Flux linkage areas of coupling current loops for different shape cable-in-conduit conductor

For large scale application such as fusion magnets, the cable-in-conduit conductor (CICC) is the most promising conductor because of its high mechanical strength under large electromagnetic force. However, there are still remained issues about degradation of critical current of Nb₃Sn conductor and unpredictable AC loss. With regard to the second item, inter-strand coupling current loss is dominant among the AC losses and unpredictable before fabricating large scale conductor. The strand displacements which are caused by the compaction of the conductor in order to increase its current density would cause the loss. In order to do quantitative investigation of the relation between the loss and the strand displacements, we measured strand traces for circular conductor and rectangular conductor. The evaluation of the flux linkage areas which are driving forces of the coupling current indicated that the flux linkage areas have strong dependence on the changing magnetic field only for the rectangular one. It also indicated that the loss should be large when the field is applied from the direction which is perpendicular to the wide surface of the conduit.