Technical problem and resolution of superconductor for the ITER magnet

Nunoya, Yoshihiko; Nabara, Yoshihiro; Takahashi, Yoshikazu; Oshikiri, Masayuki; Tsutsumi, Fumiaki; Takamura, Jun; Chuheishi, Shinji; Shibutani, Kazuyuki*

Japan Atomic Energy Agency is responsible for NbSn Cable-in-Conduit conductors or the Central Solenoid (CS) and the Toroidal Field (TF) coil under the ITER project. Full-size conductor test was performed to confirm performance using SULTAN facility at Switzerland, especially effect of electromagnetic load cycles on the current sharing temperature (Tcs). The original (reference) conductor which had relatively long twist pitch cabling design is called as the normal twist pitch (NTP) conductor. NTP conductor showed Tcs decrease with increasing the number of cycles. By introducing short twist pitch conductor, performance during electromagnetic cycles was improved and concern of Tcs decrease in ITER CS is eliminated. Improvement is understood that shorting pitch of the triplet in the first stage make more engagement of strand providing more stiffness of the cable that prevent strand deformation like buckling observed in the destructive examination of the previous SULTAN sample.