Current Sharing in Superconducting REBCO Cables-FEM Modeling

For winding the high energy physics magnets superconducting cables must be used. They will lead to a significant reduction of the magnet self-inductances which enables their fast-ramping operation. A particular interest in this application is focused on REBCO Roebel and CORC or STAR cables. Apart from their high T-c (around 90 K) they also have their strands transposed or twisted which reduces their ac losses and magnetizations. Low ac loss levels allow higher ramp rates of the magnets and low magnetizations improve their field homogeneity. Here we present thermal FEM modeling results on current sharing in double sided tape-stacks containing broken elements. The FEM model assumed a magnetic field of 8 T at a temperature of 4.2 K. A stack of 7 non-insulated double sided REBCO tapes immersed in liquid He bath and containing a defect located in their REBCO films was modelled. Effects of surface resistance on stability and current sharing were explored. Magnetic coupling of the two REBCO films in the double- sided tape and their ac losses as a heating element is also analyzed.