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

Systematic measurements have been made of the engineering critical current density (Je) and N-value (where E=αJN) 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 wireʹs properties. The Je data were fully reversible up to 0.67% strain, and can be approximately parameterised by the scaling law Fp(4.2 K,B,ε)=JeB=A[Bc2∗(4.2 K,ε)]0.5b0.5(1−b)2, where A=1.28×1010 Am−2 T0.5. However it is noted that the maximum pinning force density is not a single-valued function of Bc2∗, 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.