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