Highly Strengthened Nb₃Sn Superconducting Wires

Abstract

The superconducting wire in a lrge-scale high-field magnet experiences a large electromagnetic force. This force causes an axial tensile stress in the wire as well as a transverse compressive stress, if the radial displacement of the winding is limited by some constraints. There have been many attempts to reinforce superconducting wires in order to improve the mechanical properties and strain tolerance of I _c [1–4]. In wires for compact high-field magnets made by the wind-and-react technique, the choice of the reinforcing material is important because the reinforcing material and the superconducting composites are heat-treated collectively. In order to avoid a decrease in overall critical current density, simple addition of reinforcing material as an internal reinforcing method is not preferable. Replacement of copper in the superconducting composite wire by a material with high strength as well as high electric conductivity such as Ta [5], alumina-particle-dispersed Cu [6–9] and Cu−Nb microcomposite [10–18] is promising, although the stability of the wire is reduced to some extent [5,14,18].