Development of strain-applying apparatus for evaluation of ITER NbSn strand

Nunoya, Yoshihiko; Isono, Takaaki; Koizumi, Norikiyo; Hamada, Kazuya; Nabara, Yoshihiro; Okuno, Kiyoshi

Japan Atomic Energy Agency has successfully developed NbSn strand which fulfilled ITER requirement. The achieved Jc value are more than 700A/mm for bronze process and more than 800A/mm for internal tin process, as well as hysteresis value is less than 1J/cc. Because NbSn are very susceptible to an external strain such as reducing critical current, critical temperature, and critical field, it is necessary to evaluate strain dependency of developed NbSn strand to make the database for optimization of the conductor design. The apparatus to measure the strain dependency was newly developed. It has horseshoe-shaped ring on whose outer surface the strand is soldered. This shape produces uniform axial compressive or tensile strain along strand length by expanding or closing the opening of the ring, furthermore this expanding and closing movement can be transmitted by translation motion without torque, which improves versatility of the ring especially in case of large scale application. The critical current under the magnetic field can be measured by the apparatus in the range of 4.2K to 15K temperature and -0.8% to 0.5% strain. The maximum allowable current is about 250A. Measurement result and the detail of the apparatus will be presented.