Anomalous Critical Currents in Superconducting Noninductive Coils of Nb-25% Zr Wire

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Abstract
The critical current vs preset magnetic field has been measured for a number of multilayer bifilar noninductive coils wound with cold-worked 0.025-cm-diam Nb-25% Zr wire. In an applied field greater than 8 kG and less than 24 kG the superconducting to normal transitions are not single-valued and show an effect analogous to ``antitraining.'' It is shown that the anomalous critical currents are due to cooling in a constant applied field. The conditions for obtaining, avoiding, and eliminating the different values of critical current have been investigated and the results are compared with short-sample and magnet data. The experimental results suggest the unorthodox view that high transport currents are obtained when induced magnetization currents are initially present and low transport currents are measured when only the reversible magnetization is present in part of the noninductive coil.