Reversible and irreversible effects of strain on the critical current density of a niobium–tin superconducting wire

Systematic measurements have been made of the engineering critical current density (Je) and N-value (where E 1⁄4 aJN ) of a jellyroll Nb3Sn wire as a function of magnetic field and strain at 4.2 K. Strain cycling to very high tensile strains at 4.2 K was used to investigate the reversibility of the wire’s properties. The Je data were fully reversible up to 0.67% strain, and can be approximately parameterised by the scaling law Fpð4:2 K;B; eÞ 1⁄4 JeB 1⁄4 A1⁄2B c2ð4:2 K; eÞ b0:5ð1 bÞ, where A 1⁄4 1:28 10 Am 2 T. However it is noted that the maximum pinning force density is not a single-valued function of B c2, so that highly accurate parameterisation requires that A depends on strain. The N-values are a strong function of strain, peaking at 0.33% with values nearly double the equivalent zero-strain values. 2002 Elsevier Science Ltd. All rights reserved.