Performance of Polyvinyl Formal Insulated Cu–Nb/Nb3Sn Wires for React-and-Wind Process

In this study, polyvinyl formal (PVF) insulated Cu-Nb/Nb
₃
Sn wires were successfully developed for react-and-wind (R&W) process. The bronze-processed Nb
₃
Sn wires, composed of the Nb-rod-method Cu-Nb reinforcing stabilizer around the Nb
₃
Sn filament bundle, have superior mechanical strength against tensile and bending stress, not only at low temperature but also at room temperature. The Cu-Nb/Nb
₃
Sn wires of 0.8- or 1.3-mm bare-diameter were heat-treated at 670 °C for 96 h on the stainless bobbins of predetermined diameter. Then, prebending strains were applied to the reacted wires under individual conditions. After that, the PVF insulation was applied with a thickness of 20 or 40 μm. Enhancement of the critical currents occurred by applying the appropriate prebending treatments and controlling the strain under PVF insulation processing to ±0.5% or less. This paper presents the performance of the PVF-insulated Cu-Nb/Nb
₃
Sn wires applicable to R&W coils.