Internally Cu-stabilized RHQT NbAl superconductors with Ta matrix

Takeuchi, Takao*; Tagawa, Kohei*; Noda, Tetsuji*; Banno, Nobuya*; Iijima, Yasuo*; Kikuchi, Akihiro*; Kitaguchi, Hitoshi*; Kosuge, Michio*; Tsuchiya, Kiyosumi*; Koizumi, Norikiyo; Nishimura, Arata*

Next generation nuclear fusion magnets would require a high-current conductor in fields more than 16 T. A CIC conductor of the rapid RHQT processed NbAl may be a promising candidate. Good deformability of intermediately-formed bcc supersaturated-solid solution indeed allowed fabricating such a CIC conductor, which would be subsequently transformation annealed. Ag has been internally included as a basic constituent of a round strand so far, because Ag is almost non-reactive with Nb matrix during the RHQ. However, both of Ag and Nb are not suitable nuclei from the viewpoint of radioactivity when irradiated with neutrons. Recently, we have succeeded in replacing the Nb matrix with Ta that has the advantage of shorter half-life of radioactivity. In the present study, an attempt has been made to replace the Ag internal stabilizer with Cu, in the aim of further reducing radioactivity, based on anticipation that Ta would be less reactive with Cu than Nb did.