CHAPTER 9: Critical-Current Measurements

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FIG. 9.1
Typical plot of a superconducting voltage vs. current characteristic

FIG. 9.2
Cross section of a practical multifilamentary Nb3Sn superconducting composite

FIG. 9.3
Critical J–B–T surface for Nb–Ti and Nb3Sn

FIG. 9.4
Critical J–B–ε surface for commercial Nb3Sn superconductors at 4.2 K

FIG. 9.5
Test configurations for critical-current measurement for (a) transmission lines and (b) electromagnet applications

FIG. 9.6
Different types of background magnets and sample configuration for critical-current measurements in transverse magnetic field

FIG. 9.7
Schematic diagram of electrical instrumentation for critical-current measurements

FIG. 9.8
Basic circuit diagram of a series-transistor-regulated current supply

FIG. 9.9
V–I curve shapes: (a) ideal characteristic, (b) inadequate current-transfer length between current contacts and voltage taps, (c) damaged sample, (d) premature thermal runaway, and (e) switching effect

FIG. 9.10
Schematic diagram of a data-logging system, illustrated for the case of critical-current measurements

FIG. 9.11
Three methods of controlling current for critical-current measurements: (a) continuous ramp, (b) step and hold, (c) pulse

FIG. 9.12
Double-axis apparatus for full solid-angle measurements of low-current specimens in a solenoidal magnet

FIG. 9.13
High-current helium-gas-flow cryostat for measuring critical current at variable temperature and magnetic-field angle

FIG. 9.14
Apparatus for measuring critical current as a function of axial strain and magnetic field

FIG. 9.15
Coil sample holder for measuring the effect of strain on the critical current of long superconductor samples

FIG. 9.16
U-bending beam for measuring strain effects on short samples

FIG. 9.17
Coil sample holder designed for measuring the effect of strain on critical current at both variable temperature and magnetic field

FIG. 9.18
Loading apparatus for applying hoop stress to a superconducting composite coil: (a) top view of cone assembly; (b) cross-sectional view

FIG. 9.19
Illustration of fixture for continuous bend testing

References
Listing of all References for Chapter 9 Figures