Performance of Thin Cu-Nb/Nb₃ Sn Round Wires and Tapes Pre-Bent for R&W Process

Cu-Nb/Nb3Sn wires have high mechanical strength and large compressive residual strain. In this study, we successfully developed thin Cu-Nb/Nb3Sn round wires and tapes to avoid the critical current (Ic) degradation caused by damage of brittle Nb3Sn filaments in React-and-Wind (R&W) process with small bending diameters. Both the Cu-Nb/Nb3Sn round wires of 0.45 mm diameter and the tapes of 0.40 mm thickness had Ic increase by pre-bending treatments up to bending strains of ±0.6% in the Nb3Sn filamentary area including the tin-diffusion barrier. The pre-bent tapes of thicknesses 0.9-0.25 mm (aspect ratio 1.5-10.2) showed higher Ic characteristics than as-reacted tapes independently of magnetic field directions. The R&W spiral coils of 39 mm diameter, which were wound with the pre-bent round wire of 0.45 mm diameter and the pre-bent tape of 0.48 mm thickness, retained higher Ic-B characteristics than those of the W&R spiral ones.