Effect of stainless steel reinforcement on the critical current versus strain characteristic of multifilamentary Nb3Sn superconductors

Abstract

A series of multifilamentary Nb3Sn superconductors were fabricated containing from 0% to 52 vol % stainless steel reinforcement strands as an integral part of the conductor. Critical current versus strain measurements are reported which show that the stainless steel introduces a relatively large compressive prestrain, εm, into the superconductor, ranging from εm ≂0.3% for no stainless steel reinforcement to εm =0.84% for 52 vol % stainless steel. Accompanying this high compressive prestrain in the reinforced conductors is a large degradation of the conductor’s critical current, Ic. The Ic degradation relative to the strain-free value has been measured, for example, to be more than 50% at 13 T for εm =0.64%. Several methods are discussed for reducing the large Ic degradation in A15 superconductors containing internal reinforcement.