An AC quench phenomenon in hard superconducting wires

Abstract

The process leading to the quench of superconductivity in a nonideal type II superconducting wire carrying an audio-frequency alternating transport current in a normally applied static magnetic field was studied. The quench of superconductivity was found to initiate from particular points of 10-mil diameter Nb25 percent Zr wire in repeated tests. In the course of the experimentation a nucleation site was closely bracketed by potential probes and the voltage response of this segment at currents less than the quench current was studied. Utilizing a limited current density model to describe the ac conduction process, the previous voltage response measurements were used to calculate values for the model parameter J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> . The model was extended to include heating effects and a regenerative process that leads to a quench of superconductivity. Quench current predictions based on voltage measurements prior to the quench at a single frequency agree favorably with measured quench currents over a relatively wide frequency range.