Effect of prebending strain on CuNb/Nb₃Sn superconducting coils using a react and wind method

We have found that superconducting properties such as a critical current for bronze route Nb₃Sn superconducting wires were enhanced by prebending strain (ε_pb), which is the repeated bending strain at room temperature. In this study, four kinds of react and wind (R&W) processed CuNb reinforced bronze route Nb₃Sn coils with ε_pb = 1.0, 0.8, 0.5 and 0% were prepared. We investigated the effect of prebending strain for the coils. In the electromagnetic compressive stress condition, a critical current (I_c) of the R&W processed coil was enhanced by the prebending strain. These I_c values are larger than those of a short sample wire without prebending strain. In the hoop stress condition, the I_c of four coils revealed a similar value. Therefore, it is considered that the I_c was limited by the large tensile stress for all coils in the hoop stress states. These results suggest that the I_c enhanced by the effect of prebending strain is applicable for the R&W coil design without degradation in large stress and strain states.