A New Model to Simulate Critical Current Degradation of a Large CICC by Taking Into Account Strand Bending

The ITER model coil experiments have revealed that degradation of the critical current (I_c) and n index occurred in large Nb ₃Sn CICC´s and the larger the electromagnetic force, the larger was the degradation. However, such degradation was not observed in the Nb₃Al CICC. The authors developed a new model, in which the degradation of the I_c and n index of an individual strand was taken into account, to interpret these results. Analytical model corrected from experimental results of a single strand is used in this model to estimate the degradation of each strand. The calculation results are in good agreement with the CICCs´ test results. In addition, it is indicated that in case of the Nb₃Sn CICC, the normal transition occurs from the strands at low field side in CICC cross section, where transverse load due to the electromagnetic force is the largest, resulting in the significant degradation in the I_c and the n index. In contrast, in the case of the Nb₃Al CICC, the normal transition takes place from the strands at high field in the CICC cross section, where the transverse load is small, resulting in no degradation in the I_c and the n index