REBCO Coil With Robust Behavior Against Local Defects Wound Using Two-Tape Bundle

REBa₂Cu₃O_7-δ (RE: rare earth/Y) coated conductors have good critical current characteristics under high magnetic fields. Their application to superconducting magnets generating above 25T is under active study. However, performance inhomogeneity along their length may cause damaging hotspots. Adapted winding technologies are needed to mitigate this phenomenon. One of such winding techniques is the two-tape bundle co-winding method, where two REBCO tapes are co-wound along with an isolating tape to form the conductor. To test this solution, a double pancake coil was wound with one of the pancakes having an artificially degraded short section on one of the tapes, where the critical current is close to 0. The I-V characteristics of both damages and undamaged pancakes are compared and analyzed based on critical current density J_c(T,B,θ) data, in terms of operation margins. At low voltage levels, similar I-V characteristics for damaged and undamaged pancakes are observed. The behavior is found similar to the expected behavior of a coil whose critical current I_c is locally reduced by 50%, demonstrating the effectiveness of two-tape bundle for current redistribution in case of local defect, even under high current density.