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| 1996 Part 1 |
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Front Cover (1996 - Part
1)
No author information
available
Summary: Not
available |
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Table
of Contents (1996 - Part 1)
No
author information available
Summary: The
following topics were dealt with: large scale applications of
superconductivity; superconducting materials; superconducting
electronics. |
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Conference Information
(1996)
No author information
available
Summary: Not
available |
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Superconductivity
in electronics
A.H.
Silver
Summary: Superconductivity is an
emerging technology for high performance electronics. It
offers unique and beneficial attributes for sensor, signal
processing, and communication systems. Yet, industry faces
technical hurdles and market obstacles to identifying business
targets. The author presents his vision of the future of
superconductor electronics in space, his perspective of the
past, and his approach for achieving success. The ability to
define and achieve successful paths which overcome the
technical and market barriers will determine the viability of
superconductivity in the electronics industry, and
coincidentally of applied research in this
technology. |
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High-temperature
superconducting materials: a decade of impressive advancement
of T/sub c/
C.W.
Chu
Summary: In the decade after the
discovery of high-temperature superconductivity, more than one
hundred non-intermetallic compounds have been found to
superconduct above 23 K, which is the record transition
temperature (T/sub c/) of conventional low-temperature
intermetallic superconductors. These high-temperature
non-intermetallic superconductors belong to three compound
families: the cuprates, the bismuthates, and the fullerites.
In this presentation, I shall restrict myself to the cuprates
with a T/sub c/ above the liquid nitrogen boiling point of 77
K. They show a current record T/sub c/ of 134 K at ambient and
164 K at high pressure. I shall recall events that led to the
discovery of superconductivity at 93 K to bring down the 77 K
temperature barrier and summarize subsequent efforts to raise
the T/sub c/ to its present record. Prospects for future
higher T/sub c/ are discussed. |
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The
road to conductors of high temperature superconductors: 10
years do make a difference!
D.C.
Larbalestier
Summary: Amongst all the
predictions for a superconducting future that were made in the
early days after the discovery of high temperature
superconductivity, most depended on the development of
conductors from which magnets, motors, power cables etc. could
be constructed. Until 1989, there seemed little prospect of
such a technology because polycrystalline forms of HTS were
granular and transmitted current very poorly. Starting with an
empirical breakthrough in 1959, a strong set of large scale
demonstration devices have been made with high temperature
superconductors. The foundation of all this technology lies in
the conductor. For HTS conductors, 10 years does indeed make a
difference, as this review summarizes. |
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Superconductor
electronics, 1986-1996
T. Van
Duzer
Summary: This paper reviews progress in
superconductor electronics over the decade since the discovery
of the high temperature oxide superconductors (HTS). Almost
simultaneously with that discovery was the development of a
new process for low temperature superconductor (LTS) devices
based on the Nb/AlOx/Mb whole wafer tunnel junction. Both of
these developments facilitated a strong growth in
applications. We review first the applications based on thin
films with no Josephson junctions. This is mostly using HTS,
which permits more convenient cooling thus making applications
mere commercially viable. With their need for only one or two
Josephson junctions, SQUID magnetometers have succeeded to the
market place using HTS materials. Finally, we review progress
in the volt standard and digital circuits, both of which
require large numbers of junctions and at present can only be
realized with LTS materials. |
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Superconductivity
and electric power: promises, promises ... past, present and
future
P.M.
Grant
Summary: The long-awaited marriage of
superconductivity with electric power has undergone a lengthy
engagement to say the least. Whether those nuptials will
indeed ever take plate is a question we here dare answer,
recognizing full well the pitfalls entailed, Almost
immediately after its 1911 discovery, superconductivity was
popularly touted as the key to the lossless delivery of
electricity ... at least until the type I nature of these
early materials was appreciated ... a cycle of excitement and
disillusionment that unfortunately has typified the field
throughout its history. With the emergence and exploitation of
Type II superconductors in the middle decades of the century,
tremendous technical progress was made toward power
application embodiments, resulting in operating prototypes of
transmission cables and rotating machinery by the early 1980s,
nonetheless, these achievements did not mature into commercial
power products, primarily because of economic and social
factors that had evolved by that time ... successful
conservation efforts had lowered expected electricity load
growth such that, ironically, the incremental efficiencies
offered by superconductivity were no longer required at the
cost involved ... an important lesson in that the successful
deployment of a technology often rests on factors unforeseen
and outside its internal development. The years from 1986 to
the present have witnessed the discovery of the copper oxide
perovskite high temperature superconductors and their
coming-of-age in practical wire form. These events, plus a
renewed and growing world-wide demand for electric energy,
give hope that the final vows will actually take place during
the first quarter of the coming century. |
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The
future prospects for large scale applications of
superconductivity
D.B.
Montgomery
Summary: Predictions of future
market growth for large scale applications of
superconductivity are very bullish. This paper discusses there
predictions in the context of research applications, defense
and space, instruments for science and medicine, machine
tools, materials processing, transportation, energy and
national security. The status and the technical and
non-technical market factors likely to influence growth for
each of these applications are discussed. |
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A
quench initiation and propagation study (QUIPS) for the 45 T
hybrid
O.R. Hill, J.R. Miller,
W.J. Kenney and V.J. Toplosky
Summary: In an
ongoing effort to understand stability and quench
characteristics in large high field superconductivity systems,
a series of Quench Initiation and Propagation Studies (QUIPS)
is being employed. The goal is to establish a database of
stability and quench information for the present 45 T Hybrid
project and for future applications. To reach the goal in an
efficient, cost effective manner, novel techniques are
implemented to model high field stability and quench behaviour
in cable in conduit conductors (CICC) at relatively low
fields. A relatively low J/sub c/ superconductor having a
comparable critical temperature is used to approach the
operating temperature margins of the Nb/sub 3/Sn conductor in
the A subcoil of the 45 T Hybrid. One particular technique was
the heat treatment of the single triplex NbTi CICC to degrade
the J/sub c/ for stability matching purposes. Design
parameters and operating conditions of the long solenoid are
also tailored for optimal sealing. This paper discusses the
analytical methods, processes, and their associated effects on
the model. |
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Spike
voltages seen during "quick charge" ramp limitation tests on
Nb/sub 3/Sn cable-in-conduit
conductors
M. Takayasu, V.S.
Vysotsky, S. Jeong, P.C. Michael, J.H. Schultz and J.V.
Minervini
Summary: Spike voltages observed
during ramp rate limitation tests on sub-sized Nb/sub 3/Sn
cable-in-conduit superconductors are analyzed using current
loop model. The effects of loop currents on the ramp
limitations of multi strand superconducting cables are
discussed. Current loops existing in multi strand cables
generate excess local currents that quench strands and produce
voltage spikes. Experimental results previously reported as
abnormal ramp rate limitations are explained by loop current
phenomena. |
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Thermal
properties of impregnating materials for stable
superconducting magnets
K. Seo,
M. Morita, H. Yoshimura, S. Nishijima and T.
Okada
Summary: The minimum quench energies
(MQEs) of superconducting (SC) wires have been measured
precisely by means of a 'Carbon Paste Heater'. The thermal
behavior just before the normal generation of the heavy loaded
SC wire was observed to determine the quenching. We learned
that once a normal region is produced, it should spread
rapidly regardless of the surrounding conditions. The MQE,
however, would increase when a local temperature rise before
quenching is prevented by using certain materials around the
SC wire. For example, high thermal diffusivity in impregnating
materials or low thermal conductivity in wire insulation will
be needed when disturbances occur outside of the SC wires. In
the previous paper, we showed the effects of enamel insulation
for improving stability. Thus, in this study, we examine the
relation between MQE and the thermal properties of the
impregnating material. Several kinds of impregnating materials
were selected and the thermal properties are compared with
enlarging MQE in mind. We have searched for an impregnating
material that has the thermal property required for improved
stability. |
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Quench,
thermal, and magnetic analysis computer code for
superconducting solenoids
Y.M.
Eyssa, W.D. Markiewicz and J. Miller
Summary:
An update report on the National High Magnetic Field
Laboratory (NHMFL) magnet analysis code is presented. Among
the recent improvements to the code is the ability to address
complex conductors, windings and reinforcements in terms of
thermal and magnetic diffusion. In this article we present
several examples showing the capabilities of this code. For
example copper/stainless steel, Cu/SS wires that are used in
pulse magnets as an alternative to other conductors such as
CuAg or CuNb have shown to have excellent thermal and
mechanical properties. It was found that the rule of mixtures
holds in predicting their properties. As a result it is
expected that wires that have 10%Cu and 90%SS will essentially
keep the SS high modulus and strength. However the 10% copper
will improve the conductivity of this reinforcement that it
can act as quench-back circuit in case of a quench. In this
study we simulated a quench of a high field (20 T) magnet
system and varied the Cu/SS ratio. The modeling results show
that 5%Cu is enough to make the reinforcement act as
quench-back circuit. |
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Simulation
of wire movement in a superconducting
coil
S. Nishijima, T. Kushida, T.
Okada and S. Namba
Summary: Wire movement in
a superconducting coil has been simulated dynamically by means
of solving the equation of motion of each winding with time to
study the instability of a superconducting magnets. The force
applied to each wire considered here were Lorentz, hoop,
wire-wire and wire-bobbin interaction. As the transport
current was increased, Lorentz force which is calculated as
the product of transport current and magnetic field applied to
the wire was increased and resulted in the floating of winding
from the coil bobbin. The minimum quench energy (MQE) of each
winding was also calculated and was compared with the
frictional heating. The quench current was defined as the
current where the frictional heating exceeds the MQE. The
degradation induced by frictional heating can be reproduced.
The effect of the misalignment of the wire was also examined.
It was found that the misalignment of the coil degraded the
quench current. |
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Calculation
of wire motion in a superconducting
magnet
T. Kushida, S. Nishijima
and T. Okada
Summary: The wire dynamic
simulation has been performed in the superconducting magnet to
get the selection standard of structural materials for stable
magnet. The equation of motion of each winding was solved with
time to simulate the wire motion in a superconducting magnet.
The transport current was increased with time, and hence
applied force to the wire was changed with time. The minimum
quench energy of each winding was calculated and compared with
the frictional heating. The quench current was decided when
the frictional heating was more than MQE. The material
parameters and the winding tension were changed and the wire
motion in a superconducting magnet was analyzed. |
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Quench
description by the characteristic time
constants
V.E. Keilin and A.V.
Gavrilin
Summary: The problem of a quench
consequences of superconducting windings is considered.
Inherent features of a quench behavior can be described by
three characteristic time constants: (1) the normalization
time t/sub n/ when normal zone would propagate over all
winding volume provided transport current I/sub 0/ is kept
constant, (2) the time of the current decay t/sub i/ provided
the winding resistance R/sub 0/ is kept constant, and (3) the
time of current decay t/sub n/ due to an external dump
resistance R/sub e/. In a simple model where the normal zone
velocities in longitudinal and transverse directions are
proportional to the decaying current, a quench behavior (hot
spot temperature, maximum internal voltage and stored energy
evacuation efficiency) is analysed in dimensionless form
depending upon the dimensionless time constants /spl tau//sub
i/=t/sub i//t/sub n/ and /spl tau//sub e/=t/sub e//t/sub n/.
It is shown that the active protection is efficient only if
/spl tau//sub e/<1. In the absence of the active protection
(/spl tau//sub e/=/spl infin/), for magnets with /spl tau//sub
i/<1 the overheating is dangerous, while for those with
/spl tau//sub i/>1 the internal voltages are dangerous.
These results are confirmed by numerical examples which also
show that the normalization time t/sub n/ is the most
important parameter in the description of quench
behavior. |
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Normal
propagation velocity and quench energy of the rotor model for
a 70 MW class superconducting
generator
K. Shimohata, M.
Morita, H. Yoshimura, T. Hirao, K. Suzuki, A. Ueda and K.
Toyoda
Summary: A rotor model was fabricated
to estimate the performance of the 70 MW class superconducting
generator. The normal propagation velocity and quench energy
for the rotor model in the rotational field are measured at
various rotating speeds. An analytical model is proposed in
order to explain the experimental data. In the calculation,
the heat transfer and the temperature rise of liquid helium in
the rotational field are considered. The calculated results
are compared with the experimental data, and these agree well.
Therefore it becomes possible to precisely design field
windings of superconducting generator. |
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Quench
localization and current redistribution after quench in
superconducting dipole magnets wound with Rutherford-type
cables
S. Jongeleen, D. Leroy, A.
Siemko and R. Wolf
Summary: Quench
development is studied for the first few milliseconds after
the start of a quench with the help of voltage taps and pickup
coils in the LHC accelerator dipole models. The reliability of
the pickup coil method (the so called quench antenna) is
discussed. By studying the flux through the pick-up coils as a
function of time information about the current redistribution
after the quench in the magnet cable is obtained. Several
possible current redistribution models are studied: current
transfer between the two layers of the cable, adjacent strand
current transfer and redistribution governed by
magnetoresistance, strand and interstrand resistance.
Comparison of the simulations with the measurements in the
magnets shows that the magnetoresistance of the copper in the
cable matrix is the main mechanism responsible for current
redistribution just after a quench. |
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Statistical
estimation of quench characteristics of quadrupole
magnets
T. Takao, O. Tsukamoto,
M. Furuse and K. Tsuchiya
Summary: Quench
tests of 9 quadrupole magnets for the TRISTAN accelerator were
performed at the National Laboratory for High Energy Physics
(KEK). Those magnets, with same specifications, had different
training characteristics. Each magnet has 4 coils of the same
winding configuration connected in series, and, in total,
quench behaviors of 36 coils of the same configuration were
obtained. Quenches were considered to be caused by conductor
motions. In the paper, we explain the training behavior of the
coils based an our previously derived theory which
statistically estimates the expected number of quenches for
the magnet current to reach a certain value. The theoretically
estimated results are compared with the experimental results
and the validity of our theory is discussed. It is also shown
that the theory is useful for designing stable and
high-current density magnets. |
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Quench
protection by passive resonant oscillation
network
D.A.
Gross
Summary: A new class of coil and
associated components network topology produces increased
efficiencies of conductor utilization with improved quench
protection in a passive mode. The electrical circuit
characteristics result in a uniform and rapid global
exhaustion of the stored energy. The electrical network design
includes eigenvalue spectrum frequencies that are much higher
than the dominant, which corresponds to the natural rate of
energy decay by resistive dissipation. The high frequencies
are associated with large fractional shifts of system currents
and energies. The fast transients allowed by the high
frequency channels produce substantial losses and quick
reduction of critical margin. |
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Quench
current level-time characteristics of AC insulated
multi-strand superconducting
cables
T. Kato, H. Shimizu, Y.J.
Tang, N. Hayakawa, Y. Yokomizu and T.
Matsumura
Summary: The quench current level
of a multi-strand superconducting (SC) cable for AC use varies
with the magnitude of AC overcurrent. We have defined this
feature as the quench current-time characteristic, i.e. the
I/sub q/-t characteristic. In this paper, we experimentally
compared the I/sub q/-t characteristics of two kinds of SC
cables, with and without a low resistive stabilizing matrix.
The results proved that the different I/sub q/-t
characteristics were caused by the difference of the current
redistribution process where each SC strand quenches
successively. Furthermore, it was pointed out by numerical
simulation using an equivalent electrical circuit model that
the difference in resistivity of SC strand could be the reason
for the various I/sub q/-t characteristics. |
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Quench
evolution of YBCO ring based on weak link
model
Minseok Joo, Chan Joo Lee
and Tae Kuk Ko
Summary: The quench process of
a YBCO high temperature superconducting ring was studied in
relation with the electromagnetic and thermal effect. The
characteristics of the resistance in the high-Tc
superconducting ring after it quenches to resistive state was
numerically evaluated with the heat conduction equation. An
experimental model consists of a primary coil and a secondary
high-Tc superconducting ring, which are magnetically coupled
through the magnetic core. The quench process is initiated by
a fast increase of an induced ac current exceeding a critical
value in the weak link. The characteristics of the quench
process in a bulk ring are well explained by numerical
analysis. This analysis could be used for designing real
devices such as a high temperature superconducting switch and
a current limiter. |
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Three-dimensional
numerical analysis of the stability of Ag/Bi/sub 2/Sr/sub
2/Ca/sub 2/Cu/sub 3/O/sub x/ tape
conductors
E.E. Burkhardt and J.
Schwartsz
Summary: As the properties of
high-T/sub c/ superconducting tapes improve, practical design
considerations require more detailed analysis. Here we report
investigations of the stability of high-T/sub c/
superconducting tapes. As a result of the broad range of
temperature during a transition and the strong temperature
dependence and anisotropy of the material properties, the
finite element method (FEM) is used to solve the
three-dimensional heat conduction equation. The heat source is
determined using the operating current, the resistivity of the
materials and the critical current density of Bi/sub 2/Sr/sub
2/Ca/sub 2/Cu/sub 3/O/sub x/ (BSCCO). The minimum quench
energy for several sources is determined for both infinitely
long and planar uniform sources in the BSCCO and the two cases
are compared. |
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Transient
stability analysis in Bi-2223/Ag superconducting
tapes
S.B. Kim and A.
Ishiyama
Summary: This paper presents
numerical results of the finite element method (FEM) with
Bi-2223/Ag superconducting multifilamentary tapes in order to
estimate the transient stability, and to find out the most
suitable analytical model and the behaviors at normal
transition of high-Tc superconductors. We investigated the
analytical model and the normal transition in the longitudinal
direction using the three dimensional FEM and in the
transverse direction using the two dimensional FEM and
compared these with the case of low-Tc
superconductors. |
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Intrinsic
stability of high T/sub c/ superconducting tapes including the
effect of anisotropic J/sub
c/
L.Y. Xiao and S.W. Van
Sciver
Summary: In the present paper, a
modified form of the critical state model is suggested to
describe the anisotropic J/sub c/ effect of BSCCO high T/sub
c/ superconducting tapes. By this model, the intrinsic
stability of a tape conductor is analyzed. The criterion
suggests that the width and the thickness of the tape should
be limited in combination. For a given tape thickness, a
critical width (corresponding to a given angle) under which
the tape becomes intrinsically stable is proposed, This
criterion suggests a 2D limitation for high T/sub c/
superconducting tape, Additionally, the model suggests that
flux-jump field is a function of the field
orientation. |
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Superconducting
pulse coil set for stability test of superconducting
cables
S. Jeong, V.S. Vysotsky,
M. Takayasu and J.V. Minervini
Summary: A
superconducting pulse coil set was constructed for transient
stability experiment of CICC (cable-in-conduit conductor). The
pulse coil set was composed of an inner and an outer coil
connected in series. With 5 T background field, the pulse coil
produced an additional 2 T on the CICC. In order to simulate
the TPX (Tokamak Physics Experiment) plasma initiation
scenario, 2 T field drop from 7 T was tried with an
approximate ramp rate of -25 T/s. This paper describes the
design for the coil and presents the experimental results of
its successful AC operation. |
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Electrical
circuit models among superconducting strands in real-scale
CICCs
M. Ono, T. Hamajima, T.
Fujioka, T. Ito, N. Koizumi, T. Ando and H.
Tsuji
Summary: Stability margin of the
cable-in-conduit conductor is greatly influenced by current
transfer performance among strands. When we estimate the
stability margin analytically, we must assume the electrical
circuit model among strands, but it is difficult to know it
for real-scale cables, because the cable has many parallel
circuits with a lot of strands and twisted stages. The
measurement of the frequency characteristics of impedance
among strands shows that the circuit can be regarded as
two-wire model. By this measurement we can judge whether the
circuit behaves like a distributed constant circuit or a
lumped element circuit within the intended frequency band.
When the circuit is a lumped element circuit, we can also get
the interval distance between each contact point and its
resistance. This paper also shows that stable conductors are
often represented with a lumped element circuit that has
well-contacted points with a short interval. |
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Stability
simulation of a cable-in-conduit conductor on a non-uniform
mesh
N. Koizumi, T. Ito, Y.
Takahashi and H. Tsuji
Summary: A new
stability simulation code of a cable-in-conduit conductor
(CICC), POCHI, has been developed. In POCHI, a large amount of
CPU time could be saved by applying an implicit time-dependent
scheme and linearization technique for a fluid dynamic
equation. This linearization also makes the scheme stable.
However, the use of the uniform mesh makes the CPU time long
for stability simulation of a long CICC. POCHI has therefore
been improved to make the grids fined only on the necessary
regions. As a result, more CPU time could be saved. The
simulated and experimental results of stability for a small
CICC were compared for verification of the improved code. The
results were in good agreement, resulting in verification of
the code. |
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Discussion
of the stable thermal equilibrium current of a superconductor
during tests of high-speed rotor
windings
K. Kaiho, H. Nomura, S.
Sekine, N. Higuchi, I. Ishii, N. Natori, H. Tateishi, S.
Fuchino, K. Arai, K. Kajikawa and N. Tamada
Summary:
Research and development of superconducting generation
equipment has been conducted. As a part of the design research
for the superconducting generator, the stability of
superconducting field winding is being studied. The goal of
this study is to formulate a design philosophy for a stable
superconducting field winding in the presence of large
disturbances. In the present paper, we describe the stable
thermal equilibrium current of the superconductor, which is
measured during the stability test. Modifying the equal area
criterion presented by Maddock et al., a simple graphical
scheme has been presented and the minimum stable thermal
equilibrium current calculated. |
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Magnetic
instability of AC multifilamentary wire due to transport
current and its dependence on phase of external AC magnetic
field
S. Fukui, M. Ito, O.
Tsukamoto and N. Amemiya
Summary: We
performed AC quench current tests of AC superconducting
multifilamentary NbTi and Nb/sub 3/Sn wires in AC external
field by changing the phase difference between the transport
current and the external field. The Nb/sub 3/Sn AC wire was
more stable than the NbTi wire and the peak value of the AC
quench currents reached to the levels of the DC quench current
while the quench current of the NbTi wire was much less than
the DC quench current. The data also showed strong dependence
of the quench currents on the phase difference. We made a
theoretical model to analyze the stability of AC wire assuming
that the instability was caused by the magnetic instability
due to the transport currents. In the analysis, the wire
temperature was numerically evaluated by calculating
instantaneous AC losses and solving the thermal equilibrium
equation. The quench current was estimated. In the paper, the
experimental results are compared with theoretical ones and it
is shown that the theoretical model explains AC quench
behaviors of the wire subject to the external AC magnetic
field. |
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Improvement
of transient stability of non-insulated A.C. multi-strand
superconducting cables
T.
Yoshino, M. Tsuda and A. Ishiyama
Summary:
For A.C. application, superconducting strands are
bundled and twisted to make a cable with large current
capacity. The quench characteristic of the cable depends on
the contact thermal and electrical conductivities between
strands, significantly. For improvement of the stability of
non-insulated multi-strand cables, it is necessary to decrease
the local rise of temperature by the Joule heating in the
current redistribution among strands. For this purpose, we
have analytically investigated non-insulated strand cables in
which the surface of each strand is covered with Cu-sheath.
The transient stability of this cable is discussed
analytically and experimentally. |
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Ramp
rate instability of multifilamentary superconductors due to
longitudinal magnetic field
N.
Banno, N. Amemiya, K. Kajikawa and H.
Tateishi
Summary: Ramp rate instability due
to an external longitudinal magnetic field of Cu/NbTi
multifilamentary superconductor was studied experimentally and
theoretically. Quench current was measured when transport
current and external magnetic field with transverse and
longitudinal component were ramped up simultaneously. At
increasing ramp rate, quench current of S-twisted
(anticlockwise-twisted) multifilamentary superconductor was
degraded in the positive longitudinal magnetic field parallel
to the transport current. The calculated stability limit
agreed with the experimental quench current within an error of
17%. Furthermore, we numerically estimated the dependence of
stability limit on ramp rate and longitudinal magnetic field
for a multifilamentary superconductor in practical large scale
devices. |
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Opportunities
for superconductivity in the electric power
industry
T.L. Mann, J.C. Zeigler
and T.R. Young
Summary: The US Federal Energy
Policy Act of 1992 has fostered the rapid evolution of a
competitive electric power industry. Its implementation by the
Federal Energy Regulatory Commission (FERC) and the various
state public utility commissions has created an opportunity
for vastly expanded application of superconducting devices in
transmission and distribution systems. Historically, the
entrance of new technologies into the electric power system
has been a long laborious process. Conservative electric
utility technologists focused on reliability and long track
records on someone else's system. The long range planning
process (5-10 years) required in the regulatory environment
further delayed implementation of newer technologies. Finally,
regulations that limited return on investment fostered high
cost generation over transmission. This has changed. The
functional unbundling of the utilities into generation,
transmission and service components has put in place new
management teams. Regulations are focusing on increased
performance and reduced costs as well as reliability. A
favorable environment is developing for a wide range of new
devices that include transmission enhancement SMES, microSMES
for power quality applications and superconducting fault
current limiters, motors, generators, transformers and
transmission lines. It is important for technologists to fully
understand how the changes in the $270 B electric power
industry are opening unprecedented opportunities for
superconductivity as an enabling technology. |
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Super-GM
and other superconductivity projects in Japanese electric
power sector
K. Ueda, T. Ageta
and S. Nakayama
Summary: This paper
summarizes the R&D trends of superconductivity
applications in the electric power sector of the Japanese
government and power companies. The background of
superconducting generators (SCG) and superconducting magnetic
energy storage are mentioned. The recent results of
low-temperature/high-temperature superconductors for power
apparatus in the Super-GM project are reported and the
progress, field testing, and analytical method of SCG are also
described. |
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Status
of the Large Hadron Collider and magnet
program
N.
Siegel
Summary: The Large Hadron Collider
(LHC), approved by the CERN Council in December 1994, is a 7+7
TeV proton accelerator-collider, to be installed in the
existing 27 km long LEP tunnel. It will represent a unique
research facility for particle physics, allowing proton-proton
collisions with a luminosity of 10/sup 34/ cm/sup -2/ s/sup
-1/ capable of providing also heavy ion (Pb-Pb) collisions
with a luminosity of 10/sup 27/ cm/sup -2/ s/sup -1/, using
the existing CERN heavy ion source. The main technological
challenges of the machine are the superconducting magnet
system, in total over 8000 magnet units immersed in superfluid
helium, with the lattice dipoles operating at 8.4 T, and the
very large cryogenic system, which maintains the entire string
of cryomagnets at its working temperature below 2 K. The paper
discusses briefly the main issues which have led to the
present layout of the LHC, gives an overview of the different
machine components and characteristics and describes in more
detail the recent development work and results of the LHC
magnet program. |
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Current
distribution and coupling losses in superconducting cables
being partially in magnetic
fields
S.
Takacs
Summary: The diffusion equation for
flux penetration into flat superconducting cables is derived,
for magnetic fields changing along the cable and solved for
cables exposed only partially to applied field. From these
solutions, the current distribution in the strands, the AC
losses and the corresponding time constants are determined. At
low frequencies, the transverse losses inside the field region
are enhanced due to currents induced outside this region,
being negligible in field-free regions. At higher frequencies,
both contributions are nearly the same of skin effect type, as
in normal conductors The time constant for decaying the
induced current is proportional to the cable length and can be
much larger than calculated for spatially homogeneous AC
fields. The result, analogous to those previously obtained for
the EURATOM-LCT conductor 25 years ago, explain the existence
of long living oscillatory currents (or super coupling
currents) in some cables for accelerator magnets, as well as
in some model cables. |
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The
influence of Lorentz force on the AC loss in sub-size
cable-in-conduit conductors for
ITER
A. Nijhuis, H.H.J. Ten Kate
and P. Bruzzone
Summary: The cable-in-conduit
superconductors for the ITER coils have operating current in
excess of 40 kA and function under last ramp conditions and
fields up to 13 T. The transverse Lorentz force acting on
strands may reduce the effective contact resistance between
strands in the cable and as a consequence, the coupling loss
will increase. This influence is investigated with a sub-size
jacketed cable having 81 Cr-coated Nb/sub 3/Sn strands. The AC
loss is measured with a sinusoidal and trapezoidal magnetic
field superimposed to a stationary background field of 1 or 2
T while the cable carries a constant transport current up to
about 30 kA. The AC loss is determined by a pick-up coil
system and partly with a calorimeter for calibration purposes.
The n/spl tau/ at 0 current declines after cyclic loading,
from 9 ms in the virgin state to 2 ms after several loads. The
increase of the interstrand coupling loss due to Lorentz
effects, accompanied by resistance-hysteresis and relaxation
effects as observed in the loss are discussed. The total loss
increases considerably due to interference of transport
current and induced coupling currents with rising transport
current and DC field. |
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Analysis
of losses in ITER joints in a varying parallel
field
N.N.
Martovetsky
Summary: One of the options for a
design of a Central Solenoid in ITER and other tokamak
machines is pancake wound modules. In this configuration
joints have to be placed in maximum magnetic field with high
changing rate. Joints should be designed to have at least the
same or larger temperature margin as that for the conductor in
the same field. We show that joints in parallel field can be
designed to meet this requirement along with reasonably low DC
resistance. Losses in parallel field are calculated and design
features which can suppress AC losses without increasing DC
resistance are discussed. Recommendations for low loss, low DC
resistance joints are made. |
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Boundary-induced
coupling currents in a 1.3 m Rutherford-type cable due to a
locally applied field change
A.P.
Verweij
Summary: In this paper the existence
of so called Boundary Induced Coupling Currents (BICCs) is
experimentally demonstrated in a 1.3 m long Rutherford-type
cable. These BICCs are induced by applying a field change
locally onto the cable and can be represented by a non-uniform
current distribution between the strands of the cable during
and after the field sweep. In order to better understand the
characteristic time, amplitude and characteristic length of
these coupling currents and the parameters by which they are
influenced, a special set up has been built. With this set-up
it is possible to scan the field induced by the BICCs along
the full length of a Rutherford-type cable. Special attention
is paid on the influence of the contact resistance between
crossing strands on the characteristics of the BICCs and
results are presented where parts of the cable are soldered,
simulating the joints of a coil. |
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Magnetisation
measurements on technical superconductors at high frequencies
(0-42 Hz)
P. Bauer, H. Fikis and
H. Kirchmayr
Summary: In many applications
superconductors are exposed to alternating magnetic fields,
sometimes in combination with a DC bias field. Induced eddy
currents form closed loops within the resistive matrix
material, heat the material and may provoke quenches of the
superconductor. Since the total field loss (P/sub lot/=P/sub
hysteresis/+P/sub eddycurrent/$ ds) is proportional to the
area enclosed by the magnetisation loop it may be found from
magnetisation measurements. We perform magnetisation
measurements in a hysteresis measurement facility operating
with the inductive integration method. The facility operates
at liquid helium temperatures (2.0-4.2 K), in a broad
frequency range (quasistatic-60 Hz) and offers the possibility
to produce simultaneously an AC-field (1 T at 50 Hz) and a DC
bias-field (maximally 3.6 T). Measurements in the upper
frequency range on NbTi/copper-matrix strands not conceived
for AC applications show a peculiar behaviour, namely a
deviation from the expected hysteresis loop. We compared the
experimentally obtained hysteresis curves to curves obtained
with calculations. |
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AC
losses characteristics of AC superconducting wire in combined
action of AC magnetic field and AC transport
current
Ji-Kwang Lee, Dong-Hun
Kim, Song-Yop Hahn, Gueesoo Cha and Ho-Seong
Kim
Summary: External magnetic field is
usually applied to the superconducting wire which is used for
superconducting machines. Phases of the external field and
self field are generally not the same. This difference of the
phases is known to have an important role in the generation of
the AC loss. The AC loss is influenced mainly by longitudinal
magnetic field component which is generated by the
twisted-structure of the filament and strand. This paper
describes the AC loss of an AC superconducting wire under the
combined action of an AC transport current and AC magnetic
field for various phase differences. Experimental results are
compared with calculated results. |
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AC
losses of AC superconducting cable due to transport current in
external AC magnetic field
S.
Fukui, O. Tsukamoto, N. Amemiya, K. Miyashita and M.
Hakamata
Summary: Transport current AC losses
of superconducting cables of the (6+1) configuration (6 AC
superconducting multifilamentary strands bundled around a CuNi
center wire) and the single strand composing the cable were
measured in an AC external magnetic field. The measured AC
loss data of the cables of different twist pitches and
directions were compared with those of the strand. It was
shown that the transport current AC losses of the cables were
affected by the twist directions and pitches of the cables. A
theoretical model to evaluate the AC loss due to transport
current was derived. In the model, the effect of the
longitudinal magnetic field subjected to the strands and the
current density vs. electric field characteristics of the
strand were taken into consideration. Our theoretical model
well explains the measured characteristics of the
cable. |
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Electrical
AC loss measurements in superconducting
coils
H. Daffix and P.
Tixador
Summary: Electromagnetic losses occur
in superconducting wires when they are exposed to time-varying
fields or currents. The total losses are the sum of the
hysteresis component, the coupling currents in the resistive
matrix, the self field effect... In order to separate these
different contributions, an electrical measurement method has
been developed. The self field effect signal is analysed in
LTc multifilamentary superconducting wires. The influence of
the current wave shape (sinusoidal, triangular) is shown, To
compare the loss mechanisms in HTS, a high temperature
superconducting Bi coil has been studied. As for LTc material,
they seem to be governed by the self field effect, but the
eddy currents are no longer negligible and may be predominant
at high frequencies. |
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Long
length calorimetric measurement of AC losses of Bi-2223
external field oriented perpendicular to the tape
width
G. Snitchler, J. Campbell,
D. Aized, A. Sidi-Yekhlef, S. Fleshler, S. Kalsi and R.
Schwall
Summary: AC applications are
projected to be a significant market for HTS conductor. The AC
magnetic fields perpendicular to the wide face of Bi-2223
conductor (or parallel to the crystallographic c-axis of the
oxide superconductor) are responsible for a significant
portion of the total loss in AC coils. ASC has developed a
calorimetric apparatus which can measure long lengths of
conductor in a uniform continuous perpendicular field. This
apparatus provides Accurate measurement of interfilament or
interstrand coupling losses. Calorimetric measurements from
long lengths of twisted multifilamentary conductor are
presented. |
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A
nonlinear model of silver sheathed Bi(2223) high temperature
superconducting tape
B. Dutoit,
N. Nibbio, D. Djukic, H. Dedieu and G.
Grasso
Summary: The use of high temperature
superconducting Ag sheathed Bi(2223) tapes as a component of a
circuit requires a good understanding of their behavior in
under-critical and upper-critical working conditions. We
propose a modeling of such a device described by an inductance
and non-linear resistors. Our model not only describes the AC
behavior but represents more generally the dynamic behavior
for frequencies below one hundred Hz and currents higher than
the critical one. A special equivalent circuit configuration
is considered to take AC losses into account. The
identification of the model parameters can be performed by the
electrical measurement of sample tapes using a lock-in
technique. |
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Electromagnetic
properties in parallel conductors composed of Bi2223
multifilamentary wires for power transformer
windings
M. Iwakuma, K. Funaki,
H. Shinohara, T. Sadohara, M. Takeo, K. Yamafuji, M. Konoo, Y.
Kasagawa, K. Okubo, I. Itoh, S. Nose, M. Ueyama, K. Hayashi
and K. Sato
Summary: The authors study,
theoretically, the AC losses in superconducting parallel
conductors exposed to a transverse alternating magnetic field
in relation with transposition among the strands. They
obtained an analytical expression of the additional coupling
loss for the deviation of transposition from an optimum
condition. The AC losses for the alternating external field
were measured in parallel conductors composed of Bi2223 and
NbTi multifilamentary wires. The additional losses can be well
explained by the theoretical expression in a wide range of the
amplitude of external field. They also estimated,
experimentally, the current distribution among the strands in
solenoidal coil of the parallel conductor and discussed the
effect of transposition on the current
distribution. |
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Test
of two prototype high-temperature superconducting transmission
cables
J.W. Lue, M.S. Lubell,
E.C. Jones, J.A. Demko, D.M. Kroeger, P.M. Martin, U. Sinha
and R.L. Hughey
Summary: Two 500-A class
prototype high-temperature superconducting (HTS) power cables
have been constructed by Southwire Company and tested at Oak
Ridge National Laboratory (USA). In the first power cable, no
insulation was used to separate the individual HTS tapes. In
the second cable, Kapton tape was used to insulate the HTS
tapes between successive layers for the study of AC loss and
current distribution. The power cables were tested with both
DC and AC currents in liquid nitrogen from 77 to 69 K. Both
cables achieved DC critical current, I/sub c/ greater than 500
A. A calorimetric technique that measures the cable
temperature rise under AC currents was used to measure the AC
loss of the tables. The noninsulated cable showed a
cryoresistive behavior under the 60 Hz AC currents. The
insulated cable started to show measurable at loss at current
where there was corresponding DC resistive
voltage. |
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Self-field
ac loss of Bi-2223 superconducting
tapes
K.-H. Muller and K.E.
Leslie
Summary: The self-field ac loss of a
monofilamentary Bi-2223/Ag tape has been measured using an
improved lock-in amplifier technique. To investigate the
dependence of the ac power loss on the phase-angle error of
the lock-in amplifier, theoretical calculations of the ac
power loss of a flat superconducting strip in a perpendicular
ac magnetic field were performed. The expressions derived also
predict the dependence of the apparent loss on the size of the
lead extension of the voltage contacts. For zero phase-angle
error and an infinite lead extension the Norris formula is
obtained. The voltage wave-form for ac current amplitudes
greater than the tape's critical current has been measured and
calculated. Theoretical predictions agree well with the
experimental data. |
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AC
loss calorimeter for three-phase
cable
D.E. Daney, H.J. Boenig,
M.P. Maley, D.E. McMurry and B.G. DeBlanc
Summary:
A calorimeter for measuring AC losses in meter-long
lengths of HTS superconducting power transmission line cables
is described. The calorimeter, which is based on a temperature
difference technique, has a precision of 1 mW and measures
single-, two-phase (coupling), and three-phase losses. The
authors' measurements show significant coupling losses between
phases. |
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Influence
of external magnetic field and its orientation on transport AC
losses in Bi-2223 and Tl-1223 silver sheathed
tapes
M. Ciszek, B.A. Glowacki,
A.M. Campbell, S.P. Ashworth, W.Y. Liang, P. Haldar and V.
Selvamanickam
Summary: In the paper we report
measurements of energy losses caused by an AC transport
current in silver sheathed multifilamentary Bi-2223 and mono
core Tl-1223 tapes, as a function of the magnitude and
orientation of the applied external magnetic field. The
external magnetic field was rotated in the range of 0 to /spl
plusmn/90 degrees with respect to the plane of the tapes, and
was In all cases perpendicular to the transport current flow.
The transport current losses in a range of DC applied fields
are consistent with the Norris equation provided the DC
critical current at the same applied field is used in his
expression for the loss. |
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Energy
loss in superconducting bearing
systems
Z.J. Yang and J.R.
Hull
Summary: The field- and
frequency-dependent AC susceptibility of a melt-textured
Y-Ba-Cu-O was measured at 77 K and under various field
conditions. The RMS values of the applied AC induction (B/sub
ac,rms/) were scanned up to 13 mT, and the DC inductions were
0, 20, 40, 75, and 100 mT. The frequencies scanned ranged from
10 to 3800 Hz. The experiments show that AC susceptibility of
the HTS largely depends on frequency and on both the AC and DC
induction. |
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Computational
comparison of AC losses in different kinds of HTS composite
conductors
J. Paasi and M.
Lahtinen
Summary: AC losses of different
kinds of available or anticipated HTS composite conductors
were computed by using a magnetic diffusion model. The model
takes into account the real current density-electric field
characteristic of the superconductor and the spatial
dependence of the current density, The computation was carried
out for self-field losses due to transport current ramps and
for magnetization losses in magnet operation due to ramping
external magnetic field. Special attention was paid to
filament coupling in various conductor models at different
ramp rates. |
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AC
losses in a superconductor for the quick response type 70 MW
class superconducting
generator
H. Takigami, H.
Nakamura, M. Arata, E.S. Yoneda, M. Sugimoto, A. Kimura, H.
Sakamoto, Y. Furuto, K. Inoue and K. Sato
Summary:
The authors have been developing a 70 MW class model
superconducting generator aiming at a 200 MW class pilot
machine. The superconductor developed for the field winding of
the generator has a configuration of double stranded cable,
consisting of NbTi, Cu, and CuNi. Then, for the purpose of
decreasing intra-strand AC losses, a strand with additional
Cu-0.5 wt%Mn fins in the Cu sheath has been developed. The
authors have carried out tests and analytical studies of the
generator AC losses. They then compared cables with additional
fins in the Cu sheath with cables without fins. The results
show that both eddy current losses and coupling losses in the
strands were considerably reduced by additional fins in the Cu
sheath. |
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AC
loss measurements of the experiments on a single inner
vertical coil (EXSIV) for the Large Helical
Device
T. Mito, K. Takahata, A.
Iwamoto, R. Maekawa, N. Yanagi, T. Satow, F. Sumiyoshi, S.
Kawabata and N. Hirano
Summary: The AC losses
of the Inner Vertical (IV) coil have been measured during the
Experiments on a Single Inner Vertical coil (EXSIV). The IV
coils are the smallest poloidal coils of the Large Helical
Device (LHD) and their inner and outer diameters are 3.2 m and
4.2 m, respectively. The coil consists of 16 pancake coils
wound with the cable-in-conduit conductors (CICC) whose
strands are NbTi/Cu without any surface coating. The AC losses
were measured with a calorimetric method during excitation
tests and current shut-off tests. In addition to the usual
inter-strand coupling losses with short time constants,
unexpected coupling losses were observed due to the coupling
current of a long time constant. |
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Study
of self-field AC losses in mono and multi-filamentary Bi-2223
tapes for power applications
S.A.
Awan, S. Sali, C.M. Friend and T.P. Beales
Summary:
The self-field ac losses in mono, 7, 37 and 49 filament
tapes near power frequencies are presented. Although the
losses in a mono and 37 filament tape showed good agreement
with those predicted for a 'strip' and 'elliptical' geometry,
respectively, the measured losses in the 7 and 49 filament
tapes could not be accurately described by the Norris
equations. This difference in loss behaviour can be attributed
to the inter-filament connectivity and inhomogeneous J/sub c/
distribution in the tapes. Non-linear inductance variation,
due to flux linkage with the measuring leads, with applied
current, is compared to a model for a homogeneous elliptical
conductor and its significance to the corresponding measured
ac losses is also discussed. |
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Recent
developments in HTS power cable
applications
A. Bolza, P. Metra,
M. Nassi and M.M. Rahman
Summary: Practical
investigations into superconducting power transmission
applications have been initiated as a result of the discovery
of high-temperature superconductors (HTS). These actions are
presently following the parallel courses of materials and
technology improvement and an increasingly detailed technical
and economical analysis of superconducting power transmission
applications within the system grid. Insofar as power cable
applications are concerned, the most recent advances have been
the manufacture of a machine-stranded, 50 m long, 3300 A HTS
cable conductor and the detailed specification of several
prototype HTS cable system installations. Many different HTS
application options are being considered, each offering varied
and distinct potential benefits to the electrical power
industry. Some of these potential applications are already in
development, while others are being systematically analyzed
for compatibility with associated technical and economic
evaluations. |
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HTS
large scale application using BSCCO
conductor
K. Sato, K. Hayashi, K.
Ohmatsu, J. Fujikami, N. Saga, T. Shibata, S. Isojima, S.
Honjo, H. Ishii, T. Hara and Y. Iwata
Summary:
The basic property of high-Tc superconducting cables
(HTS cables) using Bi-2223-based Ag-sheathed multifilamentary
wire (Ag-sheathed wire) have been investigated for the
realization of large-scale and compact cables, these being
replaceable with conventional cables in existing ducts or
tunnels. The AC performance of multi-layer HTS conductors, and
three-phase HTS cables with coaxial superconducting magnetic
shielding structure was evaluated. The characteristics of the
HTS conductor and cable models of long length was investigated
on a 50 m scale. |
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Design
and construction of LN/sub 2/-cooled prototype superconducting
transmission cable
U. Sinha, R.L.
Hughey, J. Hesterlee, J.W. Lue, M.S. Lubell, R.A. Hawsey, P.M.
Martin and J.A. Demko
Summary: The Southwire
Company (USA) has initiated an R&D project to develop
superconducting underground power transmission cables using
newly developed high-temperature superconductors (HTS). In
collaboration with Oak Ridge National Laboratory, two 500 A
and one 2000 A prototype cables have been designed,
constructed and tested. The cables were wound with Bi-2223/Ag
HTS tapes acquired from Intermagnetics General Corporation and
tested with both DC and AC currents in liquid nitrogen (LN/sub
2/). Critical currents of 900 A DC or better were achieved for
the first two cables. The third cable was tested to an AC
current over 2200 A/sub RMS/. This paper describes the design
rationale, the construction process and the highlights of the
test results. |
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Bi-2223
multifilament tapes and multistrand conductors for HTS power
transmission cables
M. Leghissa,
B. Fischer, B. Roas, A. Jenovelis, J. Wiezoreck, S. Kautz,
H.-W. Neumuller, C. Reimann, R. Nanke and P.
Muller
Summary: For application in high-power
transmission cables, multifilamentary 2223 BPSCCO/Ag tapes
have been prepared using the powder-in-tube (PIT) process.
Critical current densities at 77 K of 33 kA/cm/sup 2/ in short
samples and 22 kA/cm/sup 2/ over 400 m have been achieved.
Machine stranded flexible cable conductors have been made with
a length up to 10.5 m. The electrical performance has been
evaluated at 77 K both under DC and AC conditions, yielding a
current capacity up to 1420 A and purely hysteretic AC losses.
Tests of the mechanical stability under bending conditions and
repeated thermal cycling showed no serious degradation of the
electrical performance. |
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Test
results of the 5 kA/sub RMS/-50 kV/sub RMS/ HTS AC
lead
P.F. Herrmann, C.
Cottevielle, A. Leriche and M. Quernener
Summary:
In the framework of a BRITE/EURAM project, an AC 5
kA/sub RMS/-50 kV/sub RMS/ hybrid superconducting lead has
been built and tested. The horizontal and coaxial lead design
approaches the requirements for feed-through for power links.
This design, which uses very short lead parts (0.1 m for the
superconducting Bi-2212 part and 0.2 m for copper normal
part), has turned out to be a good compromise between AC
losses, heat conduction, cryogenics, vacuum and high voltage
requirements. High voltage and high current tests have been
carried out successfully at the target values. The 4 K heat
load value can be reduced by a factor 5 and the global
refrigeration load (room temperature power consumption) was
reduced by a factor of 3 compared to a classical all-metal AC
lead. |
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Test
results of a 1.5 kA HTS current lead for /spl
mu/SMES
J.M. Pfotenhauer and O.D.
Lokken
Summary: A pair of 1.5 kA current
leads incorporating a conventional (copper) upper stage, a
lower BSCCO stage, and intermediate cooling from a
twin-cold-finger GM cryocooler have been designed, fabricated
and tested. A lower stage has been fabricated and tested using
a stacked-tape sample of BSCCO-2223 material donated by
American Superconductor Corporation. Test results characterize
the helium boil-off rate, cryocooler power consumed, and joint
resistances measured during the base line operation of the
current leads at various currents. Additionally, the transient
performance of the leads in response to a loss of cooling is
reported. Here the temperatures and voltage drops at
significant locations on the leads are reported as a function
of time for the various operation conditions. Test results
show that the most significant factor in determining the
allowable operation time subsequent to a loss of cooling is
the thermal inertia of the cold bus connecting the current
leads to the cryocooler. The current leads are designed for
use in a /spl mu/SMES system and incorporate the necessary
lead-to-lead voltage isolation within the body of the
cryocooler. |
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High
current and pulse response of YBCO and BSCCO
junctions
G.O. Zimmerman, Y.Z.
Negm and R.E. Powers
Summary: One of the
crucial elements in the use of HTS materials as current leads
between 77 K and 4.2 K is the nature of their contact to
normal and LTS metals. We report here a set of measurements
made on junctions of polycrystalline YBCO and BSCCO bulk rods
to copper wires. The surface area and the nature of the
surface, as well as the method of making the junctions,
influence the junction's behavior. In a related measurement,
high current short duration pulses were applied to HTS leads.
It was found that the ability of the leads to withstand the
stress of high current pulses depended on the previous history
of the material. |
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Highest
performance of TESLA 9-cell superconducting RF cavities by
overcoming quenches in superfluid
LHe
Quan-Sheng Shu, M. Fouaidy,
T. Junquera, W.-D. Moeller and D. Proch
Summary:
Accelerating gradients Eacc=26 MV/m with a world record
Q of 3/spl times/10/sup 10/ in 9-cell TESLA superconducting RF
(SRF) cavities have been reached in CW and pulsed RF modes. On
the way to reaching the excellent performance, we
experimentally characterized quench natures (most serious
obstacle to higher gradients), investigated the Kapitza
conduction and boiling heat transfer between cavities and LHe
II, and studied the quench behaviors both in He II and normal
LHe. Finally, we discuss the possibilities of further greatly
raising the accelerating gradients to 50-100 MV/m by use of
Nb/sub 3/Sn and some HTc superconducting
materials. |
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Tests
of a prototype magnetostrictive tuner for superconducting
cavities
J.F. Benesch and M.
Wiseman
Summary: The Continuous Electron Beam
Accelerator (CEBA) uses mechanical tuners at 2 K driven by
room temperature stepping motors in a feedback loop to
maintain cavity frequency at 1497 MHz. A modification of the
existing system was designed, replacing a passive section of
the mechanical tuner with a magnetostrictive tuning element
consisting of nickel rod and an industrially supplied 0.25 T
superconducting solenoid. This assembly was tested with
several magnetic shield configurations designed to keep the
stray flux at the niobium cavity below 1 /spl mu/T when the
cavity was normal, to maintain cavity Q. Results of the tests,
including change in cavity performance when the cavity was
locally quenched near the end of the solenoid, showed that a
multilayer shield of 6 mm of steel, with sheets of mu metal,
niobium and mu metal spaced appropriately outside the thick
steel, was effective in containing the flux, both remanent and
current-driven, preventing any change in cavity Q upon
cooldown or quench with an external heater near the end of the
solenoid. Hysteresis attributed to the nickel magnetostrictive
element was observed. |
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Magnetic
shielding of the superposition of a hybrid ferromagnetic
cylinder over a BPSCCO
cylinder
K. Mori, T. Minemoto and
M. Itoh
Summary: The value of the maximum
shielded magnetic flux density (B/sub s/) for a high critical
temperature superconductor (HTS) cylinder was shown to be
improved by the superposition of a hybrid ferromagnetic
cylinder over a Bi-Pb-Sr-Ca-Cu-O (BPSCCO) cylinder. This was
termed the hybrid BPSCCO superimposed cylinder. The value of
B/sub s/ for the hybrid BPSCCO superimposed cylinder was found
to be about 52 times greater than that of a single-BPSCCO
cylinder. The value of B/sub s/ was analyzed with the use of
several different models. It was found that the theoretical
values of B/sub s/ agree well with experimental values. The
results confirm that an important criterion was determined for
use in the design of an effective shield for large
chambers. |
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Design
of a superconducting magnetic suspension system for a liquid
helium flow experiment
M.R.
Smith, Y.M. Eyssa and S.W. Van Scivrr
Summary:
We discuss a preliminary design for a superconducting
magnetic suspension system for measurement of drag on
rotationally symmetric bodies in liquid helium. Due to its
diamagnetic properties, a superconducting model (for example
made or coated with Nb) is inherently stable against
disturbances. In addition, drag measurement may be achieved by
a passive technique, where the body is allowed to deflect from
its neutral position under the influence of drag. The
resulting shift in flux is detected via a superconducting
pickup coil. The pickup coil may he connected either to a
SQUID, or a secondary loop wound around a Hall
probe. |
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Mechanical
stability of a high-T/sub c/ superconducting levitation
system
T. Sugiura, M. Tashiro, Y.
Uematsu and M. Yoshizawa
Summary: This
research deals with dynamics of a permanent magnet freely
levitated above an excited high-T/sub c/ superconductor.
Vertical restoring forces acting on the magnet were evaluated
by analysis based on the critical state and flux flow models.
The results show nonlinearity and frequency-dependence of the
forces, which were observed in experiments. Vertical vibration
properties of the system were also evaluated analytically by
considering the above properties of the restoring forces. The
results show good agreement with experimental ones, which
include effect of the frequency-dependent stiffness on the
resonant frequency, the primary resonance characteristics,
stability of the steady-state motions and so on. |
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Measurements
of the magnetic noise spectra in HTS cylinders for magnetic
shielding
M. Itoh, S. Iguchi, T.
Minemoto and S. Yoshizawa
Summary: Idealized
magnetic shielded vessels can be realized by use of
high-critical temperature superconductors (HTS). It is,
however, generally, very difficult to evaluate the limit of
the value of magnetic shielding and the fluctuation of the
magnetic flux within the HTS vessel. In this present research,
the magnetic noise power spectra (NPS) within the
Bi-Pb-Sr-Ca-Cu-O (BPSCCO) cylinder was measured using a HTS
dc-SQUID, under an application of a magnetic field B/sub cx/
less than the value of B/sub s/ (the maximum shielded magnetic
flux density, 3.2/spl times/10/sup -4/ T at 77 A K). The value
of NPS was determined as 5.0/spl times/10/sup -6//spl
phi/o/sup 2//Hz at 1 kHz excluding B/sub cx/ which was the
background noise of the SQUID control system, and 1.0/spl
times/10/sup -5//spl phi/o/sup 2//Hz at 1 kHz for a B/sub cx/
of 3.0/spl times/10/sup -4/T. The value of NPS at 1 kHz
increased linearly with values of B/sub cx/ in the region of
0.0 T to 3.0/spl times/10/sup -4/ T. Also shown are the
important criteria for the design of effective shielded
vessels for low magnetic measurements. |
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Tests
of disk type magnetic flux pump with the ability of high
voltage output
H. Tsukiji,
Kyeong-Dal Choi, M. Tsukiyama, T. Nishiya, T. Hoshino, E.
Mukai and I. Muta
Summary: Using a
superconducting magnetic flux pump, thick power leads for a
superconducting magnet could be replaced with thin string
leads to excite the excitation magnet of the superconducting
flux pump. We have developed a new type of flux pump with
high-voltage output to shorten the charge and discharge time
of the load magnet. The test of the pump with four stacked
disks as the exciter for the load magnet has been carried out.
This disk type flux pump yielded 70 mV of voltage across its
terminal and 10 A of current through a 85 mH load magnet which
was the field winding of 20 kVA class fully superconducting
generator within 12 seconds. This output voltage of the new
flux pump is about 10 times larger than that of our previous
work. Moreover since it is easy to stack disks for a
superconducting flux pump, the high-voltage exciter for a 1 H
class superconducting magnet could be expected to be made
easily. |
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Conceptual
system design of a 5 MWh/100 MW superconducting flywheel
energy storage plant for power utility
applications
H.J. Bornemann and
M. Sander
Summary: The authors have designed
a 5 MWh/100 MW superconducting flywheel energy storage plant.
The plant consists of 10 flywheel modules rated at 0.5 MWh/10
MW each. Module weight is 30 t, size is /spl phi/ 3.5 m/spl
times/6.5 m high. A synchronous type motor-generator is used
for power input/output. Each flywheel system consists of four
disk modules made from a carbon fibre composite material,
rated at 125 kWh and weighing 3 t. Passive superconducting
bearings, integrated into the disk modules, are used for
frictionless levitation. The operating speed will be in the
2250...4500 RPM range. Maximum rim velocity is 600 m/s with a
maximum tensile stress of 810 MPa. Details of the system
layout are discussed, addressing thermal design and subsystems
such as power conditioning system and cooling facilities. A
preliminary cost analysis has been worked out. In the Western
European UCPTE (Union for the Coordination of Production and
Transport of Electricity) high power system, the plant could
be used to provide spinning reserve for about 30 s while
conventional thermal generating units ramp up to meet the
increased load during peak power periods. Other applications
in the electric utility field include power conditioning and
stabilization in portions of a high-voltage power
system. |
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Development
of quench protection heaters for superconducting
solenoids
C.A. Swenson and W.D.
Markiewicz
Summary: Our approach to applying
quench heaters to epoxy impregnated coils is to encapsulate
the heaters within the epoxy and glass on the coil
circumference. The mechanical integrity of the epoxy and glass
in the neighbourhood of the heater is critical. The interface
is subject to large temperature gradients and mechanical
stress during operation of the protection system.
Characterization of this interface allows the reliable design
of heater networks on large epoxy impregnated coils. The
heater is a thin stainless steel strip located axially on the
outside of the coil. The geometry may be further complicated
by the presence of steel over-banding on the coil perimeter.
We have fabricated models demonstrating heater interfaces with
and without overbanding. We characterize the interface using a
damage threshold concept in the context of cyclic life testing
on the interface. This paper reports the results from cyclic
life testing in liquid helium. |
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Characterisation
of superconducting components using
PSPICE
O.A. Shevchenko, H.G.
Knoopers and H.H.J. Ten Kate
Summary: A
customer library of superconducting (SC) components for the
PSPICE is under development in our group. The new library
includes models of both low and high T/sub c/ superconductor
based components. For large scale applications typical
examples of simulated components are: a SC filament, composite
wire and tape, a cable, a magnet, a switch, a transformer, a
rectifier. Each model can he easily customised for a
particular application. When the scheme is ready, it can he
analysed using the powerful tools offered by PSPICE. The
current status of the theory and model development and a few
typical examples together with brief review of the practical
conductors are presented and discussed in the
paper. |
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Measurement
of thermal contraction properties for NbTi and Nb/sub 3/Sn
composites
C.A. Swenson, I.R.
Dixon and W.D. Markiewicz
Summary: Accurate
knowledge of winding composite thermal contraction properties
is critical to the design of large epoxy impregnated Nb/sub
3/Sn and NbTi coils. Measurement of thermal contraction
properties allows the reliable design prediction of cold coil
dimensions, the state of the coil form interface, resulting
mechanical stresses from cool-down, and the correct locations
of coils in an assembly. NbTi and Nb/sub 3/Sn epoxy glass
winding composites have been built to precisely model the
material, packing factors, and processing steps consistent
with coil fabrication. Thermal contraction properties are
measured using a strain gage measurement technique where gage
signals are compared to known reference samples. Composites
are inherently anisotropic. Gages are placed on each sample to
measure the thermal contraction along each principal axis of
the composite. This paper reports these measurement
results. |
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Large-bore,
superconducting magnets for high-energy density propellant
storage
M.S. Lubell, J.W. Lue and
B. Palaszewski
Summary: A study has been
conducted on the design of large-bore, superconducting
solenoid magnets in an effort to determine how weight and cost
scales with field and size. The fields considered ranged from
0.5 to 20 T and bore sizes from 3 to 10 m. The designs are
based on light-weight, high-performance superconducting magnet
designs using cable-in-conduit niobium-titanium and
niobium-tin conductors. All methods to reduce the weight of
the magnets are used, and both aluminum and stainless steel
are considered for the structure, With the length of the
magnets fixed at 10 m, the amount and cost of the conductor is
determined for each field and bore size. The largest magnets
are determined for each field value that have weights under
10/sup 4/, 10/sup 5/, and 10/sup 6/ kg. The cost scales as the
square root of stored energy and in millions of dollars is
twice the product of field (T) and bore (m). |
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Incorporation
of a SMES coil into a superconducting LVdc transmission
system
B.K. Johnson, R.H.
Lasseter and F.L. Alvarado
Summary: The
performance of a superconducting low voltage direct current
(LVdc) transmission system can be significantly enhanced
through the addition of a superconducting magnetic energy
storage (SMES) coil. The power conversion equipment necessary
for connecting a SMES coil to a dc system is much simpler and
easier to control than the interface needed to connect a SMES
coil to an ac system. There is also added flexibility if the
LVdc system is mesh connected. The LVdc system already has the
power conditioning necessary for connection to the ac load and
supply systems. The SMES coil can be connected to the LVdc
mesh either through a dedicated dc-dc converter or it can be
added directly into the mesh and controlled using the
converters already present on the mesh. The rectifier voltage
regulation schemes control the charging and discharging of the
coil. If one of the rectifiers is supplied by a unit-connected
generator, a simpler rectifier scheme can be used, and the
generator field excitation control can be used to control the
SMES coil. The SMES coil could then be used both to level
generator loading and provide added reliability in case of
disturbances on the ac supply system. |
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A
cryocooler cooled 5 T superconducting magnet with a horizontal
and vertical room temperature
bore
K. Jikihara, K. Watazawa, H.
Mitsubori, J. Sukuraba, Y. Sugizaki, T. Hasebe, H. Okubo, M.
Ishihara and K. Watanabe
Summary: We designed
and constructed a cryocooler cooled 5 T superconducting magnet
with a horizontal room temperature bore of 50 mm and a
vertical room temperature bore of 90 mm without liquid helium.
The magnet, which is directly cooled by 4 K Gifford-McMahon
cryocooler in vacuum, consists of NbTi coil, Bi(2223) bulk
current leads and cryostat. The coil with an inner diameter of
130 mm, an outer diameter of 301 mm, a height of 66 mm and a
gap of 80 mm is made using NbTi wires and Cu-plated SUS
bobbin. Bi(2223) bulk current leads are thin-walled sintered
cylindrical tubes. The outer diameter, height and weight of
the magnet are 510 mm, 730 mm and 260 kg, respectively. The
magnet is cooled down to 3.8 K in approximately 62 hours. A
continuous operation at 5 T, which is generated by an
operating current of 122 A, has been performed. |
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Insert
model coil wound by Al/sub 2/O/sub 3/-Cu strengthened Nb/sub
3/Sn wire
K. Koyanagi, S.
Nakayama, S. Murase, S. Nomura, K. Shimamura, M. Urata, N.
Shiga, S. Awaji and K. Watanabe
Summary: With
the aim of fabricating large-bore, high-magnetic-field magnets
with low coil weight and volume, an alumina-Cu reinforced
Nb/sub 3/Sn wire of 1 km in length has been developed by
improving the workability of the tube process. Two kind of
insert model coils were made using the developed wire and the
conventional Cu-matrix wire. The maximum quench current
observed was 126 A in a backup field of 11 T, which
corresponds to an electromagnetic force of 244 MPa. The coil
strain for the reinforced coil was always smaller than that
for the Cu-matrix coil. |
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A
design of a compact superconducting magnet for a 40 T hybrid
magnet
K. Koyanagi, S. Nomura, M.
Urata, M. Arata, Y. Sumiyoshi, K. Watanabe, S. Awaji, N.
Kobayashi, T. Fukase and M. Motokawa
Summary:
A superconducting magnet for a 40 T hybrid magnet was
designed to be as compact as possible, and to be constructed
with epoxy-impregnated layer winding using highly strengthened
Nb/sub 3/Sn wires. The magnet generates 16 T in a 420 mm inner
diameter of windings. The total coil mass of 4.1 tons,
approximately 40% of the conventional cryostabilized magnet
wound with copper-matrix wire was attained. |
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Development
of a 15 T/17 T solid state NMR magnet
system
D.M. Coffey, R.W. McGhee,
Y. Wu and S. Keener
Summary: A high field NMR
magnet system, up to 17 Tesla at 2.0 K with magnet bore of 52
mm was developed. This magnet system will be used to perform
NMR experiments in the field of condensed matter physics. The
magnet consists Nb/sub 3/Sn and NbTi solenoids. The central
field is 15 T at 4.2 K and 17 T at 2.0 K. The field
homogeneity is better than 10 ppm over 1 cm diameter sphere
volume without shims. The magnet can be operated in the
persistent mode and driven mode. A persistent switch was
installed on the magnet and the field decay rate was less than
5 ppm/hour in persistent mode operation. The complete magnet
was built into a cryostat equipped with a lambda plate
refrigerator. In this paper, the magnet test results are
presented. |
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An
optimal design method for high-field superconducting magnets
with ferromagnetic shields
S.
Noguchi and A. Ishiyama
Summary: This paper
describes an optimal design method for high-field and highly
homogeneous superconducting magnet systems with hybrid iron
and active shielding. The presented design technique is a
combination of the equivalent magnetization current method for
the computation of the magnetic field problem, which includes
nonlinear and saturated iron, and the simulated annealing for
solving the corresponding optimization problem. The equivalent
magnetization current method is superior in estimating the
field homogeneity at the center of the magnet systems. By
using the simulated annealing, the positions of each coil are
optimized as continuous design variables, while the number of
turns and layers of the coil windings are treated as discrete
design variables. In this paper, the detail of the algorithm
and the example of its application to 9 T magnet system with
hybrid iron and active shielding are shown. |
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Performance
of the quench detection system for
ITER
C. Marinucci, L. Bottura, S.
Pourrahim and M. Zhelamskij
Summary: The
purpose of this study is to assess the expected response of
conventional and non-conventional quench detection sensors
proposed for the ITER coils. The assessment is based on
simulation of thermo-hydraulic transients in the coils for
various operating conditions, and a tentative definition of
the transfer functions of each sensor concept. For the
investigated conditions, the co-wound voltage tap shows the
best performance of the six sensors which are
analyzed. |
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Performance
of the US quench detection systems in the QUELL
experiments
S. Pourrahimi, S.P.
Smith, J.H. Schultz, J.V. Minervini, S. Ezekiel, A. Anghel, G.
Vecsey and Y. Takahashi
Summary: The Quench
of Long Length (QUELL) experiments have been completed. The US
contribution was to develop and implement both conventional
and novel techniques in quench detection. The results of the
quench detection experiments demonstrate that all US systems
functioned as expected. The most important criteria for the
comparison of the various quench detection systems were the
time constant of the response and noise rejection by the
system. The novel US internal (inside the CICC) sensors
included; (1) a cowound voltage sensor, and (2) a fiberoptic
temperature sensor. The internal sensors combined fast
response with high noise rejection capacity, and proved to
offer potentially high reliability for ITER. The conventional
sensors, namely the absolute pressure transducer and Venturi
flowmeters, confirmed inherent thermo-hydraulic time response
limitations in measurements of pressure and flow that excludes
them as quench detectors for ITER and other large scale CICC
applications. |
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Detection
of the normal zone with cowound sensors in cable-in conduit
conductors
N.N. Martovetsky and
M.R. Chaplin
Summary: Tokamaks in the future
will use superconducting cable-in-conduit-conductors (CICC) in
all Poloidal Field (PF) & Toroidal Field (TF) magnets.
Conventional quench detection, the measurement of small
resistive normal-zone voltages (<1 V) in the magnets will
be complicated by the presence of large inductive voltages
(>4 kV). In the quench detection design for TPX, we have
considered several different locations for internal co-wound
voltage sensors in the cable cross-section as the primary
mechanism to cancel this inductive noise. The Noise Rejection
Experiment (NRE) at LLNL has been designed to evaluate which
internal locations will produce the best inductive-noise
cancellation, and provide us with experimental data for
comparison with developed earlier theory. The details of the
experiments and resulting data are presented and
analyzed. |
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Principles
of advanced quench detection design in cable-in-conduit (CICC)
magnets
J.H. Schultz, S.
Pourrahimi, S. Smith and P.W. Wang
Summary:
The design and development of novel quench detection
systems for the International Thermonuclear Experimental
Reactor (ITER) and the Tokamak Physics Experiment (TPX) has
advanced our knowledge of design principles governing quench
detection systems. Design studies have quantified the
detection signal-noise ratios for several types of quench
detector, including external and cowound voltage sensors,
fiber optic temperature sensors, and optical and
piezoresistive flow meters. The effects of sensor placement
and subdivision have also been studied. Sensor topologies with
the highest signal-noise ratios are identified. Fiber-optic
and voltage sensors have been fabricated for the ITER QUELL
experiment, that have demonstrated the capacity to survive
cabling and compaction, heat treatment, and cooldown to low
temperature with tight conduit bend radii. Extraction
techniques have been developed that use redundant seals and
coefficient-of-expansion matching to guarantee leak-tightness.
Electrical integrity is guaranteed in a design through the
control of electrical fields in the feedthrough geometry and
insulation material selection. |
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Design
and R&D results of the joints for the ITER
conductor
P. Bruzzone, N.
Mitchell, D. Ciazynski, Y. Takahashi, B. Smith and M.
Zhelamskij
Summary: In the scope of the
Engineering Design Activity (EDA) for ITER (International
Thermonuclear Experimental Reactor), a R&D task has been
launched in 1993 for development, manufacturing and testing of
subsize and full size joints, to be used in the layer-to-layer
and pancake-to-pancake connections of the ITER coils. A set of
design criteria and manufacturing choices is initially agreed
as a common basis for the work carried out in parallel by the
four ITER parties (Japan, European Union, United States,
Russian Federation). The staged work includes variations of
layout parameters in subsize samples, technological
investigations for manufacturing methods and performance
analysis. As a last stage of the task, full size joint
samples, manufactured from sections of the ITER conductors,
are tested in the PTF and SULTAN test facilities under ITER
relevant operating conditions. |
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Coupled
electromagnetic and thermohydraulic analysis of the ITER cable
joint
A.E. Duke, V.V. Kokotkov,
V.L. Kotov, V.P. Kukhtin, E.A. Lamzin, N.A. Shatil, S.E.
Sytchevsky, V.N. Vasiliev and M.V.
Zhelamskij
Summary: An analysis of the
current distribution in a joint of International Tokamak ITER
has been carried out using two separated models (3D static
transport current model and 3D thin conducting shell model for
eddy current). The calculations were made by two finite
element packages KOMPOT/C and TYPHOON. The total resistance of
the joint and the total Joule loss created by the transport
current and induced currents due to the external magnetic
field change were estimated. Different modes of ITER operation
were considered. Thermohydraulic response of the cooling
system on transient and steady state disturbances in the joint
were modeled by the VINCENTA code, which allows to define the
transient temperature behavior of the joint assembly materials
and Cable-In-Conduit Conductor (CICC) cooled by supercritical
helium which flows in thermally and hydraulically coupled
channels. |
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Design
and manufacture of the US-ITER pre prototype joint
sample
C.Y. Gung, P.C. Michael,
R.N. Randall, B.A. Smith, T. Hrycaj, J.V. Minervini and D.B.
Montgomery
Summary: The US-ITER pre prototype
joint sample which has been fabricated at the MIT Plasma
Fusion Center is the first attempt to fabricate an optimized
full size joint which can be stably operated in ITER required
AC background fields at reduced coupling losses. This paper
presents an overview of the joint's construction and
fabrication, highlighting some of the procedural steps that
have since been incorporated into fabrication of current
terminations for the inner module ITER central solenoid (CS)
model coil. |
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Electrical
testing of large scale IR&D dummy coil for TPX magnet
insulation design
verification
J.F. Roach, P.A.
Sanger, D. Hartman and J.R. Miller
Summary:
Electrical test results are reported characterizing the
dielectric properties, insulation capability, and equivalent
circuit parameters of a 1.8 m OD, 24 turn IR&D dummy coil
built by the Westinghouse TPX Team to address magnet coil
manufacturing issues and to verify electrical insulation
design for TPX PF and TF magnet coils. Induced voltage tests
at 77 K were performed at the National High Magnetic Field
Laboratory (NHMFL) to 200 V per turn without dielectric
failure. High voltage testing was performed at Everson
Electric under room temperature factory conditions. The coil
turn insulation was surge tested to 21 kV without failure. The
coil groundwall insulation was hipot tested up to 58 kV with
48 kV minimum withstand to the imbedded groundplane screen
electrode. The coil was sectioned and examined for insulation
impregnation quality and manufacturing
tolerances. |
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Excitation
test results on a single inner vertical coil for the Large
Helical Device
K. Takahata, T.
Mito, T. Satow, A. Nishimura, S. Yamada, H. Chikaraishi, N.
Yanagi, A. Iwamoto, R. Maekawa, S. Imagawa, H. Tamura, S.
Yamaguchi, S. Satoh, S. Tanahashi, K. Yamazaki, J. Yamamoto,
O. Motojima, T. Kai, K. Nakamoto, T. Yoshida, Y. Wachi and M.
Ono
Summary: Excitation experiments on a
single inner vertical coil for the Large Helical Device (LHD)
were carried out to confirm its performance. The coil is one
of the LHD's poloidal field coils and consists of a
forced-flow Nb-Ti cable-in-conduit conductor (CICC). After
cooldown for 250 hours, the superconducting transition of the
whole coil was confirmed. Pressure drops were measured during
the cooldown to determine the coil's hydraulic
characteristics. Then, the coil was successfully energized up
to the specified current, 20.8 kA. In the experiments, heat
generation of joints, radial displacement and acoustic
emission (AE) were measured. |
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Ramp
rate experiments on a Nb/sub 3/Sn CICC wind-and-react
magnet
E.P. Balsamo, R. Bruzzese,
A. Catitti, O. Cicchelli, M. Cuomo, A. della Corte, P. Gislon,
G. Pasotti, M.V. Ricci and M. Spadoni
Summary:
The central solenoid of ITER is designed to operate at
13 T, 0.5-1 T/s, 5.8 K. There is an experimental evidence that
reduced performances in variable field, not explained by AC
loss, could occur in CIC conductors. Such ramp rate
limitations have to be well understood in order to be avoided
in the ITER conductors. The ENEA Nb/sub 3/Sn solenoid is a 1 m
OD, 0.6 m ID coil, made of a CIC conductor which is a factor 8
smaller than the ITER full size cable. The total conductor
length, 750 m, is ITER relevant. An experimental setup has
been assembled, allowing ramp rate and DC tests on the ENEA
coil up to 8 T, 2-4 T/s, 12 K. Main objectives of the program
are experimental data on ramp rate limitation, pulsed current
distribution in the s/c cable, limiting currents and global AC
loss. This paper reports the results of the measurements
carried out up to now. |
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Effect
of cooling the support structure on CICC stability of the TPX
toroidal field magnet
Y. Lvovsky,
G.W. Neeley, Wei Tong, K.E. Grut and T.A.
Antaya
Summary: The paper presents thermal
design and analysis of toroidal field (TF) magnets for Tokamak
Physics eXperiment (TPX), performed at Babcock and Wilcox.
Magnet coils are wound of Nb/sub 3/Sn cable-in-conduit
conductor and encased in a stainless steel support structure,
which receives most of the operational heat load of the
magnet. Channels cooled by supercritical helium are
incorporated in the structure to intercept heat which would
otherwise reach the winding and undermine CICC stability. A
joint 3-D thermal-hydraulic model has been developed which
includes two submodels iteratively coupled through boundary
conditions. First submodel describes helium flow in CICC
winding with thermal coupling between turns/pancakes, while
the second determines temperature and heat flux distribution
in the structure and cooling channels. Effectiveness of
cooling arrangement is assessed, amount of heat intercepted by
channels in the structure is determined. Specifics of
temperature profiles and stability margins for inner and side
double pancakes are discussed; obtained margins are compared
with the allowables. |
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TPX
magnet helium stub penetration and
joining
P.A. Sanger, R.J.
Hillenbrand, G.W. Swartzback, W.M. Urban and J.T.
Salkin
Summary: In support of the TPX magnet
project, a program was initiated to develop a technique to
attach the helium cooling piping to the cable in conduit
conductor. The requirements placed on the technique were high
reliability without degrading either the properties of the
superconductor or the structural performance of the conductor
at the attachment point. The design that evolved consisted of
piercing a hole with a roto-broaching tool and TIG welding of
the stub to the conductor. The results of the testing that was
performed indicated: 1) this joint was leak tight at a
sensitivity of 10/sup -10/ std cc/sec, 2) remained so after 5
thermal cycles to 77/spl deg/K and pressurization to 100 atm,
and 3) critical current degradation was limited to two of the
162 strands of the cable. A full description of the design and
the testing program is presented in the paper. |
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A
comparison between 1- and 2-fluid simulations of the QUELL
conductor
R. Zanino, L. Bottura
and C. Marinucci
Summary: In QUELL (QUench
Experiment on Long Length) a cable-in-conduit-conductor with
central cooling hole has been tested under fusion reactor
relevant conditions. A first comparison is presented here
between the results of a recently developed 2-fluid
code-Mithrandir-and those of the reference 1-fluid
code-Gandalf-for the case of the QUELL conductor. Mithrandir
allows for different thermodynamic properties of the helium in
the hole and that in the bundle, thereby providing a more
accurate description of the physics involved when a central
cooling hole is present. |
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TPX
TF magnet structure design
T.A.
Brandsberg, K.E. Grut and T.A. Antaya
Summary:
The design of the Tokamak Physics Experiment (TPX)
utilized 16 superconducting toroidal field (TF) magnet coils
supported by a wedged structure. The TF magnet structure
supports and locates the poloidal field (PF) coils and must
restrain the twisting and expansion forces generated by the
interaction of currents and magnetic fields. This structure
must also leave significant open space to permit access to the
plasma chamber. The geometry and alignment of the magnet
structural components must be controlled to meet very tight
tolerances with respect to the operating toroidal magnetic
field errors. During the preliminary design phase, the TPX TF
magnet structure configuration was revised from a welded and
bolted field assembly to one utilizing bolted joints only.
These electrically insulated joints were specifically designed
for ease of assembly and to provide the flexibility to adjust
coil alignments at assembly to accommodate for manufacturing
tolerance stackups. We report on the final preliminary design
which meets all project design requirements. |
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Magnetic
field error analysis on TPX superconducting magnet
misalignment
Minfeng Xu and T.A.
Antaya
Summary: The Tokamak Physics
Experiment (TPX) requires that certain magnetic field errors,
in terms of Fourier components, be in the order of 10/sup -4/
of the field at the major radius. We have studied the field
errors introduced from rigid coil displacements for both the
toroidal field (TF) and poloidal field (PP) magnets. Fourier
decomposition of the field errors was performed on a plasma
surface with a D-shaped cross-section. For TF coils, field
errors were calculated for all six degrees of freedom in
displacements, and for PF coils, three degrees of freedom were
considered. Superposition and linearity were verified for
small displacements. To obtain the field errors of a whole TF
magnet, a statistical approach with Monte-Carlo simulations
was taken to combine the field errors from all 16 individual
TF coils with each in six degrees of freedom. The simulation
results suggested a new approach for allocating the field
errors to different subsystems. The results also helped us to
identify the major and minor contributors in field errors
during the design and manufacturing stages for controlling the
tolerances in parts and assembly. |
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Test
results of a cable-in-conduit superconductor for the
WENDELSTEIN 7-X stellarator
R.
Heller
Summary: The superconducting magnet
system of the modular stellarator WENDELSTEIN 7-X consists of
50 nonplanar and 20 planar coils. The nominal current is 16 kA
at 6 T and at 4.2 K. The minimum bending radius of 0.2 m
required the development of a suitable conductor. The concept
is based on a NbTi forced-flow superconductive cable embedded
in an aluminium alloy jacket. This is relatively soft during
coil winding but gets its design strength by hardening during
the impregnation process of the winding. As a step of the
development programme, two 200 m long conductor lengths were
fabricated by Europa Metalli, Italy, and Noell, Germany,
together with SwissMetal, Switzerland. At Tesla, UK, each
conductor length was wound to a planar coil of 0.2 m inner
radius using the same winding and impregnation procedure as
intended for the future series coils. The model coils were
tested in the STAR facility at the Forschungszentrum Karlsruhe
in order to investigate the behaviour of a long sample
conductor. The model coils have been operated at various
temperatures under self-field and background field conditions.
Experimental results of the second model coil are presented,
and a comparison to test results obtained for the LMI
conductor is given. |
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A
superconducting magnet system for MHD propulsion
research
Yunjia Yu, Heli Nan,
Shousen Song, Shiliang Wang, Zuxiang Ye, Huaming Wen, Yinming
Dai, Ping Ye, Luguang Yan, Haoshu Chen, Chaoji Zhang and
Xitong Zhou
Summary: A superconducting magnet
system for MHD propulsion research is being constructed at the
IEE CAS. The magnet is a large bore dipole with an inner
diameter of 205 mm, the winding is a layer wound 60/spl deg/
circular saddle with a design central field of 4 T and a
length of 830 mm. The outer diameter, the total length and
height of the cryostat are 650 mm, 1300 mm and 1390 mm
respectively. Equipped with a removable current lead and a
superconducting switch, the system will be operated for 5 days
with available liquid helium of 50 liters. The magnet system
will be used for a MHD propulsion model ship. |
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Homopolar
motor with high temperature superconductor field
windings
M.J. Superczynski and
D.J. Waltman
Summary: A superconducting field
winding, assembled with discrete coils wound with bismuth 2223
high temperature superconducting (HTS) wire, has been
successfully operated in an electric homopolar motor designed
and built by the Naval Surface Warfare Center. The motor's
field winding is composed of two HTS coils fabricated by
American Superconductor Corporation and two HTS coils
fabricated by Intermagnetics General Corporation. These field
winding coils were produced for the Navy under contracts with
the Naval Research Center. At a HTS field winding operating
temperature of 4.2 K, the motor produced 125 kW (167 hp) of
output power. At a temperature of 28 K the motor power
developed was 91 kW (122 hp). In comparison to other motor
types, a homopolar motor provides an ideal operating
environment for a superconducting magnet. The design,
construction, and operating characteristics of this machine
are described. Information describing the HTS field winding
and its superconducting capabilities is presented along with
that for the laboratory test facility used to measure the
performance of the machine. Motor measured performance results
and those predicted by computer simulation are compared and
presented. An assessment of the state of the engineering
development of HTS superconductors for magnet applications and
recommendations for future development are made. |
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125
HP HTS motor field winding
development
J.P. Voccio, B.B.
Gamble, C.B. Prum and H.J. Picard
Summary:
Superconducting motors offer improved efficiency as
well as reduced size and weight. A four pole coil
configuration has been developed which provides in excess of
56000 ampere turns per pole for a 125 HP motor. The winding
achieves an operating current density (Je) in excess of 6300
amp/cm/sup 2/ at the 27 K operating temperature. The
superconductor used is multifilamentary Bi-2223 in a silver
matrix. The design, development and performance of the
air-core synchronous motor coils are described with emphasis
on the static test results and implications for large motor
development. |
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A
HTS synchronous motor at different operating
temperatures
J.-T. Eriksson, R.
Mikkonen, J. Paasi, R. Perala and L.
Soderlund
Summary: A four pole synchronous
machine comprising HTS racetrack field windings has been
designed and constructed. The device has been investigated at
4.2 K, 77 K and at the nominal operating temperature 20 K. The
nominal power of 1500 W was achieved at a speed of 1500 rpm
and an excitation current of 205 A. The field coils provided
expected performance. The transition between the
superconducting and the normal state took place gradually both
at 77 K and 4.2 K, operation remained stable although the
voltage was clearly rising. Stability performance of HTS
magnets differs strongly from their LTS counterparts. The
normal zone propagation velocity is roughly 20 times higher at
liquid helium temperatures than at 77 K. These questions are
briefly addressed in this paper, along with a discussion of
test result. |
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Development
of a 70 MW class superconducting
generator
K. Yamaguchi, M.
Takahashi, R. Shiobara and K. Kimura
Summary:
A national project to develop a superconducting
generator was begun in 1988 in Japan under the New Sunshine
Project of AIST, MITI. This generator has merits of higher
efficiency and compactness for transmission lines. A 70 MW
class superconducting generator is the goal of the project.
The authors have been developing a rotor having a
superconducting field winding and a stator having an air-gap
armature winding. The field winding was designed to be
cryostable so as to recover from a partial transition to
normal conduction. The field winding was tested in a
nonrotating cryostat, and excitation performance and stability
were confirmed to be enough for the 70 MW class
superconducting generator. The rotor and the stator have been
completed and a shop test is being made. |
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Development
and fabrication of a Bi-2223 racetrack coil for generator
applications
K.G. Herd, L.
Salasoo, E.T. Laskaris, R.A. Ranze, C.G. King, P. Haldar and
J.G. Hoehn
Summary: The development and
fabrication of a layer-wound, epoxy-impregnated Bi-2223
high-temperature superconducting (HTS) racetrack coil which
generates 40000 ampere-turns of magnetomotive force (MMF) at
25 K is described. The coil was wound using Ag-sheathed
Bi-2223 tape conductor laminated with copper foils for
strength enhancement and insulated using a paper-wrap method.
After epoxy impregnation, the coil was tested over a range of
16-25 K in a vacuum dewar using a closed-cycle helium
refrigeration system. Descriptions of the tape lamination and
insulation processing, the coil winding and impregnation, and
the experimental test setup are given. |
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Test
results for a Bi-2223 HTS racetrack coil generator
applications
L. Salasoo, K.G.
Herd, E.T. Laskaris, H.R. Hart Jr. and M.V.K.
Chari
Summary: Testing, results and analysis
of a Bi-2223 model superconducting generator coil produced
under the DOE Superconductivity Partnership Initiative are
presented. The test arrangement enables coil energization with
DC and transient currents over a range of operating
temperatures to explore coil performance under conditions
analogous to those that would be experienced by a
superconducting generator field coil. Analytic calculations of
coil AC and ohmic losses and temperature rise compare well
with experimental measurements. Good performance is predicted
for a typical three-phase fault condition. Coil steady-state
and transient performance can be predicted with confidence for
full scale superconductor application. |
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Experimental
studies on field circuit of superconducting
generator
T. Nitta, Y. Shhirai
and T. Kishida
Summary: Because of the
superconducting field winding of superconducting generators
(SCGs), the resistance and voltage drop of the field circuit
are extremely low. Therefore, machine constants concerning the
field circuit are different from those of conventional
machines. In this paper, a method for obtaining these
constants is proposed. By the use of this method, the
constants are given experimentally. In SCGs with high response
excitation, which can improve transient power system
stability, the characteristics of high response excitation are
discussed both theoretically and experimentally. |
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Stacked
magnets for a muon
accelerator
G.H. Morgan, S.A.
Kahn and E.H. Willen
Summary: A proposed
muon-muon collider uses a final accelerator which is separate
from the collider ring. To minimize acceleration time and
hence loss of muons by decay, a possible design for this
accelerator consists of two, long, parallel linacs having a
large energy gain per pass and semi-circular arcs of
fixed-field magnets at each end. The muons would make 10 to 20
passes around the final accelerator ring, with an input energy
of 250 GeV and output energy of 2 TeV; the present design
assumes 16 passes. The recirculator magnets, described here
for the end arcs, consist of an array of 16 apertures arranged
in four adjacent, vertical stacks having four, 50 mm apertures
in a stack, each stack having an iron yoke in common. This
type of configuration reduces cost by taking advantage of
coupling between apertures, but results in some undesirable
skew harmonics. The highest dipole field is 7 Tesla, and there
is an 0.406 T difference between adjacent apertures in a
stack. A similar quadrupole stack having a maximum gradient of
175 T/m is also presented. |
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Design
and construction of a hybrid-Nb/sub 3/Sn, NbTi-dipole
magnet
S. Caspi, K. Chow, D.
Dell'Orco, R. Hannaford, H. Higley, A. Lietzke, A. McInturff,
M. Morrison, R.M. Scanlan and H. Von Oort
Summary:
A two layer superconducting dipole magnet-D19H, with a
Nb/sub 3/Sn inner layer and a NbTi outer layer was designed,
constructed and tested. The 50 mm bore inner layer of an
existing NbTi dipole magnet (D19A), has been removed and
replaced with a Nb/sub 3/Sn coil. The outer NbTi coil,
collars, iron yoke, ring, collets and outer skin from the
disassembled D19A magnet have all been reused. Employing glass
insulated cable with aluminum-bronze poles and end spacers the
Nb/sub 3/Sn coil was reacted at 660/spl deg/C for 240 hours
and fully epoxy impregnated. The design and construction of
the magnet are described and test results reported elsewhere
in these proceedings. |
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The
pipe-quadrupole, an alternative for high gradient interaction
region quadrupole designs
J.M.
Van Oort and R.M. Scanlan
Summary: In the
design of interaction region (IR) quadrupoles for high
luminosity colliders such as the LHC or a possible upgrade of
the Tevatron, the radiation heating of the coil windings is an
important issue. Two obvious solutions to this problem can be
chosen. The first is to reduce the heat load by added
shielding, increased cooling with fins or using Nb/sub 3/Sn to
increase the temperature margin. The second solution
eliminates the conductor from the areas with the highest
radiation intensity, which are located on the symmetry-axes of
the midplanes of the coils. A novel quadrupole design is
presented, in which the conductor is wound on four half-moon
shaped supports, forming elongated toroid sections. The
assembly of the four shapes yields a quadrupole field with an
active flux return path, and a void in the high radiation
area. This void can be occupied by a liquid helium cooling
pipe to lower the temperature of the windings from the inside.
The coil layout, harmonic optimization and mechanical design
are shown, together with the calculated temperature rise for
the radiation load of the LHC interaction region
quadrupoles. |
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16
tesla Nb/sub 3/Sn dipole development at Texas A&M
University
T. Elliott, A. Jaisle,
D. Latypov, P. McIntyre, P. McJunkins, W. Shen, R. Soika and
R.M. Gaedke
Summary: A 16 Tesla Nb/sub 3/Sn
block-coil dual dipole is being developed to extend the
available field strength for future hadron colliders. The
design incorporates several novel features. Current
programming of 3 independent coil elements is used to control
all multipoles over a 20:1 dynamic range of dipole field.
Stress management, comprising a lattice of ribs and plates
integrated into the coil structure, is used to distribute
preload and Lorentz forces so that the stress in the coil
never exceeds 100 MPa. Distributed cooling, utilizing spring
elements in each coil block, intercepts heat generated by
synchrotron radiation and beam losses. Rectangular pancake
coil geometry accommodates simple fabrication and direct
preload in the direction of Lorentz forces. The bore diameter
can be optimized for collider requirements (2.5 cm for 50
TeV/beam vs, 5 cm for 8 TeV/beam), so that a 16 Tesla
block-coil dipole for 50 TeV/beam requires the same amount of
superconductor/TeV as the 8.5 Tesla LHC dipole for 8 TeV/beam.
A first model of the dipole is currently being
built. |
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Development
of a 56 mm aperture superconducting dipole model magnet for
LHC
T. Shintomi, A. Yamamoto, Y.
Doi, T. Haruyama, N. Higashi, H. Kawamata, S.W. Kim, N.
Kimura, V. Kovachev, T. Nakamoto, N. Ohuchi, T. Ogitsu, K.
Tanaka, A. Terashima, K. Tsuchiya, R. Perin, D. Leroy, S.
Kato, K. Makishima, T. Orikasa and A.
Tanaka
Summary: A 56 mm single aperture
superconducting dipole model magnet, which is one of the
frameworks of the LHC collaboration between KEK and CERN, has
been developed. A central field of 8.65 T is provided at a
load line ratio of 90% with a 5 block coil wound with NbTi
superconducting cables. The magnet has a straight section of
0.8 m and a total length of 1.2 m. The distinctive features of
the magnet are a magnetically symmetrical configuration being
applicable to the twin aperture magnet and mechanical
consideration sharing the magnetic forces with a high
manganese steel collar and a horizontally split iron yoke. The
magnet showed almost no training at 4.4 K. The first quench
current at 1.8 K was 91% of the short sample I/sub c/ and the
magnet reached a central magnetic field of 8.8 T. Finally it
could be excited with the current of more than 99% of the
short sample limit which corresponds to a central field of
9.63 T. |
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Design
of the 70 mm twin aperture superconducting quadrupole for the
LHC dump insertion
G.A. Kirby, R.
Ostojic, T.M. Taylor and G. Trinquart
Summary:
The LHC dump insertion features a pair of
superconducting quadrupoles located on either side of a 340 m
long straight section. Two horizontally deflecting kickers,
located in between the quadrupole pairs, and a septum in the
centre of the insertion, vertically deflect the two
counter-rotating beams past the quadrupoles on the downstream
sides, and into the dump areas. Due to the layout, the optical
/spl beta/ function in the quadrupoles is around 640 m, the
largest around the LHC at injection. The quadrupoles must
therefore have enlarged aperture and specially designed
cryostats to allow for the safe passage of both the
circulating and ejected beams. In this paper we present the
design of the twin aperture dump quadrupole based on the 70 mm
four layer coil proposed for the LHC low-/spl beta/
quadrupoles. In preparation for model construction, we report
on improvements of the coil design and a study of the
retaining structures. |
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Mechanical
analysis of a high gradient quadrupole for the
LHC
T. Heger and J.
Kerby
Summary: The magnetic design of the LHC
interaction region quadrupole by the BNL, FNAL, LBNL
collaboration eliminates the manufacturing complication of a
graded cable splice in the outer coil and still attains a
maximum gradient above 235 T/m. The mechanical design includes
strong preloaded collars, shims to adjust the fit between
components when warm, contact between the collar and iron when
cold for better coil support, and a closed iron to reduce
harmonics. This paper summarizes mechanical finite element
results for assembly, cooldown to 1.8 K, and excitation to
maximum gradient. |
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Test
results of spare TRISTAN insertion quadrupole magnet with yoke
added in superfluid helium
K.
Sasaki, K. Tsuchiya, T. Ogitsu, N. Ohuchi, Y. Doi, T.
Haruyama, H. Kawamata, S.W. Kim, T. Nakamoto, N. Kimura, T.
Shintomi, K. Tanaka, S. Kato, A. Terashima, A. Yamamoto, G.A.
Kirby and V.T. Kovachev
Summary: One of the
TRISTAN insertion quadrupole magnets, iron-free magnet with an
inner aperture of 140 mm and a length of 1.45 m, was tested at
1.8 K with a thick iron yoke assembled around the magnet. Two
testing cycles were performed, and during the first test, the
magnet current reached 5086 A after six training quenches,
which corresponds to 94% of the short sample critical current.
After warming up to room temperature, the second test was
performed where the magnet current reached 5067 A without a
training quench. The current was almost the same as the
maximum current during the first test, indicating that the
previous training effect was not lost after warmed up to room
temperature. |
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Field
quality measurements of spare TRISTAN insertion quadrupole
magnet with yoke added
N. Ohuchi,
T. Ogitsu, Y. Ajima, S. Sasaki and K.
Tsuchiya
Summary: One of the TRISTAN
insertion quadrupole magnets was yoked and tested. The
original magnet was an iron free magnet. The magnetic field
measurements of the original and the yoked magnets were
performed at 4.2 K. The transfer functions of the original and
yoked magnets were measured and compared. The multipole fields
as a function of axial position and magnet current are
presented for the both magnets. |
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Thermal
design of a high gradient quadrupole for the LHC interaction
regions
Y. Huang, J. Kerby, P.O.
Mazur, T.J. Peterson and A. Zlobin
Summary:
The LHC high gradient quadrupole coils are subject to a
continuous heat load due to the beam-induced energy deposition
during operation. All heat deposited in the coil must be
removed so that the magnets will remain in a superconducting
state. The quadrupole magnets are designed to be cooled with
stagnant pressurized He II. This paper summarizes the heat
flow analyses from the insulated coil to the boiling saturated
He II for the LHC interaction region quadrupoles. The effects
of cable surface heat flux and cooling channel heights on the
thermal characteristics of the magnets are studied. He II heat
exchanger designs, arranged internally and externally are
compared. |
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Quench
protection of a high gradient quadrupole for the LHC
interaction regions
A.V.
Zlobin
Summary: The energy stored in a
superconducting (SC) accelerator magnet is usually dissipated
after a quench in the normal zones of the coil, heating the
coils and producing a voltage drop between the turns inside
the magnet and between coil and ground. This paper presents
the results of the analysis of the quench protection problem
for a high gradient quadrupole for the LHC interaction
regions. |
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Mechanical
studies of the Fermilab low beta quadrupole collared
coils
D.V. Mitchell, T. Heger, A.
Nobrega and J.P. Ozelis
Summary: Finite
element results of Low Beta Quadrupole magnets are compared to
measurements from three mechanical models. Stress, as measured
with internal strain gauges, and radial deflections, as
measured with a precision measuring device, are compared to
the finite element analysis. The results indicate that
measured internal pressures are in agreement with calculations
but measured deflections are approximately lower than
predicted. The findings will help develop better analyzing and
manufacturing techniques to be used on developing the High
Gradient Quadrupole magnet. |
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Development
of collar lamination strain gauges for coil stress
measurements in superconducting accelerator
magnets
J.P. Ozelis, P. Bause, R.
Bossert, J. Dominguez, S. Feher and T.
Heger
Summary: A new type of strain gauge has
been developed for measuring coil stresses in superconducting
magnets. It consists of commercial film-type strain gauges
mounted directly on the pole-tip area of coil collar
laminations. These gauges are extremely simple to manufacture,
calibrate, and install in prototype magnets. We discuss the
motivation for and design of these gauges, present results
from calibration tests performed at 300 K and 4.2 K, and
compare these results with calibration of existing beam-type
transducer gauges. We discuss calibration reproducibility,
reliability, and accuracy. We also present preliminary coil
stress measurements using these gauges in a model quadrupole
magnet during the collaring, yoking, cool down, and excitation
processes. |
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Progress
in the development of the 1-m model of the 70 mm aperture
quadrupole for the LHC low-/spl beta/
insertions
S.R. Milward, J.M.
Morris, S. Nobes, K.D. Smith, A.J. Street, M.C. Townsend, J.R.
Treadgold, J.M. Wiatrzyk, G.A. Kirby, R. Ostojic, T.M. Taylor
and J. Strait
Summary: Within the LHC magnet
development program Oxford Instruments has built a one metre
model of the 70 mm aperture low-/spl beta/ quadrupole. The
magnet features a four layer coil wound from two 8.2 mm wide
graded NbTi cables, and is designed for 250 T/m at 1.9 K. The
magnet has previously been tested between 4.5 K and 23 K. In
this paper we review the magnet rebuild and the subsequent
tests. Results on magnet training at 43 K and 1.9 K are
presented along with the results related to quench protection
studies. We also present the first results of magnetic field
measurements done at room and liquid nitrogen
temperatures. |
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Tests
of Fermilab low-/spl beta/
quadrupoles
R. Bossert, S. Feher,
S.A. Gourlay, T. Heger, J. Kerby, M.J. Lamm, P.J. Limon, P.O.
Masur, T. Nicol, F. Nobrega, D. Orris, J.P. Ozelis, T.
Peterson, P. Schlabach, J. Strait, J. Tompkins, A. Zlobin, A.
Lietske, A.D. McInturff and R. Scanlan
Summary:
The recently revived superconducting magnet program at
Fermilab is currently focused on the development of high
gradient quadrupoles for possible use in the Large Hadron
Collider (LHC) interaction regions at CERN. In order to
provide input for the new quadrupole design which will operate
in superfluid helium, we have tested a Fermilab Tevatron
low-/spl beta/ quadrupole cold mass and compared its low
temperature performance to a newly assembled heavily
instrumented version which was mechanically modified to take
advantage of the gain in critical current. |
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Field
errors decay and "snap-back" in LHC model
dipoles
L. Bottura, L. Walckiers
and R. Wolf
Summary: The magnetic field in
accelerator magnets decays when the current is kept constant
during the particles injection phase, and returns quickly
(snaps back) to the original values as soon as ramping is
restarted. Here we show results of measurements of the decay
of the field errors in 10 m long LHC model dipole magnets. In
accordance with previous findings, precycles and stops at
intermediate current levels influence the decay. We discuss a
possible mechanism causing the decay and snap-back, based on
the internal field change in the cable. |
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Superfluid
performance of Tevatron IR quad
heaters
A. Lietzke, A.D.
McInturff, R.M. Scanlan, R. Bossert, S. Feher, S.A. Gourlay,
M.J. Lamm, P.J. Limon, F. Nobrega, J.P. Ozelis and A.V.
Zlobin
Summary: Laboratories measured the
performance of a Tevatron interaction region (IR) quadrupole
at temperatures from 1.8 K to 4.4 K. These studies included
measurement of their performance as a function of temperature
as well as measurement of the effectiveness of the protection
heaters. Heater diffusion times were measured for various
temperatures, current levels, and power densities. These
results and their implications on the design of magnet
protection systems and magnet design operating in this
temperature range will be discussed. |
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Performance
of the high gradient, large aperture quadrupoles for the NSCL
superconducting spectrometer
B.
Zhang, A.F. Zeller, S. Bricker, R. Burleigh, J.C. DeKamp, P.
Johnson, B. Sherrill, R. Swanson and R.
Zink
Summary: Two superconducting
quadrupoles, for use as spectrometer elements, have been
constructed and mapped. A sextupole, which is within one of
the quadrupoles, has been mounted on the helium vessel bore
tube. All the elements are assembled into the same cryostat.
The mapped results, obtained with a three axis Hall probe, are
compared to 3-dimensional calculations over the entire range
of operation. Operation experience and heat loads are
presented. |
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Magnetic
measurements of large aperture superconducting quadrupole
magnets for TJNAF's High Momentum
Spectrometer
S.R. Lassiter, S.A.
Wood and P.D. Hrindza
Summary: The results of
the field mapping measurements of Thomas Jefferson National
Accelerator Facility's three large aperture, cold iron,
laminated yoke superconducting quadrupole magnets for the High
Momentum Spectrometer will be presented. These magnets were
mapped using a rotating coil assembly housed within a G-10
drum. A description of the apparatus and technique used to map
the magnets over an excitation range of 0 to 2 Tesla will be
described. This method of mapping provides for an almost real
time measurement of field strength, effective field length,
field gradient, transfer function and the determination of
symmetry planes. The hysteresis loop and affects of eddy
currents will be shown. A comparison of the measured field
values with calculated values will also be
given. |
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Superconducting
toroidal magnet design for the G0 experiment at
TJNAF
P.D. Brindza, D. Beck, R.
Laszewski, L. Bartoszek, R. Wands and D.
Mitchell
Summary: An eight coil
superconducting toroidal magnetic spectrometer has been
designed for the G0 experiment to be performed at Thomas
Jefferson National Accelerator Facility (TJNAF). The toroid is
designed so that the particle trajectories pass through the
magnet insulating vacuum. The magnet is made of aluminum
structural components with a copper stabilized indirectly
cooled conductor. The toroid is 2 meters long, 4 meters
outside diameter and is oriented with its major axis
horizontal. This orientation allows its use as an eight fold
symmetric focusing spectrometer. The SC magnet has a stored
energy of 6.5 Mjoules. The design and analysis of this device
are presented. The plans and status of magnet system
procurement are presented. |
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A
superconducting spectrometer magnet system for the detection
of heavy isotopes
M.A.
Green
Summary: LASSY is a proposed large
angle gas filled spectrometer for detecting and analyzing
heavy nuclei generated when a heavy ion beam (such as fully
stripped argon) collides with an actinide thin film target
(such as curium). With luck, superheavy nuclei, up to atomic
number 114 to 116, produced at the target. In order to improve
acceptance and resolution of the shortest lived nuclei, the
length of the magnet system must be as short as possible. The
LASSY spectrometer consists of a 4 to 6 T superconducting
magnet that produces 2.5 Tm of bending (bend radius induction
product) with a bend angle of 135 degrees or more. Particles
generated at the target (and there decay products) must be
focused on an electronic detector less than 3 meters from the
target, The resulting spectrometer magnet is quite complex
with sections that focus as well as bend the particles from
the target. This report presents two possible designs for a
large superconducting bending magnet that is a pure bending
magnet in the center with defocusing bending sections at the
ends of the magnet. This paper shows how one might build
bending magnet that is in sections, with each section having a
tunable quadrupole and sextupole field in addition to the
dipole field. |
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Test
results of the g-2 superconducting solenoid magnet
system
G. Bunce, W.M. Morse, J.
Benante, J.R. Cullen Jr., G.T. Danby, K. Endo, G.V.
Fedotovich, J. Geller, M.A. Green, A. Grossmann, M.
Grosse-Perdckamp, U. Haeberlen, H. Hseuh, H. Hirabayashi, V.W.
Hughes, J.W. Jackson, L.X. Jia, K. Jungmann, F. Krienen, R.
Larsen, B. Khazin, D. Kawall, W. Meng, C. Pai, I. Polk, R.
Prigl, G.Z. Putlitz, S. Redin, B.L. Roberts, N. Ryskulov, Y.
Semertzidas, R. Shutt, L. Snydstrup, T. Tallerico, P. von
Walter, K. Woodle and A. Yamamoto
Summary:
The g-2 experiment dipole consists of a single 48 turn,
15.1 meter diameter outer solenoid and a pair of 24 turn inner
solenoids, 13.4 meters in diameter. The inner solenoids are
hooked in series and are run at a polarity that is opposite
that of the outer solenoid, thus creating a dipole field in
the space between the inner and outer solenoids. The dipole
flux is returned by a C shaped continuous iron yoke. The
superconducting solenoid coils are closely coupled to the
solenoid mandrels and as such are subject to quench back. This
report presents the results of various tests on the g-2 magnet
system operating within its iron return yoke. These tests
include quench back time constant measurements for the inner
and outer solenoids and measurements of the response of the
two-phase forced cooled helium cryogenic system to magnet
quenches. The overall effectiveness of the g-2 magnet quench
protection system was measured. |
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Progress
in the design and manufacture of the KLOE solenoid for the
DAPHNE ring at Frascati
K.D.
Smith, A.J. Broadbent, M. Greenslade, S.M. Harrison, D.M.
Jenkins, J.S.H. Ross, A. Street, M.C. Townsend, J.M. Wiatrzyk
and J.L. Franzini
Summary: Oxford Instruments
took over the manufacture of the 5.7 m outer diameter 4.5 m
long 0.6 T Solenoid for the KLOE detector on the DAPHNE ring
when the Austrian company ELIN closed its magnet manufacturing
plant. The paper begins by discussing the magnet design before
going on to describe the approach Oxford has taken to the
completion of the magnet. The status of the system will be
described along with the proposed completion
schedule. |
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Stability
of Al-stabilised conductors for high energy physics
application
P. Fabbricatore, L.
Boldi, R. Musenich, R. Parodi and G. Gemme
Summary:
The stability of superconducting magnets wound with
Al-stabilized conductors is studied using Finite Element code
for thermal transient analysis. The computations show that
standard concepts, developed for steady state analysis, as
Minimum Quench Energy and Minimum Propagating Zone, have still
a meaning in the transient analysis. An important role is
played by the finite magnetic diffusivity, which strongly
reduces the stability margin. The methods used to carry out
the analysis are described and the stability margin of some
existing thin wall solenoids and magnets under design is
calculated. |
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Conceptual
design of the ATLAS thin superconducting solenoid
magnet
Y. Makida, Y. Doi, T.
Haruyama, T. Kondo, K. Tanaka, A. Yamamoto and H.
Yamaoka
Summary: A thin superconducting
solenoid has been designed to be installed into one of the
major colliding particle detecting facilities, ATLAS, for LHC
(Large Hadron Collider) project at CERN. The thin solenoidal
coil wound with stiffened aluminum stabilized superconductor
is indirectly cooled by forced two-phase helium through one
serpentine tube on the outer support cylinder. The coil is
installed into a common vacuum vessel with another co-axial
cryogenic component, LAr-Cal, to save the wall material to
trajectories for particles. Triangle-shape supporting elements
on both ends of the coil are newly introduced to reduce a
radial thickness of the cryostat. |
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A
20 T hybrid solenoid for the collection of pions for a muon
collider
M.A. Green and R.J.
Weggel
Summary: In order to generate intense
muon beams for a muon collider, intense pion beams must be
produced in a stationary proton beam target. The pions
produced by the target must be captured before they can go
through phase rotation and decay into muons. A 20 T solenoid
with a clear bore of 150 mm can capture particles with a
transverse momentum of 225 MeV/c or less. As the captured
particles leave the capture solenoid, the magnetic induction
is decreased to 5 T while the beam pipe diameter increases to
300 mm. Phase rotation of the pions and the decay of the pions
to muons will occur at 5 T. The capture solenoid and the
solenoids just downstream from the capture solenoid are
subject to high heat loads (up to 4.8 MW) and radiation loads
from the target. The conventional inner solenoid of the 20 T
hybrid magnet system and the water cooled absorber will absorb
virtually all of the particle energy from the target thus
protecting the superconducting part of the solenoid system
from excessive radiation heating. This report also describes
the solenoid magnets from the capture zone to the solenoidal
beam channel within the phase rotation RF
cavities. |
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Performance
tests of Bi-2212 insert magnets fabricated by Ag sheath method
and dip-coating method
H.
Kumakura, H. Kitaguchi, T. Kiyoshi, K. Inoue, K. Togano, M.
Okada, K. Fukushima, K. Tanaka, K. Kato and J.
Sato
Summary: We have fabricated small
magnets using Bi-2212/Ag tapes prepared by the combination of
a powder-in-tube method or a dip-coating method and a
wind-and-react method. The magnets were inserted in a 21 T
superconducting magnet and tested under various bias fields at
4.2 K. All of the magnets could sustain large electromagnetic
force under high magnetic fields, and no damage was introduced
during the test. Critical current density of a magnet
consisting of 4 double pancake coils was 9.5/spl times/10/sup
4/ A/cm/sup 2/ in 21 T which corresponded to the central
generated field of 1.76 T. Thus the total field of 22.76 T was
attained in a full superconducting state. No degradation of
superconducting properties was produced by a thermal cycle and
moisture in air. |
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HTS
high gradient magnetic separation
system
M.A. Daugherty, J.Y.
Coulter, W.L. Hults, D.E. Daney, D.D. Hill, D.E. McMurry, M.C.
Martinez, L.G. Phillips, J.O. Willis, H.J. Boenig, F.C.
Prenger, A.J. Rodenbush and S. Young
Summary:
We report on the assembly, characterization and
operation of a high temperature superconducting (HTS) magnetic
separator. The magnet is made of 624 m of Silver/BSCCO
superconducting wire and has overall dimensions of 18 cm OD,
15.5 cm height and 5 cm ID. The HTS current leads are designed
to operate with the warm end at 75 K and the cold end at 27 K.
The system operates in a vacuum and is cooled by a two stage
Gifford-McMahon cryocooler. The upper stage of the cryocooler
cools the thermal shield and two heat pipe thermal intercepts.
The lower stage of the cryocooler cools the HTS magnet and the
bottom end of the HTS current leads. The HTS magnet was
initially characterized in liquid cryogens. We report the
current-voltage (I-V) on characteristics of the HTS magnet at
temperatures ranging from 15 to 45 K. At 40 K the magnet can
generate a central field of 2.0 T at a current of 120
A. |
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Recent
progress of 70 MW class superconducting
generators
K. Inoue, K. Ezaki, K.
Kimura, K. Toyoda and T. Ichikawa
Summary:
This paper describes progress in an 11 year project for
research and development of superconducting generators in
Japan. Three types of 70 MW class superconducting generators
(called model machines) have been manufactured. Rotational
tests on two slow response excitation type rotors have been
conducted at each factory. The quick response excitation type
rotor is in manufacturing and a partial rotor model of the
same type has already been tested at the factory. Also, the
characteristics of a stator, which is to be commonly used for
three rotors at the verification test facility, are measured
by combining with one of the slow response excitation type
rotors at the factory. Verification tests on the first machine
are scheduled to be started early in 1997. Tests on the other
two model machines will follow the test on the first
one. |
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Design
and characteristics analysis of superconducting tubular linear
induction motors
J.P. Xu, S. Iino
and A. Ishiyama
Summary: The design and the
characteristics analysis of two kinds of superconducting
tubular linear induction motor are described. One has oxide
superconducting primary windings (Bi-2223), the other has NbTi
superconducting primary windings. The basic structure and
design values are shown in this paper. |
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HTS
coils for the Navy's superconducting homopolar
motor/generator
D.W. Hazelton,
M.T. Gardner, J.A. Rice, M.S. Walker, C.M. Trautwein, P.
Haldar, D.U. Gubser, M. Superczynski and D.
Waltman
Summary: We report here on the
development of HTS coils at Intermagnetics for the Navy's
homopolar motor/generator program. Two coil sizes were used. A
series of small test coils (14.0 cm i.d./spl times/15.0 cm
o.d./spl times/1.4 cm long) were employed to evaluate various
conductor winding, insulation and epoxy impregnation issues.
Based upon the results of these test coils, the larger coil
modules (19.37 cm i.d./spl times/24.35 cm o.d./spl times/2.54
cm long) for the homopolar motor/generator were fabricated.
Several coils each of three types of react-and-wind coils were
produced, one type with monocore BSCCO-2223, one type with
multifilamentary BSCCO-2223 and the other type with surface
coated BSCCO-2212. Test results are presented as well as
discussions on various coil technology issues. |
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The
determination of equivalent circuit parameters due to
continuous switching action in the superconducting flux
pump
Minseok Joo and Tae Kuk
Ko
Summary: The mechanism of continuous
switching action in the flux pump which takes place in the
superconducting foil has been studied. The Helmholtz equation
has been used to find the distribution of the superconducting
current on the boundary between the superconducting and normal
region. The distribution of the current, the magnetic field
and the electric field in the superconducting foil have been
derived theoretically and numerically. These distributions
could determine the parameters of the equivalent electric
circuit as well as the pole-shape design for the flux pump as
an electric power supply. The agreement between the
theoretical model and the practical one is fairly
good. |
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The
design, manufacture and characteristic experiment of a
superconducting fluxpump with superconducting excitation
coil
Joon Han Bae, Yun Sang Oh,
Sang Jin Lee and Tae Kuk Ko
Summary: This
paper describes a series of experiments to investigate the
operational characteristics of a superconducting fluxpump with
a superconducting excitation coil. In this experiment, the
idea of excitation in the fluxpump is introduced to control
the pole-flux in the air gap of the machine. The operating
current of the fluxpump is designed to have the value of 300
amps. for the rotational speed of 600 rpm. Sensors installed
on the Nb sheet yield the information on the spatial and
temporal behaviors of the magnetic field in spot and on the
characteristics of the fluxpump. The experimental observations
are compared with the theoretical predictions. |
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The
analysis of the temperature distribution with respect to heat
generation on Nb sheet in the superconducting
fluxpump
Yunsang Oh, Myungkon
Song and Taekuk Ko
Summary: The temperature
distribution with respect to heat generation on Nb sheet in
the rotating-spot superconducting fluxpump is analyzed by
using the heat transfer equations. The generated heat was
conducted within the region of 30% distance from the center of
the normal spot, but most of the heat was transferred to
liquid helium (LHe). The increase of the rotating speed makes
maximum temperature larger than that of the applied field.
Therefore, we can conclude that the velocity of the normal
spot is the main designing factor of the superconducting
fluxpump. |
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Stability
of HTS current leads considering unstable equilibrium
temperature profile
K. Machata,
Y. Mizokami, K. Ishihashi, M. Takeo, T. Mito and J.
Yamamoto
Summary: One of the equilibrium
temperature profiles along the conductor is found to be the
unstable solution between well-known upper and lower solutions
of the energy balance equation of high temperature
superconducting (HTS) current leads. The transient behavior of
the temperature profile of the HTS leads is analyzed by
perturbing the unstable equilibrium temperature profile. The
stability of the leads against thermal disturbances is
explained by the use of results of the transient analysis. The
stability of ideal gas cooled leads is compared with that of
the conduction cooled leads. |
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Development
of HTS current leads for 1 kWh/1 MW module type SMES system.
I. Design study
M. Konno, K.
Sakaki, T. Uede, A. Tomioka, T. Bohno, S. Nose, T. Imayasho,
H. Hayashi, K. Tsutsumi and F. Irie
Summary:
We have been developing high-temperature
superconducting (HTS) current leads for a 1 kWh/1 MW
module-type SMEs. Each module of a module-type SMES requires a
pair of current leads. Therefore, we employed bulk HTS in
order to reduce the heat load of the current leads. It is
important that HTS current leads for SMES be reliable. The HTS
current leads described in this paper have been designed to
minimize the heat load and to maintain a high level of
reliability. The HTS current leads are designed to hold the
heat load at the cold-end terminal to less than 0.1 W. They
are also designed with safety leads to bypass current in the
event the HTS is quenched and with metal superconductors to
assure the continuation of SMES operation even if the HTS
should fail or deteriorate in performance. This paper
describes an optimal design and the results of a heat load
evaluation of HTS current leads for SMES. |
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Development
of HTS current leads for 1 kWh/1 MW module type SMES system.
II. Manufacturing and testing of prototype
leads
T. Bohno, A. Tomioka, S.
Nose, M. Konno, K. Sakaki, T. Uede, T. Imayoshi, H. Hayashi,
K. Tsutsumi and F. Irie
Summary: For pt.I see
ibid., vol.7, no.2, p.684-7 (1997). We have been developing
HTS current leads for a 1 kWh/1 MW module type SMES system
(which we call "ESK" for Experimental SMES of Kyushu Electric
Power Co., Inc.). Each module of a module type SMES system has
a pair of current leads. For the purpose of reducing the heat
load from the current leads, we have employed a bulk HTS. As a
step in the preparation of HTS current leads for ESK, we trial
produced HTS current leads and tested them to evaluate their
characteristics. Our test results indicated that the heat load
in a steady state at a rated current of 1 kA and with a rated
flow rate of 0.05 g/s was 0.035 W, well below the specified
value of 0.1 W. Also, our results indicated that the HTS
current leads can be satisfactorily energized for pulsing
operation at a rated current for ESK of 500 A-1 kA. The heat
load under such conditions was 0.025 W, approximately 80% of
that under normal 1 kA operating conditions. It was also
verified that operation could be continued for 15 minutes even
when the coolant flow was stopped. |
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Development
program of a 60 kA current lead using high temperature
superconductors
R. Heller, G.
Friesinger, W. Goldacker, H. Kathol, B. Ullmann, A.M. Fuchs,
B. Jakob, G. Pasztor, G. Vecsey and R.
Wesche
Summary: The use of high temperature
superconductors in current leads to reduce the refrigerator
power consumption has been investigated in the last few years
by many groups. Potential candidates are Y-123 and Bi-2212
bulk material as well as Bi-2223 tapes sheathed with an Ag/Au
alloy. In the frame of the European Fusion Technology
Programme, FZK Karlsruhe and CRPP Villigen have started a
development program for design and construction of a 60 kA
current lead for the ITER Toroidal Field Coils. The task
composes of three parts: material selection based on test
results of 1 kA current leads, construction and test of 10 and
20 kA leads using the selected HTSC material giving proof of
the modularity and scale-ability of the design, and finally
construction and test of a 60 kA current lead which will
replace an existing conventional lead in the superconducting
coil test facility TOSKA at FZK. The paper describes the
status of the development program. Experimental results of the
first step and a first approach of the realisation of the 10
kA HTSC lead are given. |
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Prediction
of burnout of a conduction-cooled BSCCO current
lead
S.Y. Seol, Y.S. Cha, R.C.
Niemann and J.R. Hull
Summary: A
one-dimensional heat conduction model is employed to predict
burnout of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ current lead.
The upper end of the lead is assumed to be at 77 K and the
lower end is at 4 K. The results show that burnout always
occurs at the warmer end of the lead. The lead reaches its
burnout temperature in two distinct stages. Initially, the
temperature rises slowly when part of the lead is in flux-flow
state. As the local temperature reaches the critical
temperature, it begins to increase sharply. Burnout time
depends strongly on flux-flow resistivity. |
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Development
of current leads using dip coated BSCCO-2212
tape
S.M. Ting, K.R. Marken Jr.,
L. Cowey, W. Dai, S. Hong and S. Nelson
Summary:
Current leads have been developed that use dip coated
BSCCO-2212 tape. Techniques have been developed for stacking
multilayers of the basic coated tape as well as for sheathing
of the completed stack. The base tape can be coated in a wide
range of widths and thicknesses. These methods provide great
flexibility for tailoring the geometry and current capacity to
fit particular applications. Silver alloys were examined as
the substrate and sheathing material to minimize thermal
conductivity, while allowing comparable J/sub c/ to a pure
silver substrate. Prototype current leads have been fabricated
in configurations to allow various current ratings, structural
supports, and connecting end pieces. |
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The
use of the Bi-2223 superconducting
tubes
V. Plechacek, J. Hejtmanek
and V. Sima
Summary: The work is mainly
devoted to the possibility of the use of the BPSCCO tubes as
permanent superconducting magnets, i.e. to the increase of the
critical current density J/sub c/ and the trapped magnetic
flux density B/sub tr/. The obtained results are also applied
for the superconducting current leads and fault current
limiters. The Bi-2223 tubes were prepared by the isostatic
pressing using a pressing mandrel and they were
thermomechanically processed several times. It was shown that
the texture formed during the process and favorably
influencing J/sub c/ is more pronounced in tubes with thinner
walls. With regard to this fact, a superconducting magnet
composed of many thinner tubes was prepared. The trapped
magnetic flux density in the hole of the magnet reached up to
0.5 T at 20 K and, after cooling the magnet at 15 K, the B/sub
tr/ value of 0.5 T was maintained seemingly without relaxation
for five days. This multi tubes magnet was also compared with
one composed of two tubes of thicker walls. The J/sub c/ of
about 1000 A/cm/sup 2/ (at 77 K and under self field of about
20 mT) achieved for the single tubes indicates an advantage of
the use of relatively thin Bi-2223 tubes for the
superconducting current leads and fault current
limiters. |
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Experimental
apparatus for critical current measurement above 5 K using
Bi-based oxide current leads
T.
Hasebe, H. Mitsubori, J. Sakuraba, M. Ishihara, S. Awaji and
K. Watanabe
Summary: Experimental apparatus
for the measurement of temperature dependence of critical
current within a strong magnetic field has been developed.
Samples, which are tested by the four probe method are cooled
by a Gifford-McMahon (GM) type cryocooler to the lowest
temperature of 5 K. The sample holder has a diameter of 70 mm
and a height of 70 mm. Transport currents, up to 150 A, are
supplied to two samples through Bi-based oxide superconducting
current leads. An external magnetic field of up to 15 T, which
is applied to the samples perpendicular to the sample axis, is
generated by a water cooled single Bitter magnet with a room
temperature bore of 82 mm. As a performance test, the critical
current properties of a silver clad Bi-based oxide tape have
been measured at 5.5 K, 30 K and 50 K within a magnetic field
up to 15 T. This experiment has demonstrated the validity of
this experimental apparatus. |
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Design
of a high-current AC down link using Bi-based
superconductors
B.L. Fisher, M.T.
Lanagan, U. Balachandran, S. Honjo and T.
Hara
Summary: Recent processing developments
in Bi/sub 1.8/Pb/sub 0.4/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/.
(BSCCO-2223) bars have produced bulk BSCCO-2223 bars with
properties advantageous for power applications. Cold
isostatically pressed (CIP) and sinter-forged BSCCO-2223 both
have low AC loss, which make them desirable for use in power
devices. Thermal conductivity of the CIP bars is lower than
that of the previously used sinter-forged samples by a factor
of 2. CIP bars with cross-sectional areas of /spl ap/0.75
cm/sup 2/ and carrying 250 A RMS transport current have AC
loss values of 30 /spl mu/J/cycle-cm at 50 Hz and 77 K. A pair
of prototype downlinks were designed and built with sinter
forged bars to deliver a continuous AC current of 1500 A over
a temperature gradient of 77 to 4.2 K while delivering about
/spl ap/200 mW of heat to the liquid-helium-cooled end. This
paper discusses the design considerations and modeling of
downlinks, which supply high AC currents over the 77 to 4.2 K
temperature gradient with low thermal losses. |
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One
dimensional simulation for Peltier current
leads
H. Okumura and S.
Yamaguchi
Summary: Current leads, which
connect superconducting magnets at the liquid helium
temperature and power supplies at the room temperature, are
the major source of heat leaking into cryostats, and therefore
largely determines the running cost of magnet systems. Heat
leak can be reduced by using high-temperature superconductors
as the low-temperature (4 K-77 K) segments of current leads.
Another method to reduce heat leakage, recently proposed, uses
Peltier thermoelectric elements as the high-temperature (200
K-300 K) segments of current leads. These thermoelements
effectively pump heat out of cryostats without using separate
sources of electricity. The authors carried out experiments
and numerical calculations with such Peltier current leads and
found out that they reduce heat leak at 77 K by 20-30
percent. |
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Superconducting
power cables in Denmark-a case
study
J.
Oestergaard
Summary: A case study of a 450
MVA, 132 kV high temperature superconducting (HTS) power
transmission cable has been carried out. In the study, a
superconducting cable system is compared to a conventional
cable system which is under construction for an actual
transmission line in the Danish grid. The study considers the
design and development of a calculation model for an HTS cable
system including auxiliary facilities. From calculations of
the selected transmission line, conclusions on the feasibility
of HTS cables in Denmark are made. HTS cables appear to be
feasible in Denmark. Calculations indicate that HTS cables
will be less expensive for high power ratings, have lower
losses for lines with a high load, and have a reduced reactive
power production. The use of superconducting cables in Denmark
accommodate plans by the Danish utility to make a substantial
conversion of overhead lines to underground
cables. |
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Modelling
boundary-induced coupling currents in Rutherford-type
cables
A.P.
Verweij
Summary: In this paper, it is shown
that spatial distributions in the field-sweep rate and in the
contact resistances along the length of Rutherford-type
superconducting power cables provoke a nonuniform current
distribution during and after a field sweep. This process is
described by means of boundary-induced coupling currents
(BICCs) flowing through the strands over lengths far larger
than the cable pitch. The dependence of the BICCs on the cable
parameters (geometry, contact resistances etc.) is
investigated by modelling the cable by means of a
comprehensive network model. Working formulae are presented
that give a first estimate of the characteristic time, the
amplitude, and the characteristic length of the BICCs in any
kind of magnet wound from a Rutherford-type cable. The results
of these calculations show that BICCs can attain large values
in multistrand cables, and hence play an important role in the
ramp-rate limitation and field quality of high-field
accelerator magnets even if the field-sweep rate is
small. |
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Superconducting
magnets for accelerators: a
review
M.N.
Wilson
Summary: Superconducting magnets have
enabled the construction of some very large accelerators to
explore the structure of matter at the highest energies. Small
superconducting accelerators are used in medicine and
industry. We review the special demands which accelerators
make on superconductor technology, describe the magnets for
large and small accelerators and mention some exciting
prospects for the future. |
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Application
of Nb/sub 3/Sn superconductors in high-field accelerator
magnets
A. den Ouden, S. Wessel,
E. Krooshoop and H. ten Kate
Summary: Last
year a record central field of 11 T at first excitation at 4.4
K has been achieved with the experimental LHC model dipole
magnet MSUT by utilising a high J/sub c/ powder-in-tube Nb/sub
3/Sn conductor. This is the first real breakthrough towards
fields well above 10 T at 4 K. The clear influence of
magnetisation and coupling currents on the field quality, the
quench behaviour and the temperature development in the coils
has been measured and is discussed. For application in
high-field accelerator magnets (10-15 T dipoles, 300-400 T/m
quadrupoles) these experimental results clearly reveal the
potential, the present limitations and the necessary
improvements of Nb/sub 3/Sn technology with respect to strand,
cable and coil design and manufacturing. A brief review of
developments in this field is presented. The focus is on
accelerator dipole magnets but the key issues for quadrupole
magnets are quite similar. |
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Test
results for a Nb/sub 3/Sn dipole
magnet
A.F. Lietzke, R.
Benjegerdes, S. Caspi, D. Dell'Orco, W. Harnden, A.D.
McInturff, M. Morrison, R.M. Scanlan, C.E. Taylor and J.M. Van
Oort
Summary: A cosine theta type dipole
magnet using Nb/sub 3/Sn conductor have been designed, built
and tested. D19H is a two-layer dipole magnet with a Nb/sub
3/Sn inner layer and a recycled NbTi outer layer. Coil-pairs
are connected with two of the four Nb/sub 3/Sn splices in a
high field region, and compressed by a ring and collet system.
The ramp-rate sensitivity and the splice resistances were
pleasingly low; and the 4.4 K training was rapid. At 1.8 K,
however, the unusually high frequency of outer-coil
fast-motion events increased with current, effectively
creating a training-ceiling at 90% of the expected outer-layer
limit (10.2 T). A low end-load applied to a relatively fluffy
outer layer is believed to have caused this training limit.
The end-load was increased; but a retest was aborted after the
magnet failed a precautionary hipot test. |
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Superconducting
dipoles and quadrupoles for a 2 TeV muon
collider
M.A. Green and E.
Willen
Summary: At 2 TeV the mean lifetime
for a muon is 41.6 ms. In order to achieve high luminosity at
the collider collision point, the dipole central induction for
the storage ring should be over 8 T. The storage ring carries
muon over 1000 turns through the ring before they decay away.
Muons decay to two neutrinos and an electron or positron
(depending on the charge of the decaying muon). Seventy
percent of the muon energy will be taken away by the
neutrinos. The electrons (at average energies of 700 GeV) and
the photons (at energies up to 2.1 GeV) are quite penetrating.
At the design luminosity of the muon collider, the
superconducting dipoles and quadrupoles in the storage ring
must contain muon beams (up to 1.4/spl times/10/sup 14/ muons
per second) that will deposit over 1.8 kW per meter of energy
into the storage ring. This report presents two design
approaches for superconducting dipoles and quadrupoles that
can be used for the muon collider storage ring. |
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Design
study of a superconducting insertion quadrupole magnet for the
Large Hadron Collider
A.
Yamamoto, K. Tsuchiya, N. Higashi, T. Nakamoto, T. Ogitsu, N.
Ohuchi, T. Shintomi, A. Terashima, G. Kirby, R. Ostojic and
T.M. Taylor
Summary: The conceptual design
study of a high gradient superconducting insertion quadrupole
magnet has been carried out in collaboration between KEK and
CERN for the Large Hadron Collider (LHC) to be built at CERN.
A model magnet design has been optimized to provide a nominal
design field gradient of 240 T/m with a bore aperture of 70 mm
and an operational field gradient of 225 T/m at 1.9 K under
radiation environment with a deposition of several watts per
meter in the superconducting coils. The design and its process
are discussed. |
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Development
of a high gradient quadrupole for the LHC interaction
regions
R. Bossert, S. Feher,
S.A. Gourlay, T. Heger, Y. Huang, J. Kerby, M.J. Lamm, P.J.
Limon, P.O. Mazur, F. Nobrega, J.P. Ozelis, G. Sabbi, J.
Strait, A.V. Zlobin, S. Caspi, D. Dell'Orco, A.D. McInturff,
R.M. Scanlan, J.M. Van Oort and R.C. Gupta
Summary:
A collaboration of Fermilab, Lawrence Berkeley National
Laboratory and Brookhaven National Laboratory is engaged in
the design of a high gradient quadrupole suitable for use in
the LHC interaction regions. The cold iron design incorporates
a two-layer, cos(2/spl theta/) coil geometry with a 70 mm
aperture operating in superfluid helium. This paper summarizes
the progress on a magnetic, mechanical and thermal design that
meets the requirements of maximum gradient above 250 T/m, high
field quality and provision for adequate cooling in a high
radiation environment. |
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Commissioning
the superconducting magnets for the High Momentum Spectrometer
(HMS) at TJNAF
P.D. Brindza, M.J.
Fowler, R.T. Wines, S.R. Lassiter, S.R. Milward, S. Pearmain,
J. Schouten, N. Oda, K. Tamura, F. Ramsauer, S. Wenger, P.
Bogensberger, H. Sammer and H. Dermoetz
Summary:
The High Momentum Spectrometer (HMS) became operational
in June 1994 and is now in routine use as a nuclear physics
spectrometer in Hall C at TJNAF. The commissioning including
installation, cooldown, initial operation, testing and
acceptance of the SC quadrupoles and SC dipole of the HMS will
be discussed. Results of measurements performed on the magnets
will be presented. The loss of a dipole current lead, failure
analysis and the repairs will be discussed. A brief discussion
of the Hall C SC magnet cryogenics will be
included. |
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Simulation
of the ITER-CS coil operation including the effect of the ramp
rate limitation
M. Shimada and M.
Mitchell
Summary: A model to simulate
conductor performance of the Central Solenoid (CS) coil of the
International Thermo-nuclear Experimental Reactor (ITER) is
discussed. The conductor for the ITER-CS coil consists of
multistage cables, where a non-uniform current distribution
may be expected during operation which affects the stability
of the conductor. A probable mechanism for the non-uniform
distribution in a pulsed coil is flux loops between the
strands or cable substages as the current is ramped up or
down. A model for this distribution is presented. Simulations
are then performed to quantify the effect of parameters, such
as the unbalanced voltage of each strand caused by the flux
loops, on the stability limit of the ITER-CS
coil. |
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EU
conductor development for ITER CS and TF Model
Coils
A. della Corte, M.V. Ricci,
M. Spadoni, G. Bevilacqua, R.K. Maix, E. Salpietro, H. Krauth,
M. Thoener, S. Conti, R. Garre, S. Rossi, A. Laurenti, P.
Gagliardi and N. Valle
Summary: A significant
effort is underway in the European Union for the manufacture
of superconducting conductors for ITER TF and CS Model Coils.
For the CSMC the EU will contribute about 6.5t of bronze
Nb/sub 3/Sn strand, 1200 m of full size cable and the
jacketing of the entire conductor length, 5787 m. The TFMC
conductor, on the other hand, will be entirely manufactured
within EU: 4t of internal tin Nb/sub 3/Sn strand, cabling and
jacketing of 1 km of TF conductor. This paper deals with the
present status of the industrial activities. The achievements
and lessons learned from the various manufacturing processes
are presented. |
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Experimental
study on the characteristics of current distribution in
Rutherford cables and parallel
strands
S.W. Kim, Y. Makida, T.
Shintomi, T. Mito, A. Iwamoto and J.
Yamamoto
Summary: The current distribution in
a multi-stranded superconducting cable such as Rutherford
cable plays an important role in the stability. Rutherford
cables consist of many strands which are twisted and
electrically contacted together. Because of this complexity,
it is hard to know factors that effect to the current
distribution and hence to the stability. The most important
factors may be interstrand contact resistances and mutual
inductances between strands mainly caused by twisting strands.
To evaluate the effect of contacting and twisting, we compared
the characteristics of Rutherford cables with parallel
strands. We have performed experimental studies on these items
for parallel strands with and without insulation by heating
with a spot heater. The results for insulated parallel strands
show very similar behaviors to those obtained in Rutherford
cables. From the fact, we came to the conclusion that the
contact resistances at the edges are relatively low in
comparison with side-by-side ones between two adjacent strands
in the Rutherford cable, and then that the current commutation
occurs mainly at the edges. Rest of the transport current
could not change the steady state current distribution. To
clarify this is remained as a future research. |
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Effects
of the current redistribution within Nb/sub 3/Sn
compacted-strand cable on its
stability
N. Hirano, T. Mito, K.
Takahata, A. Iwamoto, R. Maekawa, J. Yamamoto, B. Ikeda, Y.
Kubo, M. Morita, O. Taguchi and R. Saito
Summary:
The effects of current redistribution on the stability
have been studied using two kinds of Nb/sub 3/Sn
compacted-strand tables with chrome coating and without any
coating. The minimum quench energy (MQE) has been measured in
various external magnetic field and with various transport
current. The MQE of the cable with chrome coating was slightly
larger than that of the cable without coating when the
transport/critical current ratio, I/I/sub c/, is small. The
effects of the different surface condition of the strands on
the stability becomes smaller, when the transport current
approaches the critical current. The normal zone propagation
process of these cables were also different. The initiation of
the normal zone propagation in the cable without coating was
slower than that in the cable with coating. |
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Current
distribution in a 12 strand Nb/sub 3/Sn CICC and its influence
on ramp rate limitation
V.S.
Vysotsky, M. Takayasu, P.C. Michael, J.H. Schultz, J.V.
Minervini and Sangkwon Jeong
Summary: Direct
measurements of the current in each strand of a chrome coated
Nb/sub 3/Sn CICC were performed during current and/or external
magnetic field ramps. Severe non-uniformity of the strand
currents was found immediately before quench. The currents in
some of the strands were also observed to change abruptly at
various points during external field ramps. The observed
peculiarities of the strands' current behaviors are considered
in the present paper and a simple "ad hoc" model of the ramp
rate limitation phenomenon is proposed based on the hypothesis
that current non-uniformity is a main cause of RRL. This model
is compared with the experimental results. |
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Magnetic
stability of AC superconducting wire in self
field
G. Nishijima, T. Okamura,
S. Kabashima, T. Kurusu, T. Yazawa, S. Nomura, H. Nakagome and
H. Maeda
Summary: Magnetic stability of AC
superconducting wires was investigated experimentally. In a
long superconducting wire, self-field cannot diffuse
sufficiently, and it has been thought that flux jumping occurs
when the thickness of the saturated region is larger than some
threshold value in multifilamentary superconductors. In this
paper, we measured a current sweep rate dependence of quench
current of the AC superconducting wire. The experimental
results indicated that AC superconducting wires were
magnetically stable and could carry the critical current at
the sweep rate that was 100 times higher than a threshold
value which was estimated from one-dimensional diffusion
equation. |
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An
iron core circuit to balance the current of insulated strands
in superconducting cables
S.
Yamaguchi
Summary: Cables of insulated
strands reduces ac losses in superconducting magnets even at
frequencies below 1 Hz. Their current imbalances, however,
make the magnet unstable, and this problem has been discussed
for the last 15 years. I have proposed to insulate the normal
strands of the current leads to each other and to connect them
individually to the superconducting strands of the magnet. The
currents of the strands in this design are balanced well by
the electrical resistance present in the current leads. This
is, however, not effective at high frequencies which require
high resistance. In order to balance the current of strands
carrying dc and ac of higher, including commercial
frequencies, I propose to pass two insulated strands through
an iron core and to send currents through them in opposite
directions. This current balancer has as many iron cores as
there are strands. Even in a very large magnet, where the
inductance variation of individual insulated strands circuits
is of the order of 10 /spl mu/H and the current is about 100
A, strand currents would be balanced well with iron cores of
only a few centimeters in size. |
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DC
measurement of electrical contacts between strands in
superconducting cables for the LHC main
magnets
D. Richter, J.D. Adam,
J.-M. Depond, D. Leroy and L.R. Oberli
Summary:
In the LHC main magnets, using Rutherford type cable,
the eddy current loss and dynamic magnetic field error depend
largely on the electrical resistance between crossing (Rc) and
adjacent (Ra) strands. Cables made of strands with
pre-selected coatings have been studied at low temperature
using a DC electrical method. The significance of the
inter-strand contact is explained. The properties of resistive
barriers, the DC method used for the resistance measurement on
the cable, and sample preparation are described. Finally the
resistances are presented under various conditions, and the
effect is discussed that the cable treatment has on the
contact resistance. |
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Examination
of contacts between strands by electrical measurement and
topographical analysis
J.-M.
Depond, D. Leroy, L.R. Oberli and D.
Richter
Summary: The contact resistance
between crossing strands of Rutherford type superconducting be
an essential parameter the main magnets in accelerators like
the LHC. A strong development program to study the parameters
fixing its value has been launched at CERN. The electrical
contact resistance of individual strands with pre-selected
coatings has been studied at 4.2 K under varying loading force
by means of a 3 contacts DC method. The electro-mechanical
properties of contacts have been studied on bare strands and
strands with Sn, Ni, or Zn based coatings. The contact
resistances measured on strands were compared to measurements
made on cables. Contact resistance properties were analysed
with respect to the requirements for the LHC main magnet
cables. |
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Determination
of interstrand contact resistance from loss and field
measurements in LHC dipole prototypes and correlation with
measurements on cable samples
R.
Wolf, D. Leroy, D. Richter, A.P. Verweij and L.
Walckiers
Summary: Loss and field errors due
to ramping in LHC accelerator dipole magnets are mainly
determined by the contact resistance between the strands of
the magnet cable. It is therefore important to develop cables
having sufficiently high contact resistance in the magnets in
order to ease operation of the future LHC collider during
ramping. In this paper the contact resistance R/sub c/ and its
distribution in the magnet windings are determined for several
dipole prototypes using both the measured loss and field
errors during ramping of the magnet. We compare these results
with interstrand contact resistance measurements made on short
samples of the cables used in these magnets. |
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Experimental
evidence of boundary induced coupling currents in LHC
prototypes
L. Bottura, L.
Walckiers and Z. Ang
Summary: The field
quality of 10 m long LHC dipole models has been measured with
short rotating coils to explore its dependence on time and
position. Multipoles exhibit longitudinal periodic variation,
with period equal to the twist pitch length. This periodicity
is shown here to have at least two components with very
different time constants. The amplitude of the component with
the shorter time constant, in the range of 100 to 300 s,
depends on position and time. Larger amplitudes are measured
at early times after a ramp and close to regions with
incomplete cable transposition with respect to the non-uniform
external field change. As the multipoles periodicity is due to
current imbalance in the cables, we attribute the short time
scale variations to the presence of space and time decaying
boundary induced coupling currents (BICC's) in the cable. An
estimate of their value is given. |
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Experimental
study of current sharing and transfer in superconductor
joint
S. Mizumaki and A.
Yamamoto
Summary: A fundamental study of
current sharing and transfer in superconducting joint has been
carried out. The variation of the current sharing in the
joint, with increasing the joint current, has been observed by
using Hall probes attached to the joint block. The measured
result is consistent with a proposed current transfer model in
the joint. The experimental method and the test results
reported in this paper. |
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The
relation between transverse mechanical and electrical
properties of the multi-twisted stage cables of
CICC
M. Ono, M. Arata, T.
Hamajima, H. Maeda, H. Takano and T.
Fujioka
Summary: The transverse resistance
among strands of multi-stage twisted cables is one of the most
important parameters to decide the stability and the AC
losses. This value is varied with the cable compression
affected by the void fraction or the Lorentz forces under
charging. Furthermore it is also influenced by cyclic number
of transversal compression. This paper describes the basic
mechanical property of the chrome plated NbTi cable for the
transverse compression, and the relation of the transverse
resistance and the internal loads of the cable by measuring
the impedance and the rigidity for various internal loads. It
shows that the transverse resistance, which is much influenced
with the performance of conductor, is always changed
corresponding to the compressive load and dose not indicate
the same resistance after release from the compression because
of its elastic hysteresis. |
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The
effect of electromagnetic and mechanical stresses on critical
current of Nb/sub 3/Sn cable developed for superconducting
generator
S. Torii, H. Kasahara,
S. Akita, K. Goto, S. Iwasaki, N. Sadakata, T. Saitoh, O.
Kohno and J. Yoshitomi
Summary: A Nb/sub 3/Sn
superconducting cable for use as the field winding conductor
of a superconducting generator was developed with the in-situ
process. A magnetic field of up to 7 T, and a transverse
compressive mechanical force of up to 29.4 MPa were applied to
the conductor, and the critical current and strain of the
cable were measured. A cyclic compressive mechanical force was
also applied in order to simulate DSS operation of the
generator for up to 30 years. Over 10,000 loading cycles, the
critical current showed no degradation and was constant. By
changing the magnetic field direction while maintaining the
current direction, both compressive and tensile
electromagnetic stresses were applied to the cable, and the
critical currents were measured under both conditions. The
critical current under compressive stress was smaller than
that under tensile stress. Thus, it became apparent that
electromagnetic strain must be considered when measuring the
critical current of large current capacity Nb/sub 3/Sn
superconducting cables. |
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Development
of composite flexible Nb/sub 3/Sn cables suitable for the
react-then-wind approach
S.
Pourrahimi and K. DeMoranville
Summary: This
effort introduces the possibility applying the react-then-wind
approach to the construction of magnet modules by using
flexible reacted Nb/sub 3/Sn cables. The key to the
flexibility is that the strands are transported by twisting,
small in diameter, and free from bonds to other strands.
Flexible, reacted subcables were made by; (1) cabling of
reacted strands, and (2) controlled heat treatment of
unreacted cables. The J/sub c/ of these cables, after bending,
showed no degradation over the J/sub c/ of the undeformed
single strands. Composite flexible cables of Nb/sub 3/Sn and
Cu strands were fabricated eliminating the need for a tin
diffusion barrier and Cr plating of the strands. In addition
to numerous advantages in the cost and engineering, flexible
cables using fine strand appear to provide better stability
than conventional cables. |
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The
intrinsic magneto-resistance of cryogenic
joints
J.H. Parker Jr. and M.P.
Krefta
Summary: An intrinsic joint resistance
can arise due to circulating Hall currents flowing across the
joint interface between dissimilar metal conductors carrying
transport current in a magnetic field. Calculations have been
performed to determine this resistance for a number of generic
joint geometries, including butt, sandwich, and lap, as a
function of the magnetic field strength for Cu-Al and Cu-SC
pairs. This type of joint resistance may play a role in the
coupling loss and stability of filamentary superconductors.
The results are discussed in terms of their implication for
superconducting coil and conductor design. |
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Preliminary
tests of a 500 kVA-class oxide superconducting transformer
cooled by subcooled nitrogen
K.
Funaki, M. Iwakuma, M. Takeo, K. Yamafuji, J. Suchiro, M.
Hara, M. Konno, Y. Kasagawa, I. Itoh, S. Nose, M. Ueyama, K.
Hayashi and K. Sato
Summary: The authors have
designed and fabricated a 500 kVA-class oxide superconducting
power transformer operated in sub-cooled nitrogen. The primary
and secondary windings are three- and six-strand parallel
conductors of Bi-2223 Ag-sheathed multifilamentary tapes,
respectively. In the parallel conductors, the strands are
transposed several times for uniform current distribution
among them. A transformer, cooled by liquid nitrogen of 77 K,
was steadily operated with a 500 kVA secondary inductive load.
The efficiency in full operation at 77 K was 99.1 %, even with
the refrigeration penalty of liquid nitrogen, 20, for the
thermal load to the coolant. They installed the transformer in
a continuous flow system of sub-cooled nitrogen as a
fundamental step for compact superconducting transformers
operating in sub-cooled nitrogen with a single-stage
refrigerator. Short-circuit tests of the transformer were also
performed in a region of temperature below 70 K. The
transformer was operated with no quenching up to a level of
critical current at 66 K, that is equivalent to 800 kVA. The
efficiency estimated was improved to 99.3 % in the sub-cooled
nitrogen. |
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Resistive
current limiters with YBCO
films
B. Gromoll, G. Ries, W.
Schmidt, H.-P. Kramer, P. Kummeth, H.-W. Neumuller and S.
Fischer
Summary: The aim of this work is to
develop a function model of a resistive HTSC fault current
limiter. The switching elements of the fault current limiter
are bath-cooled in a liquid nitrogen cryostat. The elements
consist of YBaCuO films which are deposited on different
substrates with critical current densities of up to 3/spl
middot/10/sup 6/ A/cm/sup 2/. For the most effective limiting
samples so far the peak let-through current was twice tile
nominal current and the steady short-circuit current below
nominal current. The concept of a 100 kVA function model is
introduced. |
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Testing
and modelling of inductive superconducting fault current
limiters
J.R. Cave, D.W.A.
Willen, R. Nadi, W. Zhu, A. Paquette, R. Boivin and Y.
Brissette
Summary: Fault current limiters are
expected to be amongst the first applications of
high-temperature superconductors in power engineering. The use
of the intrinsic property of a superconductor to transit from
a zero (or near zero in the case of AC currents) resistance
state to a highly resistive state when the critical current is
exceeded is the basis for a fast acting fault current limiter.
In this article, the authors report test results (43 kVA
nominal power: 450 V RMS and 95 A RMS) and comparisons to
theoretical simulations. Circuit analysis is used to study
design issues and to extract the superconducting material's
(BSCCO 2212) properties during the application of the
short-circuit. EMTP simulation is employed to predict fault
current limiter behaviour in the utility network in order to
coordinate with other equipment. |
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Simulation
of the transient response of a high-T/sub c/ superconducting
current limiter inserted in an electrical distribution
system
N.E. Reimann, R.
Cherkaoui, B. Dutoit, D. Djukic and G.
Grasso
Summary: The ever-increasing demand
for electrical power leads to reinforced power systems.
Therefore, the overcurrents resulting from contingencies such
as short-circuits are increasingly higher. In order to reduce
these overcurrents, a protection system composed of a
superconducting current limiter and a traditional breaker
seems to provide a promising solution for future power system
operation. In this context, the authors aim is to analyze the
transient response to a fault of a resistive type high-T/sub
c/ superconducting fault current limiter inserted in an
electrical power system. In order to do this, simulations were
carried out with the well-known EMTP software. The fault
current limiter was represented using a preliminary tape model
that includes the AC losses contribution and is valid for any
current wave shape. This tape model was developed at the Swiss
Federal Institute of Technology in Lausanne, using
measurements of the dynamic behavior of Ag-sheathed Bi-2223
tapes. |
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Design
and construction of the 4 Tesla background coil for the navy
SMES cable test apparatus
D.W.
Scherbarth, D.T. Hackworth, T.D. Hordubay, O.R. Christianson
and W.V. Hassenzahl
Summary: The design and
construction of a background coil being built by Westinghouse
STC for the Navy SMES cable test apparatus are presented. One
objective of the Navy SMES development program is to develop
and test improved superconductors for SMES use. The background
coil generates a 4 Tesla field on a 1.85 meter diameter SMES
conductor sample. The coil stores 49.4 MJ, and has an inner
diameter of 2.13 meters. The background coil and SMES
conductor sample are housed in separate, concentric cryostats
so that the SMES conductor samples can be changed without
warming the background coil. The background coil is a pancake
style winding, utilizing a Rutherford cable conductor cowound
with a stainless steel strap and mylar
insulation. |
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Development
of a 1 kWh-class module-type SMES-design
study
T. Imayoshi, H. Kanetaka,
H. Hayashi, K. Honda, K. Tsutsumi, F. Irie, M. Takeo, K.
Funaki, H. Okada, T. Ezaki and F. Sumiyoshi
Summary:
The authors are planning to build a 1 kWh/1 MW (maximum
stored energy/maximum power capability) module-type SMES
(named ESK; experimental SMES of Kyushu Electric Power) as a
first step towards the realization of practical SMESs for
power line control. The main points of the design are those
of: module-type coils for the development of SMES capacity
scale-up; the choice of low loss stranded cables for reducing
pulse operating loss; the choices of modified D shape coils
and the reduction of stresses in the conductor-which become
more serious in scaling-up and high-T/sub c/ superconductor
(HTSC) current leads for covering weak points due to thermal
loss in a module-type SMES which need many current leads. Some
other points are also studied such as the design of the
cooling system in which a single coil quench does not induce
that of others, and harmonics suppression in the SMES power
converter system. |
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Superconducting
magnetic energy storage for substation
applications
M. Parizh, A.K.
Kalafala and R. Wilcox
Summary: Requirements
and possible configurations for a SMES operating in 15 kV
substations are discussed. The system will experience /spl
sim/25 full discharges a year. Such a SMES system should
provide 1 to 2 second-ride through capability, a response time
of less than 8 milliseconds, and demonstrate a high
efficiency. |
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Design,
manufacturing and cold test of a superconducting coil and its
cryostat for SMES applications
A.
Bautista, P. Esteban, L. Garcia-Tabares, C. Peon, E. Martinez,
J. Sese, A. Camon, C. Rillo and R. Iturbe
Summary:
This paper describes the design and manufacturing of a
25 kJ superconducting coil as well as its cryostat and magnet
support, including current leads and cryogenic services, for
an SMES. The coil design is based on a minimum volume
criteria. The cryostat is designed for 60 l of liquid helium,
and the magnet support with current leads optimised for 150 A.
Using numerical modelling, the total heat transfer into the
liquid is calculated and minimised. The manufacturing of both
components is also presented, as well as the complete system
operation. Finally the paper presents the power converter
topology that is controlled in optimal PWM mode with a low
switching frequency. In order to compensate different power
oscillations, the power converter quickly interchanges
adjustable and uncoupled levels of real and reactive
power. |
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Quench
protection and stagnant normal zones in a large cryostable
SMES
Y. Lvovsky and C.M.
Rey
Summary: The quench protection system for
a 30 MW SMES built by Babcock and Wilcox is discussed. The
magnet uses a cryostable conductor with an aluminum stabilizer
cooled by pool boiling helium. A general approach to the
protection of a cryostable magnet is presented. The phenomenon
of stagnant zones is identified as a catastrophic process
which can raise the conductor temperature in a localized area
to hundreds of K in several minutes and has been selected as
the target for quench protection systems. A stagnant zone can
appear in an area covered by vapor and is characterized by
uncontrollably growing temperature in the center, while its
fronts slowly advance in cryostable regions. Stagnant zones
are difficult to detect because of the cryostable nature of
the conductor and the existence of other types of normal zones
analyzed in the paper, such as steady zones or traveling
normal zones, each with its unique behavior. The complexity of
quench detection for cryostable magnet and the authors'
approach to the problem are discussed. |
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Experimental
and simulated results of a SMES fed by a current source
inverter
I.J. Iglesias, A.
Bautista and M. Visiers
Summary: This paper
presents the first experimental results obtained with a
6-pulse, 50 kW GTO current source inverter (CSI) feeding a 25
kJ superconducting coil. This SMES system is the first step
into the project AMAS500 which consists of developing a 1 MJ
SMES fed by a 500 kW CSI. The complete system will be in
operation at the end of this year, but this paper shows the
first results of the 25 kJ SMES when compensating a voltage
oscillation in a scaled network. The paper is mainly focused
on showing the experimental results of the 50 kW power
converter and its comparison with simulation results obtained
by means of EMTP and SABER/sup TM/ simulators. The very good
agreement obtained between both results has validated the
simulation models. Based on these models, the design of a 500
kW power converter has been carried out. The results of
simulating the 12-pulse 500 kW CSI feeding a 1 MJ
superconducting coil are also presented in this
paper. |
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Structural
advantages of disk magnets for
SMES
P.H.
Titus
Summary: A simple reorientation of the
strip solenoid allows improvements in the support of an SMES
magnet. A large diameter storage magnet is the focus of the
study, but smaller applications are discussed. For large
diameters, the peak field and energy storage are nearly the
same for a strip solenoid and a disk magnet. The
characteristics and benefits of the disk magnet arrangement
are discussed. The disk geometry allows improved access for
maintenance, reduces excavation and facilitates the repair of
conductors. Shimmed radial support at the outer edge allows
controlled thermal contraction and control of conductor
strains and is a simplification over rippled solutions
proposed independently. Winding pack radial loads produce
compressive stresses, no out-of-plane loads develop and there
are no bending or shear loads in the winding
pack. |
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Comparison
of availability between 4.2 K and 77 K SMES
concepts
P. Saari and R.
Mikkonen
Summary: The influence of nitrogen
cooled superconductors on the availability of a 100 kWh SMES
concept has been analysed. A conceptual design of a reference
unit at 4.2 K has been used as a basis of the study. This kind
of unit, with independent control of real and reactive power,
is suitable for load management-for example in foundries. A
comparison of availability has been performed between the 77 K
and 4.2 K concepts. In order to perform this analysis, one has
to assume that the mechanical and electrical performance of an
HTSC cable is equivalent to that of a conventional one. The
method used is based on failure modes, effects and criticality
analysis (FMECA). Fault trees describe the outage logic based
on the functional analysis. Event trees clarify the
consequences of the primary events and the criticality of
these consequences is expressed as a system downtime. The
existing database is very limited, so extrapolation of data
from other technologies cannot be avoided. |
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Superconducting
Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ closed-loop coils
carrying persistent current at temperatures above 77
K
Z. Han, P. Vase, Y.Q. Shen and
T. Freltoft
Summary: We have succeeded in
producing superconducting closed-loop coils from Bi/sub
2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ tape. These coils can be
operated in a persistent current mode even at temperatures
above the boiling point of liquid nitrogen. The persistent
current density value has been deduced to be 600 A/cm/sup 2/
at 77 K and the current has been estimated to run for 10/sup
16/ years. The persistent critical current density in our
coils was about one order of magnitude smaller than the
critical current density value determined by a 1 /spl mu/V/cm
criterion. The decay behaviour of the current in the coils was
clearly separated in two regimes, an initial fast decay of the
order of minutes followed by a slow logarithmic-like decay. In
this paper, experimental results of the persistent current
density as a function of temperature and applied magnetic
field are also presented. |
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Current
decay evaluation of closed HTS coil
circuits
T. Kiyoshi, K. Inoue, M.
Kosuge, H. Wada and H. Maeda
Summary:
Persistent current mode operation of HTS coils is one
of the key technologies required for very high-field NMR
magnets composed of LTS and HTS coils. We prepared four closed
circuits which consisted of an HTS coil made of a single
conductor, a persistent current switch and their joints. Three
HTS persistent current switches were fabricated for this study
and they functioned well. The current decay behavior of the
four circuits was measured in liquid helium by monitoring the
magnetic field in the HTS coil with a Hall probe. One circuit
maintained 80 % of the initial current even after 50 hours. A
resistance less than 1.6/spl times/10/sup -11/ /spl Omega/ was
obtained in another circuit. The small resistivity of HTS
coils, caused by their small index number values, was thought
to accelerate the current decay. |
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High
voltage generation with a high T/sub c/ superconducting
resonant circuit
J.X. Jin, S.X.
Dou, H.K. Liu and C. Grantham
Summary: An
electronic resonant circuit is introduced with the
consideration of using an inductor made by a Ag-clad
(Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub 10+x/, HTS
wire. With this inductor, substantially higher voltages
compared with using normal copper winding inductor can be
built up by the circuit. Therefore this method can be used to
generate high voltages with the HTS inductor from a low
voltage source. An electronic controller has been built and
used for the testing, and the resonant circuit, using the HTS
inductor, is analyzed. |
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HTS
insert coils for ultra high field NMR
spectroscopy
D.W. Hazelton, M.T.
Gardner, J.M. Weloth, J.A. Rice, L.R. Motowidlo, Y.S.
Hascicek, H.W. Weijers, W.D. Markiewicz and S.W. Van
Sciver
Summary: In this paper we describe the
design, fabrication and test of a model high field insert
magnet utilizing react and wind BSCCO-2212 surface coated (SC)
tape conductors. An added central field of 1.2 T and 1.08 T
was achieved at 4.2 K over a technologically useful 50 mm
clear bore in applied background fields of 0 and 5.5 T
respectively, In addition, we report the results of high field
measurements to 17.5 T made on a double pancake coil module
fabricated using react and wind BSCCO-2212 powder-in-tube
(PIT) tape. The insert magnet and pancake coil modules are
part of a continuing effort to demonstrate the application of
HTS conductors for the generation of the high magnetic fields
required for NMR systems operating at the 1.0 GHz
level. |
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Performance
of coils wound from long lengths of surface-coated, reacted,
BSCCO-12212 conductor
M.S.
Walker, D.W. Hazelton, M.T. Gardner, J.A. Rice, D.G. Walker,
C.M. Trautwein, N.J. Ternullo, Xin Shi, J.M. Weloth, R.S.
Sokolowski and F.A. List
Summary:
React-before-wind surface-coated BSCCO-2212 is being
established as a relatively low cost HTS conductor for
practical applications. Quality tape is presently being
manufactured in lengths of 450 to 500 m at a cost estimated to
be 1/3 to 1/5 of the industry costs of BSCCO-2223
powder-in-tube tape. Robust, mechanically sound coils for
applications ranging from NMR insert magnets to transformer
windings are being made from this BSCCO-2212 tape. The coils
have performed consistently through test and thermal cycling
without degradation and operate as projected from short sample
measurements. A hybrid approach, which uses mainly BSCCO-2212
augmented by BSCCO-2223 conductor in the high radial field end
regions, is expected to halve the overall superconductor cost
for magnet systems. |
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Construction
and normal zone propagation analysis of high-T/sub c/
superconducting Bi(Pb)-2223/Ag class II coils and
magnets
Nghia Van Vo, Hua Kun Liu
and Shi Xue Dou
Summary: Once the production
of high quality long length Bi(Pb)-2223/Ag tapes have been
achieved considerations such as fabrication into practical
applications without degrading the performance of the tape
become the major issues. Here, the application involves the
construction of class II coils and magnets. The main problems
concerned are usually related to the winding procedures (e.g.
wind-react and react-wind), the insulating material, the
construction or stacking of coils if they are pancake-shaped
and the study of quench propagation parameters. This paper
investigates these issues in coil design and construction by
means of measurement techniques from small scale coils and
magnets made from high-T/sub c/ superconducting Bi(Pb)-2223/Ag
composite tapes. |
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Electrical
motor with bulk Y-Ba-Cu-O
pellets
P. Tixador, A. Tempe, P.
Gautier-Picard, X. Chaud and E. Beaugnon
Summary:
The interaction between a magnetic field and a
superconducting (SC) bulk sample produces not only levitation
forces but also transverse ones. They may be used in an
electromagnetic coupling device to transmit a torque or in an
electrical motor to produce a torque. The authors have
designed and built a disk type motor (vertical axial gap) with
a static three-phase armature resistive winding and a rotating
part composed of eight YBaCuO pellets immersed in a liquid
nitrogen vessel. The SC samples are melt textured using the
top seed melt texturing method. The armature winding is fed by
a power converter. Then the supplied frequency and the speed
of rotation are variable. The motor was tested in different
conditions and operated without magnetizing the SC samples. It
works in a way as a variable reluctance motor even if the
hysteresis behaviour of the SC pellets complicates the
operation. Other experiments were carried out magnetizing the
SC samples before their use as an inductor. The operation is
close then to a permanent magnet motor. The experimental set
up and the different tests are reported. |
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Magnetic
processes in hysteresis motors equipped with melt-textured
YBCO
T. Habisreuther, T.
Strasser, W. Gawalek, P. Gornert, K.V. Ilushin and L.K.
Kovalev
Summary: Several hysteresis motors
have been constructed with an output power up to 500 W at T=77
K. The rotors of these machines consist of melt-textured YBCO.
In this work, the authors present detailed investigations on
the magnetic processes in these rotors. Spheres were cut from
melt-textured YBCO and investigated by rotating in vector-VSM.
From these measurements, torque moments on the sample,
hysteretic losses and the slip between external field and the
sample can be calculated. The same dependence of the output
power on the magnetic field for the samples as for the
constructed motors can be derived. Influences of the critical
current density and the domain size can be separated by
changing the temperature. |
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Dynamics
of vibrating system containing HTS
damper
Yu.A. Bashkirov, L.S.
Fleishman, V.A. Malginov, O.L. Poluschenko and N.K.
Nizhelskii
Summary: A study was made of the
vibration characteristics of a model vibrating system with a
permanent magnet/HTSC damper. Both free and forced vibration
techniques were used. The damping factor was found to decrease
at small vibration amplitudes due to small flux penetration
depth at low applied oscillating fields. The HTSC samples
showed both hysteresis and flux-flow types of energy losses in
damping unit. The measured resonance characteristic was
typical of a nonlinear vibrating system. |
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Magnetic
gradient levitation using high-Tc bulk
superconductors
P. Ohsaki, M.
Takabatake and E. Masada
Summary: Magnetic
gradient levitation systems using high-T/sub c/ bulk
superconductors and iron rails have been studied by numerical
analysis of their electromagnetic field. This system enables
stable levitation, even at standstill, without active control,
by the flux pinning of the superconductors. Emphasis is put on
the analysis of the dependence of the levitation
characteristics on the critical current density in the
superconductor. Numerical analysis results show that
levitation characteristics are strongly dependent on the
critical current density. Bulk superconductors with a critical
current density higher than 2/spl times/10/sup 8/ A/m/sup 2/
are required for stable levitation and sufficient force can be
generated in the case of the system model considered in this
paper. |
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Eddy
current loss reduction of superconducting magnets for MAGLEV
with a multilayer superconducting
sheet
M. Arata, M. Kawai, T.
Yamashita, M. Fujita, T. Hamajima, Y. Sanada, A. Miura, M.
Yamaguchi, M. Yamaji, M. Terai and S.
Inadama
Summary: Superconducting conductors
and magnets used in the fields of power transmission,
generators, MRI, MAGLEV etc. experience AC magnetic fields
causing heat generation in the magnets' structure and AC
losses in the superconductors. Therefore, AC magnetic shields
with wide frequency range in high magnetic fields are
desirable to reduce heat generation within the cryogenic
region and increase system efficiency. This paper describes
the performance of a multilayer superconducting sheet as an AC
magnetic field shield, eddy current analysis of MAGLEV coil
and eddy current loss measurement of an R&D cryostat with
a superconducting magnet. Eddy current loss was reduced to
about one fourth of the loss level without a superconducting
shield. |
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Advanced
hysteresis model for levitating applications of HTSC
materials
I. Vajda and L.
Mohacsi
Summary: For the numerical
calculation of the magnetic field and forces between high
temperature superconducting (HTSC) materials and permanent
magnets (PM), an algorithm and a 2D finite difference computer
code have been developed. The superconductor has been treated
with its nonlinear DC magnetization curve. The model also
incorporates anisotropic HTSC materials with different
magnetization characteristics along the coordinate axes. The
magnetization curves are used as input characteristics for the
field calculations. The calculations may be carried out both
in the Cartesian and the cylindrical coordinate systems. The
HTSC and PM parts or elements may have arbitrary shapes within
the limits of the accuracy of the finite difference mesh. The
model includes both the field-cooled and zero-field-cooled
cases. The code is capable of simulating the movement of
either of the objects. |
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Stability
and losses of levitating superconducting disks and
cylinders
C. Navau and A.
Sanchez
Summary: The authors present a model
for calculating the levitation force, magnetic stiffness and
damping for a superconductor in the presence of the magnetic
field of a permanent magnet. Bulk and thin film shapes are
chosen for the superconductor. They compare the results for
both and conclude that, in general, the thin film shape
enhances the magnitude of the force while maintaining a good
stability and without increasing the losses associated with
small displacements. |
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Dynamic
properties of superconducting magnetic
bearings
T.A. Coombs, D.A.
Cardwell and A.M. Campbell
Summary: The
potential use of YBa/sub 2/Cu/sub 3/O/sub 7/ as an active
component in a magnetic bearing is being investigated.
Although the load bearing capacity is high and increases with
the square of the magnetic field trapped, the stiffness is
low. Both the stiffness and the levitation height are a
function of the loading history of the bearing. The authors
have been investigating the effects of dynamic loading such as
single large excursions from steady state loads and cyclically
applied loads such as vibrations. Since a superconducting
bearing has little inherent damping, cyclic loads applied at
or near its natural frequency can have catastrophic effects.
The information being gathered by the authors will be used to
enable these effects to be mitigated in the bearing design
process. |
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High-speed
magnetic rotor with HTS bearings for precision energy losses
investigation
A.A. Kordyuk and
V.V. Nemoshkalenko
Summary: The authors
investigated physical mechanisms for flux pinning and energy
losses due to inter- and intragrain flux motion by a
high-accuracy experimental technique that uses the levitation
effect. Low-power self-stabilizing magnetic rotors with HTS
bearings have been designed on the basis of the obtained
results, with rotational speeds up to 200,000 RPM. The low
energy consumption of the rotor enabled the determination of
the energy losses in any sample in alternating magnetic field
with an accuracy down to 10/sup -11/ W. By this method, the
authors investigated magnetic flux dynamics in Y-123 and
Bi-2223 granular superconducting samples and determined that
flux motion in a Y-123 sample is described by intragranular
thermally assisted flux flow with viscosity equal 8/spl
middot/10/sup -5/ kg/m/spl middot/sec. They have also studied
the frequency dependencies of energy losses for rotors with
nonideal magnetic symmetry and found optimization criteria for
rotor design. |
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Study
on vibration phenomena of superconducting magnets for
MAGLEV
T. Shudo, S. Nakagaki, T.
Uchida, T. Yamashita, H. Nakao, Y. Sanada, A. Miura, M.
Yamaji, M. Terai and S. Inadama
Summary: Heat
loads occur in the superconducting magnets for Maglev
applications due to vibration during train operation. To
control this heat load, it is necessary to understand the
vibration phenomena in the superconducting magnet. In this
study, vibration evaluation and control for superconducting
magnets were addressed from both experimental and analytical
approaches, and verification tests were conducted with a
prototype model. This paper describes verification results for
the prototype model and the results for an actual
superconducting magnet which was constructed based on the
prototype model. |
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Design
and fabrication of a high aspect ratio cable for a high
gradient quadrupole magnet
R.
Scanlan, A.D. McInturff, C.E. Taylor, S. Caspi, D. Dell'Orco,
H. Higley, S. Gourlay, R. Bossert, J. Brandt and A.V.
Zlobin
Summary: The Large Hadron Collider
interaction regions require quadrupoles with a 70 mm diameter
bore, a gradient of 250 T/m, and good cooling so that the
magnets can operate in a high radiation background without
quenching. In order to meet these stringent requirements, a
two-layer magnet with a high aspect ratio cable has been
designed. This cable utilizes the SSC inner and outer layer
strands, which have been optimized and are available in large
quantities. The initial design parameters for both cables are
15.2 mm width; the inner cable has 38 strands of 0.8 mm diam
wire and a keystone angle of 0.99 deg. The outer cable has 46
strands of 0.65 mm diam wire and a keystone angle of 0.69 deg.
These cables have been fabricated and then subjected to a
number of tests to insure their performance in the quadrupole.
These test results, including model coil winding studies,
electrical property measurements, and mechanical property
measurements will be presented. |
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Design,
fabrication and testing of a production line for TPX
demonstration conductor
K.P.
Hwang, P. Finkel, A. Wallace, G. Naumovich, J. Zbasnik and N.
Martovetsky
Summary: A complete production
line for fabricating CICC dummy conductor has been designed,
constructed and tested for TPX program. The line is capable of
producing up to 500 meters of CICC conductor and is scaleable
up to 1.5 km in length. The line consists of a payoff spool
for feeding cable inside the tubes, a welding station, a
drawing station which includes dies and a bull-block, and a
takeup spool. We have demonstrated the fabrication of the
conductors. Two types of conductor, one for TF and the other
one for PF coil have been produced The conduit materials are
Incoloy 908, which are formed from strips. The cables are made
from OFHC copper strands. The detail design, fabrication and
testing of each component of the system is presented in this
paper. |
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Experimental
study on current re-distribution and stability of multi-strand
superconducting cables
N.
Amemiya, H. Yonekawa, N. Tsuchioka and O.
Tsukamoto
Summary: Stability of multi-strand
superconducting cables against local disturbances should be
influenced by the current re-distribution among strands in
quench or recovery processes. The current re-distribution and
its influence on stability are examined experimentally with
two types of three-strand cable. One is made of chrome-plated
strands, and another is made of strands with bare-copper
surface. A heat pulse is applied to short part of a strand,
and normal voltage and current in each strand are measured.
The large contact resistance between strands in chrome-plated
cable affects the current re-distribution. The minimum heater
energy required for quench is measured. The experimental
results prove that the stability against local disturbances is
improved by the current re-distribution. |
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Stability
in the ventilated, cabled superconductor proposed for the Navy
SMES cable test apparatus
O.R.
Christianson, W.V. Hassenzahl and D.W.
Scherbarth
Summary: Improved superconductors
for SMES devices will be developed and tested in the Navy SMES
cable development program. To test these improved SMES cables,
Westinghouse Science and Technology Center is constructing a
background field coil for the SMES cable test apparatus that
will provide a magnetic field of up to 4 T on a 1.8 meter
diameter test specimen. The background coil superconductor
design operating point is determined by stability
considerations and the superconductor critical surface.
Stability ventilated, cabled superconductor proposed
background field magnet is reviewed in terms of cryostability,
current redistribution, and enthalpy stabilization of
surrounding liquid helium. |
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Calculation
of minimum quench energies in Rutherford
cables
M.N. Wilson and R.
Wolf
Summary: The Minimum Quench Energy (MQE)
of a conductor may give some indication about the likelihood
of training in magnets. We have used a numerical solution of
the heat flow equation to calculate the MQE of a single
superconducting wire and have found the results to be in good
agreement with experiment. This model was then extended to an
approximate representation of Rutherford cable by including
current and heat transfer between strands. Reasonable
agreement with experiment has been found, although in some
cases it appears that the effective thermal contact between
strands is greater than expected from electrical resistance
measurements. |
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Minimum
quench energies of Rutherford cables and single
wires
A.K. Gosh, W.B. Sampson and
M.N. Wilson
Summary: The stability of magnet
conductors may be characterized by their minimum quench energy
(MQE), i.e. the minimum energy pulse (of small extent and
short duration) needed to trigger a quench, Using small
graphite paste and epoxy heaters, we have measured the MQE on
a broad range of single wires and Rutherford cables as a
function of current, field, temperature and pulse duration.
Surface heat transfer to the helium plays an important role.
For the cables, we find that specially processed
'porous-metal' cables have by far the highest degree of
stability. Measurements are compared with
theory. |
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Rutherford
cables with anisotropic transverse
resistance
J.D. Adam, D. Leroy,
L.R. Oberli, D. Richter, M.N. Wilson, R. Wolf, H. Higley, A.D.
McInturff, R.M. Scanlan, A. Nijhuis, H.H.J. Ten Kate and S.
Wessel
Summary: Putting a resistive core into
the center of a Rutherford cable increases resistance between
strands in the crossover direction, which greatly reduces the
coupling currents, even when the resistance to adjacent turns
remains small. This allows one to improve stability by
soldering strands together or using porous metal, without
incurring a penalty of increased coupling. We describe our
manufacturing methods and an experimental measurement of
coupling. |
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Suppression
and control of coupling currents in stabrite-coated Rutherford
cable with cores of various materials and
thicknesses
E.W. Collings, M.D.
Sumption, S.W. Kim, M. Wake, T. Shintomi, A. Nijhuis, H.H.J.
Ten Kate and R.M. Scanlan
Summary:
Calorimetric and magnetic measurements of AC loss have
been performed on stabrite-coated Rutherford cable conforming
to the Large Hadron Collider (LHC) winding (28 strand)
specification, with the field directed either perpendicular to
the broad face (the face-on, FO, orientation) or parallel to
it (edge-on, EO). It was found that the insertion of a thin
metallic or insulating core into the cable suppressed the FO
AC loss under typical conditions by a factor of 10 and
rendered it practically insensitive to the application of cold
uniaxial stress (of up to about 78 MPa). The FO loss having
been suppressed, it could also be controlled (i.e. finely
adjusted) by changing the level compaction (by varying core
thickness at thickness) or external compaction (by changing
the overall thickness of the cable). Of course the EO loss was
much less sensitive to the presence of a core, the use of
which therefore enabled the FO and EO losses to be
independently adjusted. |
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Coupling
losses in cables for fusion application: influence of the
strand
J.L. Duchateau, T. Schild
and D. Ciazynski
Summary: The coupling time
constant of conductors for fusion magnets must be kept at a
sufficiently low value to minimize the temperature increase
related to the rapid field variations experienced by the
pulsed coils during a run. Some parameters such as the twist
pitches and the void fraction are well known to Influence the
coupling time constant. Another parameter which can play a
role is the strand itself through its electrical
characteristics. Two identical conductors can have very
different time constants and it is important to understand the
strand parameters which govern this effect. To demonstrate
that, several 36 strands subcables have been made with strands
coming from different companies and associated to different
manufacture processes (bronze Nb3Sn, internal tin Nb3Sn,
NbTi). As far as possible the other parameters of these cables
have been kept identical. Contact resistance and time
constants have been measured and compared for the different
samples. |
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HTS
SMES magnet design and test
results
S.S. Kalsi, D. Aized, B.
Conner, G. Snitchier, J. Campbell, R.E. Schwall, J. Kellers,
T. Stephanblome, A. Tromm and P. Winn
Summary:
This paper describes design, construction, and testing
of a 5 kJ superconducting magnetic energy storage (SMES)
magnet. This magnet was built by American Superconductor
Corporation (ASC) for Gesellschaft fur Innovative
Energieumwandlung und Speicherung (EUS) of Germany. The magnet
consists of a solenoidal coil constructed from a
silver-sheathed BiPb/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 2/O
(Bi-2223) conductor which was reacted before winding. The coil
is epoxy impregnated and cooled with single stage Gifford
McMahon (G-M) cryocoolers for operation at 100 A (DC) with
substantial AC components due to the frequent variation of
current (ramp-up and ramp-down.) The magnet was tested in
early spring of 1996 and was shipped to EUS in mid June. The
successful operation of this magnet illustrates that the
technology of cooling HTS magnets with G-M type cryocooler is
now fully established. The long-term operation of this magnet
at EUS will verify the reliability of HTS magnet system in
critical applications and will open future applications for
HTS in the area of SMES and other magnets. |
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Welded
splice design in a mid-size superconducting magnetic energy
storage system
Wei
Tong
Summary: The splice design is one of the
most important issues in the design of a superconducting
magnetic energy storage (SMES) system. A welded splice is made
by overlapping two sheath-free stabilized conductors and
welding at the sides of the contact interface. To achieve the
ultimate goal in the SMES reliability, one of the primary
concerns is the electrical resistance across welded joints
though high-purity aluminum (HPA) stabilizers. Highly
resistive welds could lead to conductor instability. This
paper addresses the splice design for a 30 MW, 1800 MJ
mid-size SMES system. The splices are required to transmit
current at the level of 16,000 A under the normal operating
conditions. Gas-tungsten arc welding has been chosen its the
joining method for its high reliability, high quality, low
distortion and low cost. The welding setup and welding
parameters mere determined for the present splice design.
Other design issues such as the splice protection, support and
cooling, have been also addressed. |
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Fabrication
of ITER Central Solenoid Model Coil inner
module
R. Jayakurnar, D. Gwinn,
B. Montgomery, J. Minervini, Chen Yu Gung, R. Randall, W.
Beck, R. Childs, E. Thibeault, B. Smith, T. Hycaj, J.
Wohlwend, D. Paganini, P. Gertsch, L. Hawley, G. Miyata, N.
Martovetsky, J. Zbasnik and R. Reed
Summary:
The US Home Team is responsible for the design and
fabrication of the inner module for the ITER Central Solenoid
Model Coil, to be installed and tested at JAERI, Japan. The
design of the coil has been completed and the fabrication is
being carried out. In the first phase, all the tooling for the
fabrication have been installed, facilities established,
process specification developed and materials procured. The
fabrication approach will be confirmed by various trials, and
fabrication of two full-size dummy layers. Following this, the
fabrication of the 10 layer module occurs between June 1996
and December 1997. The paper describes the tooling and
facilities, the process and supporting R&D. Progress in
the fabrication is reported. |
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High
temperature superconducting fault current limiter
development
E.M. Leung, I.
Rodriguez, G.W. Albert, B. Burley, M. Dew, P. Gurrola, D.
Madura, G. Miyata, K. Muehleman, L. Nguyen, S. Pidcoe, S.
Ahmed, G. Dishaw, C. Nieto, I. Kersenbaum, B. Gamble, C.
Russo, H. Boenig, D. Peterson, L. Motowildo and P.
Haldar
Summary: A near term high-temperature
superconductor (HTS) application is the fault current limiter
(FCL). This paper describes the development and testing of a
2.4 kV, 2.2 kA(RMS) fault current, 150 A(RMS) continuous
current, HTS FCL that uses a Bi-2223 Ag-based conductor. The
Lockheed Martin team, which included Southern California
Edison (SCE), American superconductor Corporation (ASC) and
Los Alamos National Laboratory (LANL), completed in October
1995 a two year Phase I program. This unit has undergone a
six-week extensive testing at SCE's Center Substation in
Norwalk, California. The unit's capability and test results
are presented. Plans for the construction of higher rating
units including a phase II program are outlined. Descriptions
of the underlying principle of a FCL and how it can benefit
the power utility industry are also presented. |
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Transient
analysis of HTS inductive fault current
limiter
M. Majoros, L. Jansak, S.
Sello and S. Zannella
Summary: High
temperature superconductors (HTS) have been considered for
current limiting devices based on the fast transition from the
superconducting state to the resistive one when the current
overcomes the critical current. Recent developments have shown
the feasibility of the inductive fault current limiters using
HTS in the form of hollow cylinders or stacked rings. In the
present work, an inductive fault current limiter consisting of
a primary copper winding, a HTS cylinder or ring as the
secondary winding and an iron core is analysed. A mathematical
model, taking into account the real current-voltage
characteristics of HTS as well as the nonlinearity of B(H)
(magnetic flux density as a function of field) curve of the
iron core, is proposed and solved. Some typical results are
presented and compared with experimental ones. |
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Performance
of a high-Tc superconducting fault current limiter-design of a
6.6 kV magnetic shielding type superconducting fault current
limiter
H. Kado and M.
Ickikawa
Summary: Superconducting fault
current limiters for electric power systems have been
researched. A magnetic shielding type superconducting fault
current limiter is developed in the authors' research on
superconducting fault current limiters. This limiter consists
of a copper primary winding, a superconducting cylinder, an
iron core and a control coil. The superconducting cylinder has
a Bi2212 thick film on a MgO substrate. The control coil
consists of some metallic rings, and the fault level can be
adjusted by changing the number of the rings. To design a
prototype limiter, the AC magnetic shielding and loss
characteristics of small models were measured. The prototype
limiter is 6600 V in rated voltage and 400 A in rated current.
The superconducting cylinder is 0.45 m in diameter and about 1
m in height. Only the superconducting cylinder was designed to
be cooled by liquid nitrogen. The experimentally manufactured
limiter is about 1.3 m in width, about 0.6 m in depth and
about 2 m in height. |
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Position
of quench initiation in 6 kV-200 A class superconducting fault
current limiter
H. Shimizu, Y.
Yokomizu, T. Matsumura, T. Kato, Y.J. Tang, T. Nagafusa and N.
Hashimoto
Summary: The authors have developed
a 6 kV-200 A class superconducting fault current limiter
(SC-FCL). The SC-FCL has eight co-axial coils connected in
order to minimize total inductance. In the present paper,
taking consideration of the self-magnetic field in the SC-FCL,
they discussed the position of quench initiation. They
calculated spatial profiles of the strength and the direction
of the self-magnetic field in the SC-FCL. As a result, the
self-magnetic field is applied to sections of the
superconducting cable (SC cable) in the transverse direction
(maximum value: 6.42/spl times/10/sup -4/ T/A). The connective
section between coils, however, suffers a magnetic field with
a longitudinal component of 3.34/spl times/10/sup -4/ T/A. In
the case of a short sample of the SC cable which was used for
the SC-FCL, the quench current levels were found to decrease
at the rate of 40 A per 0.1 T in a transverse magnetic field
and 100 A per 0.1 T in a longitudinal field. Taking these
results into consideration, the authors pointed out that the
quench may be initiated in the connective section between
coils, where the self-magnetic field is applied in the
longitudinal direction. |
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Development
of flux-lock-type fault current limiter with high-T/sub c/
superconducting element
T.
Matsumura, T. Uchii and Y. Yokomizu
Summary:
The present paper proposes a new the fault current
limiter (FCL), which consists of a high T/sub c/
superconducting (HTS) element, three coils wound on the same
core, and a magnetic field coil covering the HTS element. In
this FCL, the initial limiting current level can be controlled
by adjusting the inductances of the coils. Furthermore, an
external AC magnetic field is applied to the HTS element to
get higher resistance in the current-limiting phase. A
current-limiting experiment by a model FCL was carried out,
and the limiting performance of the FCL was observed. Both the
initial limiting current level and the limiting impedance
could be increased in this FCL compared with the corresponding
values of the HTS element itself. |
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Novel
design and operational characteristics of inductive high-Tc
superconducting fault current
limiter
Minseok Joe and Tae Kuk
Ko
Summary: A novel prototype of an inductive
superconducting fault current limiter with an iron core and an
air gap was fabricated and tested. If its impedance is not
high enough to limit the fault current, then destructive
damage occurs in the power system. The authors attained
magnetic saturation under the higher current by introducing an
air gap in the three-legged magnetic core. The fault current
was successfully limited to two times as much as the nominal
current without high fault current within 1/4 cycles at a 60
Hz source having an effective voltage of 70 V. |
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Electrical
application of high T/sub c/ superconducting saturable
magnetic core fault current
limiter
J.X. Jin, S.X. Dou, H.K.
Liu, C. Grantham, Z.J. Zeng, Z.Y. Liu, T.R. Blackburn, X.Y.
Li, H.L. Liu and J.Y. Liu
Summary: A
saturable magnetic core electrical fault current limiter (FCT)
designed with a high T/sub c/ superconducting (HTS) DC bias
winding is described. The HTS winding is prepared by using a
Ag-clad (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub O10+x/ HTS
wire. The limiting behaviour of this FCL is investigated, and
its electrical application is considered in an electrical
power transmission system. The results show that this FCL
limits fault currents effectively and is a possible solution
for reducing power system fault currents. |
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Stability
analysis of air-core superconducting power
transformer
H. Yamaguchi and T.
Kataoka
Summary: The air-core superconducting
power transformer is being investigated as a transformer
having the function of a shunt reactor. From the results of
the authors' previous analysis, the magnetic field acting on
the superconducting wires of an air-core transformer under
load includes the rotating component besides the alternating
component. Since this rotating component has a possibility of
affecting the wire stability, the influence should be
clarified. In this paper, a method of stability limit analysis
based on the instantaneous magnetic field calculation is
proposed. Quench tests of an experimental air-core
superconducting transformer are carried out, and the stability
limit of the air-core superconducting transformer is analyzed
by using the proposed method. From the results of the
analysis, it is seen that the load factor of the
superconducting wire, which is defined in this paper, is
almost the same regardless of the superconducting power
transformer load. |
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Current
limitation using high T/sub c/
materials
P. Tixador, O. Belmont,
E. Floch, J.M. Barbut, J. Noudem, L. Porcar, D. Bourgault and
R. Tournier
Summary: The superconducting (SC)
current limiter is one of the most attractive applications of
superconductivity because it is an innovative device without
any conventional equivalence. Following the emergence of ultra
low AC loss NbTi strands in the eighties, several devices have
been designed and built using these superconductors. The
discovery of high T/sub c/ materials has created numerous
potential applications such as particularly for current
limiters. The operation at higher temperatures and the very
different nature of the SC oxides compared to low T/sub c/
strands deeply modify the limitation process. The authors have
carried out some experiments to study the transition of high
T/sub c/ samples fed by voltages with the objective of making
a resistive limiter. The quench behaviour of sintered and
textured Bi compounds have been studied and compared. Grain
boundaries play a very important part in the limitation
process. The resistive transition seems to begin at the grain
boundaries. The complete resistive transition of the sample
has never been recorded. The propagation of the transition
from the resistive part to the entire sample is very low. To
overdrive the quench, a magnetic field has been applied. In
this paper, the results are reported to show the grain
boundaries role in the transition. |
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Current
limiting properties of superconducting YBa/sub 2/Cu/sub
3/O/sub 7/ films on various
substrates
R. Wordenweber, J.
Schneider, A.I. Zaitsev, R. Kutzner, T. Konigs and P.
Lahl
Summary: Nb-Ti wires of different
composition and metallurgical state have been studied near the
upper critical field (H/sub c2/) in an attempt to separate
H/sub c2/, the irreversibility field (H*) and the resistively
measured transition field (H/sub r/). For optimized
multifilamentary Nb-47wt.%Ti wire, we find that H*=10.2 T,
H/sub C2/ =10.8 T and H/sub r/=11.8 T at 4.2 K. The
transitions were studied by extended electric field vs.
current density curves, magnetization and small current
transport measurements. We found a strong correlation between
magnetization, bulk flux pinning (F/sub p/) extrapolation and
extended E-J curves for the value of H*, all giving H*=10.2 T.
We have also shown that the maximum in H/sub r/ occurs for
Nb-44wt.%Ti. |
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Study
of fault current limiter using YBCO thick film
material
D.J. Moule, P.D. Evans,
T.C. Shields, S.A.L. Foulds, J.P.C. Price and J.S.
Abell
Summary: A small scale inductive fault
current limiter has been designed, modelled and tested. The
device outlined in this paper utilises a simple ferrite E-core
arrangement. Electromagnetic analysis is used to predict its
performance and this has been subsequently compared with
experimental results. The merits of several different
arrangements of the components of the fault current limiter
are then outlined. Melt processed thick film YBa/sub 2/Cu/sub
3/O/sub 7-/spl delta// (YBCO) rings have been fabricated. The
thick films are in planar form, screen printed and fired on
yttria stabilised zirconia (YSZ) substrates. The
characteristics of the superconducting rings have been studied
and compared in the fault current limiter (FCL). |
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Quenching
of high-T/sub c/-superconductors and current limitation
numerical simulations and
experiments
M. Lindmayer and H.
Mosebach
Summary: Numerical simulations of
the combined thermal and electrical behavior have been carried
out to study the influence of inhomogeneities along the HTSC
length on the quenching behavior. A two-dimensional finite
difference method (FDM) has been used to investigate the
current-limiting performance of YBCO film with a critical
current density around 10/sup 6/ A/cm/sup 2/ on a ceramic
substrate, 1% of the length was assumed to have reduced
critical current and temperature. The equalization properties
of an additional thin conducting layer on the quench process
has been demonstrated for varying degrees of inhomogeneity.
Furthermore a sample of YBCO film was investigated
experimentally and compared to calculated data. The results of
the experiments show good agreement with the numerical
simulations. |
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Transmission
loss of prospective power transmission model system integrated
under superconducting
environment
H. Shimizu, Y.
Yokomizu, T. Kato, Y.J. Tang, T. Matsumura, Y. Kito, K. Satoh
and W. Satoh
Summary: The authors have
developed a "prospective power transmission model system
integrated under superconducting environment", abbreviated to
PROMISE, with a transmission capability of 6 kV-1000 kVA. The
PROMISE consists of a superconducting transformer (SE-Tr), a
superconducting fault current limiter (SC-FCL) and a
superconducting power cable (SC-power cable). These components
are cooled down at liquid helium (LHe) temperature, 4.2 K, in
a cryostat with a volume of 854 l. The paper indicates a
computing procedure of a total heat leak 4.2 K into the
cryostat and discusses transmission losses of the
superconducting electric power system, which evaporate the
LHe. P/sub leak/, core loss P/sub core/ of the SC-Tr and AC
loss P/sub ac/ in the superconductor were measured in the
PROMISE to be 43 W, 180 W and 50 W, respectively. The measured
P/sub leak/ agreed with the theoretical one. In the
superconducting power transmission system, the power to
operate the refrigerator for liquefying the evaporated helium
must be taken as the transmission loss. If the penalty factor
was 500, the transmission loss was estimated to be 137 kW and
took 13.7% of the transmission capability in the
PROMISE. |
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Properties
of freeze-dried Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+d/:
effects of Ag doping and analysis of powder-in-tube
tapes
T.A. Deis, N.G. Eror, M.
Lelovic, B.C. Prorok and U. Balachandran
Summary:
Low level doping (/spl les/1 atomic%) of Ag in Bi/sub
2/Sr/sub 2/CaCu/sub 2/O/sub 8+d/ was performed via
freeze-drying of nitrate solutions. Effects of Ag doping on
the c-axis lattice parameter, oxygen content and critical
temperature were monitored, Powder-in-tube tapes were
fabricated using both Ag-doped and undoped Bi/sub 2/Sr/sub
2/CaCu/sub 2/O/sub 8+d/ powders. Tapes were processed using a
partial melt heat treatment in flowing oxygen. The effects of
Ag doping on the critical current and microstructure were
investigated, specifically the Ag-Bi/sub 2/Sr/sub 2/CaCu/sub
2/O/sub 8+d/ interface region. |
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Effect
of heat treatments on superconducting properties of Nb/sub
3/Sn strands developed at GEC
ALSTHOM
C.E. Bruzek, P. Sulten,
E. Sirot, C. Kohler, P. Mocaer, F. Peltier and G.
Grunblatt
Summary: Two different Nb/sub 3/Sn
strands have been processed at GEC ALSTHOM using the internal
tin process. Conductors were composed with seven sub-elements,
made up with NbTa7,5wt% filaments, surrounded by a Nb/Ta
diffusion barrier to isolate the core from the copper shell.
Effects of 9 different heat treatments (HT) on superconducting
properties such as critical current densities, critical
temperatures, critical magnetic fields and hysteresis losses
have been investigated. The use of heat treatments adapted to
the strand design showed an increase in critical current up to
48% with only a slight increase in the level of hysteresis
losses. The low variation of losses is correlated to filament
locations and bridging distributions across the conductor
section. The critical current enhancement is achieved under a
more complete transformation of the filaments into Nb/sub 3/Sn
and also by the refinement of Nb/sub 3/Sn grains controlled by
particular conditions of germination. As a result, critical
current density Jc/sub nonCu/=800 A/mm/sup 2/ at 12 T with
hysteresis losses Q/sub nonCu/spl plusmn/3 T/=490 mJ/cm/sup 3/
have been measured. |
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Integrated
two stage dc SQUID-based amplifier with double transformer
coupling scheme
D.E. Kirichenko,
A.B. Pavolotskij, O.V. Snigirev, R. Mezzena, S. Vitale, A.V.
Beljaev and Yu.V. Maslennikov
Summary: The
integrated version of a two stage dc SQUID-based low frequency
amplifier has been designed, fabricated and tested. The value
of the gain of the applied flux d/spl Phi//sub SQ2//d/spl
Phi//sub SQ1/ in the range 30-70 and an overall
flux-to-voltage transfer factor d/spl Phi//sub SQ2//d/spl
Phi//sub SQ1/ as high as 3 mV//spl Phi//sub 0/ have been
obtained. An effective input inductance L/sub IN/ equal to 1.8
/spl mu/H, a current sensitivity 1.33 /spl mu/A//spl Phi//sub
0/, and an effective coupling coefficient k/sup 2//sub IN/
close to 0.1 have been found in the accordance with the
design. |
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PTF,
a new facility for pulse field testing of large scale
superconducting cables and
joints
B.A. Smith, J.R. Hale, A.
Zhukovsky, P.C. Michael, J.V. Minervini, M.M. Olmstead, G.L.
Dekow, J. Rosati, R.J. Camille Jr., Chen-yu Gang, D. Gwinn, F.
Silva, S.A. Fairfax, S. Shen, H.G. Knoopers, S. Wessel, H.J.G.
Krooshoop, O.A. Shevchenko, A. Godeke and H.H.J. Ten
Kate
Summary: A magnetic Pulse Test Facility
(PTF), in which samples of CICC electrical joints from each
ITER home team will be tested, has been fabricated at the MIT
Plasma Fusion Center under an ITER task agreement.
Construction of this facility has recently been completed, and
an initial test phase on the first CICC joint sample has
begun. PTF includes capabilities for sample currents up to 50
kA from a superconducting transformer developed by the
University of Twente, magnetic fields up to 6.6 T with ramp
rates to +1.5 T/s and -20 T/s, and a cryogenic interface,
supplying supercritical helium with flow rates to 20 g/s
through each CICC leg at controlled temperatures to 10 K and
pressures to 10 atmospheres. A sophisticated, multiple-channel
data acquisition system is provided to processed, digitally
recorded sensor signals from both the sample and the facility.
The facility is totally remote-controlled from a control room
through a fiber optic link, and qualified users worldwide are
afforded secured access to test data on a 24-hour basis via
the Internet. The facility has successfully exercised the
first joint sample over the ITER test spectrum with positive
results. |
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A
miniature SQUID magnetometer with direct read-out
electronics
V. Polushkin, M.
Wallis, D. Glowacka, A. Matthews and J.M.
Lumley
Summary: A novel miniature SQUID
magnetometer with direct read-out electronics has been
developed. A high flux-to-voltage transfer factor of up to
2500 mV//spl Phi//sub 0/ is achieved without additional
positive feedback (/spl Phi//sub 0/ is the flux quantum). A
flux resolution of 8/spl times/10/sup -7/ /spl Phi//sub
0//Hz/sup 1/2 /, corresponding to a magnetic moment
sensitivity of approximately 2/spl times/10/sup -2/0 Am/sup
2//Hz/sup 1/2 / has been measured. This magnetometer can be
used to study the dynamic magnetization properties (including
NMR and MRI) of micron and sub-micron size particles and for
high-resolution surface magnetometry. |
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Current-phase
relation of high-T/sub c/ bicrystal and step-edge Josephson
junctions
V. Zakosarenko, E.V.
Il'ichev, R.P.J. Usselsteijn and V.
Schultze
Summary: The real and imaginary part
of the rf impedance of a phase-biased weak link based on
YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films were investigated
experimentally at 77 K. The investigated weak links were
step-edge or bicrystal Josephson junctions incorporated into a
washer type superconducting ring with a small inductance
L=80...300 pH. The ring was inductively coupled to a tank
circuit with a resonant frequency of about 23 MHz. The phase
shift /spl alpha/ between the rf voltage and rf current
through the tank circuit was found to be a convenient measure
of the change of inductance of a weak link. From the
dependence of /spl alpha/ on the magnetic flux in the ring one
can deduce the current-phase relation I(/spl phi/)=I/sub c/
f(/spl phi/) of the weak link. The influence of thermal noise
on f(/spl phi/) was estimated numerically using a Gaussian
distribution of the noise amplitude. The experimentally
observed dependence /spl alpha/(/spl phi/) for the bicrystal
weak link can be sufficiently good described with f(/spl
phi/)=sin (/spl phi/) and with a reasonable value of the noise
amplitude. The step-edge junction shows remarkable deviation
from the sinusoidal current-phase relation. |
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Magnetic
separation of kaolin clay using a high temperature
superconducting magnet system
J.
Iannicelli, J. Pechin, M. Ueyama, K. Ohkura, K. Hayashi, K.
Sato, A. Lauder and C. Rey
Summary: A team
consisting of Aquafine, Sumitomo Electric and DuPont has
performed a successful magnetic separation for removal of
mineral contaminants from kaolin, a white clay used
extensively in paper processing, using an HTS magnet. The
magnetic separation tests consisted of removal of
ferromagnetic and paramagnetic mineral contaminants from five
different types of kaolin clays representing major kaolin
deposits worldwide. Tests were performed using both
conventional and HTS magnets operating at 2.0 T. In addition,
magnetic separation tests were performed at 2.5 T using the
HTS magnet. All post processed clays were analyzed using the
brightness tests in accordance with the TAPPI standard.
Results showed that at 2.0 T, conventional and HTS magnets
produce consistent brightness results while operating under
similar test conditions. Most important was the determination
that the higher magnetic field of 2.5 T, generated by the HTS
magnet, enabled higher clay slury throughput without loss of
quality. The details of the HTS magnet design and operation
and the results of the kaolin tests are briefly
discussed. |
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Characterisation
of YBCO bulk samples by local
AC-susceptometry
M. Zeisberger,
A.M. Campbell, W. Lo and D.A. Cardwell
Summary:
Melt processed HTSC bulk samples usually show a high
inhomogeneity. These inhomogeneities influence
application-relevant properties such as the levitation force
or the trapped field. In this contribution a technique is
presented which allows investigation of these inhomogeneous
properties. The measurements are performed by scanning the
sample surface with a small coil system and detecting the
first and third harmonic of the inductive response. The
critical current density j/sub c/ is calculated from the
measured signal using a modified critical state model. J/sub
c/-distributions yielded by this technique are
shown. |
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50-m
long HTS conductor for power
cable
S. Mukoyama, K. Miyoshi, H.
Tsubouti, M. Mimitra, N. Uno, N. Ichtyanagi, Y. Tanaka, M.
Ikeda, H. Ishii, S. Honjo, Y. Sato, T. Hara and Y.
Iwata
Summary: The long conductor fabrication
is one of key technologies to realize the High-T/sub c/
superconducting power cable. A 50-m long conductor was
fabricated by helically winding the High-T/sub c/
superconducting tape onto a former with a winding machine. The
conductor consisted of ten layers of Ag-sheathed Bi-2223 tape
which had a high critical current density of 10,000 A/cm/sup
2/ (at 77 K). AC losses and layer-by-layer current
distribution were measured, feeding AC current of 100 to 2,000
Arms to the conductor cooled by LN2. The results showed that
most of the current flowed in the outer layers where the
impedance was low, and that AC losses were remarkably reduced
by making the current distribution uniform. |
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A
125-180 GHz fixed-tuned SIS mixer for
radioastronomy
A. Karpov, J.
Blondel, P. Pasturel and K.H. Gundlach
Summary:
An ultra low noise fixed-tuned SIS mixer covering an
instantaneous band of 45% around 150 GHz has been developed
for radioastronomy. A new type of coplanar tuning circuit for
the SIS junction is introduced. The Nb/Al oxide/Nb junctions
are 2 /spl mu/m/sup 2/ with critical Josephson current density
of 4.2 KA/cm/sup 2/. The minimum DSB mixer noise is 11 K. The
minimum DSB receiver noise is 19 K, while the average noise is
25 K in the 130-175 GHz range with a 1 GHz IF band. A speedup
of the observations by a factor 2-3 is possible with the new
receiver at 30 m IRAM radiotelescope. |
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Noise
and gain in frequency mixers with NbN SIS
junctions
A. Karpov, B. Plathner,
J. Blondel, M. Schicke, K.H. Gundlach, M. Aoyagi and S.
Takada
Summary: We study noise and conversion
gain in the SIS mixers with Nb/MgO/NbN junctions at the
millimeter and submillimeter wavelengths in order to estimate
the possibility to extent the low noise operation towards the
theoretical limit of 4/spl Delta//h=2.4 THz. We present as
preliminary result the lowest achieved receiver noise with NbN
SIS junctions of 65 K with conversion gain of -6 dB at 162 GHz
and 230 K receiver noise with conversion gain of -10 dB at 306
GHz. The junction area is 2 /spl mu/m/sup 2/ and Josephson
critical current density is 1.4 KA/cm/sup 2/. The optimum
R/sub N//spl omega/C of NbN junction for mixers is estimated
as 600 GHz/V. In preliminary tests the junctions R/sub N//spl
omega/C is 10-20 time superior to the optimum and a
significant improvement of NbN SIS mixers may be expected. The
noise sources in the NbN SIS junctions are studied and a
possible mixer sensitivity improvement is discussed. The
thermal properties of the SIS NbN are studied. The frequency
limit of the low loss integrated tuning structure in NbN is
estimated as at least as 1.5 THz. |
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Author
Index (1996 - Part 1)
No author
information available
Summary: Not
available |
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