Numerical analyses for ramp rate limitation from the standpoint of heat generation during current redistribution [in superconducting cables]

The ramp rate limitation (RRL) must be improved for large applications, for instance fusion machines. In superconducting multi-strand cables, adding to the coupling loss, the heat generation during current redistribution (moderation of a nonuniform current) causes temperature rises. Especially for cables in conduit-type conductors (CICC), the relation between the heat capacity of the coolant and the total heat dissipation determines the temperature rise. When this rises above the current sharing temperature, the conductor must quench. To establish stability against nonuniform current distribution, a small contact resistance between strands is preferable. However a smaller contact resistance results in a larger inter-strand coupling loss. Therefore, the contact resistance must be optimally designed to prevent the cable from RRL. In this study, the authors analyzed the current redistribution in a three-strand cable with electrical contact between strands. The heat generation due to: (1) normal resistance; (2) contact resistance between strands; and (3) terminal joint resistance were evaluated in the cases of a variety of contact resistances and cooling conditions. Finally, some of the particular phenomena reported as being found in experiments with multi-strand cables were simulated by analyses and then discussed.