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 ( J e ) and N -value (where E = αJ N ) of a jellyroll Nb 3 Sn 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 J e data were fully reversible up to 0.67% strain, and can be approximately parameterised by the scaling law F p (4.2 K ,B,e)=J e B=A[B c2 ∗ (4.2 K ,e)] 0.5 b 0.5 (1−b) 2 , where A=1.28×10 10 Am −2 T 0.5 . 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.