Stability and Protection of Two REBCO Tape Bundle-Winding Coil

Abstract

Local degradation of critical currents in REBa₂Cu₃O_y (REBCO, RE: rare-earth and Y) coated conductor is one of the serious issues especially for high field superconducting magnets. It may give rise to a localized hotspot, followed by a burn-out in the magnet. To mitigate such phenomena, a co-winding of bundled two REBCO coated conductors is considered. The bundled REBCO double pancake coil with a local damaged area was made and tested in LN₂ and conduction cooling conditions. The I_c of the damaged coil showed more than 90 % of that of the non-damaged coil. The comparison of the I_c distribution in the coil and the I_c value at the damaged area can explain the good Ic performance of the damaged coil. Even if the operation current exceeds the local I_c due to the local damage, the coil can be protected if we would detect the quench with a threshold of less than 18 mV for the practical 30 T cryogen-free superconducting magnet.