Development of a NbAl conductor for toroidal field coils

Koizumi, Norikiyo; Ando, Toshinari*; Nakajima, Hideo; Matsui, Kunihiro; Sugimoto, Makoto; Takahashi, Yoshikazu; Okuno, Kiyoshi; Kizu, Kaname; Miura, Yushi; Tsuchiya, Katsuhiko; Sakasai, Akira; Ishida, Shinichi

NbSn cConductors have already been developed for the TF coils operating at 13 T. However, the critical current of NbSn degrades due to a strain, and the amount of degradation becomes larger when the magnetic field increases, which set a limit of the NbSn application to a large coil at around 13 T. NbAl is considered, therefore, to be a next generation superconductor, since the critical current of NbAl is superior to that of NbSn and less sensitive against strains. JAERI has been developing NbAl conductor since 80s. As the first step, mass production technique of NbAl strands was established. In the second step, coil fabrication technique was developed and could successfully be charged to the nominal point of 13 T and 46 kA. From these advantages, JAERI is also promoting R&D activities to develop NbAl TF coils for JT-60SC. The prototype NbAl conductor has already been made. A D-shaped coil was fabricated and successfully tested. These activities constitute the basic approaches to develop TF coils whose operating field is expected to be around 16 T.