Development of a Bypass Circuit for a REBCO Coil Using Flux Flow Resistance

Abstract

When superconducting magnets are operated in a conduction-cooling system, if a malfunction of the cryocooler or an abnormality in the heat transfer path occurs, the temperature of the coil increases. In most cases, the operating temperature limit is designed so that thermal runaway of the coil can be prevented by charging-down or shutdown of the magnet. Therefore, the temperature margin should be considered carefully. In this research, a bypass circuit for a REBCO coil was developed using the flux flow resistance generated inside the coil when the load factor rises. Low resistors were connected to both ends of a test coil composed of a stack of four single pancakes wound with 4-mm-wide REBCO tape having an inner diameter of 200 mm and an outer diameter of 291 mm in the cryostat. Automatic suppression of the current flowing through the coil at high load factor was attempted. In this report, the test and simulation results of the coil operation when the cryocooler was intentionally stopped under conduction-cooling conditions are compared and discussed.