Numerical simulation of the critical current and n-Value in Nb ₃Sn strand subjected to bending strain

To demonstrate the applicability of Nb₃Sn Cable in Conduit Conductors (CICC's) to International Thermonuclear Experimental Reactor (ITER) coils, four, Nb₃Sn model coils have been constructed and tested. The experimental results showed that the measured critical current of the conductors degraded compared with what is expected from the ability of the strands. In addition, the larger is the applied electromagnetic force, the larger the magnitude of the degradation is. A degradation in n-value was also observed. One of the explanations of this degradation is supposed to be a local strand bending. This consideration has been supported by test results, in which a similar degradation in the critical current and n-value was observed when applying periodic bending strains to a single strand. However, general dependence of critical current on periodic bending strain has not been clarified in this test since the experiments were carried out at a certain magnetic field, temperature and strain. Therefore, a numerical simulation code was developed to study the general dependence of the critical current and n-value of Nb₃Sn strand on periodic bending strain. A distributed constant circuit model is applied to simulate current transfer among the filaments in the strand. The simulation results show relatively good agreement with the experimental results but some modification in modeling is required for more accurate simulation.