Fabrication and Evaluation of CuNb-Reinforced Nb3Sn React-and-Wind Coils

Nb₃Sn wires are used in many high-field magnets, such as those used in accelerators and nuclear fusion reactors. The react-and-wind (R&W) method, in which coils are fabricated using heat-treated wire, provides several advantages in the manufacturing of Nb₃Sn coils. For instance, no furnace is required for coil heat treatment, and impregnated resins and supports can be used without considering high-temperature durability. However, in R&W production, the degradation of the critical current owing to the strain in Nb₃Sn should be considered, including the strain caused by the windings. Recently, a polyvinyl-formal-coated CuNb-reinforced Nb₃Sn wire with a diameter of 0.88 mm was developed by Furukawa Electric Company. The wire has a small diameter among CuNb/Nb₃Sn wires and can reduce the strain caused by bending, enabling the fabrication of R&W coils with a small bending radius. We use the wire for manufacturing coils with a minimum radius of 55 mm via the R&W method and present the performance evaluation results.