Influence of indentation on the critical current of NbSn strands

Suwa, Tomone; Nabara, Yoshihiro; Takahashi, Yoshikazu; Oshikiri, Masayuki; Tsutsumi, Fumiaki; Shibutani, Kazuyuki*; Nunoya, Yoshihiko; Murakami, Yukinobu*; Miyashita, Katsumi*; Sim, K.-H.*; Kwon, S. P.*

Japan Atomic Energy Agency is procuring all of the NbSn cable-in-conduit conductors for ITER Central Solenoid (CS). The of short-twist-pitch (STP) conductors were stable under electromagnetic cycles because of the improvement in the bending property of STP cables. However, the short twist pitch increases the pressure between two strands at contact points, and strands become indented before the heat treatment for the reaction of NbSn. Therefore, the influence of indentations on the critical current () of NbSn strands need to be investigated. measurements were carried out for indented bronze-route (BR) and internal-tin (IT) NbSn strands. The were measured at 4.2 K and 12 T. When decreased 5%, the critical depths of the indentations were 0.26 mm and 0.37 mm for the BR and IT strands, respectively. The of both strand types decreased drastically with depth over dc. In order to maximize the superconducting properties of the NbSn cable, the depth of indentation should be smaller than dc in the cable.