Influence of Mechanical Constraints on Critical Currents of Superconducting Surface Layers of Nb₃Sn on Niobium and V₃Ga on Vanadium in Transverse Magnetic Fields

Abstract

Soft superconductors in general show an increase In critical temperature [¹] when strained In one direction. However, elastic torsion seems to have no Influence on the critical field [²]. Past work [³] has shown that superconducting surface layers of Nb₃Sn on niobium and core wires [⁴] under pull, torsion, and uniaxial compression exhibit a decrease in critical temperature which Is governed by a parabolic relationship. This effect has now also been established for superconducting surface layers of V₃Si and V₃Ga on vanadium. These results have led us to the search for a similar empirical relationship- between the critical currents and constraints In transverse magnetic fields. Such a reproducible relationship could not be found since a well-defined equation for the quenching curve does not exist. However, a remarkable decrease in the critical currents was found at fixed magnetic field with Increase of the applied constraint. This is In contrast to results for Nb-Zr [⁵], a ductile material, which shows an increase in critical current after suitable deformation.