Three-Dimensional Strain Model on the Superconducting Properties Under the Strain for ${\rm Nb}_{3}{\rm Sn}$ Wires

It is very important for the application of high field magnets to understand the strain effect of the superconducting properties for Nb₃Sn wires. We found that the axial strain dependence of the superconducting properties for various kinds of the bronze route Nb₃Sn wires can be described clearly, in the case that the deviatoric and hydrostatic strains are determined experimentally as the three-dimensional strain. In addition, we constructed a modified three-dimensional strain model of B_c2 for bronze route Nb₃Sn wires based on the deviatoric and invariant strain models. This modified model can fit the axial strain dependence of B_c2 for various kinds of bronze route Nb₃Sn wires by only a set of the parameters. It is suggested that three parameters such as axial residual strain and lateral one, and the ratio of the axial and the lateral strain determine various superconducting properties for Nb₃Sn wires under the axial tensile strain.