-effectiveness
can be demonstrated on production size quantities. The status
and accomplishments of this program are reviewed, and the
plans for the scale-up program are presented. |
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Persistent
current effects in BSCCO common coil
dipoles
W.B. Sampson, A.K. Ghosh,
J.P. Cozzolino, M.A. Harrison and P.J.
Wanderer
Summary: A series of one-meter long
racetrack-shaped windings has been fabricated from BSCCO tape
conductors obtained from four manufacturers. Two coils were
built from each conductor type and tested in the "common coil"
dipole configuration in liquid helium. The effect of the
remnant magnetization currents determined by measuring the
residual dipole sextupole fields after cycling the magnets to
progressively higher currents. Two coil sets have been
measured and the results are compared to those obtained from a
Nb/sub 3/Sn ribbon magnet of the same geometry. |
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Fabrication
of the shell-type Nb/sub 3/Sn dipole magnet at
Fermilab
D.R. Chichili, G.
Ambrosio, N. Andreev, E. Barzi, S. Caspi, V.V. Kashikhin, P.J.
Limon, R. Scanlan, I. Terechkine, J. Tompkins, M. Wake, S.
Yadav, R. Yamada, V. Yarba and A.V. Zlobin
Summary:
A 43.5 mm aperture dipole magnet with a nominal field
of 11 T is being fabricated at Fermilab. The design is based
on a two-layer shell-type coil structure made of
Rutherford-type Nb/sub 3/Sn cable with wind and react
technology. The mechanical support structure consists of
vertically split iron yoke locked by two aluminum clamps and a
8 mm thick stainless steel skin. This paper summarizes the
fabrication details of the first dipole model and test results
from a 2110 mm long mechanical model. |
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Fabrication
and test of Nb/sub 3/Sn racetrack coils at high
field
B. Benjegerdes, P. Bish, D.
Byford, S. Caspi, K. Chow, D. Dietderich, S.A. Gourlay, R.
Gupta, R. Hafalia, R. Hannaford, W. Harnden, H. Higley, A.
Jackson, A. Lietzke, N. Liggins, A. McInturff, G. Millos, J.
O'Neill, E. Palmerston, G. Sabbi, R. Scanlan and J.
Swanson
Summary: A program based on exploring
the benefits of racetrack coil designs for utilization of
brittle superconductors to achieve high fields is underway at
LBNL. As an intermediate step in the experimental program, a
set of Nb/sub 3/Sn racetrack coils, using state-of-the-art
conductor, have been built and tested. The coils were
configured to maximize the field, providing a means to study
the effects of stress on conductor performance. In addition,
several design improvements were added which will be
implemented in the next step of the program; construction of a
racetrack dipole with a field of 14 Tesla. An evaluation of
the design modifications and test results are
given. |
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Common
coil magnet program at BNL
R.
Gupta, M. Anereila, J. Cozzolino, J. Escallier, G. Ganetis, A.
Ghosh, M. Harrison, G. Morgan, J. Muratore, B. Parker, W.
Sampson and P. Wanderer
Summary: The goal of
the common coil magnet R&D program at Brookhaven National
Laboratory (BNL) is to develop a 12.5 T, 40 mm aperture dipole
magnet using "react and wind technology" with high temperature
superconductors (HTS) playing a major role. Due to its
"conductor friendly" nature, the common coil design is
attractive for building high field 2-in-1 dipoles with brittle
materials such as HTS and Nb/sub 3/Sn. At the current rate of
development, it is expected that a sufficient amount of HTS
with the required performance would be available in a few
years for building a short magnet. In the interim, the first
generation dipoles will be built with Nb/sub 3/Sn
superconductor. They will use a "react and wind" technology
similar to that used in HTS and will produce a 12.5 T central
field in a 40 mm aperture. The Nb/sub 3/Sn coils and support
structure of this magnet will become a part of the next
generation hybrid magnet with inner coils made of HTS. To
develop various aspects of the technology in a scientific and
experimental manner, a 10-turn coil program has been started
in parallel. The program allows a number of concepts to be
evaluated with a rapid throughput in a cost-effective way.
Three 10-turn Nb/sub 3/Sn coils have been built and one HTS
coil is under construction. The initial test results of this
"react and wind" 10-turn coil program are presented. It is
also shown that a common coil magnet design can produce a
field quality that is as good as a conventional cosine theta
design. |
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Development
of react and wind common coil dipoles for
VLHC
G. Ambrosio, N. Andreev, E.
Barzi, P. Bauer, D. Chichili, K. Ewald, L. Imbasciati, V.
Kashikhin, S.W. Kim, P. Limon, I. Novitski, J.P. Ozelis, R.
Scanlan, G. Sabbi and A. Zlobin
Summary:
Common coil magnets are a promising option for post LAC
hadron colliders. Fermilab, in collaboration with LBNL, is
involved in an R&D program to develop 11 T, 30-40 mm
aperture, common coil dipoles. The use of Nb/sub 3/Sn wound
after reaction is chosen in order to address cost reduction
that is a key issue for future hadron colliders. The common
coil design concept allows a large bending radius at the coil
ends and is well suited to the react-and-wind technique with
brittle superconductors. The horizontal component of the
magnetic forces in a common coil is larger than the radial
component in a shell type layout, imposing demanding
requirements on the mechanical structure. Both a 2-layer and a
single layer design have been studied. The development of the
program is presented focusing on the mechanical designs and
assembly techniques. R&D activities and plans are also
presented. |
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Magnetic
designs of 2-in-1 Nb/sub 3/Sn dipole magnets for
VLHC
V.V. Kashikhin and A.V.
Zlobin
Summary: The paper presents the
results of a conceptual design study of double aperture Nb/sub
3/Sn dipole magnets for VLHC based on the cos-theta and common
coil geometry with cold and warm iron yoke. The study included
an optimization of the iron yoke geometry to achieve the
maximum transfer function, small fringe fields and low-order
field harmonics as well as an optimization of the coil
geometry to correct a quadrupole field component (normal or
skew) inevitable for 2-in-1 magnet designs. |
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A
thin superconducting solenoid for use in a phase rotation
induction linac
M.A. Green, J.
Fockler, R.E. Lafever, D.L. Vanecek and S.S.
Yu
Summary: One of the proposals for
delivering a cooled muon beam to a muon collider or a high
intensity neutrino source uses an induction linac to phase
rotate the muons that result from the decay of pions produced
by a high intensity proton beam on a target. An induction
linac with an acceleration gradient of 2 MV per meter is
proposed to produce bunches of muons that have a momentum of
200 MeV/c. The induction accelerator is assembled around the 3
T superconducting solenoids needed to contain the muon beam.
The superconducting solenoid must have a warm 100 mm gap at
1000 mm intervals down the phase rotation channel. The
acceleration structure for the induction linac is around this
gap. The superconducting solenoid will have an inside warm
radius of 201 mm. The thickness of the superconducting magnet
and its cryostat must be about 60 mm near the acceleration
gap. An access region of 85 mm between induction linac
sections is allowed for the superconducting coil cold mass
supports, the electrical leads and the supply of cryogenic
cooling. This report presents a design for a 3 T phase
rotation induction linac superconducting magnet system, its
cryostat, and its cooling system. |
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Development
of a Nb/sub 3/Sn quadrupole magnet
model
A. Devred, M. Durante, C.
Gourdin, F.P. Juster, M. Peyrot, J.M. Rey, J.M. Rifflet, J.M.
Streiff and P. Vedrine
Summary: One possible
application of Nb/sub 3/Sn, whose superconducting properties
far exceed those of NbTi, is the fabrication of short and
powerful quadrupole magnets for the crowded interaction
regions of large particle accelerators. To learn about Nb/sub
3/Sn technology and to evaluate fabrication techniques,
DAPNIA/STCM at CEA/Saclay has undertaken an R&D program
aimed at designing and building a 1 m-long, 56 mm
single-aperture quadrupole magnet model. The model relies on
the same coil geometry as the LHC arc quadrupole magnets, but
has no iron yoke. It is expected to produce a nominal field
gradient of 211 T/m at 11870 A. The coils are wound from
Rutherford-type cables insulated with quartz fiber tapes,
before being heat-treated and vacuum-impregnated with epoxy
resin. Laminated, austenitic collars, locked around the coil
assembly by means of keys restrain the Lorentz forces. After
reviewing the conceptual design of the magnet model, we report
on the cable and cable insulation development programs and we
present the results of NbTi-Nb/sub 3/Sn cable splice
tests. |
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Multiphase
AC loss mechanisms in HTS prototype multistrand
conductors
J.O. Willis, D.E.
Daney, M.P. Maley, H.J. Boenig, R. Mele, G. Coletta, M. Nassi
and J.R. Clem
Summary: We report on
multiphase AC losses in four-layer prototype multi-strand
conductors (PMCs) wound from high temperature superconducting
(HTS) tape provided by American Superconductor Corporation,
"Two-phase" losses are induced with no current flowing in the
PMC but with an AC magnetic field generated by currents
flowing in the two normal conductors arranged at the remaining
corners of an equilateral triangle forming a three-phase
configuration. This is a typical configuration that a power
cable of the "warm dielectric" design could have. The losses
were measured at 65 to 76 K, in a frequency range from 10 to
180 Hz, and for currents from 600 to 1600 Arms. We compare the
losses for two PMCs, one wound conventionally with equal pitch
angles for all layers and the second wound to achieve uniform
current distribution (UCD) among the layers. The UCD method
results in reduced single-phase losses at currents greater
than about 1/2 of the critical current. However, the two-phase
losses are somewhat larger for the PMC wound by the UCD
method. We investigated this difference empirically and
theoretically. |
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AC
losses of HTS power transmission cables using Bi-2223 tapes
with twisted filaments
S.
Mukoyama, K. Miyoshi, H. Tsubouti, H. Tanaka, A. Takagi, K.
Wada, S. Megro, K. Matsuo, S. Honjo, T. Mimura and Y.
Takahashi
Summary: TEPCO and Furukawa have
been developing compact 66 kV HTS power cables that can fit
into 150 mm ducts. To realize these compact and highly
efficient cables, decreasing AC losses in the cables is
important. An effective method for reducing the AC losses is
to suppress the electromagnetic coupling between layers and
between filaments: equalizing the impedance of each layer
suppresses the electromagnetic coupling between layers; and
using twisted filaments in Bi-2223 tape suppresses the
electromagnetic coupling between filaments. An HTS conductor
was fabricated using Ag-Mg sheathed tapes that had twisted
filaments, and the AC losses in the conductor were measured.
The AC losses were lower than that of nontwisted filamentary
conductors. Furthermore, the AC losses in an HTS cable were
measured at temperatures ranging from 67 K to 77 K, using a
device that can cool liquid nitrogen to less than 77 K. As a
result of twisting the filaments in the tape and uniform
current distribution for the conductor, the AC losses were
reduced to the lowest levels ever achieved. |
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Low
loss conductors for power
applications
C.M. Friend, D.M.
Spiller, Y.B. Huang and E. Martinez
Summary:
The AC losses of (Bi,Pb)SrCaCuO tapes and wires and a
YBaCuO tape have been measured in self and applied fields. The
transport losses of the YBCO tape are much higher than any
predictions using the critical state model. In this situation,
the Bi-2223 wires and twisted tapes have the lowest losses. In
applied perpendicular fields the losses of all conductors are
currently too high and should be reduced. The Bi-2223 wires
are the most flexible and provide the greatest scope for
further loss reduction in the short to medium
term. |
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Local
calorimetry to measure the AC losses in structures of HTS
conductors
S.P. Ashworth and M.
Suenaga
Summary: We have previously shown
that it is possible to measure losses of a conductor in almost
any combination of field and current using calorimetric
method. We now extend this technique to structures of
conductors where the AC magnetic fields generated by the
structure as a whole influence the losses of the individual
conductors. Using our calorimetric technique we are able to
measure the losses at specific locations within a coil or
array. In this paper we present as examples loss measurements
made on a simple solenoidal coil and in a multi-tape, high
amperage conductor. |
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V-I
curves of a 100-kVA class high-T/sub c/ resonator
coil
O.A. Shevchenko, J.J.
Rabbers, A. Godeke, B. ten Haken and H.H.J. Ten
Kate
Summary: Potentially, coils made with
BSCCO-2223/Ag tape and operating in liquid nitrogen at 50-60
Hz are interesting for power related applications. The
electrical characteristics of such a coil depend on the radial
magnetic field in the windings. One way to suppress the radial
field is by placing small iron pieces around coil edges. V-I
curves of the 100 kVA coil are calculated and measured for two
cases: coil edges without and with iron pieces. The coil is a
solenoid with inner and outer diameters and a height of 470,
474 and 614 mm respectively. A numerical model adapted to the
coil geometry is used to calculate the conductor losses. The
loss voltage is also evaluated by measuring the coil
temperature. The total loss of the coil is measured
electromagnetically. Calculated and measured losses are in
agreement. Finally, the loss V-I curves of the coil are
simulated in the frequency range of 0 to 400 Hz. The results
are applied to the design of a 1 MVA resonator
coil. |
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Origins
of errors in AC transport current loss measurements of HTS
tapes and methods to suppress
errors
O. Tsukamoto, J. Ogawa, M.
Ciszek, D. Miyagi, I. Okazaki, Y. Niidome and S.
Fukui
Summary: This paper addresses an
electrical measurement method of AC transport current losses
in HTS tapes. In the method, there are various origins of
errors e.g. improper arrangement of leads from the voltage
taps on an HTS tape, phase errors of a current measuring
device and inductive voltage cancellation device, external
magnetic field, magnetization of neighboring tapes and common
mode noise in the voltage signal from the sample. Influence of
those errors are studied, and methods to suppress the errors
are discussed. In the paper, some techniques which can
minimize the errors are recommended. |
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Analysis
and measurement of AC transport current loss in BSCCO tape in
external magnetic field
S. Fukui,
M. Ikeda, T. Sano, H.S.M. Yamaguchi and T.
TYakao
Summary: A numerical model to
calculate current distribution and AC loss in a high
temperature superconducting tape carrying AC transport current
exposed to an external magnetic field was developed. The model
considers the electric field and current density relation and
the shape of wire. The authors measured the AC transport
current losses in a conventional Bi2223/Ag multifilamentary
tape in a DC external magnetic field and the results were
compared with the numerically calculated AC losses. The
measured AC transport current losses increase as the DC
external field increases. It is also shown that the measured
losses per cycle decrease with increasing frequency. These
characteristics cannot be explained by the critical state
model. The numerical losses by their model reasonably agree
with the measured data. The transport loss characteristics
under the DC field and their dependence on the frequency are
explained by the numerically calculated current distribution
in the wire. |
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The
experimental study of AC loss dependency on joint method in
BSCCO-2223 tape
Hyoungku Kang,
Jung Ho Kim, Hoon Hwangbo, Jinho Joo, Wansoo Nah, Mihye Jang,
Ho Kin Kim, Yong Soo Yoon, Sang-Soo Oh, Kang-Sik Ryu and Tae
Kuk Ko
Summary: In case of manufacturing
applied superconducting machines using high-Tc superconductors
(HTS) such as SMES, MAGLEV and superconducting generators,
superconducting joints are very important because they need
very long tapes. For this reason, the investigation of AC loss
of jointed tapes should be considered as well as that of the
AC loss of jointless tapes, and so the authors investigated
the tendency of AC loss with superconducting joint, and
compared the AC loss of jointed tapes with that of jointless
tapes. In this paper, the AC loss in BSCCO-2223 silver (Ag)
sheathed tapes was measured by using the four-probe transport
technique at 77 K. Firstly, it was shown that the experimental
measurement of AC loss in the tapes agree well with the
calculated values provided by the Norris equation. Moreover,
it was shown that the AC loss depends on amplitude of
transport current. Finally, it was shown that the AC loss
depends on joint resistance and index n. |
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Effect
of the neighboring tape's AC currents on transport current
loss of a Bi-2223 tape
K. Ryu,
K.B. Park and G. Cha
Summary: Bi-2223 tapes
have been developed for low-field power applications at liquid
nitrogen temperature. When the Bi-2223 tapes are used in an
application such as a power transmission cable or a power
transformer, they are supplied with an AC transport-current
and exposed to an external magnetic field generated by
neighboring tape's AC currents simultaneously. AC loss. taking
into account such real applications. is a crucial issue for
power applications of the Bi-2223 tapes to be feasible. In
this paper, the transport losses for different AC current
levels and arrangements of the neighboring tapes have been
measured in a 1.5 m long Bi-2223 tape. The significant
increase of the transport losses due to neighboring tape's AC
currents is observed. An increase of the transport losses
caused by a decrease of the Bi-2223 tape's critical current is
a minor effect. The measured transport losses could not be
explained by a dynamic resistance loss based on DC
voltage-current characteristics in combination with the
neighboring tape's AC currents. The transport losses do not
depend on the frequency of the neighboring tape's AC currents
but its arrangements in the range of small current
especially. |
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Calibration
of Hall sensor AC loss
measurements
M. Staines, S. Rupp,
D. Caplin, D. Yu and S. Fleshler
Summary:
Accurate measurements of the magnetic AC loss in short
samples of conductor are essential for the design of
superconducting power devices and guide the development of
superconducting wire with low AC losses. The authors report
quantitative AC loss measurements at power frequencies at 77 K
obtained with a Hall sensor magnetometer (HSM) using a
calibration method which involves assumptions about the
current distribution within the sample. The samples included
strips of pure silver and multi-filamentary Bi-2223 tapes. A
comparison using AC susceptometry and their Hall sensor
magnetometer technique shows good agreement between the two
methods for both the HTS and silver tape samples. In the case
of the silver tapes the results also agree with the predicted
power loss. AC susceptometer measurements were made using a
pick-up coil enclosing the entire sample so that the global
magnetic moment was measured, including any effects of the
sample ends. The HSM results are unaffected by sample
end-currents. The comparison confirms the accuracy of the
calibrated HSM technique. |
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Experimental
result of transport current loss in bifilar winding solenoid
type HTS coil
Ji-Kwang Lee,
Woo-Seok kim, Ji Hoon Kim, Seungwook Lee, Guesoo Cha and
Song-Yop Hahn
Summary: AC loss is very
important theme for the application of multifilamentary BSCCO
tape in power cable and transformer, and the major part of AC
loss comes from hysteresis loss generated in the filaments by
transport current in those application for practical
frequency. Until now, transport current losses were measured
in a short length specimen, and its results were compared with
the Norris equation. Also, HTS coils for power application
such as transformer has been of the wound pancake type. But
eventually, the coil for power application must be wound
solenoid type such as LTS cases. In this paper, the
experimental results for critical current and transport
current loss in solenoid type winding coil with BSCCO tapes
are presented. The authors make a bifilar winding coil for
accurate measurement of transport current loss by removing
external field effect generated by transport currents flowing
in other tapes in the coil. They compare the measured result
with calculation result using Norris equation for the
verification of the experiment. |
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Numerical
analysis of hysteretic losses on high temperature
superconducting coils
L. Bigoni,
E. Cereda, P. La Cascia, F. Negrini, V. Ottoboni and P.L.
Ribani
Summary: A model to calculate
hysteretic losses in superconducting coils made of BSCCO/Ag
tapes is described. The model is based on DC measurements of
V-I characteristic and of the dependence of critical current
of the tape from amplitude and orientation of the magnetic
field. The model can be applied whenever the current direction
is perpendicular to the magnetic field vector as in solenoidal
and toroidal coils. In this paper, an axisymmetric system is
considered and only the azimuthal component of the current
density is present. A sinusoidal time dependence of the
transport current is considered but a general time behavior
can be easily analyzed by the model. A comparison between the
calculated data and the experimental data is presented and
discussed. |
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Dependence
of spatial distribution of shielding current density in HTS
plate on applied magnetic field
profile
T. Yokono, K. Hasegawa
and A. Kamitani
Summary: The spatial
distribution of the shielding current density in the high-Tc
superconducting (HTS) plate is investigated numerically. The
multiple-thin-layer structure is assumed to modelize the IPTS
plate and the flux-flow and flux-creep model is adopted to
describe mixed states of the HTS plate. Under these
assumptions, the shielding current density flowing in the HTS
plate is governed by the integro-differential equations of the
scalar potential. By applying the FEM to the spatial
discretization of the equations, a nonlinear system of
first-order ordinary differential equations is obtained. In
order to solve the nonlinear system, the high performance
numerical method is employed. A numerical code to integrate
the equation has been developed and, by use of the code, the
time evolution of the shielding current density is
investigated. The results of computations show that the
shielding current density becomes more peaked near the edge of
the plate with an increase in the frequency of the applied
magnetic field. Moreover, it is found that, in the
high-frequency region, the phase difference between the
applied and the generated magnetic fields approaches to /spl
pi/ with an increase in the applied magnetic
field. |
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Numerical
simulation for AC losses of HTS tapes in combined alternating
transport current and external AC magnetic field with phase
shift
K. Kajikawa, A. Takenaka,
K. Kawasaki, M. Iwakuma and K. Funaki
Summary:
AC losses are numerically evaluated for a Bi-2223
tape-shaped wire in combined alternating transport current and
external AC magnetic field with a phase shift. It is
considered that the external field is applied only parallel to
the wide surface of tape. Since the multifilamentary wire
without twisting is assumed, a solenoidal coil is simplified
as a homogeneous superconducting sheet with infinitely wide
surfaces. The electromagnetic quantities are numerically
calculated by solving Maxwell's equations and the
voltage-current characteristics represented by the power law
simultaneously. The calculations of AC losses are carried out
as a function of both amplitudes of transport current and
external magnetic field. The obtained results are plotted on a
master curve for the maximum magnetic field applied to the
wire. |
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Stand-alone
solid nitrogen cooled "permanent" high-temperature
superconducting magnet system
B.
Haid, H. Lee, Y. Iwasa, Sang-Soo Oh, Hong-Soo Ha, Young-Kil
Kwon and Kang-Sik Ryu
Summary: This paper
describes a stand-alone solid nitrogen cooled "permanent"
high-temperature superconducting magnet system and presents
its performance data. The system's cold body includes the
magnet, shunted with a superconducting switch and comprised of
six double pancakes, each wound with BSCCO-2223/Ag composite
tape, and a volume of solid nitrogen and operates within a
cyclic temperature range between 20 K and 40 K. At an
operating current of 50 A the coil generates a central field
of 0.5 T in a 12-mm diameter room temperature bore; the
system's 2 liters of solid nitrogen is intended to give a
cyclic operating period, from 20 K to 40 K, of about 70 hours.
Included also in the paper is a preliminary design code that
includes magnetic and thermal requirements of the
system. |
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Magnetic
field concentration: comparison between several shapes of
superconducting shields
P.
Masson, D. Netter, J. Leveque and A.
Rezzoug
Summary: This paper deals with a
system of flux density concentration using superconducting
shields. The development of single grain high, temperature
superconductors allows the conception of large sized magnetic
shields. These shields force the flux density to be
concentrated by modifying its spatial distribution. The
authors' system consists of two low field solenoids, which
have the same arrangement as Helmoltz coils. Between these two
coils, two superconducting plates are arranged on both sides
of the axis. For this study, the superconductor is considered
as perfect. They propose to discuss the efficiency of several
concentrating devices. To make their study, they performed a
3D-field calculation tool using a Monte-Carlo method. The main
advantage of this method is a very simple algorithm to
compute, even if the geometry is complicated. The authors have
shown that if the distance between the two plates is small
enough in respect to the coils diameter, the flux density is
much higher than the one inside the coils. They also show the
influence of the shape of the shields in the guidance of the
flux lines. They have validated their simulations with an
experiment. |
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Design
study of superconducting magnets for uniform and high magnetic
force field generation
O. Ozaki,
T. Kiyoshi, S. Matsumoto, K. Koyanagi, J.-I. Fujihira, H.
Nakayama and H. Wada
Summary: Magnetic force
is one of the most promising tools to realize a virtual
microgravity environment on earth. It has been found that the
growth of protein crystals might be affected by microgravity
owing to the suppression of convectional flow. We started the
development of superconducting magnets for the generation of
uniform and high magnetic force fields to suppress
convectional flow, as it was not clear what configuration of
superconducting coils could generate most effectively high
magnetic force fields, while they maintain their uniformity.
For this purpose, we used a nonlinear programming method. The
results obtained clarified that a magnet whose inner coil is
longer than the outer one can generate more uniform and higher
magnetic force fields in a long sample space. A
superconducting magnet generating a magnetic force field of
240 T/sup 2//m has already been constructed with NbTi
conductors at the Tsukuba Magnet Laboratory. We have also
completed the design of a superconducting magnet composed of
Nb/sub 3/Sn and NbTi conductors to generate uniform magnetic
force fields up to 882 T/sup 2//m. |
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Influence
of B-dependence of critical current density on magnetic
shielding performance of MPMG-YBCO
plate
A. Kamitani, K. Hasegawa,
S. Ohshima and T. Yokono
Summary: The
magnetic shielding performance of the MPMG-YBCO plate is
investigated numerically by assuming the flux-flow and
flux-creep model as the J-E constitutive relation. The
magnetic-field dependence of the critical current density and
the flow resistivity is also taken into consideration through
the Kim model and the Bardeen-Stephan model. Under these
assumptions, the damping coefficients and the shielding
factors are calculated as functions of the frequency and the
amplitude of the applied AC magnetic field. The results of
computations show that an increase in the frequency will
enhance the shielding performance of the MPMC-YBCO plate. In
addition, there exists the lowest limit of the frequency,
above which the shielding performance is saturated, and the
limit increases with the amplitude of the applied magnetic
field. Furthermore, it turns out that the magnetic shielding
performance is hardly influenced by the magnetic-field
dependence of the critical current density. |
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Testing
of the world's largest HTS experimental magnet with
Ag-sheathed Bi-2223 tapes for Si single crystal growth
applications
K. Tasaki, M. Ono,
T. Yazawa, Y. Sumiyoshi, S. Nomura, T. Kuriyama, Y. Dozono, H.
Maeda, T. Hikata, K. Hayashi, H. Takei, K. Sato, M. Kimura and
T. Masui
Summary: Funded by the Ministry of
International Trade and Industry (MITI) of Japan, a project to
develop a cryocooler-cooled high-temperature superconducting
(HTS) magnet for Si single crystal growth applications began
in October 1997 on the basis of collaboration between Toshiba
Corp., Sumitomo Electric Industries Ltd, and Shin-Etsu
Handotai Co., Ltd. So far, we have finished a design of the
HTS magnet and basic tests using a model coil. The target
magnet is composed of 36 single pancake coils using
Ag-sheathed Bi2223 tapes and total length of the HTS tapes is
approximately 80 km. Stored electromagnetic energy of the
magnet will amount to 1 MJ at rated current operations. The
magnet is to be cooled to below 20 K by a GM (Gifford-McMahon)
cryocooler. Before fabricating the target magnet, we tested a
model coil composed of 4 single pancake coils which were the
same size as those of the target magnet, in order to
investigate basic characteristics of the HTS coils. We
performed a 290 A continuous current flowing operation using
the model coil and reached 50 kJ of electromagnetic energy
storage. |
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12
Tesla hybrid block-coil dipole for future hadron
colliders
P. McIntyre, R.
Blackburn, N. Diaczenko, T. Elliott, R. Gaedke, B. Henchel, E.
Hill, M. Johnson, H. Kautzky and A.
Sattarov
Summary: A hybrid-coil Nb/sub
3/Sn/Cu dipole is being developed for use in future hadron
colliders. It features stress management within the coil, and
the use of pure Cu strands within the coil to minimize the
quantity of superconductor while providing quench protection.
A first 7 Tesla NbTi model of the design has been built and
will soon be tested. Two designs for the first Nb/sub 3/Sn
model have been prepared. In one version, the placement of
coil blocks and the inside contour of the steel flux return
are shaped to achieve collider-quality field over a 20:1
dynamic range of operating field. In the other version, the
flux return provides a close-coupled planar boundary that
suppresses persistent-current multipoles by a factor 20, and
the same dynamic range is achieved using current programming
of the inner and outer coil elements. Both versions use the
least superconductor of any high-field collider dipole
design. |
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Progress
in the development of an 88-mm bore 10 T Nb/sub 3/Sn dipole
magnet
A. den Ouden, W.A.J.
Wessel, G.A. Kirby, T. Taylor, N. Siegel and H.H. ten
Kate
Summary: A 10 T, 2-layer cos(/spl
theta/)-dipole model magnet with an 88 mm clear bore utilizing
an advanced powder-in-tube Nb/sub 3/Sn conductor is being
developed for the LHC. A dedicated conductor development
program has resulted in a well performing Rutherford cable
containing strands that uniquely exhibit both an overall
current density of 600 A/mm/sup 2/ @ 11 T and filaments with a
diameter of 20 /spl mu/m. The resistance between crossing
strands amounts to 30-70 /spl mu//spl Omega/ by insertion of a
stainless steel core. After being exposed to a transverse
pressure of 200 MPa identical cables show negligible permanent
degradation of the critical current. The mechanical support
structure is further optimized in order to reduce the peak
stress in the mid-plane to below 130 MPa at full excitation
and to control the pre-stress build-up during system assembly.
Prior to the manufacturing of the final coils a dummy 2-layer
pole is wound, heat-treated at 675/spl deg/C and vacuum resin
impregnated. This paper presents the current status of the
magnet development program and highlights in particular the
successful conductor development. |
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The
use of pressurized bladders for stress control of
superconducting magnets
S. Caspi,
S. Gourlay, R. Hafalia, A. Lietzke, J. ONeill, C. Taylor and
A. Jackson
Summary: LBNL is using pressurized
bladders in its high field superconducting magnet program
Magnet RD3; a 14 T race track dipole, has been assembled and
pre-stressed using such a system. The bladder, placed between
the coil pack and the iron yoke, can provide 70 MPa of
pressure while compressing the coil pack and tensioning a 40
mm thick structural aluminum shell. Interference keys replace
the bladder's functionality as they are deflated and removed
leaving the shell in 140 MPa of tension. During cool down,
stress in the shell increases to 250 MPa as a result of the
difference in thermal expansion between the aluminum shell and
the inner iron yoke. A number of strain gauges mounted onto
the shell were used to monitor its strain during assembly,
cool-down and testing. This technique ensures that the final
and maximum stress in the shell is reached before the magnet
is ever energized. The use of a structural shell and
pressurized bladders has simplified magnet assembly
considerably. In this paper we describe the bladder system and
its use in the assembly of a 14 T Nb/sub 3/Sn
magnet. |
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Design
and mechanical analysis of a single-layer common coil dipole
for VLHC
I. Novitski, N. Andreev,
G. Ambrosio, P. Bauer, V.V. Kashikhin and A.V.
Ziobin
Summary: Fermilab is developing a
2-in-1, 11 T block-type common coil dipole magnet for a future
Very Large Hadron Collider. The common coil design concept
allows a large bending radius at the coil ends and therefore
is well suited for use of the react-and-wind technique with
brittle superconductors. The magnet features one-layer flat
Nb/sub 3/Sn coil wound using prereacted cable. A novel
mechanical design has been developed to provide effective coil
support against Lorentz forces, minimize conductor
displacement during excitation, reduce coil pre-load at room
temperature, and prevent force accumulation. The details of
the design concept and results of the mechanical analysis are
presented in this paper. |
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Design
of racetrack coils for high-field dipole
magnets
G. Sabbi, S. Caspi, S.A.
Gourlay, R. Hafalia, A. Jackson, A. Lietzke, A.D. McInturff
and R.M. Scanlan
Summary: The magnet group at
LBNL is in the process of developing high-field accelerator
magnets for use in future colliders. One of the primary
challenges is to provide a design which is cost-effective and
simple to manufacture, at the same time resulting in good
training performance and field quality adequate for
accelerator operation. Studies have focused on a racetrack
geometry that has the virtues of simplicity and conductor
compatibility. The results have been applied to the design of
a series of prototype high-field magnets based on Nb/sub 3/Sn
conductor. |
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Coil
end parts design and fabrication issues for the high field
dipole at Fermilab
S. Yadav, D.R.
Chichili and I. Terechkine
Summary: End parts
are one of the most costly components of a superconducting
magnet. Therefore, efforts are underway at Fermilab to develop
new technologies to reduce the fabrication time and cost of
the magnet end parts. In this paper, we discuss some of the
design and fabrication issues for the magnet end parts with a
particular specific objective in mind. |
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Mechanical
design and analysis of 2-in-1 shell-type Nb/sub 3/Sn dipole
models for VLHC
D.R. Chichili,
V.V. Kashikhin and A.V. Ziobin
Summary:
Fermilab has begun investigating Nb/sub 3/Sn twin
aperture dipole magnet designs as a next step towards the
realization of high field magnets for a Very Large Hadron
Collider (VLHC). The magnet design is based on two-layer
shell-type Nb/sub 3/Sn coils with 43.5 mm aperture. Two
different mechanical designs were investigated, one with
"cold" iron yoke and the other with "warm" iron yoke. The
former has a vertically split three-piece iron yoke with a cut
parallel to a flux line to reduce the transverse magnetic
flux. The two outer halves are locked in place by aluminum
clamps. Both the clamps and the stainless skin provide the
required pre-stress to the coils. The "warm" iron yoke design
consists of thick freestanding stainless steel collars with
wide keys and an insert separating the two coil blocks. The
paper presents both the mechanical design and analysis for the
two designs. |
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Scaling
laws for modeling large superconducting
solenoids
M.A. Green and A.D.
McInturff
Summary: The neutrino factory
cooling system will consist of a long series of
superconducting solenoids with a warm bore of 1.2 meters. In
order to minimize the cost of the 200 to 300-meter long
solenoid muon-cooling channel, the solenoids must be
fabricated so that their mass is minimized. This report
discuses how one can model the stress, strain and quench
behavior of these large solenoid sections by building
one-third to one-half scale models of the magnets. The cost of
building and engineering the scale model magnets is a small
fraction of the cost of fabricating a full-scale magnet
section. This report discusses the limitations of the scaling
approach as well as the types of superconducting solenoids for
which the modeling technique is suitable. |
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A
test of a superconducting solenoid for the mucool RF
experiment
M.A. Green, J.Y. Chen
and S.T. Wang
Summary: This report describes
the results of a series of tests of a 440-mm warm bore split
solenoid used for testing 805 MHz RF cavities. The solenoid
consists of two coils each 250 mm long separated by a gap of
140 mm. The solenoid was designed to operate in two modes; a
solenoid mode with the two coils hooked in the same polarity
and a gradient mode with the two coils hooked in opposite
polarity. In the solenoid mode, the magnet is designed to
produce an induction of 5 T over a region that is about 400 mm
long. In the gradient mode, the solenoid produces a field
gradient of 25 T per meter along the axis over a distance of
about 300 mm. The solenoid was designed to carry a force of
over 3 MN that pushes the two coils apart, when the magnet is
operated in the gradient mode. In order to carry this force,
the coils are encased within aluminum shells, both inside and
outside. Since this solenoid is encased in aluminum and the
coils are potted, training was observed. The magnet training
history and magnet field measurements are presented in this
report. |
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Bent
superconducting solenoids with superimposed dipole
fields
R.B. Meinke and C.L.
Goodzeit
Summary: Superconducting solenoid
magnets with superimposed dipole field have been proposed for
the cooling channel for a future high luminosity muon
collider. The magnets are typically bent into a 180/spl deg/
are with a centerline radius of about 0.5 m and an aperture of
0.3 to 0.4 m. They are characterized by having an on-axis
solenoidal field of about 4 T with a 1 T superimposed dipole
field. A cost-effective design is proposed, in which the
dipole field is generated by tilting the winding planes of the
solenoid coil. The magnetic and mechanical design of such
magnets are presented. |
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Investigation
of Bi-HTS wires for high field insert
coils
F. Hornung, A. Rimikis, R.
Kimmich and Th. Schneider
Summary: In the
High Magnetic Field Laboratory of the Institute for Technical
Physics, the test facility HOMER II is currently under
construction. In a first step, a magnetic field of 20 T in a
bore of 180 mm produced by advanced LTS materials is aspired.
In a second step, insert coils built of HTS wires are planned
to be added in order to obtain resulting fields up to 25 T.
With these intentions in the background, the superconducting
properties of different Bi-HTS wires were investigated in a
bath cooled superconducting magnet system at 4.2 K and
magnetic fields up to 10 T. The critical current I/sub c/ was
examined resistively using a high resolution four-point
measurement technique. In consideration of the determined
current carrying capacity of the wires, two layouts for HTS
insert coils are presented. |
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An
optimal design method for superconducting magnets using HTS
tape
S. Noguchi, M. Yamashita, H.
Yamashita and A. Ishiyama
Summary: This paper
describes an optimal design method for superconducting magnets
wound with high temperature superconducting (HTS) tapes (e.g.
Bi2223/Ag tapes). The properties of HTS tapes have been
advancing and HTS magnets have been constructed and
demonstrated. However, the HTS tapes have thermally different
characteristics compared with the low temperature
superconducting (LTS) wires. Therefore it is necessary to
consider these characteristics of HTS tapes at the magnet
design stage. We propose a new configuration of the
superconducting magnets using Bi2223/Ag tapes. The proposed
configuration is optimized by using simulated annealing (SA),
which is one of the optimization algorithms, under a lot of
constraints such as B-I characteristic, central magnetic
field, field homogeneity and so on. The details of the
optimization method and an example of its application to a
12-Tesla superconducting magnet using Bi2223/Ag tape are
shown. |
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Development
of a hybrid LTS-HTS solenoid magnet for future intense muon
beam lines
Y. Kuno, T.
Shimonosoho, T. Yokoi, K. Shimada, Y. Sumiyoshi and A.
Yamamoto
Summary: A hybrid R&D magnet for
future Phase Rotation Intense Secondary Meson (PRISM) beam
project was designed and fabricated. The R&D solenoid
magnet, which consists of an inner HTS coil and outer LTS
coils, provides a central magnetic field of 10.6 T at 90 A in
a warm bore diameter of 40 mm. The inner HTS coil was made by
solenoid-winding technique without degradation of the BSCCO
tapes. The R&D magnet was successfully cooled by using
cryocoolers, and was stably operated at the design central
field and was tested up to the maximum central field of 11.6
T. |
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Proofing
tests of a fiber-reinforced type of niobium-tin superconductor
by small coil experiments
H.
Tateishi, J. Kondoh, M. Umeda, K. Agatsuma, K. Arai, K. Gotoh
and T. Saitoh
Summary: We have been
developing fiber-reinforced type of niobium-tin superconductor
for a large-scale high field magnet. This conductor has a
niobium-tin filament reinforced by a tantalum core of about
20-micrometer diameter. Tantalum is selected as a reinforcing
material since it has good ductility with mechanical strength
comparable to stainless steel. We have tested this conductor
in the form of a small solenoid with the diameter of 50 mm
under a backup magnetic field of 15 Tesla. Results of the test
showed that it has a uniform superconducting property over a
length of 250 meter. Furthermore, we developed another
conductor with larger current carrying capacity and tested
this conductor in the coil form. Strain measurement of the
second coil revealed that the windings behave elastically
within the range of operation. |
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New
concept of a semi-superconducting
magnet
K. Watanabe and M.
Motokawa
Summary: Superconducting power
applications are based on zero resistance. The critical
current densities for traditional low temperature
superconductors obtained in a very sharp boundary between the
superconducting and the normal state have surely indicated the
critical applications under the zero resistance state. In high
temperature superconductors, the critical current density
derived from the usual criterion accompanies the finite
resistivity of around 10/sup -11/ /spl Omega/cm. From a
viewpoint of power applications, such a low resistive state
should be distinguished from the superconducting state. The
authors call the stable low resistive state the
semi-superconductivity. As a semi-superconducting application,
a semi-superconducting Bitter magnet is introduced using
Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ disks. |
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Optimization
of winding geometry of Bi(2223)Ag coils with respect to
external magnetic field
J. Pitel,
P. Kovac, A. Kasztler and H. Kirchmayr
Summary:
A theoretical model, which enables to estimate the
critical currents distribution in the winding of HTS
cylindrical coils exposed to external magnetic field, was
developed. The model takes into account the real angular
dependence (anisotropy) of the I/sub c/(B) characteristic of
Bi(2223)Ag tape. It is shown how the change in the winding
geometry within the same overall tape length and the value of
applied external magnetic field parallel with the magnet axis
influences both, the critical current and the resulting
magnetic field generated by the magnet itself. It is predicted
that applying a low magnetic field parallel to the HTS magnet
axis may result in a relatively high increase in the magnet
critical current (up to 30-40%) if compared with the magnet
critical current achieved without the presence of external
magnetic field. An example of optimizing the magnet winding
geometry by using the different lengths of the Bi(2223)Ag
multifilamentary tape of Vacuumschmelze GmbH production is
presented. |
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Superconducting
vibrator for low frequency
emission
V.A. Mai'ginov, I.H.
Nevmyanov, M.V. Sidorov, A.M. Vaculenko and S.G.
Deryagin
Summary: The feasibility of
superconducting magnets using low frequency generators is
investigated. Namely superconducting magnet systems consisting
of two coaxial DC coils and operating as a magnetic quadrupole
is developed. This system generates a radial magnetic field up
to 1 T in a "warm" volume of 16 cm in diameter and 20 cm long.
In this nearly space-constant field a copper coil is placed at
a temperature of 77 K. This coil is energized with DC and AC
current in the 1-100 Hz range. Forces and characteristic of
the forced vibration of both rotor and rotor with iron core
are calculated and measured. An influence of AC magnetic field
of the copper coil on losses in the superconducting windings
is analyzed measured by a thermocouple inside the
winding. |
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Improvement
of superconducting cylindrical linear induction
motor
T. Kikuma and A.
Ishiyama
Summary: The authors have
constructed a model superconducting cylindrical (tubular)
linear induction motor (SCLIM) to clarify the behaviors (AC
loss, stability and so on) of AC superconducting windings in a
realistic operational environment of electrical rotating
machines. The studies of an AC superconductor's development in
regard to the reduction of AC loss and the improvement of
current capacity have been advanced. From now on, the
valuation of characteristic of AC superconducting windings in
a realistic operational environment should be investigated. In
the previous paper, the authors presented the design and
construction of an SCLIM model system composed of AC
superconducting primary windings, FRP cryostat and VVVF power
supply with quench detection and protection circuit, and the
results of fundamental driving experiments. In this paper, the
authors optimize the current distribution in primary windings
to enhance the thrust characteristics and the quench detection
and protection system for AC superconducting machines by a
numerical approach based on a developed FEM computer program.
The measurements of the thrust force, the distributions of the
magnetic flux density and primary current in the SCLIM model
are also shown. |
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Output
power limit of 200 MW class brushless superconducting
generator excited with magnetic
flux-pump
H. Tsukiji, T. Hoshino
and I. Muta
Summary: A study on excitation
system would be important to enhance potentials of
superconducting AC generators. The authors have fabricated a
20 kW class fully superconducting machine with the brushless
excitation system which consists of a magnetic flux-pump. By
many tests of power generation using this machine, they have
investigated theoretically and experimentally the feasibility
of the brushless superconducting generator and magnetic
flux-pump. Based on these results, this paper proposes the
conceptual design and electric characteristics of a practical
scale flux pump for an exciter system of a 200 MW class
superconducting generator (Super-GM). Furthermore, the paper
presents a comparison of output power limits for such as
different excitation methods; a persistent field current mode
and a conventionally adjusting field current
mode. |
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Analysis
of the operational characteristics of discrete-sheet type
low-Tc superconducting power
supply
Ho Min Kim, Yong Soo Yoon,
Min Cheol Ahn, Yong Chu, Sang-Jin Lee, Tae-Su Han, Sang-Soo Oh
and Tae Kuk Ko
Summary: This paper deals with
comparison of characteristics of continuous-sheet type low-Tc
superconducting (LTS) power supply and discrete-sheet type LTS
power supply. These characteristics have been analyzed through
experiments. These power supplies consist of two exciters, a
rotor, a stator, and LTS Load. A continuous-sheet type has a
single continuous niobium (Nb) sheet attached to the inner
surface of on the stator. In the case of discrete-sheet type,
four separated Nb sheets are used. This experiment uses a 1.81
mH LTS magnet load and maximum 30 A DC exciter current. A
discrete-sheet type is expected to produce much better pumping
rate than a continuous-sheet type. The experimental
observations have been compared with the theoretical
predictions. In this experiment, the maximum pumping-current
has reached about 926 A. |
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Experimental
study on sudden-short-circuit characteristic of synchronous
generator with SCFCL
B. Hatta, T.
Nitta, S. Muroya, Y. Shirai and T. Kitagawa
Summary:
Superconducting fault current limiters (SCFCLs) are
expected to improve the reliability of power systems. An SCFCL
of a transformer type with adjustable trigger current level
was proposed. Three SCFCLs of this type for 3-phase AC power
source were designed and made. The trigger current level of
each trial SCFCL can be adjusted to equal value, and the
SCFCLs can be used as a 3-phase SCFCL. As preliminary tests,
sudden-short circuit tests with a 20 kVA synchronous generator
are carried out. Limiting tests of the 3-phase SCFCL at fault
are carried out with the synchronous generator. The effect of
3-phase SCFCL and the characteristics of the synchronous
generator are studied experimentally. |
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Development
and operation of superconducting NMR magnet beyond 900
MHz
T. Kiyoshi, A. Sato, T.
Takeuchi, K. Itoh, S. Matsumoto, O. Ozaki, H. Wada, M.
Yoshikawa, T. Kamikado, S. Ito, T. Miki, T. Hase, M. Hamada,
S. Hayashi, Y. Kawate and R. Hirose
Summary:
As a milestone in the 1-GHz NMR magnet project being
carried out at the Tsukuba Magnet Laboratory, a 900-MHz class
NMR magnet was successfully manufactured and operated in
December 1999. The developed magnet is made of
15%Sn-bronze-processed (Nb,Ti)/sub 3/Sn, Ta-reinforced
(Nb,Ti)/sub 3/Sn, and NbTi conductors. The room temperature
bore of the cryostat is 54 mm is diameter. All the coils are
cooled with pressurized superfluid helium. The magnet
generated a field of 21.20 T in a driven mode and then
operated in a persistent mode at 21.17 T corresponding to a
proton NMR frequency of 902 MHz. The field may be raised to
the range of 21.6 T (920 MHz) in the near
future. |
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Development
and testing of HTS cables and terminations at
ORNL
M.J. Gouge, J.A. Demko, P.W.
Fisher, C.A. Foster, J.W. Lue, J.P. Stovall, U. Sinha, J.
Armstrong, R.L. Hughey, D. Lindsay and J.
Tolbert
Summary: The Oak Ridge National
Laboratory (ORNL) and the Southwire Company have used the ORNL
5 m cable test facility to develop high-temperature
superconducting (HTS) cables and terminations to support the
first industrial demonstration of an HTS cable at the
Southwire manufacturing complex. Two 5 m, cold dielectric
cables have been tested for direct current (DC) voltage,
alternating current (AC) losses, AC withstand at 18 kV,
thermal-hydraulic performance, heat load, and long-term
operation at rated voltage (7.2 kV) and current (1250 A). Two
separate termination concepts, one operating at 10/sup
-4/-10/sup -5/ mbar vacuum and the other operating with
pressurized nitrogen gas at <10 bar, have been developed
and tested with the 5-m cables. A 5-m cable has been removed
from the facility and bent in a test rig to simulate transport
in a spool. A testing program for a third 5-m cable with a
splice is in progress. The test program at ORNL has validated
the basic design of the cables and terminations and indicated
areas for further R&D to optimize this technology for
electric utility applications. |
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Qualification
results of a 50 m-115 kV warm dielectric cable
system
M. Nassi, N. Kelley, P.
Ladie, P. Corsato, G. Coletta and D. von
Dollen
Summary: A collaboration between
Pirelli Cables and Systems, EPRI, and the DOE for the
development of warm dielectric HTS power cables concluded in
early 1999 with the completion of a testing program on a
complete cable system prototype. The development program
addressed early concerns regarding the possibility to
manufacture complete cable assemblies using industrial
processes, and whether the high performance obtained with
short samples would be possible with longer cables. A 115 kV
warm dielectric HTS power cable was designed and fabricated to
serve as a retrofit upgrade for the vast quantity of existing
high pressure fluid filled (HPFF) cable systems. The program
objectives included achieving a 400 MVA circuit rating,
representing a 100% power rating increase in a compact design
which could be installed in a typical 8 inch pipe, as well as
the design, fabrication and testing of accessories necessary
for a commercial system. This paper presents the relevant
technical system information and superconducting and
dielectric testing prototype system. Furthermore, the
implications of these results are discussed in the context of
their application to future cable systems. |
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Progress
in manufacturing of HTS power transmission
cable
S. Spreafico, P. Caracino,
N. Kelley and M. Nassi
Summary: In order to
cover the numerous HTSC cable laminated designs that consist
of a reinforcement of the projects that Pirelli Cavi e Sistemi
has undertaken with different US and European utilities, a
dedicated production facility has been established. This
facility is exclusively dedicated to the development and the
manufacturing of high temperature superconducting (HTS) power
cables. Its production capability, estimated in 12 km/year, is
presently oversized. To date, almost 1500 m of both dummy
(copper) and real (HTS) conductors have been produced, using
about 35 km of HTS Ag/BSCCO tapes (for the "real" conductors).
HTS tapes, supplied by American Superconductor, termed
"laminated wires" have very good mechanical properties due to
the use of thin strips of stainless steel in a sandwich
configuration. This paper reports the results of different
cable manufacturing and cable trials. The success of this
program represents the basis of the reliability demonstration
of HTS cable manufacturing. The paper also presents the
comparison between the theoretical and the experimental
results relevant to the degradation of the tape electrical
properties due to mechanical stresses experienced by the cable
from manufacturing up to cool-down. |
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Design
and production of high-Tc superconducting power transmission
cable
K. Miyoshi, S. Mukoyama, H.
Tsubouchi, A. Takagi, S. Meguro, K. Matsuo, S. Honjo, T.
Mimura and Y. Takahashi
Summary: The design
and production of high temperature superconducting (HTS) power
transmission cables was studied. In the production of HTS
cable, difficulties are mainly caused by the poor mechanical
properties of HTS tapes, because critical currents of the HTS
tapes deteriorate due to the strains applied during cable
production and usage. Therefore, two basic characteristics of
HTS cables were experimentally analyzed to improve HTS cable
design and production: (1) the mechanical-electrical
properties of the HTS cable; and (2) the properties of
electrical insulation. The analysis results indicate that the
most important technology is the control of the strains
applied to the tape in the cable. Based on the results, the
design of the HTS cable was then improved, and the machines at
Furukawa Electric fabricated a three-phase prototype HTS cable
of 30 m in length. The results of the performance test of the
cable demonstrated the proposed design and the production
method are appropriate. |
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A
study on the application effects of HTS power cable in
Seoul
K.C. Seong, S.B. Choi, J.W.
Cho, H.J. Kim, Y.K. Kwon, K.S. Ryu, B.T. Kim and I.K.
Yu
Summary: In this study, the authors
examined the long-term plans of expansion for the conceptual
design of HTSC power cables in the Seoul area. In Korea
recently, the desire for underground power cables on the rise
in light of the increasing demand for electric power and the
environmental restrictions in the urban area. Since the HTSC
power cable has high power transmission density and low loss
characteristics, compared to conventional power cables, they
have assumed its application between the downtown area and the
outskirts of the city, where there is large transmission of
power. This paper demonstrates the effects of applying HTSC
power cables in Seoul based on the power system
analysis. |
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Development
of HTS transmission power
cable
Y.B. Lin, L.Z. Lin, Z.Y.
Gao, H.M. Wen, L. Xu, L. Shu, J. Li, L.Y. Xiao, L. Zhou and
G.S. Yuan
Summary: A 1500 A/6 m HTS DC
transmission power cable has been developed and tested at the
Institute of Electrical Engineering, Chinese Academy of
Sciences. The conductor of the HTS cable consists of 4 layers
of Bi-2223/Ag tapes helically wound on a flexible stainless
steel former. The Bi-2223/Ag tapes have been developed by the
Northwest Institute for Nonferrous Metal Research and the
Beijing General Research Institute for Nonferrous Metals. The
cable core has a 45.3 mm outer diameter and 6 m length and is
housed in a cryogenic envelope. The E-I characteristic and the
total joint resistance of the cable have been measured at 77
K. The critical current of the cable is 1473 A and the total
joint resistance is 0.1 /spl mu//spl Omega/ at 77 K. The main
properties of the Bi-2223/Ag tape and the development and test
results of the HTS cable are presented in this
paper. |
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Energy
losses of superconducting power transmission cables in the
grid
J. Oestergaard, J. Okholm,
K. Lomholt and O. Toennesen
Summary: One of
the obvious motives for development of superconducting power
transmission cables is reduction of transmission losses. Loss
components in superconducting cables as well as in
conventional cables have been examined. These losses are used
for calculating the total energy losses of conventional as
well as superconducting cables when they are placed in the
electric power transmission network. It is concluded that high
load connections are necessary to obtain energy saving by the
use of HTSC cables. For selected high load connections, an
energy saving of 40% is expected. It is shown that the thermal
insulation and cooling machine efficiency are the most
important loss element in a superconducting cable
system. |
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Analysis
of the optimal location of magnetic field probes for the
determination of the current distribution inside S/C
cables
F. Bellina, P. Bettini and
F. Trevisan
Summary: During the tests on
superconducting cables, the magnetic field is often measured
by means of pick-up or Hall probes and these data are used to
reconstruct the current distribution inside the cable. The
efficiency and the accuracy of the reconstruction procedure
depend on the algorithm adopted and on the location of the
field probes. For a given geometry of the lines of current,
the determination of the current distribution can be
mathematically formulated as a linear inverse problem, in
which the residual between the measured and the computed field
values at the probe locations is minimised. A linear
least-squares problem results, which is solved by means of the
truncated singular value decomposition technique, applied to
the matrix G which relates the unknown currents to the
computed magnetic field values. The condition number of G is
proposed here as an index of the quality of the location of
the probes: a good location corresponds to a well conditioned
G, while a bad location gives a worse conditioned matrix. In
this paper a reconstruction procedure is presented and a
criterion for the optimal probe positioning is
shown. |
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Highly
sensitive magnetic sensor made with a superconducting
Y-Ba-Cu-O thick film
K. Yamagata,
A. Omura, M. Itoh, M. Ishidoh and T.
Minemoto
Summary: In the research, Y-Ba-Cu-O
(YBCO) thick film was fabricated to form a highly sensitive
magnetic sensor, constructed to maintain the superconducting
state at the boiling point of liquid nitrogen (77.4 K).
Superconducting film will, in general, break the
superconducting state of the flow of current at the value of
current density J greater than that of the critical current
density J/sub c/, when the resistance R/sub sen/ to the flow
of current occurs. The magnetic sensitivity increases as the
value of the resistivity /spl rho//sub seu/ of R/sub sen/
decreases. The value of /spl rho//sub sen/ can be readily
controlled by the value of J. The average sensitivity S of
this magnetic sensor was determined as about 154%/gauss, over
the magnetic range of 0 gauss to /spl plusmn/40 gauss. In
addition,the sensitivity is about 154 times that of a giant
magneto-resistance sensor. The paper examines the fabrication
process and conditions, the characteristics of S as related to
/spl rho//sub sen/, and the magnetic response of the highly
sensitive magnetic sensor. |
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Evaluation
of the magnetic field within a BPSCCO cylinder superimposed by
multi-layered soft-iron cylinders by use of an HTS
DC-SQUID
Y. Horikawa, A. Omura,
K. Mori and M. Itoh
Summary: The evaluation
of the maximum shielded magnetic flux density B/sub s/ of a
high-critical temperature superconducting (HTS) cylinder
acting as a magnetic shielding vessel, is required to improve
the value of B/sub s/ for practical use. The authors have
improved the value of B/sub s/ by the superposition of
multi-layered soft-iron cylinders over a Bi-Pb-Sr-Ca-Cu-O
cylinder which is termed the superimposed cylinder. Little is
known, however, of the characteristics and evaluation
procedures for the magnetic flux density B/sub ia/ within the
innermost of the superimposed cylinders when the value of the
external magnetic flux density B/sub ex/ is less than that of
B/sub s/. The present research has evaluated the shielding
effect for the superimposed cylinder with the use of an HTS
DC-SQUID magnetometer and spectrum analyzer. The present paper
examines the magnetic step response of B/sub in/ to the
applied B/sub ex/, the characteristics of B/sub in/ when
exposed to a B/sub ex/ having a value less than that of B/sub
s/, and the magnetic noise power spectra within the
superimposed cylinder. In addition, a discussion is conducted
on the relationship between the number of layers of the
multi-layered soft-iron cylinder and the value of B/sub
in/. |
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Quench
detection of Bi-2223 HTS coil by partial active power
detecting method
N. Nanato, M.
Yanagishita and K. Nakamura
Summary: This
paper presents the results of the quench detection tests of a
high Tc superconducting coil (HTS coil) wound with Bi-2223
tape, impregnated by epoxy resin and cooled by LN/sub 2/ using
a partial active power detecting method we have proposed as a
new type quench detecting method. The tests were carried out
for DC and AC current. The results showed that the proposed
method was useful for the quench detection of the HTS
coil. |
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RF
magnetic shielding effect of a sealed bottom HTS
cylinder
E. Itoh, Y. Hotta, M.
Itoh, N. Munser, J. Pleva, W. Jaszczuk and H.
Altenburg
Summary: The high-critical
temperature superconductor (HTS) is an ideal material for use
as a RF magnetic shielding vessel, which employs perfect
diamagnetism. In general, however, the detailed
characteristics of the radio frequency (RF) for a HTS vessel
are unknown. In the present research, measurements are made of
the RF shielding effect SD, that is, the ratio of the output
powers of the receiving antenna with and without the shielding
vessel, of a sealed bottom YBCO bulk cylinder. It was found
that the values of the magnetic shielding effect SD/sub u/ for
the sealed bottom YBCO cylinder exhibit constant values in
frequency from range from 1 MHz to 10 MHz, and decrease with
an increase in frequency from 30 MHz to 3000 MHz of the
applied electromagnetic wave. It was also found that the
shielding displayed no evidence of dependence on the RF
magnetic power P/sub H/. For the RF electric shielding effect
SD/sub E/, the cylinder exhibited no remarkable
characteristics. Furthermore, it was found that the
characteristics of SD/sub E/ for the cylinder displayed no
evidence of dependence on the values of the RF input power
P/sub E/. In addition, the shielding effects were shown to be
improved by the superposition of a sealed bottom copper
cylinder over the sealed bottom YBCO cylinder. |
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Three-phase
fault current limiter with one DC S/N transition
element
T. Satoh, M. Yamaguchi,
S. Fukui, K. Morikoshi, K. Kaiho, T. Matsumura, H. Shimizu and
N. Murayama
Summary: The authors developed a
DC S/N transition type three-phase fault current limiter, the
primary element of which, is made of the superconducting bulk
material, Bi-2223. This element is connected to secondary
windings of transformers, through a modified half control
bridge. This unique, single element device simultaneously
limits and interrupts fault current, in three-phase power
systems. This paper describes the results of tests, using a
small scale model and simulation results. |
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Thermal
and magnetic characteristics of bulk superconductor and
performance analysis of magnetic shielding type of
superconducting fault current
limiter
H. Ueda, A. Ishiyama, H.
Kado and M. Ichikawa
Summary: Superconducting
fault current limiter (SCFCL) is expected to be the first
application of a high-temperature superconductor (HTS) to
electric power systems. The authors have been developing a
magnetic shielding type of SCFCL that uses a cylindrical
Bi-2223 HTS bulk. Short-circuit fault tests in a small SCFCL
model were performed experimentally. A computer program based
on the finite element method (FEM) taking the voltage-current
(E-J) characteristics of the bulk material into account was
developed to analyze the performance in the short-circuit
fault tests and to investigate the dynamic electromagnetic
behavior within a bulk superconductor. Because the E-J
characteristic of HTS bulk depends on temperature and magnetic
field, they investigated experimentally the E-J
characteristics of a bulk superconductor in various operating
temperatures and magnetic fields. The computer program
considering the measured E-J characteristics simulated the
electromagnetic behaviors in an SCFCL test model successfully
(BiPb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub
10/. |
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Quench
behavior of the switching elements of a hybrid HTS current
limiter
X. Granados, T. Puig, J.
Teva, E. Mendoza and X. Obradors
Summary: In
the hybrid HTS current limiter, current limitation is due to
the transition to the normal resistive state of YBCO bars,
which are shorting the secondary of a transformer. The HTS
bars act as current driven switches allowing two states, a low
impedance state in which the bar is in its superconducting
state and a higher impedance state arisen after the quench.
From the authors' measurements, one can conclude that the
triggering current is essentially related to the contact
resistance, which induces a hot spot. The resistance developed
during the switching time enables the limiter to work.
However, the maximum resistance which can be arisen during the
quench is limited by the low propagation speed of the
transition front, from the contacts to the center of the bars,
in the adiabatic approach. In order to stimulate a multi hot
spot quench, the authors have adjusted the triggering current
by Mg doping the YBCO, thereby homogenizing the quenching
current along the bars. They have also developed switching
elements based on a quasi isothermal approach of the quench,
which diminishes the high thermal gradients developed in the
adiabatic quench induced by a hot spot. Measurements of the
performances of both switching systems are
reported. |
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Study
on degradation of trigger current level of superconducting
fault current limiter of transformer
type
K. Fujikawa, Y. Shirai, M.
Shiotsu, T. Nitta and H. Hatta
Summary: A
superconducting fault current limiter (SCFCL) of a transformer
type with adjustable trigger current level was proposed in
previous works. Basic tests were performed using the trial
SCFCL of proposed type. The degradation of the trigger current
level of the SCFCL was observed. It is observed that the
trigger current level depends on the frequency of the power
source. The measured AC loss is about seven times as large as
the calculated hysteresis loss and the coupling loss. It is
assumed that an excessive loss generated at the short-circuit
contact of the secondary winding causes the degradation. The
new trial SCFCLs with the improved contact are made. The
degradation of the trigger current level does not appear for
the new trial SCFCLs. |
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Initial
quench development in uniform Au/Y-Ba-Cu-O thin films
[superconducting fault current
limiters]
Hye-Rim Kim, Hyo-Sang
Choi, Hae-Ryong Lim, In-Seon Kim and Ok-Bae
Hyun
Summary: The authors investigated the
initial quench development process in resistive
superconducting fault current limiters based on YBa/sub
2/Cu/sub 3/O/sub 7-/spl delta// thin films of uniform quench
current. The film was coated insitu with a gold layer and
patterned into pairs of 1 mm wide and 26 cm long meander lines
by photolithography. Voltage taps were mounted along the
meander lines to detect quench development. Fabricated
limiters were tested with simulated AC fault currents. Upon
fault current passing quench current, all sections of the
meander line made transitions into the pull flow regime
simultaneously with similar flux flow resistivity. Transfer of
the generated Joule heat, however, soon changed its
distribution. At lower source voltages the center area of the
meander line always had the highest resistivity and the edge
area the lowest. At higher voltages quench started first and
propagated fastest in the area close to the center electrode.
But, once quench was completed, the resistivity became the
highest in the central area of the meander line. This
phenomenon was observed in all uniform samples on which
measurements were taken and should be considered in design of
fault current limiters made from uniform YBa/sub 2/Cu/sub
3/O/sub 7-/spl delta// thin films. The heat transfer from
limiter meander lines to surroundings explains the
results. |
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Quench
properties of Y-Ba-Cu-O films after overpowering quenches
[superconducting fault current
limiters]
Hyo-Sang Choi, Hye-Rim
Kim, Ok-Bae Nyun and Sang-Joon Kim
Summary:
The authors present the property degradation and quench
behavior of a current limiting element under repeated
quenches. The current limiting element was meander type
YBa/sub 2/Cu/sub 3/O/sub 7/ stripes deposited on Al/sub
2/O/sub 3/ substrates and coated with a Au shunt. The films
showed reproducible quench properties under repeated quenches
when the gold layer was coated in-situ on the YBCO film. The
films, however, revealed apparent degradation in properties
even after the second quench when the gold layer was coated
ex-situ on the YBCO film. The authors speculate that
incomplete contact between the YBCO and the gold layer
produced negative effect on the limiter property. The quench
current density J/sub q/ was improved at source voltages up to
300 V/sub rms/ and saturated afterwards when the voltage was
increased stepwise by 10 V/sub rms/ from 100 V/sub rms/ to 350
V/sub rms/. It is believed that the thermal shock in a rapid
superconducting-normal transition gives the annealing effects
to the sample. X-ray diffraction and Rutherford backscattering
spectroscopy data did not change considerably after repeated
quenches but some minor change appeared. This change might be
related to the improvements in the quench current
density. |
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Surface
YBa/sub 2/Cu/sub 3/O/sub 7/ receive coils for low field
MRI
D. Bracanovic, A.A. Esmail,
S.J. Penn, S.J. Webb, T.W. Button and N.M.
Alford
Summary: The authors present results
from magnetic resonance imaging experiments using
superconducting thick film YBa/sub 2/Cu/sub 3/O/sub 7-/spl
delta// (YBCO) receive coils. The coils' properties and image
qualities are compared with identical copper and silver It was
found that the SNR (at 77 K) and image quality obtained using
the YBCO coil is significantly increased relative to metal
coils of identical geometry at 77 K. |
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Performance
test of a persistent current switch insulated with cotton
tape
Rock-Kil Ko, Joon-Han Bae,
Ki-Deok Sim, Eon-Young Lee, Hae-Jong Kim, Young-Kil-Kwon and
Kang-Sik Ryu
Summary: In order to design
thermally trigger controlled persistent current switches
(PCSs) for superconducting magnet systems, it is very
important to know information of adiabatic method and
condition to obtain designed resistance and characteristics.
In this work, the authors used cotton tape as a thermal
insulator and calculated averaged thermal conductivity of it
around 10 K on the assumption that the adiabatic structure of
PCS is the shape of a pipe. The result of about 0.29 W/m/spl
middot/K was verified a reasonable value by computer
simulations and estimation of test PCS, which was designed and
manufactured with different dimensional parameters. The
experimental results of test PCS were in good agreement with
the calculated results. |
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Development
of A 600 MHz wide bore (89 mm) NMR system using internal tin
wires
Weijun Shen, M. Coffey and
Wayne McGhee
Summary: Employing high
performance internal-tin Nb/sub 3/Sn superconducting wire in
NMR superconducting magnets, it is possible to reduce NMR
magnet system cost. A 600 MHz NMR magnet system with 89 mm
room temperature bore has been designed, constructed and is
being tested. The magnet and cryostat were designed to meet
existing 600 MHz NMR superconducting magnet standards. The
design involved extensive mechanical analysis of stress/strain
of the coils and coil forms. Construction also involved the
development of superconducting joints. The magnet, which is
cooled by liquid helium at 4.2 K, consists of three Nb/sub
3/Sn coils and five NbTi coils. The operating current, stored
energy, outer diameter and the height of the whole system are
87.5 A, 2 MJ, 865 mm and 2020 mm, respectively. In this paper,
an overview and analysis of the design is presented and
preliminary test results are reported. |
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AC
loss calculation of a multi-layer HTS transmission cable
considering the twist of each
layer
Ji-Kwang Lee and Gueesoo
Cha
Summary: The superconducting transmission
cable is one of interesting part in HTS power application
using high temperature superconducting tape. One important
parameter in HTSC cable design is a transport current sharing
because it is related with a current transmission capacity and
a loss. The current sharing is decided by cable length
(inductance) and resistance (by joint and AC losses). The AC
loss in power transmission cable is studied only transport
current loss. But, although it is applied no external field,
any tapes constituting transmission cable are experienced
magnetic fields given by currents flowing in other tapes of
cable. In this paper, the authors calculate current sharing
for each layer of a 4-layer cable. The transport current loss
and magnetization loss for various cable length considering
the twist of each layer are also studied. |
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Results
of AC loss tests on twisted and untwisted HTSC tape exposed to
external field
T. Hardono, C.D.
Cook and F. Darmann
Summary: This paper
presents the results of magnetic loss tests on twisted and
untwisted 37 multifilament tapes exposed to an alternating
field at power frequencies. The losses are measured using
calorimetric methods, which are capable of measuring losses in
short tapes with the accuracy of several microwatts per
centimeter of tape. The losses of the tape due to the
longitudinal field of the untwisted tape agree well with
theoretical calculations. The measurement results on the
twisted filament tape, with 50-mm twist pitch, show that the
losses are slightly lower than that in the untwisted tape.
This is due to the reduction of the coupling losses between
the filaments in the tape. It is also shown that in this
presence of normal fields, the losses are about one order
higher than for longitudinal fields because of the anisotropic
properties of the superconducting parts and because of the
existence of eddy current loss in the silver
sheath. |
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AC
losses in transport current regime in applied AC magnetic
field: experimental analysis and modeling [superconducting
cables]
S. Zannella, L.
Montelatici, G. Grenci, M. Pojer, L. Jansak, M. Majoros, G.
Coletta, R. Mele, R. Tebano and F.
Zanovello
Summary: Bi-2223 silver sheathed
tapes are currently used in prototypes of HTSC power devices,
where they generally carry an electrical AC current and are
exposed to an alternating magnetic field that may have
different orientation with respect to the tape. In this work,
the authors describe the experimental set-up for measuring AC
losses of HTSC tapes due to the simultaneous presence of AC
current and AC magnetic field. The experimental results have
been compared and contrasted with a numerical model purposely
developed for the evaluation of current distribution and AC
loss in HTSC tapes. |
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Coupling
losses of round HTS wires with radial filaments and honey comb
filaments
Jungwook Sim, Gueesoo
Cha and Ji-Kwang Lee
Summary: In
superconducting power machines, such as transformers and
motors, an external magnetic field is applied to the
superconducting wire. When the external magnetic field is
applied to the superconducting wire, coupling loss is
generated in the normal metal stabilizer. This paper describes
the calculation of the coupling losses of the round HTS wires
by the finite element method. Effects of filament arrangement
and filament size of the round HTS wire are considered. Three
types of filament arrangement (single layer, double layer and
honey comb arrangement) are considered. Calculation results
show that coupling loss of the single layer arrangement is the
smallest among the three cases. |
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Study
of frequency dependence of AC transport current losses in HTS
conductors subject to DC background
field
D. Miyagi, O. Tsukamoto and
M. Ciszek
Summary: To study a mechanism of AC
transport current losses in HTS wires, the authors measured
the AC transport current losses of two kinds of HTS wires
subject to DC background magnetic field by changing frequency
of currents. The tested wires are a multifilamentary Bi2223/Ag
sheathed tape and YBCO thin film conductors. The measurement
results show that the losses in the Bi/Ag sheathed tape and
YBCO conductors deviate from the Norris model in different
ways and are only weakly dependent on frequencies of transport
currents. In this paper, measured results are presented and
the loss characteristics are explained based on a numerical
model which they made in a previous work to analyze the AC
transport current losses. |
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Current
distributions and AC transport losses for simple parallel
conductor composed of Ag-sheathed (Bi, Pb)-2223
multifilamentary tapes
R. Inada,
A. Oota, T. Fukunaga and H. Fujimoto
Summary:
Alternating-current (AC) transport losses in
self-fields at 77 K have been investigated for simple parallel
conductors composed of several pieces of Ag-sheathed (Bi,
Pb)-2223 multifilamentary tapes with different filament
arrangements. The loss values of the conductors depend on the
filament arrangement in the tape strand and the arrangement of
tape strands in conductors, although the main contribution to
the losses comes from the hysteresis loss in the
superconductor. The conductors composed of tape strands with
sectioned filament arrangements have lower losses than those
without sectioned filament arrangements, because the
field-free core in the former is sectioned into some parts in
the filament group. Improvement for the tape arrangement in
the conductor, together with a functional design for the
filament arrangement in tape strands, is important to suppress
the loss generation in cable conductors under AC current
transmission. |
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Fabrication
and testing of Rutherford-type cables for react and wind
accelerator magnets
P. Bauer, G.
Ambrosio, N. Andreev, E. Barzi, D. Dietderich, K. Ewald, M.
Fratini, A.K. Ghosh, H.C. Higley, S.W. Kim, G. Miller, J.
Miller, J. Ozelis and R.M. Scanlan
Summary: A
common coil design for a high-field accelerator dipole magnet
using a Nb/sub 3/Sn cable with the React-and-Wind approach is
pursued by a collaboration between Fermilab and LBNL. The
design requirements for the cable include a high operating
current so that a field of 10-11 T can be produced, together
with a low critical current degradation due to bending around
a 90 mm radius. A program, using ITER strands of the internal
tin type, was launched to develop the optimal cable design for
react-and-wind common coil magnets. Three prototype cable
designs, all 15 mm wide, were fabricated: a 41-strand cable
with 0.7 mm diameter strands; a 57-strand cable with 0.5 mm
diameter strands; and a 259-strand multi-level cable with a
6-around-1 sub-element using 0.3 mm diameter wire. Two
versions of these cables were fabricated: one with no core and
one with a stainless steel core. Additionally, the possibility
of a wide (22 mm) cable made from 0.7 mm strand was explored.
This paper describes the first results of the cable program
including reports on cable fabrication and reaction, first
winding tests and first results of the measurement of the
critical current degradation due to cabling and
bending. |
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Field
demonstration of a 24-kV warm dielectric HTS
cable
N.J. Kelley, C. Wakefield,
M. Nassi, P. Corsaro, S. Spreafico, D.W. Von Dollen and J.
Jipping
Summary: Prototype HTS cable systems
have been installed in laboratories and tested successfully
around the world, proving the technical feasibility of the HTS
cable system. Commercial cable systems, however, must not only
be feasible, but meet practical requirements as well. To
facilitate the transition of HTS cable technology from the
laboratory to the field, a project has been initiated to
install the world's first HTS power cable to deliver
electricity in a utility network. This program will
demonstrate a retrofit upgrade application of the warm
dielectric HTS cable design in the Detroit Edison utility
network, and involve the design, engineering, installation,
test and routine operation of a 24-kV, 100 MVA, 3-phase cable
system. Each HTS cable will carry 2400 A RMS, a level triples
the ampacity of original cables powering this circuit. This
paper addresses the field application of HTS cables in the
context of the demonstration program. Customer perception will
play a crucial role in the adoption of HTS cable systems by
the utility industry. An updated perspective provided by the
utility industry team members is included. |
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Installation
and operation of the Southwire 30-meter high-temperature
superconducting power cable
J.P.
Stovall, J.A. Demko, P.W. Fisher, M.J. Gouge, J.W. Lue, U.K.
Sinha, J.W. Armstrong, R.L. Hughey, D. Lindsay and J.C.
Tolbert
Summary: Southwire Company has
installed, tested and is operating the first real-world
application of a high-temperature superconducting cable system
at its headquarters in Carrollton, GA, USA. The cable is
powering three Southwire manufacturing plants, marking the
first time a company has successfully made the difficult
transition front laboratory to practical field application of
an HTS cable. The cables are rated at 12.4-kV, 1250-A, 60 Hz
and are cooled with pressurized liquid nitrogen at
temperatures from 70-80 K. Before placing the cables into
service, extensive offline electrical testing was performed
including voltage withstand, measurement of DC critical
current, extended load current testing, rated voltage testing
and partial discharge measurement. The cables were energized
on Jan. 5, 2000 for online testing and operation, and by the
end of August 2000, had provided 100% of the customer load for
2164 hours. |
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Test
results of full-scale HTS cable models and plans for a 36 kV,
2 kA/sub rms/ utility
demonstration
D.W.A. Willen, F.
Hansen, C.N. Rasmussen, M. Daumling, O.E. Schuppach, E.
Hansen, J. Baerentzen, B. Svarrer-Hansen, C. Traeholt, S.K.
Olsen, C. Ramussen, E. Veje, K.H. Jensen, O. Tonnesen, J.
Ostergaard, S.D. Mikkelsen, J. Mortensen and M.
Dam-Andersen
Summary: Cable systems using
high-temperature superconducting (HTS) tapes are nearing
technical feasibility. Several large-scale demonstrations are
under way. This article summarizes the advancements and status
of a development project aimed at demonstrating a 36 kV, 2 kA
RMS AC cable system through installing a 30 m long full-scale
functional model in a power utility substation. The HTS cable
line is designed to link two medium-voltage transformer
stations in an urban environment. The expected benefits of
such a system include reduced energy loss, ease of
installation, increased power rating in a small cross section,
and insensitivity to the surrounding soil conditions. Results
will be presented from tests on several 2 kA-class AC
conductors. Electrical losses below 1 W/m at 2 kArms have been
obtained in these cable conductors. The cable system consists
of terminations, three HTS cables with conventional
room-temperature dielectric and stress cones, and a
closed-loop circulating cooling system maintaining the
temperature between 74 and 84 K. Critical issues before the
commercialization of this technology is the improvement of the
thermal insulation, the reliability and maintainability of the
cooling system, and the reduction of materials
costs. |
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Technical
and economical assessment of HTS
cables
D. Politano, M. Sjostrom,
G. Schnyder and J. Rhyner
Summary: Besides
the option of HTS cables as retrofit elements in densely
populated areas, the technically most attractive aspect of HTS
is the possibility of high power transmission at reduced
voltage. In this paper, the authors concentrate on this second
aspect. High power/low voltage HTS lines are analysed from the
technical and economical point of view in two case studies:
(i) a 110 kV/1 GVA transalpine line replacing a 380 kV
overhead line; and (ii) a 30 km/600 MVA line connecting a
nuclear power plant with a densely populated area. The
technical analysis shows that high power cables at reduced
voltages (>20 kV) and with acceptable electrical properties
(losses, dimensions, reactive power) are technically feasible.
In the economical analysis, the life cycle costs of the
different scenarios are calculated including the investment
and operation costs of the cable, the undergrounding costs and
the costs of secondary equipment (fault current limiter,
converter, cooling). The analysis shows that the DC HTS line
can be interesting, whereas the AC HTS cable systems can
hardly compete economically with conventional AC cable
installations. |
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Homogeneous
current distribution in a coaxial superconductor with and
without return current path
M.
Tsuda, A.K.M. Alamgir, Y. Ito, N. Harada, T. Hamajima, M. Ono
and H. Takana
Summary: The authors have
developed a theoretical method based on magnetic flux
conservation between adjacent layers. One of the advantages of
this method is that one can directly obtain twisting pitch and
radius for realizing homogeneous current distribution in
coaxial multi-layer superconductor. A set of the obtained
twisting pitch and radius was employed in a sample three-layer
conductor comprised of silver-sheathed multi-filamentary
BSCCO-2223 tapes and the current distribution was measured by
a Rogowski coil. Agreement between the experiment and the
theory on current distribution is quite remarkable. Using this
theory, the authors analytically investigated the influence of
the manufacturing error of twisting pitch and radius on
current distribution. The results revealed that the
manufacturing errors of twisting pitch and radius have large
effect on current distribution and a suitable set of twisting
pitch and radius against manufacturing error can be found.
They also investigated the relationship between twisting pitch
and current distribution in coaxial six-layer conductor with
return current path. The characteristics of twisting pitch in
the conductor with return current path are different from
those of the conductor without return current
path. |
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Transient
characteristics of a high-T/sub c/ superconductor tube
subjected to internal and external magnetic
fields
Y.S. Cha and T.R.
Askew
Summary: Transient response of a
melt-cast-processed BSCCO-2212 tube at 77 K was studied using
a pulsed current supply. Tests were conducted with a copper
drive coil either inside or outside the superconductor tube.
Experimental results show that the superconductor tube can
shield the magnetic field generated by the current in the coil
up to a certain limit when the coil is either inside or
outside the superconductor tube. Both configurations should
work for fault-current limiters. Delayed field penetration
(the delay between the penetrated field and the excitation
current) was observed in both cases. This delay can be
explained by the concept of nonlinear magnetic diffusion,
which is valid when the characteristic length of the system is
much shorter than the wavelength of the driving field. The
rate of magnetic diffusion is increased when (a) the local
current density exceeds the critical current density and (b)
the local temperature rises as a result of dissipation in the
superconductor. |
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FCL
location selection in large scale power
system
M. Nagata, K. Tanaka and
H. Taniguchi
Summary: Maximum short circuit
current of a modern power system is becoming so large that the
current should be reduced to make more efficient use of power
system transmission capability. The fault current limiter
(FCL) is a promising solution of this problem and it can be
categorized into two types: constant impedance type FCL and
current limiting type FCL. Current limiting type FCL such as
rectifier type superconducting FCL (RSFCL) has variable
equivalent impedance depending on the limit of the current
through FCL and power system impedances. In this paper, a
method is proposed to incorporate RSFCL into short circuit
current analysis, which is needed to evaluate the
effectiveness of FCL installed in a large scale power system.
Also, an efficient method to find FCL locations suitable for
reduction of short circuit currents of more than one fault
location is developed. The efficiency and effectiveness of
these methods are shown by numerical examples. |
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Quenching
behaviour of superconductors in an inductive fault current
limiter
Y.C. Tan and P.D.
Evans
Summary: Earlier papers introduced a
new form of inductive superconducting fault current limiter
(FCL) in which the primary and secondary windings were
interleaved symmetrically, producing current sharing in the
multiplicity of secondary coils. A new FCL which employs
similar structure but in a higher rating has been designed and
constructed. The new FCL, has eight series connected primary
coils interleaving with at least eight isolated secondary
superconductor rings around a toroidal iron core.
Investigation of this FCL when carrying a different number of
superconductor rings has showed the ability to reduce the
leakage fields around the windings hence improving the current
rating of the FCL by increasing the number of superconductor
rings in the FCL. However, being isolated, each superconductor
ring has a different switching profile as a result of the
development of normal regime resistance at different current
values. A new way of characterising this nonuniform quenching
behaviour of the superconductors in the FCL as the fault
occurs is reported. |
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Performance
verification of a practical fault current limiter using YBCO
thin film
M. Takasaki, S. Torii,
H. Taniguchi, H. Kubota, Y. Kudo, H. Yoshino, H. Nagamura and
M. Shibuya
Summary: Aiming at a practical use
of superconducting fault current limiter, a newly designed
device which consists of YBCO thin films and normal conducting
films has been developed. The configuration allows increase of
the resistance of the YBCO film without excess heating and
partial overvoltage. To verify the current limiting
performance and the reliability of the device, an analogue
simulator test with a condition equivalent to a typical
distribution system has been conducted. The developed device
can limit a fault current to a target level within a half
cycle and the increasing speed of the resistance is fast
enough to mitigate the current overshoot after the fault. The
series and parallel connection of the unit devices are
feasible to attain large capacity. These test results prove
that the proposed device has sufficient performance for
applying to an actual power system. |
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HTS
materials for AC current transport and fault current
limitation
T. Verhaege, P.F.
Herrmann, C. Cottevieille, J. Bock, A. Wolf, G. Moulaert, H.C.
Freyhardt, A. Usoskin, J. Lehtonen, J. Paasi and M.
Collet
Summary: The European SUPERPOLI
project aims to define a MV fault current limiting power link,
and to demonstrate its feasibility by a functional model. It
includes the development of two alternative low-AC-loss
conductor designs suitable for current limitation: a low-cost
composite tubular Bi-2212 conductor with moderate Jc; and a
coated tubular Y-123 conductor, presenting a very high J/sub
c/. BSCCO tubes are developed by Alcatel HTS (length: 650 mm
and diameter: 50 mm) with silver contacts on both ends. These
tubes have an effective thickness of the superconducting layer
of 1.5 mm. This layer is reinforced by an additional
nonsuperconducting layer in order to increase mechanical
stability. Based on theoretical simulations, Alcatel HTS seeks
to develop tubes with a Jc scattering lower than 2%. The main
issue with Y-123 films is to find a way for producing them in
long reproducible lengths. A novel high rate PLD technique
with a repetition rate of 300 Hz has been developed and used
for manufacturing films on large-area substrates, made of
flexible stainless steel foils buffered by IBAD. The largest
samples prepared are of 34 mm/spl times/1 m in size, and
present a Jc of 4000 A/mm/sup 2/ (77 K self-field). For a
sample with dimensions of 10 mm/spl times/0.5 m, Jc exceeds
6000 A/mm/sup 2/. |
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Characterization
of BSCCO 2212 bulk material for resistive current
limiters
S. Elschner, F. Breuer,
A. Wolf, M. Noe, L. Cowey and J. Bock
Summary:
It is demonstrated that melt cast processed (MCP) BSCCO
2212 bulk material is an excellent candidate for resistive
superconducting current limiters. For rod shaped samples it
could be shown that a homogeneous voltage of more than 1 V/cm
can be established over the whole length of the sample leading
to a substantial limiting of short circuit current. The
require long lengths of superconducting material can be easily
obtained by machining the MCP-tubes into (bifilar) coils. The
measured critical current density and its homogeneity over
these large lengths were determined and proven to be
sufficient for the designated application. |
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Design
and test results of 6.6 kV high-Tc superconducting fault
current limiter
T. Yazawa, E.
Yoneda, J. Matsuzaki, M. Shimada, T. Kuriyama, S. Nomura, T.
Ohkuma, Y. Sato and Y. Takahashi
Summary: A
6.6 kV single-phase fault current limiter (FCL) using a
high-Tc superconducting coil as a limiting coil was developed.
The development is a preliminary step to investigate the
feasibility of the FCL application for high-voltage
transmission lines. The FCL is of the rectifier type and is
mainly comprised of a limiting coil, a sub-cooled nitrogen
cryostat with a cryocooler, and a rectifier bridge. The
limiting coil, wound as a solenoid by Ag/Mn sheathed Bi-2223
tapes, has an inductance of 30 mH. It is immersed in a liquid
nitrogen bath in the cryostat. A Gifford-McMahon cryocooler
cools the cryogen below 77.3 K. A pressure regulator keeps the
cryogen at an atmospheric pressure. The coil has a critical
current of 70 A at 64 K and endures a 50 Hz overvoltage of 22
kV against the ground. In a fault current limiting test with a
short-circuit generator, a short-circuit current of 12.5 kA
was limited to 1.2 kA. |
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Three
phase inductive HTS fault current limiter for the protection
of a 12 kVA synchronous
generator
I. Vajda, S. Semperger,
T. Porjesz, A. Szalay, V. Meerovich, V. Sokolovsky and W.
Gawalek
Summary: The concept of high
temperature superconducting (HTSC) mini power plant model is
presented. An HTSC fault current limiter (FCL) for the
protection of a generator unit was designed. The simulation
and test results of a one phase overload case are shown.
Duration tests to reveal the dependency of the limited current
and the FCL voltage on the activation number were performed. A
new representation of the sudden short circuit current and
voltage are proposed. |
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Development
of Bi-2223 magnetic separation
system
H. Kumakura, T. Ohara, H.
Kitaguchi, K. Togano, H. Wada, H. Mukai, K. Ohmatsu, H. Takei
and H. Okada
Summary: A prototype of a
cryocooler cooled Bi-2223 magnet system for magnetic
separation was constructed. The magnet system has 200 mm room
temperature bore and generates fields higher than 1T in
11-liter room temperature space. The magnet was tested at
various temperatures and excitation speeds. The magnet was
cyclically excited up to 1.7 T at the speed of 1.7 T/min with
various periodic times. The temperature gradually increased
with the number of excitations, however, the temperature
saturated at 28-38 K for the periodic times longer than 9 min,
and stable operation of the magnet was obtained. A
demonstration of magnetic separation of aquatic slurry
containing fine /spl alpha/-hematite paramagnetic particle was
performed by using ferromagnetic stainless steel fibers as a
magnetic filter. Almost 100% of hematite particles were
successfully separated from the slurry. |
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10
T conduction cooled Bi-2212/Ag HTS solenoid magnet
system
H. Morita, M. Okada, K.
Tanaka, J. Sato, H. Kitaguchi, H. Kumakura, K. Togano, K. Itoh
and H. Wada
Summary: A high-field HTSC
conduction cooled magnet system is considered to be the most
promising system for superconducting magnets of the next
generation. The authors have been developing a 10 T Bi-2212/Ag
solenoid magnet system with a room temperature bore of 50 mm.
This system consists of inner, mid and outer coils. The coils
are designed to generate 10 T at 10 K with Bi-2212/Ag
ROSATwire (ROtation-Symmetric Arranged Tape-in-tube wire).
This wire shows almost isotropic field dependence of J/sub c/
and ease of solenoid winding. The details of design of the
system have been completed, and inner test coils and also a
conduction cooling system have been built. Approximately a
total of 3 km long Bi-2212/Ag ROSATwire has been employed for
windings of the coils. In this paper, design of the magnet
system, the preliminary results of trial operation of the
inner coil and test result of the conduction cooling system
are presented. |
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Test
results of a demonstration HTS magnet for
minesweeping
S. Ige, D. Aized, A.
Curda, D. Johnson and M. Golda
Summary:
American Superconductor completed building a
demonstration HTS minesweeping magnet for airborne
superconducting mine countermeasure system in December 1999,
The demonstration magnet consisted of a single-layer HTS coil
wound on a 457-mm G-10 mandrel, and housed in a 560 mm
diameter by 1.5-m long stainless steel vacuum vessel. It is
conduction cooled with a two-stage cryocooler. It has a
magnetic moment of 15 kAm/sup 2/. The magnet was successfully
ramped up to 400 A at /spl sim/35 K. The magnet current was
kept at 400 A for six hours without any voltage run-away. The
magnet was also successfully tested for 50% AC modulation (200
A to 400 A) with a trapezoidal current waveform. Experimental
data from these tests are presented. |
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ALS
Superbend magnet system
J.
Zbanik, S.T. Wang, J.Y. Chen, G.J. DeVries, R. DeMarco, M.
Fahmie, A. Geyer, M.A. Green, J. Harkins, T. Henderson, J.
Hinkson, E.H. Hoyer, J. Krupnick, S. Marks, F. Ottens, J.A.
Paterson, P. Pipersky, G. Portmann, D.A. Robin, R.D.
Schlueter, C. Steier, C.E. Taylor and R.
Wahrer
Summary: The Lawrence Berkeley
National Laboratory is preparing to upgrade the Advanced Light
Source (ALS) with three superconducting dipoles (Superbends).
In this paper we present the final magnet system design which
incorporates R&D test results and addresses the ALS
operational concerns of alignment, availability, and economy.
The design incorporates conduction-cooled Nb-Ti windings and
HTS current leads, epoxy-glass suspension straps, and a
Gifford-McMahon cryocooler to supply steady state
refrigeration. We also present the current status of
fabrication and testing. |
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Design
of a 60-kA HTS current lead for fusion magnets and its
R&D
T. Ando, T. Isono, K.
Hamada, G. Nishijima, H. Tsuji, A. Tomioka, T. Bohno, Y.
Yasukawa, M. Konno and T. Uede
Summary: A 60
kA HTS current lead has been designed for large fusion magnets
such as the ITER magnet. The actual refrigeration input power
required to cool the current lead is specified to be reduced
to one third that of the conventional copper lead. The HTS
part of the 60 kA lead consists of 48 units installed with
cylindrical array into the outer surface of a stainless steel
tube with a diameter of 146 mm. Each unit is composed of six
Bi2223/Ag-10at%Au tapes, and its cross-sectional dimension is
6.5 mm/spl times/2.7 mm. The HTS part is cooled by conduction,
and the warm and cold end temperature conditions of the HTS
part are 50 K and 4.5 K, respectively. The copper part is
cooled by helium gas, a flow rate of 3.9 g/s and the inlet
temperature of 35 K. The 60-kA lead has been designed in
consideration of safety under the long discharge time
condition of ITER-TF coil with a detection time of 2 sec, and
a discharge time constant of 15 sec. For the purpose of
verifying the reliability of the design for the long discharge
time, one unit sample has been fabricated and tested. The
result indicates that the maximum temperature rise of the HTS
part is less than 150 K for the ITER like-discharge from 1.25
kA corresponding to 60 kA of the full lead with 48
units. |
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AMI-MIT
1-kA leads with high-temperature superconducting
sections-design concept and key
parameters
Haigun Lee, P.
Arakawa, K.R. Efferson, R. Fielden and Y.
Iwasa
Summary: This paper presents the design
concept and key parameters of a pair of 1-kA AMI-MIT Leads,
comprised of a high-temperature superconducting (HTS) section
that, over a short distance at the warm end (80 K), operates
in the current-sharing mode and a vapor-cooled copper lead
that covers the temperature range above 80 K. Because of their
reliance on vapor cooling, AMI-MIT Leads are applicable only
to liquid helium cooled superconducting magnets such as those
used in high-energy physics accelerators and fusion machines.
The new 1-kA HTS section is designed to be scalable to
high-current leads, e.g., 6 kA, 25 kA, 40 kA. |
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Design,
fabrication and tests of a 600A HTc current lead for the LHC
correction magnets
L.
Garcia-Tabares, J. Calero, P. Abramian, F. Toral, L.A.
Angurel, J.C. Diez, R. Burriel, E. Nativadad, R. Iturbe and J.
Etxeandia
Summary: This paper describes the
design and fabrication of four sets of HTc 600 A current leads
manufactured by ANTEC in collaboration with three more
Institutes to test the feasibility of industrial fabrication
of these units. This development has been made in the
framework of a CERN programme to build low thermal losses
leads for the correction magnets of the LHC. Tests performed
at the manufacturer installations are also
presented. |
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1.5
kA Bi-2223 HTS current leads for SMES
magnets
Hyun-Man Jang, Sang-Soo
Oh, Hong-Soo Ha, Jeon-Wook Cho, Dong-Woo Ha, Hae-Jong Kim,
Ki-Chul Seong, Young-Kil Kwon, Kang-Sik Ryu and Sang-Hyun
Kim
Summary: 1.5 kA class Bi-2223 HTS current
leads for superconducting magnetic energy storage (SMES)
magnets were fabricated and tested. The HTS leads were
composed of Bi-2223/Ag-1 at%Au tapes fabricated by PIT process
and stainless steel former and they were connected to
conventional gas-cooled copper leads, Using a calorimetric
method, heat input to the liquid helium through the HTS leads
was estimated to be 0.395 W/lead when the warm end part's
temperature was 65 K, which was slightly greater than the
calculated value of 0.35 W/lead. The measured critical current
of the HTS leads was about 1.6 kA when the warm end part's
temperature was 80 K. This measured value was well consistent
with computed values. |
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Effect
of the sinter-forging deformation rate on properties of
Bi-2223 current leads
X.K. Fu,
Y.C. Guo, W.M. Chen, H.K. Liu and S.X. Dou
Summary:
The influence of the sinter-forging rate on the
critical current density (J/sub c/) behaviour in an external
field and on the contact resistance R/sub c/ for Bi-2223
current leads has been investigated. The current leads were
fabricated by a combination of cold isostatic pressing (CIP)
and sinter-forging methods with the thickness reduction rate
ranging from 0% to 90%. The two silver contact terminals of
each sample were also prepared during the sinter-forging. The
results revealed that J/sub c/ was strongly affected by the
deformation rate of sinter-forging and reached a maximum of
725 A/cm/sup 2/ at a deformation rate of 80%. From the
measurements of the external magnetic field dependence on
J/sub c/. It was determined that sinter-forging could improve
the J/sub c/ behaviour in external fields, particularly in the
regime below 10/spl times/10/sup -13/ Tesla (i.e. 10 mT). The
measurements of the contact resistance R/sub c/ were conducted
for different transport currents at 77 K. The results showed
that the contact resistance for the samples with higher
deformation rates became less dependent on the transport
current over a range of 0.5 A to 50 A. |
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Transport
performance of Bi-2212 current leads prepared by a diffusion
process
Y. Yamada, M. Takiguchi,
O. Suzuki, K. Tachikawa, A. Iwamoto, H. Tamura and T.
Mito
Summary: Bi-2212 bulk cylinders have
been prepared by the diffusion process for current lead
application. The Bi-2212 oxide superconducting layer is
synthesized through the reaction between a Sr-Ca-Cu oxide
tubular substrate and a Bi-Cu oxide coating layer with Ag
addition. The Bi-2212 diffusion layer about 150 /spl mu/m in
thickness with textured structure formed around a tube 20/16
mm in outside/inside diameter. The transport current of the
tube specimen exceeds 6.250 A at 4.2 K under self-field, which
corresponds to a transport current density of 35,000 A/cm/sup
2/. The overall joint resistance is measured to be about 150
m/spl Omega/ at both ends of the specimen, composed of Cu
endcap, Sn-Pb solder and Ag contact on the specimen. The
resistivity of the commercial Sn-Pb solders is About 2 n/spl
Omega/m at 4.2 K, and one order of the magnitude higher than
that of Cu and Ag. Therefore, the soldering process is
important in reducing the joint resistance and the resultant
Joule heat. Present Bi-2212 bulk conductors with large
transport current are promising as current leads for
superconducting magnets. |
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Coaxial
configuration of Bi-2212 textured ceramics: a possibility for
improved current leads
E.
Natividad, M. Mora, J.C. Diez, J.I. Pena, M. Garcia, L.A.
Angurel and R. Navarro
Summary: The
simultaneous improvement of the critical current and the
minimization of the heat conductivity of thin Bi-2212 textured
ceramics at high temperatures has been attempted on small
diameter, thin walled superconducting tubes. Laser floating
melting zone technologies have been used to fabricate
cylindrical tubes of textured ceramic. Moreover, the
feasibility of larger performances in current lead devices
using a coaxial configuration of conductors with currents
flowing in opposite directions has been experimentally and
theoretically analyzed. |
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Evaluation
of superconducting current feeder system for the Large Helical
Device (LHD)
T. Uede, S. Yamada,
T. Mito, H. Hiue, I. Itoh and O. Motojima
Summary:
A superconducting (SC) current feeder system for LHD
has been operated since March of 1998. It consists of 9 SC
bus-lines, 9 pairs of current leads and 3 current lead
cryostats, SC bus-lines have a total length of 497 m, rated
current of 32 kA and withstand voltage of 5 kV under 77 K
helium gas condition. After 2 years operation of this system
it was demonstrated that the SC current feeder system is
reliable and useful. On the basis of these operational
experiences, the authors have evaluated the performance,
reliability and operation cost of the SC current feeder system
in comparison with nonSC type current feeder system. They have
concluded that the SC current feeder system with high current
capacity is more suitable than other current feeder systems
such as using a water-cooled busbar, especially for
large-scale SC fusion experimental devices. |
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Magnetization
as a critical defining parameter for strand in precision
dipole applications implications for field error and F-J
stability
E.W. Collings, M.D.
Sumption and E. Lee
Summary: In hadron
accelerators, between low energy particle injection and beam
accumulation, the guiding dipoles are ramped at some rate
dB/dt. Both at injection and during ramping the static and
dynamic magnetizations of the magnet windings introduce
multipolar distortions into the beam-line field. Dynamic
magnetization, controllable by cable design, is estimated and
used to provide a criterion against which to evaluate the
allowable magnitude of static (persistent-current)
magnetization, M, from a field-quality standpoint. The it is
of NbTi and advanced Nb/sub 3/Sn conductors are compared and
with regard to the latter the question of flux-jump stability
is explored. A magnetization criterion for such stability is
presented and compared to experiment. It is noted that since
/spl Delta/M is proportional to critical current density,
J/sub c/, and the strand's effective filament diameter, d/sub
eff/, the latter has frequently been specified as a critical
parameter, although it will need to be re-specified with every
increase in J/sub c/. It is pointed out that although in the
manufacture of MF Nb/sub 3/Sn composites d/sub eff/ will
continue to be useful as a processing parameter in that it
gauges the extent to which changes of processing conditions
change the degree of interfilamentary bridging, and is
measured by comparing the magnetic and transport-measured
J/sub c/s, the most useful information is embodied in the
results of the magnetization measurement alone. |
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Coupling
loss and contact resistance in cored stabrite
cables-influences of compaction and variation of core
width
M.D. Sumption, R.M. Scanlan
and E.W. Collings
Summary: AC loss due to
coupling currents in a Rutherford cable can be modified by
changing the interstrand contact resistance (ICS) by:
adjusting the level of native oxidation of the strand, coating
it, or by inserting a ribbon-like core into the cable itself.
With regard to cored cables further effective-ICR adjustments
can be achieved by changing: (i) the degree of compaction
during manufacture; (ii) the thickness of the core at fixed
overall thickness; and (iii) the width of the core. The
authors report on the results of magnetic and calorimetric AC
loss measurements on stainless-steel-cored stabrite cables
which had been: (i) externally compacted by rolling to
thicknesses of 0, 6, 9, and 11% below the standard thickness;
(ii) internally compacted by being furnished with cores of
thickness 1 mil (30 /spl mu/m) and 2 mil (50 /spl mu/m); and
(iii) furnished with cores whose widths, w/sub core/, were
about 20%, 50%, 75% and 100% of the maximum possible width.
The measurements were made in applied AC fields that were
directed perpendicular (face-on) and parallel (edge-on),
respectively to the broad cables faces. |
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Analysis
of current after normal transition in a cable-in-conduit
conductor
N. Koizumi, T. Ando, Y.
Takahashi, H. Tsuji and S. Shimamoto
Summary:
When some strands carry a large current as a result of
current imbalance, they may initially become normal and the
current is transferred to other superconducting strands. A
one-dimensional simulation code for stability and quench of a
cable-in-conduit conductor is improved to study this
phenomenon using an infinitely long distributed circuit model,
in which the current can easily be calculated. The results
show the normal zone propagation plays a significant role in
the current decay. Also, they are indicated that the conductor
is more stable for higher conductance but the stability of the
conductor seems more important to prevent instability due to
the current imbalance. |
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Numerical
investigation of the current distribution in cable-in-conduit
conductors using lumped network
models
C. Meinecke, A.M. Miri and
R. Petranovic
Summary: Magnet coils wound
from superconducting multistrand cables exhibit a reduced
current carrying capability during nonsteady-state operation.
This may be caused by a nonuniform current distribution in the
cable. The extent of this nonuniformity depends on the design
of the coil. Hence, measurements of the actual current
distribution cannot be performed on short cable samples. In
order to be able to estimate the performance of a cable for a
given coil geometry already during the design phase of the
magnet, lumped network models have been developed for a
numerical investigation based on geometrical and material data
of the coil and the cable, This work focuses on
cable-in-conduit conductors (CICCs). Actual conductor designs
have been modeled and the influence of the interstrand
conductance and the geometrical accuracy of the cable was
investigated. |
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Protection
heater performance of Nb/sub 3/Sn epoxy impregnated
superconducting solenoids
I.R.
Dixon and W.D. Markiewicz
Summary: The
response time of Nb/sub 3/Sn coils with an active protection
system is measured to quantify their performance during low
current quenches. Tests are conducted on coils with bronze
processed Nb/sub 3/Sn conductors of 0.23 and 0.41 copper
fractions and placed in a background field up to 7 T.
Stainless steel heaters imbedded within the epoxy at the outer
diameter of the coils are employed to normalize the magnets
uniformly along their axes. The heater circuit consists of up
to four heater strips connected in series in which a square
wave pulse is applied for a duration of one second. The quench
reaction time is studied as a function of heater input power,
number of active heaters, and fraction of critical current
density. |
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Analysis
of the discharge of the ATLAS barrel toroid and end cap
toroids with different configurations of the protection
circuit
E. Acerbi, G.
Baccaglioni, F. Broggi, M. Sorbi and G.
Volpini
Summary: An analysis of the discharge
of the barrel toroid and end cap toroids with different
protection circuits has been carried out in order to verify
the possibility of a new simplified and cheaper configuration
of the components of the circuit. In the study also the
presence of short circuits has been considered. The comparison
of the results and the analysis of the advantages and risks of
the different configurations should allow the choice of the
best solution for the economy and safety of the
toroids. |
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Protection
of conduction cooled Nb/sub 3/Sn SMES
coil
A. Korpela, T. Kalliohaka,
J. Lehtonen and R. Mikkonen
Summary: A
conduction cooled Nb/sub 3/Sn SMES coil requires a protection
analysis different from that of the liquid helium cooled NbTi
magnets. In an SMES coil constructed with a bronze processed
Nb/sub 3/Sn wire, hot spot temperature is high due to a slow
normal zone propagation. In a conduction cooled system, the
eddy current generated heating in the cryogenic interface
enables a quench back. In order to design a proper protection
scheme for a cryogen free Nb/sub 3/Sn SMES system operating at
10 K, a computer code has been developed. The code simulates
the quench behaviour of the coil protected with any
combination of a shunt resistor, subdivision and quench back.
The modelling of the quench back requires the solution of the
eddy current problem and the heat transfer between the coil
and the interface. These are combined with the solution of the
differential equations describing the protection with a shunt
resistor or subdivision. Utilizing the developed code, the
protection of a 0.2 MJ conduction cooled Nb/sub 3/Sn SMES coil
has been designed. |
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A
diagnosis method for properties of superconducting magnet
using fast current discharge
K.
Takeuchi, K. Asano and H. Hayashi
Summary:
The authors studied a diagnosis method to investigate
the properties of superconducting magnets throughout their
life. The magnet current, initially held constant, is damped
with a short time constant. One can evaluate the properties of
the magnet using the normal voltage, which may appear during
the damping phase. A bridge circuit, which can adjust both
amplitude and phase with over five orders of accuracy, was
developed to measure unbalance voltages. Experiments were
carried out using a small solenoidal NbTi magnet. By adjusting
bridge parameters and numerically processing the voltage
waveform, the authors measured the normal transition voltage
with the S/N ratio of over 10/sup -4/ in the damping phase.
The applicability of the diagnosis method was studied in both
numerical simulations and experiments. |
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Modeling
of electromagnetic and thermal diffusion in a large pure
aluminum stabilized superconductor under
quench
A.V. Gavrilin and Y.M.
Eyssa
Summary: Low temperature composite
superconductors stabilized with extra large cross-section pure
aluminum are currently in use for the Large Helical Device in
Japan, modern big detectors such as ATLAS at CERN, and other
large magnets. In these types of magnet systems, the rated
average current density is not high and the peak field in a
region of interest is about 2-4 T. Aluminum stabilized
superconductors result in high stability margins and
relatively long quench times. Appropriate quench analyses,
both for longitudinal and transverse propagation, have to take
into account a rather slow diffusion of current from the
superconductor into the thick aluminum stabilizer. An exact
approach to modeling of the current diffusion would be based
on directly solving the Maxwell's equations in parallel with
thermal diffusion and conduction relations. However, from a
practical point of view, such an approach should be extremely
time consuming due to obvious restrictions of computation
capacity. At the same time, there exist certain ways that
simplify mathematical models for the thermal and
electromagnetic diffusion processes for the purpose of rapidly
calculating the propagation velocity and effective simulating
of quench behavior. These models explained here were tested
and applied to quench simulation in the above-mentioned magnet
systems. |
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Test
results of a 20 kA current lead using Ag/Au stabilized Bi-2223
tapes
R. Heller, K. Takahata, G.
Friesinger, T. Mito, M. Tasca, A. Nishimura, S. Satoh and S.
Yamada
Summary: In the frame of the European
Fusion Technology Programme, the Forschungszentrum Karlsruhe
and the CRPP Villigen have been developing a 60 W current lead
for the ITER TF coils using high temperature superconductors.
In part 3 of the task, a 20 kA HTS current lead was assembled
using two Bi-2223 modules manufactured in industry. The
performance test was carried out at NIFS, Japan, as part of
the LIME project. The test covers the electrical and thermal
behaviour in both steady state and transient operation.
Current sharing was observed between two modules and the
quench current of the current lead was evaluated about 30 kA
at the design conditions. The results suggest that it is
possible to satisfy all requirements needed for the leads of
the ITER TF coils. |
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Quench
propagation in AFM Bi-2223 conductors for current lead
applications
L. Martini, F.
Barberis, R. Berti, L. Bigoni, M. Putti, G. Volpini and F.
Curcio
Summary: In this paper, the authors
report on the electrical and thermal properties of Bi-2223
composite conductors prepared by the "accordion-folding
method" (AFM). Thermal behavior study on AFM Bi-2223
conductors similar to those that have been successfully used
to assemble the cold stage of low-loss current leads for CERN,
has been performed by using a newly developed experimental
apparatus that is described in detail. |
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Development
of high temperature superconducting current feeders for a
large-scale superconducting experimental fusion
system
T. Mito, K. Takahata, R.
Heller, A. Iwamoto, R. Maekawa, H. Tamura, Y. Yamada, K.
Tachikawa, K. Maehata, K. Ishibashi, G. Friesinger, M. Tasca,
A. Nishimura, S. Yamada, S. Imagawa, N. Yanagi, H.
Chikaraishi, S. Hamaguchi, M. Takeo, T. Shintomi, T. Satow and
O. Motojima
Summary: The National Institute
for Fusion Science (NIFS), in collaboration with universities
and laboratories in Japan, the Forschungszentrum Karlsruhe
(FZK) and the Max-Planck Institut fur Plasma Physik (IPP) in
Germany, is planning to develop high temperature
superconducting (HTS) current feeders for large-scale
superconducting coils. Two programs are being progressed: one
is a current feedthrough for superfluid helium (He II) cooled
superconducting coils; the other is current leads for
experimental fusion system. The paper describes the present
status of the two programs, including joint experiments of a
20 kA Bi-2223 current lead developed by FZK and development of
a prototype YBCO bulk current feedthrough for He II cooled
superconducting coils. In addition, the test results of
Bi-2212 tubes fabricated by diffusion process, applicable to
HTS current leads, are described Bi/sub 2/Sr/sub 2/CaCu/sub
2/O/sub 8/. |
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The
effect of low temperature cryocoolers on the development of
low temperature superconducting
magnets
M.A.
Green
Summary: The commercial development of
reliable 4 K cryocoolers improves the future prospects for
magnets made from low temperature superconductors (LTS). The
hope of the developers of high temperature superconductors
(HTS) has been to replace liquid helium cooled LTS magnets
with HTS magnets that operate at or near liquid nitrogen
temperature. There has been limited success in this endeavor,
but continued problems with HTS conductors have greatly slowed
progress toward this goal. The development of cryocoolers that
reliably operate below 4 K will allow magnets made from LTS
conductor to remain very competitive for many years to come. A
key enabling technology for the use of low temperature
cryocoolers on LTS magnets has been the development of HTS
leads. This report describes the characteristics of LTS
magnets that can be successfully melded to low-temperature
cryocoolers. This report also shows when it is not appropriate
to consider the use of low-temperature cryocoolers to cool
magnets made with LTS conductor. A couple of specific examples
of LTS magnets where cryocoolers can be used are
given. |
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Development
of 9.5 T NbTi cryogen-free
magnet
Weijun Shen, M. Coffey and
W. McGhee
Summary: A 9.5 T cryogen-free
superconducting NbTi magnet system has been designed,
constructed and tested at Cryomagnetics, Inc. The system has a
horizontal /spl Phi/32 mm clear room temperature bore through
the high field region. The cryostat has a compact 432 mm
outside diameter by 305 mm length. The magnet system, featured
high-Tc BSCCO current leads and NbTi superconducting
persistent switch, and was cooled directly by a new generation
pulse tube refrigerator. Tests show that the magnet generates
a magnetic field up to 9.5 T with 0.1% homogeneity over a 10
mm diameter volume. The cool-down time from room temperature
to operating temperature is approximately 14 hours. The magnet
was charged from zero to 9.5 T In less than 10 minutes. After
intentional quench at 9.2 T. the system recovered in
temperature in less than 3 hours. In this paper, the design,
analysis and the system test results are
reported. |
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An
engineering formula to describe the AC loss of BSCCO/Ag
tape
J.J. Rabbers, B. ten Haken,
O.A. Shevchenko and H.H.J. Ten Kate
Summary:
An engineering function to describe the AC loss of
BSCCO/Ag tape conductors is developed. For a wide range of
transport currents and magnetic fields (with different
orientation) the loss is described with an uncertainty of 10%.
The equation is based on the analytical expressions available,
BSCCO/Ag tapes used in power applications at liquid nitrogen
temperature are fed with an AC transport current and exposed
to an AC magnetic field. The magnetic field in a device has
different orientations with respect to the position of the
conductor in the device. In this contribution, AC loss
measurements for simultaneously applied magnetic field (with
different orientation) and transport current are presented for
a high quality tape conductor that is used in a transformer
coil. The results are separated into a magnetic and a
transport current loss component. |
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Effect
of the geometry of HTS on AC loss by using finite element
method simulation with B-dependent E-J power
law
N. Nibbio and S.
Stavrev
Summary: Mono and multifilamentary
HTS tapes exhibit nonnegligible AC loss in self-field and
considerably higher losses in the presence of external
magnetic field. The effect of the conductor's geometry on the
AC loss has been investigated in this paper. The nonlinear
electromagnetic properties of the superconducting material are
expressed with a B-dependent E-J power law and are implemented
in finite element method commercial software. The critical
current density and the power index n dependence on B are
obtained from DC measurements of a real Bi-2223 tape. AC loss
comparison between monofilamentary conductors of rectangular,
elliptical, square and round geometry has been performed in
self-field and applied external perpendicular magnetic field.
The areas of the cross-section and the
superconducting-core-to-Ag ratio have been kept constant in
the simulations. To complement the AC loss analysis, the
distribution of the current density and the magnetic field of
the different geometries are presented. |
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Finite
element method simulation of AC loss in HTS tapes with
B-dependent E-J power law
N.
Nibbio, S. Stavrev and B. Dutoit
Summary: The
nonlinear behavior of high temperature superconductors (HTS)
is often modeled by an E-J power law in order to describe
their electromagnetic properties. This paper presents AC loss
calculations in HTS tapes, performed by means of FEM
commercial software using the A-V method. The implemented
nonlinear model of the HTS tapes takes into account the
B-dependence of the critical current density J/sub c/ and the
power index n. The expressions for J/sub c/(B) and n(B) are
obtained from electrical measurements of a Bi-2223 tape under
applied DC magnetic field. Numerical simulations of HTS tapes
under different experimental conditions have been performed,
i.e. the application of a transport current and/or AC external
perpendicular magnetic field at 59 Hz. A comparative analysis
of AC loss is then presented where J/sub c/ and n are
maintained either constant or B-dependent. The combined J/sub
c/(B) and n(B) formulation leads to a better understanding of
HTS electromagnetic behavior, especially when a perpendicular
magnetic field is applied. |
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Large
Scale Abstracts (2000 - Part
2)
No author information
available
Summary: Abstracts of papers not
included in the conference proceedings. The full papers may
appear in a later issue of IEEE Transactions on Applied
Superconductivity. |
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Author
Index (2000 - Part 2)
No author
information available
Summary: Not
available |
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