Current Sharing in Defected Superconducting REBCO Tape Stack Cables for HTS Inserts in Accelerator Magnets: FEM Modeling

In high energy physics magnets, superconducting cables are typically used, one for this reason is to limit inductance and thus voltages during magnet quench. For LTSC cables this also allows for current sharing in case of a local perturbation of a strand; such current sharing mitigates problems attendant to the low minimum quench energy seen in LTSC superconductors. For HTS strands, MQE is much larger, but an equally important function has emerged which is conductor redundancy. Heating due to small defects within the cable can be mitigated again by strand-to-strand current sharing. Of particular interest in this context are REBCO tape stacks, Roebel and CORC cables. Here small defects may arise in the original tapes, either during cabling or in service in the magnet. However they arise, local heating can be generated if current sharing is not present. In this article, we modelled the current sharing in non-insulated tape stacks (i.e., tape stack cables) containing seven double-sided tapes with defects present in some of the tapes. In this article, we used Finite Element Method (FEM) modeling, assuming critical current densities of these tapes relevant for operation at 4.2 K (boiling liquid He).