Numerical simulation of critical current performance in NbSn strand subjected to periodic bending deformation

Murakami, Haruyuki*; Ueda, Hiroshi*; Ishiyama, Atsushi*; Koizumi, Norikiyo; Okuno, Kiyoshi

In the ITER Engineering Design Activity (EDA), it was revealed the critical current of the NbSn model coil conductor degraded by periodic strand bending caused by enormous electromagnetic force. We developed a simulation code based on the distributed circuit to investigate dependency of the critical current performance on bending strain. The results of the numerical simulations were in good agreement with the experiments. The dependence of the critical current on periodic transverse load, temperature, pitch of periodic load, thickness of Ta barrier which prevents Cu stabilizer to be contaminated by Sn, twist pitch of the strand and RRR of the bronze matrix is investigated using developed code. The results show the critical current degraded less with decreasing the pitch of the transverse load and increasing the Ta barrier thickness. It suggests that shorter twist pitch of the cable and larger bending stiffness prevent the critical current degradation.