Numerical simulation of critical current and n-value in Nb₃Sn strand subjected to bending strain

Critical current of ITER model coil degraded with the increase of electromagnetic force. Analysis based on results of the experiments in which periodic transverse load is artificially applied to single strand showed that periodic bending of the strand by transverse load caused this degradation. However, since the experiments were carried out under a certain condition, general relation between transverse load and critical current was not obtained. We have therefore developed a numerical simulation code to investigate the general relation. However, there were some disagreements between the simulation and experimental results in our previous study. Our simulation model was consequently modified, resulting in good agreement with the test results. The general dependence of the critical current on periodic transverse load, temperature, and pitch of periodic load is investigated using the modified simulation code. The simulation results reveal that the reduced critical current depends on the temperature, and is a function of the bending strain independent of the pitch of the periodic load.