Performance tests of a 1.5 MJ pulsed superconducting coil and its cryostat

To demonstrate cryostability of large pulsed superconducting ohmic heating (OH) coils for Tokamak power reactors a 1.5 MJ coil was developed at Argonne National Laboratory (ANL). The coil was first charged up to 11.2 kA dc, which is the critical current of short sample cables at 4.5 T. Above the critical current, an unbalance voltage of the coil increased smoothly indicating stable current sharing between the superconducting filaments and the copper stabilizer. The coil was then pulsed with a 7 MW power supply. The highest ramping rate was 11 T/s. AC losses, mainly eddy current losses in the copper stabilizer, were proportional to with about 2.5 kW at 9 T/s. After 3000 pulses no degradation of the coil performance has been observed. A non-metallic cryostat was developed for testing of the coil to avoid eddy currents in the cryostat.