Bipolar Sweep Test of A 3 MJ Pulsed Superconducting Magnet

Abstract

The first bipolar operatinal test of an MJ-class pulsed superconducting magnet was successfully carried out in energy transfer experiments between a 3 M J magnet(load magnet) and a 4 MJ magnet(energy storage magnet) using a chopper-type energy transfer equipment. The test goal was to confirm the technical feasibility of operating an ohmic heating coil for a tokamak-type fusion reactor. A 3 MJ magnet was first charged to 4510 amperes in 1.5 seconds. It was discharged to 0 ampere in 1.5 seconds and at once was re-charged to −4510 amperes in 1.5 seconds. It was again discharged in 1.5 seconds. The maximum field and the stored energy were 5.4 T and 2.1 MJ, respectively. During this bipolar sweep test, the magnet was quite stable during charge. Instability phenomena were not observed when the direction of the current was reversed. We also found that there was no mechanical instability during operation from the results of dynamic strain measurement. Thus it can be concluded that there is no technical problem in the bipolar sweep of an MJ-class pulsed superconducting magnet.