Aspects of Nb₃Sn superconducting wires and trend of their research and development in foreign countries

Multifilamentary Nb₃Sn wires are fabricated starting from Nb/Cu-Sn or Nb/Cu/Sn composites, which facilitates their mass production. Nb₃Sn superconducting wires are now one of the key materials in modern science and technology, such as NMR, fusion and refrigerator cooled magnets. Present volume is the special issue on the recent status of mass production-scaled Nb₃Sn conductors in Japan. Then this article describes aspects of Nb₃Sn conductors, and overviews recent activities in foreign industries. Bronze process and internal tin process are common fabrication process of Nb₃Sn multifilamentary wires, whose features are briefly described in this article. The former process is dominantly used in Japan and Europe including Russia, while the latter is rather frequently used in USA, Korea and China. Thus countries are divided into roughly two groups with respect to the major fabrication technology of Nb₃Sn. Beside these, Nb tube process and powder-in-tube process are being proceeded in foreign industries. Nb₃Sn conductors still have a possibility of improvement in their fabrication technologies, and will continue to contribute for the application of superconductivity. (author)