Performance of Thin Cu-Nb/Nb3Sn Round Wires and Tapes Pre-Bent for R&W Process

Cu-Nb/Nb
₃
Sn wires have high mechanical strength and large compressive residual strain. In this study, we successfully developed thin Cu-Nb/Nb
₃
Sn round wires and tapes to avoid the critical current (
I
_c
) degradation caused by damage of brittle Nb
₃
Sn filaments in React-and-Wind (R&W) process with small bending diameters. Both the Cu-Nb/Nb
₃
Sn round wires of 0.45 mm diameter and the tapes of 0.40 mm thickness had
I
_c
increase by pre-bending treatments up to bending strains of ±0.6% in the Nb
₃
Sn 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
I
_c
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
I
_c
-
B
characteristics than those of the W&R spiral ones.