Superconducting property and strain effect study of the NbSn strands developed for ITER

Nunoya, Yoshihiko; Hemmi, Tsutomu; Nabara, Yoshihiro; Matsui, Kunihiro; Isono, Takaaki; Takahashi, Yoshikazu; Koizumi, Norikiyo; Okuno, Kiyoshi

Japan Atomic Energy Agency has developed NbSn strand for the ITER magnet, strand whose critical current density is about 1.4 times as large as that for ITER CS Model Coil. Magnetic field, temperature, and strain dependence on the critical current (Ic) of the strand are measured by the apparatus developed by the authors. Especially strain property is investigated in detail, and it is shown by strain tensor analysis that upper critical field dependence on strain can be naturally formulated by the high order polynomial terms of strain taking into account residual strain due to thermal contraction difference inside of the strand and applied strain externally. Correlation formula among field, temperature, strain and Ic for the strand is discussed and presented. Performance of superconducting cables composed of the developed strand is evaluated using the formula.