The history and future of A15s in Japan

Tapes and wires of V₃Ga were first made in Japan based on the discovery of the effect of Cu additive for the promotion of V₃Ga synthesis. The bronze process applied to V₃Ga was extended to the fabrication of Nb₃Sn. The Ti addition to the bronze matrix was also initiated in Japan so as to improve significantly high-field performance. The so-called internal tin and Nb tube processes were also initiated in Japan. These achievements on V₃Ga and Nb₃Sn lead into the recent active development of high-field, large-scale, and refrigerator-cooled superconducting magnet applications. As for Nb₃Al, which shows excellent strain tolerance, various approaches were made in Japan to achieve stoichiometry and fine grain structures. Among them the Jelly-Roll process is the most reliable method to produce long-lengths of Nb₃Al wire for fusion uses. High performance Nb₃Al conductors for high-field use are being produced by the rapidly heating, quenching and transformation annealing (RHQT) process. Future progress in the A15 conductor development in Japan may be expected through improved processes.