Influence of deviatoric strain for superconducting parameters of Nb ₃Sn wires

The tensile strain dependence of the upper critical field B_c2 for Nb₃Sn wires was measured using a new apparatus for applying tension at low temperature. The critical current I_c calculated from the strain-dependent B_c2 measurements is the almost consistent with the measured I_c. In the measurements by a new apparatus, the axial and the lateral applied strains were examined by the strain gauges attached onto the wire. The deviatoric strain ε_dev and the hydrostatic strain ε_hyd were estimated by the axial and the lateral strain. We found the deviatoric strain dependence of B_c2 is different between the tensile and compressive strain states. This means that the hydrostatic strain also should be taken into account in order to understand the strain effects on the superconducting properties of Nb₃Sn.