E– J characteristics and n-values of a niobium–tin superconducting wire as a function of magnetic field, temperature and strain

Systematic measurements have been made of the E– J characteristics of a Nb 3Sn wire over four decades of electric field (0.1–1000 μV m −1) and five decades of current density (10 3–5×10 8 A m −2) as a function of magnetic field, temperature and strain. They were parameterised using the power law E= αJ n . At low magnetic fields n tends to a constant saturation value, which decreases at high compressive and tensile strains and increases with increasing electric field. In the high magnetic-field range, n is independent of E-field and can be approximated by a strain and temperature scaling law of the form n( B, T, ε)= G( T)( B c2 *( T, ε)− B), where B c2 *( T, ε) is an effective upper critical field.