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 (epsilon(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 epsilon(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.