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| 1968 |
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Front Cover (1968)
No
author information available
Summary: Not
available |
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Table of Contents (1968)
No
author information available
Summary: Not
available |
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Special Section on Applied Superconductivity -
Preface (1968)
No author information
available
Summary: Not
available |
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Application of Quantum Superconductivity to a
New Kind of Instrumentation
J.E.
Mercereau
Summary: Under the proper
circumstances voltage can be developed across a superconductor
- this voltage V is the electromotive force induced by flux
flow through the superconducting material. Superconducting
thinfilm techniques have been developed to assure that this
flow is composed of individual flux quanta. These techniques
usually involve inhomogeneous superconductivity; the
inhomogenity either being artificially generated by flow
through a constriction (as a Dayem bridge) or intrinsic to the
material itself (as a deliberate spatial modification of
electron density, Notarys) . This resulting superconducting
structure may be thought of as a current controlled flux
valve-passing quanta /spl phi//sub 0/, at a rate v= V/spl
phi//sub 0//sup -1/. These flux valves have been incorporated
into various circuits leading to results similar to the
behavior of a Josephson Junction. In particular, inserting a
valve into a superconducting ring produces a device similar to
the Josephson Junction interferometer-highly sensitive to
magnetic field. These devices have been adopted into several
operating instruments: a differential magnetometer with a
one-second time constant and field sensitivity10/sup -10/G, a
digital magnetometer counting increments of 10/sup -7/ G at
10/sup 4//sec, and a voltmeter with a 10/sup -3/-set time
constant and sensitivity of 10/sup -14/ V. |
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Flux-Line Arrangement in Superconductors (Title
only)
U. Essmann
Summary:
Not available |
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Heat Transfer From Cylindrical Surfaces to
Liquid Helium I
K.R.
Efferson
Summary: Heat transfer from a
cyclindrical copper surface to liquid helium at 4°K has been
measured. The sample consisted of a horizontally mounted 3 mm
o.d., evacuated glass tube, 6.5 cm long, onto which was
deposited a 2000 /spl Aring/-thick copper film. It was heated
by passing an electrical current through the copper film, and
the temperature was monitored by a carbon resistor attached to
the inside of the glass tube with varnish. In initial
experiments, large temperature fluctuations were observed in
the nucleate boiling region. These temperature fluctuations
disappeared when the sample was either close to the liquid
helium surface or when vertical walls were placed around the
sample. The large temperature fluctuations were probably due
to interactions of the convective flow of liquid helium with
the boundaries of the system (Dewar walls, liquid surface,
etc.). Similar temperature fluctuations were observed with a
stainless steel sample of approximately the same dimensions.
The peak heat flux obtained in the nucleate boiling regime was
0.98 W/cm/sup 2/ for Cu and 0.66 W/cm/sup 2/ for stainless
steel. |
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Superconducting Studies in A-15 Pseudo-Binary
Systems
R.D. Blaugher and N.
Pessall
Summary: Superconductivity studies
have been performed on some A-15 pseudo-binary systems to
determine whether low-temperature annealing, conducive to
atomic ordering, will markedly raise the superconducting
transition temperature. The following systems were examined
for this behavior: Nb/sub 3/Ge-Nb/sub 3/AI, Nb/sub 3/Sn-Nb/sub
3/Al, and Nb/sub 3/Ga-Nb/sub 3/Al. Greater attention was
devoted to the Nb-Al-Ge system in view of the recent
observation of superconductivity above 20°K in this system. We
have also observed transition temperatures approaching 20°K in
nearly single phase samples of Nb-Al-Ge after low-temperature
heat treatment at 700° and 800°C. It is suggested that
crystallographic long-range ordering is responsible for the
high T/sub c/'s observed in this system. Attempts to confirm
this hypothesis by determining the degree of long-range order
were unsuccessful. The other A-l5 systems which we
investigated also exhibited an increase of T/sub c/ with
low-temperature heat treatment; however, none exceeded
18°K. |
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Magnetoresistance of Copper at 4.2/spl deg/K in
Transverse Fields up to 100 kG
M.G.
Benz
Summary: Many high-field superconducting
systems make use of copper as part of the conductor
configuration. Copper is present primarily because it combines
low resistance with moderately high strength. As copper is
exposed to high transverse magnetic fields its resistance
increases. This resistance increase, or magnetoresistance, has
been experimentally measured for several different grades and
tempers of commercially available copper at 4.2/spl deg/K and
in the field range from 0 to 100,000 G. Zero field-resistance
ratios varied from 60 to 1,200 due to ditfering degrees of
purity and amounts of cold work. The results of these
measurements fit a normalized equation of the type which gives
the fractional change in resistance as a function of
transverse field and zero field-resistance ratio. The
mechanical properties for these samples have been measured at
room temperature and 4.2/spl deg/K and the yield stress
correlated with the resistance properties. |
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Prediction of Transient Stability Limits for
Composite Superconductors Subject to Flux
Jumping
Y. Iwasa, C. Weggel, D.B.
Montgomery, R. Weggel and J.R. Hale
Summary:
A computer model is described which is capable of
predicting the maximum current, the "threshold current", which
can be carried without quenching a Nb-Ti copper composite
superconductor undergoing flux jumping. The model utilizes
standard equations governing the generation and flow of heat
in a wire to predict its voltage-versus-time response as a
function of current. Calibration of the model for any specific
thermal environment is done by means of a simple test
procedure involving measurement of the response following the
triggering of a flux jump in a small noninductively wound
solenoid of one to four layers. The combination of theoretical
and experimental techniques indicates the value of adequate
copper cross section and good thermal environment, and
suggests the superiority of porous fabric or cadmium foil over
more conventional interleaving materials, and of thin
insulation over the alternatives of thick insulation or none
at all. |
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Critical Fields of Nb/sub 3/Al/sub 1-x/Ge/sub x/
Alloys in Liquid H/sub 2/
S. Foner, E.J.
McNiff Jr., B.T. Matthias and E. Corenzwit
Summary:
Critical field H/sub c2/ vs temperature measurements
have been completed in pseudo-binary, /spl beta/-W structure,
Nb/sub 3/Al/sub 1-x/Ge/sub x/ (0.25 /spl les/ x /spl les/0.3)
compounds with both contactless rf and transverse dc
resistance measurements. Extrapolation of H/sub c2/(T) vs T
above 20 kG yields T/sub c/= 20.7/spl deg/K. This T/sub c/ is
confirmed by zero-field specific heat measurements. H/sub
c2/(T) vs T is almost linear from T/sub c/ to 14/spl deg/K,
indicating that paramagnetic limiting is almost completely
suppressed. H/sub c2/(14/spl deg/K) /spl sime/200 kG is
observed for the T/sub c/= 20.7/spl deg/K material.
Extrapolated H/sub c2/(0) values are deduced from the high-T
data and compared with other physical parameters of the
earlier T/sub c/= 20.05/spl deg/K superconducting materials.
These new superconducting materials show potential compared
with V/sub 3/Ga and Nb/sub 3/Sn, particularly in the
liquid-H/sub 2/ temperature range, if practical wires can be
developed. A brief summary of the properties of these alloys
was presented at the Eleventh Inter national Conference on Low
Temperature Physics and more detailed results will be
published elsewhere. |
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Preparation of Superconducting Compounds by the
Co-Condensation in Vacuum of the
Elements
H. Hammond, D.P. Snowden, C.H.
Meyer Jr, J.H. Pereue Jr. and G.M. Kelly
Summary:
The method of co-condensation of the elements from
separate sources in vacuum to form intermetallic compounds has
been used to make high current density superconducting
ribbons. Evaporation rate monitors and control loops have been
developed that allow control of the compound composition. The
technique has been used to make continuous lengths of ribbon,
and a number of compounds have been tested, Nb/sub 3/Sn in
particular. The condensation conditions are suitable for the
fabrication of a microstructure consisting of alternate layers
of compound superconductors and other materials, including
normal metals and dielectrics. The microstructure assists in
the pinning of transport currents in the presence of
transverse magnetic fields, and in some apparent inherent
stability against flux jumps. |
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Heat Transfer to Superfluid and Supercritical
Helium (Title Only)
V.D.
Arp
Summary: Not available |
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Anisotropic Flux Pinning in Superconducting
Niobium Single Crystals (Title Only)
I.
Williams and A.M. Court
Summary: Not
available |
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Fabrication of Niobium Rf
Cavities
R.W.
Meyerhoff
Summary: A new process for
fabricating niobium rf cavities for use in beam separators and
linear accelerators is described. The best performance to date
for a cavity made by this process was obtained with a TE/sub
011/ mode cavity, operating at 11.2 GHz at a peak magnetic
field of /spl sim/500 G, for which Q/spl ap/2X10/sup 10/. The
principle advantages of the process described over other
methods of fabricating niobium rf cavities are the following.
First, a multiplicity of integrally connected cavities can be
fabricated in a single joint free section. Second, the
finished niobium cavities have a very high-quality surface
iinish which is produced without the need of mechanical or
chemical polishing the cavities after fabrication Third, the
niobium in the completed cavity is ultrapure and thus has an
extremely low normal state resistance at liquid helium
temperatures. Fourth, a high thermal conductivity between the
niobium on the inside of the cavity and the surrounding liquid
helium bath can be obtained when the niobium is supported with
porous tungsten. |
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Automatic Tuning of a Superconducting Cavity
Using Optical Feedback
J.L. Stone, W.H.
Hartwig and G.L. Baker
Summary: The resonant
frequency of a superconducting cavity has been
photodielectrically controlled by a feedback loop which
contains an optical path. The cavity is an 870-MHz lead-plated
quarter-wave reentrant structure. A 19,000 /spl Omega//spl
middot/ cm silicon wafer terminates the quarter-wave stub. The
loaded Q is approximately 10/sup 5/ indicating the losses in
the semiconductor dominate the superconducting surface
resistance. The high Q provides a large phase error between
the input and output voltage when the driving oscillator
drifts or is modulated away from the very stable resonant
frequency of the cavity. The error is processed by a
wide-bandwidth phase detector that drives a gallium arsenide
diode to follow the frequency excursion of the oscillator by
photodielectric tuning. The 9000 /spl Aring/ light is the
optical feedback signal which corrects the phase error. The
system response typically provides a frequency deviation of
/spl plusmn/50 kHz at a 0.2 MHz rate. Higher cavity frequency
and purer semiconductor samples extend the deviation limits
and shorter free-carrier lifetimes increase the speed of
response. |
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Use of Superconducting Cavities to Resolve
Carrier Trapping Effects in CdS
W.H.
Hartwig and J.J. Hinds
Summary: The excellent
frequency stability and cryogenic environment of a
superconducting resonant cavity provides a sensitive method
for observing trap-filling in CdS and similar materials. When
used with thermally stimulated conductivity and dc
photoconductivity, it is possible to solve for trap energy,
capture cross section, density of trap states, and
free-carrier lifetime. The technique is that used by Arndt,
Hartwig, and Stone to observe optically induced changes in the
complex dielectric constant by inertia forces on free carriers
in Si and other indirect-gap semiconductors. Using TSC, pure
CdS crystals showed very weak trapping effects and CdS:Al
displayed electron traps at 0.52,0.35, and a group at 0.265,
0.20, and 0.15 eV. A quenching, or hole trapping, level was
seen at 1.6 eV below the conduction band. Deep electron trap
densities were about 10/sup 15/ cm/sup 3/ and the shallow set
was about 10/sup 17/ cm/sup -3/ each. Hole trap density was
slightly in excess of 10/sup 18/ cm/sup -3/. In CdS: Al, the
photodielectric frequency shift of an 840 MHz cavity was
proportional to the integral of photon flux, indicating the
effect was caused by polarization of electrons in traps.
Photodielectric data yielded an effective trap energy for the
three shallow levels at 0.176 eV and a total density of
3X10/sup 17/ cm/sup -3/. Density of trapped electrons is
calculated from frequency change. Capture cross section for
the shallow levels was about 10/sup -14/ cm/sup 2/. Additional
data from dc photoconductivity provide free-carrier lifetime
and location of the electron Fermi level as a function of
filled trap density. CdS:Al displays a "tap" effect which can
erase the accumulated frequency change without
warming. |
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Measurements of the Kinetic Inductance of
Superconducting Linear Structures
R.
Meservey and P.M. Tedrow
Summary: The kinetic
inductance L/sub k/ is associated with the inertial mass of
the current carriers. For a long superconductor of length I
and very small cross-sectional area /spl sig/, L/sub k/=
(m*/n/sub s/e*/sup 2/) (l//spl sig/) and is the main
contribution to the temperature-dependent. inductance L/sub
T/. We have measured L/sub T/ in superconducting tin wires and
thin film meander lines by a technique which uses a counter to
determine frequency changes of a 15 MHz tunnel-diode
oscillator whose tank circuit contains L/sub T/. The measured
frequency changes are proportional to z= [/spl lambda/(t)
//spl lambda (O)] /sub BCS/ for wires and thick films; for
thin films the frequency changes are proportional to z/sup 2/.
This result agrees with calculations of L/sub T/ from the
London theory and the values of /spl lambda/(0) agree well
with the values expected for these samples. This technique
allows measurement of the carrier concentration or penetration
depth in thin films over the whole H, T plane of the
superconducting state and can be independent of the
penetration law assumed. Frequency shifts observed with thin
film alumimum meander lines have been used to detect changes
of temperature of 5/spl sim/10/sup -7//spl deg/K, changes of
magnetic field of 10/sup -5/ G, and changes of current
associated with one quantum in a flux quantum
magnetometer. |
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Superconducting
Antennas
G.B. Walker and C.R.
Haden
Summary: A high-efficiency electrically
and physically small superconducting antenna is reported.
Antenna factors and matching circuit equivalents are
developed. Theoretical predictions of efficiency and Q
increase are derived on the basis of the superconducting
surface resistance of lead. The antenna is a loop supsended
through a ground plane and matched through a symmetrical
coaxial cavity having a resonant frequency of 400 MHz. The
loop is lead-plated and has an open area of approximately 1
cm/sup 2/. Coupling to the system is achieved through a
movable electric-field probe inserted into a slot in the wall
of the matching cavity. A normal-state electrically small
antenna of this size has a theoretical efficiency of less than
1% due to the fact that the loop resistance is much larger
than the equivalent radiation resistance. Upon cooling to
4.2/spl deg/K, the Q of the system increases to 20,000 from a
room-temperature value of 156, indicating limitation by the
radiation resistance only. The power radiation efliciency
increases by a factor of 500, as measured bv a fixed external
receiving svstem. The VSWR of the system is maintained near
unity in order to avoid the complications of
mismatching. |
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Slow-Wave Structures Utilizing Superconducting
Thin-Film Transmission Lines
P.V. Mason
and R.W. Gould
Summary: Slow-wave propagation
of electromagnetic waves in’transmission lines formed of
thin-film superconductors has been studied theoretically and
experimentally. Previous theoretical analyses have been
extended to include nonlocal theories. Strong dependence of
phase velocity is found on film thickness and interfilm
spacing when these become less than a few penetration depths.
Velocity is also modified by coherence length, mean free path,
nature of reflection of electrons at the film surfaces, and by
temperature and magnetic field. Experimental measurements were
made to verify the dependence on thickness, spacing, and
temperature by means of a resonance technique. Agreement with
theory was excellent in the case of temperature. Data taken
for varying thickness and spacing verified the general trend
of theoretical predictions. They indicate a nonlocal behavior
with some specular reflection, but scatter of the data taken
for different films prevents precise comparison of theory and
experiment. Estimates of bulk penetration depths were made for
indium, /spl lambda//sub In/=648/spl plusmn/130 /spl Aring/.
For tantalum a rough estimate could be made of /spl
lambda//sub Ta/=580 /spl Aring/. Data were consistent with the
estimate of coherence length for indium of /spl xi//spl
ap/3000 /spl Aring/. Velocity was found to be independent of
frequency in the range 50-500 MHz, while losses increased as
the square. Pulse measurements indicated that delavs of
several microseconds and storage of several thousand pulses on
a single line are feasible. |
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Tuning Superconducting Microwave
Cavities
T.I. Smith
Summary:
The extremely high Q of superconducting microwave
cavities makes them very attractive for use in many
applications. In some of these applications the resonant
frequency of the superconducting cavity must be adjustable
while the cavity is at liquid-helium temperatures. Because of
the requirement that the losses in the tuning mechaaism be
very low, in order that the Q of the cavity not be degraded,
the usual methods of tuning microwave cavities are not always
applicable to superconducting devices. One example of a case
in which new techniques have had to be developed is the
superconducting linear accelerator which is being constructed
at Stanford University. In this accelerator, 25
superconducting sections, each 20 ft long, will have to
resonate at the same frequency to within about 1 part in
10/sup 8/. The sections are being constructed to be tunable at
liquid-helium temperatures over a range of 1 part in 10/sup/4,
with a resolution of 1 part in 10/sup 4/. |
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Multiresonator Superconducting Band-pass and
Band-Reject Filters (Title Only)
F.
Arams, R. Domchick, K. Siegel, R. Sleven, J. Taub and N.
Worontzoff
Summary: Not
available |
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AC Energy Losses Above and Below H/sub c1/ in
Niobium and Niobium-25 at. % to
Zirconium
W.T. Beall Jr. and R.W.
Meyerhoff
Summary: Calorimetrically
determined energy losses for a series of niobium and
niobium-25 at.% zirconium samples carrying an af transport
current agreed with those calculated from hysteresis loops
determined by dc magnetization measurements. The results of
this study showed that the energy losses in ultra-high-purity
annealed Nb are less than those for any of the other samples
studied at magnetic fields less than 1500 G. The magnetic
field dependence of the energy losses in all of the samples
studied is given by EL= E/sub 12/h/sup m/, where EL is the
energy dissipated per unit surface area per cycle and is
independent of frequency, E/sub 12/ is a constant which
depends on the material and surface finish, and h= H/sub
p//H/sub c1/, where H/sub p/ is the peak ac field amplitude,
and H/sub c1/, is the lower critical magnetic field; m=
n/sub1/ when h /spl les/ 1, and m =n/sub 2/ when h /spl ges/
1. For both highly reversible and highly irreversible samples,
n/sub 1//spl sp/3. For the least reversible samples, n/sub
2//spl ap/4, increasing to /spl sim/8 for the most reversible
samples studied. E/sub 12/ generally increased with decreasing
reversibility and was strongly dependent on the surface finish
of the sample, increasing as the surface roughness increased.
The power loss PL per unit surface area is given by PL=
(EL)/spl conint/. This linear frequency dependence is
consistent with a hysteretic loss mechanism as is the
agreement between the calorimetrically determined losses and
those calculated from the measured hysteresis
loops. |
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Steady-State Performance of Multistrand
Superconducting Compound Conductors
W.F.
Gauster
Summary: A careful numerical analysis
of a measured steady-state I-V (current-voltage)
characteristic of a superconducting compound conductor with
very fine strands is reported. The actual, nonlinear heat
transfer from copper to the helium bath is considered. It is
shown that in the current-sharing state the flux flow
resistance of the superconductor, R/sub f/, increases from
zero to values much greater than the copper resistance, R/sub
cu/. For R/sub f//spl sim/R/sub cu/, the superconductor
current I/sub 8/, is a function of the field H, the voltage V,
and the temperature T/sub b/. For R/sub f/>>R/sub cu/,
I/sub 8/, is a function of H, independent of V, and a linear
function of T. The value of this function extrapolated to the
bath temperature T/sub b/ is appreciably greater than the
critical current. In the absence of flux jumps, the
current-sharing state should be terminated by the steady-state
condition dI/dV= 0. The actual "take off" (sudden transition
into the normal state) observed, however, took place below the
mentioned steady-state limit and before the transition from
nucleate to film boiling. The new findings on the steadystate
performance of compound conductors with very thin strands make
essential modifications of the usual theoretical approaches
necessary. It is shown how the new approach can be applied to
compound conductors with thick filaments. |
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Steady-State Flux Jumping in Superconducting
Niobium Titanium Tubes in Superimposed ac and dc Magnetic
Fields
D.A. Gandolfo, L. Dubeck and F.
Rothwarf
Summary: Steady-state flux jumping
has been observed for a thin-walled tubular sample of NbTi
subjected to coaxial superimposed ac and dc magnetic fields.
By steady state we mean flux jumping which occurs reproducibly
each cycle. The magnitude /spl utri/h of the field shielded by
a sample in the critical state decreases with increasing field
rate. A rate-dependent effective resistivity pen that exists
just prior to a given flux jump has been calculated from /spl
utri/h and the field rate. It is found that /spl rho//sub eff/
increases nonlinearly to a value of about 5X 10/sup -9/ /spl
Omega//spl middot/cm at h=7X 10/sup 5/ Oe/sec in a background
field of 10 kOe. Such a /spl rho//sub eff/ is characteristic
of the flux-creep state. |
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Theory of Electrical and Thermal Stability of a
Superconductor in the Resistive State
A.
El Bindari
Summary: The problem of electrical
and thermal stability of a superconductor when carrying a
steady-state transport current beyond the critical current has
been analyzed for a bare superconductor. The following
relation is derived v = I (I- 1) /l - /spl theta/I/sup 2/,
where u is the nondimensional voltage, I is the current in
units of the critical current, I/sub c/, of the
superconductor, and /spl theta/ is a parameter involving only
the constants of the superconductor, and the heat transfer
coefficient of the cooling medium. To have a reversible
voltage current characteristic beyond the critical current,
the parameter /spl theta/ should be <<1. Factors
affecting this parameter are analyzed. The influence of this
parameter on the propagation of a resistive front is
discussed. Furthermore, the influence of a normal metal in
good electrical and thermal contact with the superconductor is
also included. |
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Comparison Between Measured Critical Currents
and a Model of Transiently Stabilized Nb/sub 3/Sn
Magnets
E.R. Schrader
Summary:
A previously proposed model used to predict transient
stabilization in high-current superconductive solenoids is
assessed in the light of results on actual test magnets made
with a variety of fabrication parameters. The possibilities
for the use of the model is discussed with reference to the
missing elements and when considering special "short-sample"
measurements on thermal propogation characteristics and
magnetization characteristics. Results of recovery-current
tests are presented. |
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Coupling of (Ti-Nb) Filaments in a
Superconducting Multifilament Composite
Conductor
A.D.
McInturff
Summary: Magnetization measurements
were performed on variously prepared samples of multifilament
(Ti-Nb) and Cu composites. All measurements were performed at
4.2/spl deg/K, utilizing peak magnetic fields of 50 kG. The
magnetization data were obtained in a manner similar to that
described in earlier papers. The impetus for these particular
measurements was the hypothesis of P. F. Smith in regard to
the coupling of the small filaments of superconductors when
they are embedded in a low-resistivity matrix such as Cu. This
coupling, of course, is a function of /spl part/H/spl
alpha///spl part/t, but for very long lengths (e.g., magnets),
or even short lengths in the case of well annealed Cu, the
time constant for the decoupling is extremely long. The
coupling, it was suggested by Smith, could be reduced by
increasing the resistance of the matrix material, and then
twisting the composite, the equivalent of "transposition" of
the individual filaments in a two-dimensional case. Various
resistance layers are formed around each strand by the proper
heat treatment of these multifilament composites. The
filaments of the sample composites were found to be decoupled
to varying degrees depending on applied magnetic field, sample
length, and matrix resistivity. |
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Loss Measurements on Twisted Multifilamentary
Superconducting Wires
P.F. Dahl, G.H.
Morgan and W.B. Sampson
Summary: Measurements
have been made on the energy losses produced during pulsed
operrltion, of several superconducting magnets. The coils were
made from NbTi wires with solid and multifilamentary cores and
pulsed to approximately 2.5 kG. A comparison was made between
the losses produced in magnets made from the two types of
conductor. The multifilamentary wire was tested first with the
filaments straight, and then after the wire had been twisted
with a pitch of 2 turns/cm. The losses for both the solid core
and the untwisted multicore conductors were essentially
identical and increased as the cube of the maximum field. The
losses in the magnet made from the twisted material showed a
drastic reduction at high fields with the loss varying as the
first power of the maximum field. |
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Dynamic Stabilization Against Flux Jumps for
Structures Wound from Composite Superconductor-Normal-Metal
Tapes
H.R. Hart Jr.
Summary:
Magnetic instabilities or flux jumps are responsible
for many of the difficulties which have accompanied attempts
to realize the full potential of high-field superconductors in
magnet construction. Superconducting windings will be
dynamically stabler against flux jumps if the flux motion
following a disturbance is sufficiently damped by a pure
normal metal and if the superconductor is cooled well enough.
The critical-state model has been used in developing the
criteria for dynamic stability for a geometry approximating a
magnet winding formed of a composite
superconductor-normal-metal tape. It is found that there are
two classes of dynamic stability requirements; both must be
met: (i) The thickness of the superconducting layer in the
composite tape must be smaller than a critical value which is
derived. (ii) The winding formed from layers of a wide
composite tape tends to exclude (and trap) the component of
magnetic field which is perpendicular to the plane of the
tape. The winding thus acts much like an anisotropic bulk high
field superconductor and is likewise subject to flux jumps.
The dynamic stability requirements for this composite
structure are derived and discussed. Experimental results
obtained with simple geometries are used to illustrate the
main conclusions. |
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Use of a Superconducting Modulator in a
Voltmeter with 10/sup -12/ V
Resolution
R.J. Erdman
Summary:
Various methods of measuring low dc voltages at
cryogenic temperatures have been used for purposes of
investigating thermoelectric properties, resistive dependence
on various parameters, superconducting phenomena, and other
effects. These generally involve resolution on the order of
10/sup -12/ V or less and source resistances on the order of
10/sup 6/ /spl Omega/ or less. A voltmeter suitable for this
type of work is described. The instrument employs a
superconducting parametric amplifier modulator described by
Ries and Satterthwaite as a null sensing element in a feedback
system. The modulator consists of a tuning fork which creates
a time-varying mutual inductance between 2 sets of
superconducting coils. The system equations and experimental
data indicate that for low source resistance the accuracy and
time constant of the voltmeter are essentially independent of
source resistance. The noise is less than 10/sup -12/ V and
the time constant is about 1.5 set for source resistances of
zero to 3X10/sup -7/ /spl Omega/. The modulator is well suited
for production, and is quite insensitive to operating
temperature and vibration. The voltmeter has reliability and
repeatability typical of commercial room-temperature
instrumentation. |
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Frequency Dependence of the Skin Depth in
Superconducting Tin
J.
Matisoo
Summary: The first measurements of
the frequency dependence of the real part of the
superconducting skin depth /spl delta/(v, t) , in
polycrystalline tin films, are reported using a new technique
of measurement. The technique similar to the usual cavity
technique, except that the cavity in question is a rectangular
Sn-SnO/sub x/-Sn Josephson tunnel junction. The cavity is
self-excited via the ac Josephson effect; the resonant
frequencies of the cavity are measured from which /spl
delta//sub r/(v, t) is deduced. The measurements extend from
0/spl les/v/spl les/220 GHz and 0.5/spl les/t/spl les/0.952.
The results are compared with Miller’s calculations of /spl
delta//sub r/ for Sn, which are based on the Mattis-Bardeen
theory and are found to be in agreement for t/spl les/0.800.
Above this temperature only qualitative agreement exists
because the assumptions under which the calculations were made
are here only partly satisfied. |
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Frequency and Time Domain Analysis of a
Superconductive Coaxial Line Using the BCS
Theory
W.D. McCaa Jr. and N.S.
Nahman
Summary: A miniature superconductive
lead-teflon-niobium coaxial line has been analyzed in terms of
the complete BCS theory of superconductivity. The surface
impedance of both superconductors, the line attenuation, the
picosecond step responses have been calculated for a
temperature of 4.24/spl deg/K. The dielectric has been assumed
lossless. In addition, the frequency, time domain responses
obtained with the BCS theory are compared with those predicted
in 1968 by McCaa, Nahman for the same line parameters by the
two fluid model. |
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Persistent Current Magnetometer Utilizing a
Vibrating Superconducting Plane to Shuttle
Flux
J.E. Opfer
Summary:
A technique that has been developed to fabricate
niobium thin film microcircuits is described. This fabrication
technique has been employed in making a 125-cm long
superconducting inductance element that is 10/spl mu/ wide and
is contained in an area 0.5 cm on a side. A superconducting
niobium ground plane vibrating near the inductance element at
a frequency of 100 kHz has been used to shuttle magnetic flux
into and out of a superconducting loop connected in series
with the inductance element. The suitability of this method of
flux shuttling to the measurement of very small, steady
magnetic fields is considered in detail. |
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Thin Tin Superconducting Films as High-Speed
Radiation Detectors (Title Only)
C.L.
Bertin and K. Rose
Summary: Not
available |
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Results of Tests on an 8.8 Tesla, 51-cm-Bore
Magnet System
E.J. Lucas, Z.J.J. Stekly,
T. DeWinter, J. Laurence and W. Coles
Summary:
As an interim step in a program to build an 8.8 tesla,
51-cm-bore coil system, tests were run on four of the six
individual modules that comprise the system. These tests were
run on two modules wound with a stabilized reinforced Nb/sub
3/Sn strip and two modules wound with a stabilized NbTi
conductor. All of the modules were instrumented with heaters
to determine their stability characteristics. Data were taken
on the Nb/sub 3/Sn modules both at 4.2/spl deg/K and sub /spl
lambda/ temperatures while the NbTi modules were run at
4.2/spl deg/K only The performance of each module is discussed
and compared with the performance predicted from data
previously taken on small test coils. |
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Princeton Floating Multipole-Superconducting
Ring Progress
J. File, G.D. Martin, R.G.
Mills and J.L. Upham
Summary: Two independent
concentric Nb/sub 3/Sn rings carrying persistent supercurrents
have been successfully levitated and stabilized against the
slide instability. Isochoric Dewar operation has been
demonstrated with the ring stabilized against both the slide
and flip modes. The optical position sensors have been
improved. |
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Eight-foot-diameter 30-kG Superconducting Magnet
for the Brookhaven National Laboratory 7-foot Bubble
Chamber
A.G. Prodell
Summary:
An 8-ft-diam air-core superconducting magnet wound with
a superconductor-copper composite strip and capable of
generating a central magnetic field intensity of 30 kG has
been constructed at Brookhaven National Laboratory for a 7-ft
bubble chamber. The magnet, which has an over-all height of
7.5 ft, is installed in an annular Dewar contained with the
bubble chamber in a common vacuum envelope. Refrigeration for
the magnet system is supplied by a 240-W helium refrigerator
which can also be operated as a 60 liter/h liquefier. Details
of the magnet, of the cryogenic system, and of magnet test
results are given. |
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Pumped Helium Tests of a 51-cm-Bore Nb/sub 3/Sn
Magnet
W.D. Coles, G.V. Brown, E.H. Meyn
and E.R. Schrader
Summary: Performance data
are presented for tests of 51-cm-bore single coil and coil
pair magnets operated at temperatures below 2°K. The magnet
coils are wound of silver-plated, vapor-deposited Nb/sub 3/Sn
ribbon. Coil protection was provided by cross-layer shorting
strips which also provide very limited stabilization. Each
coil was designed to produce a 4.0-T center field. Results
obtained at the low temperature are compared with those
obtained at 4.2°K. System description and charging
characteristics are included in the discussion. |
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Comparison of NbTi and Nb/sub 3/Sn Quadrupole
Magnet Systems for IMP
D.L. Coffey, J.L.
Dunlap, W.F. Gauster and J.L. Horton
Summary:
IMP (Injection into Microwave Plasma) is a fusion
research device which will utilize a superconducting
mirror-quadrupole magnet system. The NbTi mirror coils have
been built, tested to short sample performance at 60 kG with
10/sup 4/ A/cm/sup 2/ over-all. Designs of the quadrupole
system using NbTi at 8500 A/cm/sup 2/, or alternatively using
Nb/sub 3/Sn at 13,500 A/ cma, have been examined. Anticipated
conductor costs favor NbTi, even though the volume of Nb/sub
3/Sn is significantly less. However, some details of
construction suggest that Nb/sub 3/Sn would result in easier
winding, possibly more reliable operation. Details of these
comparisons were given, along with discussions of electrical
stability, other technical differences in the two
approaches. |
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Critical Temperature of Some Persistent Nb/sub
3/Sn Coils
T.J. Duffy and C.E.
Taylor
Summary: The critical conditions for
several 14-cm-i.d., 2.5-cm-long Nb/sub 3/Sn tape-wound coils
was determined by increasing the temperature at constant
current. The coils are inductively energized and have no
external electrical leads. At lower temperatures, some of the
critical temperatures are well below the "short-sample." Some
data for coils energized in a gaseous helium environment
instead of in a liquid-helium environment are included. The
implications of these results for design of levitated
superconducting coils for plasma physics experiments is
discussed. |
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Magnetization Measurements in Nb-Ti
Sheets
C.E. Taylor
Summary:
It may be possible to achieve stable confinement of
large dc levitated superconducting rings for controlled
thermonuclear research by surrounding the ring with
superconducting walls. The requirements for such confining
walls are given in terms of calculated field strength and
surface current density for a superconducting ring between two
flat superconducting plates. The "spring constant" of such a
magnetic suspension has been calculated as a function of
geometry. Flux penetration data have been obtained for
0.005-in.-thick Nb-Ti sheets in several layers and are
compared with the requirements for design of stabilising
walls. |
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Modular Three-Section 1.5-in.-Bore 150-kg Magnet
(Title Only)
H.C.
Schindler
Summary: Not
available |
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Thin-film Josephson Junctions Using
Getter-Sputtered Niobium
J.E.
Nordman
Summary: Thin-film niobium-niobium
oxide-lead Josephson junctions were fabricated by use of
getter sputtering for the Nb films, thermal oxidation of the
Nb and evaporation of the Pb top films. These devices have
characteristics comparable to good Pb-PbO-Pb
devices..Temperature cycling is not harmful to the devices
although some drift with time is seen in the characteristics.
This drift is in the form of a conductance increase which has
been measured as something between a factor of 1.1 to a factor
of 20 over a period of months with the devices stored at room
temperature. |
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Fabrication of Tunnel Junctions on Niobium
Films
L.O. Mullen and D.B.
Sullivan
Summary: High background currents,
often observed in tunnel junctions when the barrier is formed
by oxidizing niobium, probably stem from the fact that one
oxide of niobium (NbO) is not an insulator. The fabrication
process described in this paper uses an active layer of gas
adsorbed on the niobium surface that reacts with the upper
film (e.g., lead) and forms the junction barrier. This
technique avoids the problem above and results in tunnel
junctions with low background currents. |
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Maximum Tunneling Supercurrents through
Josephson Barriers
W. Schroen and J.P.
Pritchard Jr
Summary: The maximum tunneling
supercurrent through Josephson barriers as a function of
barrier dimensions and external magnetic fields has been
investigated experimentally. A versatile sample preparation
technique allows a two-dimensional distribution of the
tunneling current. The results confirm earlier theoretical
predictions qualitatively. At zero applied field the maximum
tunneling supercurrent initially increases linearly with the
barrier length, then saturates due to self-limiting. At
nonzero applied field the maximum tunneling supercurrent
decreases linearly with increasing magnetic field. It is shown
that this holds also for structures in which the field is
generated by crossed-film control supercurrents. The Josephson
penetration depth of the samples has been 9-22 /spl
mu/m. |
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Barrier-Thickness Dependence of the dc Quantum
Interference Effect in Thin-Film Lead Josephson
Junctions
K. Schwidtal and R.D.
Finnegan
Summary: The barrier-layer thickness
of cross-type square Pb-PbO-Pb thin-film Josephson junctions
has been varied systematically and reproducibly by employing a
mask-substrate changer and a low-pressure-glow-discharge
oxidation technique. A series of junctions has been fabricated
in which the ratio of film width w to the Josephson
penetration depth /spl lambda/J is varied from /spl
lambda/J>>/spl omega/ to /spl lambda/J< |
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Quantum Phase Noise in Superconductors:
Temperature Dependence Measured by Quantum Interference
Techniques with Point-Contact Josephson
Junctions
B.T. Ulrich
Summary:
Thermodynamic fluctuations limit the ultimate
performance of superconducting devices of practical interest,
devices such as the quantum interference magnetometer and the
Josephson junction radiation detector. We report direct
observations of thermodynamically driven quantum phase
fluctuations near the superconducting critical temperature.
The experiments used point-contact quantum interference
techniques with niobium pointson a single-crystal tin
substrate. Near the superconducting transition of tin, T/sub
c/= 3.72/spl deg/K, the niobium points served as probes to
measure fluctuations in the phase of the superconducting order
parameter within the tin crystal. The temperature was slowly
increased, beginning well below To for tin, where the quantum
phase was stable. Quantum phase fluctuations were first
observed approximately 5 mdeg below T/sub c/. As the
temperature continued to increase through this 5 mdeg range
near T/sub c/, the characteristic frequency of the phase
fluctuations increased 6 orders of magnitude. At T/sub c/ a
discontinuous transition to a resistive state gave rise to a
finite voltage difference in the tin with the associated
driven quantum phase precession. Thermodynamic Johnson noise
voltages developed across this resistance of order 10/sup -10/
/spl Omega/ observably broadened the precession line. We will
present the detailed temperature dependence of the frequency
power spectrum of quantum phase 5uctuations below and above
T/sub c/. |
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Stable Point-Contact Superconducting Quantum
Interference Devices (SQUID) (Title
Only)
J.T. Harding and J.E.
Zimmerman
Summary: Not
available |
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Superconducting Magnet System for Intravascular
Navigation
D.B. Montgomery, R.J. Weggel,
M.J. Leupold, S.B. Yodh and R.L. Wright
Summary:
A magnet system capable of guiding a
ferromagnetic-tipped catheter through vessels in the body
would greatly facilitate many medical treatments by providing
access to parts of the body otherwise inaccessible except by
major surgery. A rotatable iron magnet which has been employed
in preliminary experiments with laboratory animals has
indicated the feasibility of this technique, but a more
advanced system is required for sophisticated medical
applications. This paper describes a proposed design for a
superconducting magnet system, with a 10 in. room-temperature
access, which can exert an arbitrarily directed force of 200
times that of gravity on a tip anywhere within the head. A
larger but otherwise similar system could be used for
cathetarization of any-part of the body. |
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Magnetic Suspension and Guidance for High Speed
Rockets by Superconducting Magnets
C.A.
Guderjahn, S.L. Wipf, H.J. Fink, R.W. Boom, K.E. MacKenzie, D.
Williams and T. Downey
Summary: Guidance of
high speed, 5000 m/set rockets in evacuated tubes may be
accomplished by eddy-current repulsion between moving
superconducting coils (on the rocket) and stationary sheets of
copper or aluminum. A method for determining lift and drag
forces of moving rectangular coils over an infinite plane
sheet is presented. The lift force saturates at high speeds v,
the drag forces decrease as v/sup 1/2 / at high speeds, while
the power dissipated increases as v/sup -1/2 / at high speeds.
Methods of determining lift and drag forces from scale models
of finite systems are discussed. The forces as obtained from
impedance measurements on scale models in circular conducting
tubes are given. |
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Flux Displacers for Pulse Generation with
Superconducting Multipole Magnets
R.J.
Thome and G.K. Gaule
Summary: Short, steep
pulses of high electrical energy are required to drive systems
such as pulsed transmitters, light sources and plasma
discharges. A low impedance stationary coil will generate such
pulses when the magnetic flux threading the coil undergoes
large and rapid changes. The rapid change can be achieved by a
"flux displacer," a conductor driven at high speed past the
stationary coil. The applied field is provided in the present
work by a superconducting magnet in order to produce a
magnetic flux of the necessary magnitude and density with
small operating loss, bulk and weight. The stationary coil
together with the load and the flux displacer were not
superconducting and were placed outside the Dewar. Two series
of experiments with flux displacers driven by a rotary prime
mover are discussed. The first series used relatively small,
isolated specimens. These experiments served to determine the
effect of displacer shape, speed and conductivity on output.
The second series used relatively large displacers formed by
pairs of cylindrical shell segments which are electrically and
mechanically connected by end plates. These experiments give
information on the influence of various system parameters on
the energy, and on the duration and shape of the pulses. The
results are presented in dimensionless form, so that the
performance of higher-energy systems can be predicted.
Ultimately, the rotary prime mover may be a lightweight
explosive drive or gas turbine or, in a vehicle or aircraft,
one of the propulsion engines. |
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Superconducting Critical Fields and Currents of
Nb-Ti-N Thin Films in Continuous Magnetic Fields to 175
kG
J. Zbasnik, L.E. Toth, Y.M. Shy and E.
Maxwell
Summary: Superconducting critical
current-field measurements were made on a series of Nb-Ti-N
thin film alloys 1000-8000 /spl Aring/) prepared by reactive
sputtering. Samples were measured in dc transverse and
parallel fields. A pronounced maximum in the critical field
occurs at approximately 20 mole %. TiN. The extrapolated zero
current value of H/sub c2/ for this composition at 4.2/spl
deg/K was greater than 180 kG. Critical current densities in
parallel fields are comparable to those of other high-field
bulk superconductors (10/sup 4/ A/cm/sup 2/ at 150 kG) Films
2000 /spl Aring/ thick and 0.1 in. wide carried a few tenths
of an ampere in fields as high as 120 kG in the transverse
fields and as high as 140 kG in parallel fields. In the
transverse orientation the critical current density appears to
be independent of thickness. Possible application of these
materials to miniature thin-film solenoids is
discussed. |
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High Field Properties of Pure Niobium Nitride
Thin Films
D.W. Deis, J.R. Gavaler, J.K.
Hulm and C.K. Jones
Summary: Thin films of
the rocksalt structure (B1) compounds of the transition metals
can be prepared by the method of reactive sputtering. By a
refinement of this technique we have produced, for the first
time, thin films of niobium nitride (NbN) with transition
temperatures similar to those of the bulk materials (/spl
gsim/15°K). Fihns have been prepared on both hastelloy and
fused silica substrates. Measurements of the normal state
resistivity pn yield values in excess of 200 /spl mu//spl
Omega//spl middot/cm. Preliminary studies of the resistive
transitions in these materials near T/sub c/ indicate that
H/sub r/(J) , the field at which /spl rho///spl rho//sub n/=
1/2 is independent of current density below 200 A/cm/sup 2/
for films 1000-4000 /spl Aring/ thick. Identifying H/sub r/(J)
(J<50 A/cm/sup 2/) with the upper critical field H/sub
c2/(t), the measurements indicate that H/sub c2/(O) is
significantly in excess of 200 kOe, and thus is substantially
higher than the values obtained for the bulk material. These
results are discussed in terms of the current theories of high
field superconductivity with particular reference to the
importance of Pauli spin paramagnetism and spin-orbit
scattering in these materials. |
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Microwave Conductivity of Granular
Superconducting Aluminum Films
R.V.
Aiello and S.J. Freedman
Summary:
Measurements of the transmission amplitude and phase of
20 GHz microwaves through superconducting granular aluminum
films were made as a function of temperature from 4.2/sp ldeg/
to 1.75/spl deg/K. The films were fabricated by vacuum
deposition in the presence of controlled amounts of oxygen,
and exhibited small grain size (/spl sim/40 /spl Aring/) and
enhanced transition temperatures of up to 2.86/spl deg/K. The
temperature coefficients of resistance (TCR) for the films
ranged from slightly positive to almost zero, and for several
films the TCR was negative. For all films measured, the
microwave transmission data agreed very well with that
computed by using the Mattis and Bardeen conductivity
functions. |
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Development of Superconducting Lenses for a
500-kV Electron-Microscope Column
R.E.
Worsham
Summary: The advantages of using
superconducting windings and cryogenic temperatures in
transmission electron microscopes have been recognized for
some time but not fully achieved; they are: improved
resolution because of higher fields and shorter focal lengths,
reduced size, better vacuum, improved mechanical stability,
and greater electrical stability with persistent mode of
operation of lens field. At ORNL, a 500-kV microscope is being
developed with the goal of 1-/spl Aring/ point-to-point
resolution in biological specimens. All lenses will use
superconducting windings operated in the persistent mode. A
quadrupole-octupole lens system will correct the primary
spherical aberration of the objective. Over-all in-instrument
magnification will be 5 X 10/sup 6/ X. An investigation of
round-lens fields shaped primarily by currents showed that low
aberrations could not be attained. Lenses using pole pieces of
1010 steel, Armco iron, and Hiperco 50 were evaluated in
magnetic field tests. Typical figures are an uncorrected
resolution limited by spherical aberration of 1.21-/spl Aring/
in an Armco iron lens with a 7.6-mm bore and 32-kG field.
Further work with Hiperco 50 and dysprosium pole pieces at
fields above 30 kG is in progress. |
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Suspension and Guidance of Vehicles by
Superconducting Magnets
H.T. Coffey, F.
Chilton and T.W. Barbee Jr
Summary: A
magnetic suspension and guidance system for a very
high-velocity (MACH 10) ground-based rocket sled facility has
been studied. These results have been extended and applied to
the study of a high speed (300 mph or greater) passenger train
using this system. Suspension and guidance forces are obtained
through the interaction of the magnetic field of an on-board
superconducting magnet with eddy currents induced in a
stationary metallic guideway. It was found that at high
velocities the levitation force can be calculated as if the
guideway had infinite conductivity. Thus, magnetic image
methods can be used resulting in an image force F/sub
i/. |
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High T/sub c/‘s in Ultra-Thin
Films
H.T. Coffey, F. Chilton and T.W.
Barbee Jr
Summary: Measurements are reported
which show that the maximum Tc, that has been reached in
quenched "softmetal" films is correlated with the maximum Tc,
computed from the analysis of McMillan, assuming an optimum
value for the electron-phonon coupling. The enhanced
electron-phononcoupling may be attributed to the lowering of
the phonon frequencies, which would be caused by the small
metallic grains and greatly increased surface area expected in
these porous quenched films. Molecular dynamics calculations
by Dickey and Paskins indicate that the changes in the phonon
frequencies in small particles are large enough to account for
the changes in Tc. Data are presented which show that the
region with the greatest increase in T, occurs within a few
monolayers of the metal-vacuum, metal-insulator, or
metal-metal surfaces. If similar, near monolayer structures
of, high Tc, transition metal alloys can be made, temperatures
above 25°K should be possible. |
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Upper Critical Field of Thin-film
Superconductors
J.E. Crow and M.
Strongin
Summary: Measurements have been made
of the critical field of cryogenically deposited Sn films
about 30 /spl Aring/ thick. In these tims, where the mean free
path is small and the spin-orbit scattering terms are
significant, we find that the typical parallel critical field
is /spl sim/50,000 Oe at T/T/sub c//spl sim/0.9. The excellent
quality of the films is illustrated by the strong dependence
of the critical field with angle. Near T/sub c/, H/sub
||//H/sub perp/ is about 100. If we assume that we can
reasonably extrapolate to 0°K from our high-temperature data,
we estimate fields well over 200,000 Oe. By using ever thinner
films, and higher Z elements to increase spin-orbit
scattering, we estimate that parallel critical fields near
1,000,000 Oe are obtainable. |
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Direct Measurement of the Effect of Strain on
T/sub c/ in Thin Films
B.W. Friday and
J.L. Mundy
Summary: Direct measurements have
been made of the effect of strain on the critical temperature
of tin, aluminum, and indium films. The films ( < 1000 /spl
Aring/) were vacuum deposited onto glass and mylar substrates
at room temperature and were then strained by mechanically
bending the substrate in liquid helium. T/sub c/ depended
linearly on the strain over the range of observation, /spl
sim/10/ sub -3/, for both tensile and compressive bending. The
slopes of the T/sub c/ vs strain curves were 8.7/spl deg/ and
9.1/spl deg/K per unit strain, respectively for tin and
aluminum films on glass substrates and 4.9/spl deg/ and
3.8/spl deg/K per unit strain for tin and indium films on
mylar substrates. Earlier measurement have indicated
considerable variation in the T/sub c/ dependence on strain
from film to film, but our data are quite reproducible and do
not seem to depend markedly on the evaporation conditions. For
an isotropic material or an anisotropic material for which the
relative orientation of the strain axis and the axes of
crystal symmetry are known it is possible to relate the change
in T/sub c/ to a corresponding volume change. On this basis
one can compare the results on thin films with strain and
pressure measurements on bulk samples. Comparing d 1nT/sub
c//d 1nV for thin films and bulk samples we find that the
values for aluminum agree within five percent, those for tin
films on glass are lower by thirty percent, and those for
indium films are higher by a factor of three. The change in
T/sub c/ due solely to a change in sample volume can be
calculated as a function of the Debye temperature on the basis
of the McMillan theory by using the Gruneisen relation and
taking /spl lambda/, the phonon-mediated electron interaction,
to be inversely proportional to the square of the Debye
temperature. Comparing experimental results with these
calculations we find that the experimental results for dT/sub
c//df/spl Theta//sub D/ lie within the limits imposed by /spl
mu/*=0.1 to 0.2 for bulk aluminum, tin, and indium and
thin-film aluminum and tin. (Materials for which the Coulomb
pseudopotential, /spl mu/*, has been measured lie within these
limits.) |
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Use of Superconductors as Thermometric Fixed
Points
J.H. Colwell, J.F. Schooley and
R.J. Soulen
Summary: The possibility of using
superconductors with sharp transition temperatures as fixed
points on a thermometer scale was examined. Annealed
polycrystalline specimens 3.2 cm long by 0.157 cm in diameter
were placed in a cryostat which would operate from 0.3 to 10.0
K; the superconductive transitions were measured with a
Hartshom bridge operating at 270 Hz. One specimen each was
made from the purest available Pb, In, Ga, Zn, and Cd-the
latter two elements are obtainable from the Office of Standard
Reference Materials. In all cases but Cd, the width of the
transitions were less than 0.001 K; for Cd it was 0.002 K. The
specimens were cycled once to room temperature and remeasured
to check their reproducibility vs two germanium resistance
thermometers. The reproducibility was better than 0.001 K.
These preliminary results indicate the strong possibilities
for this approach to fixed point thermometry. |
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Geometric Arrangement for Maximizing Power
Transmission Capability in Superconducting Transmission Cables
(Title Only)
G.
Guthrie
Summary: Not available |
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Possible Contribution of Superconducting Devices
to Nuclear Magnetic Resonance Detection (Title
Only)
R.A. Kamper
Summary:
Not available |
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