Test of the GA 12 T model coil at 4.2 K and with helium II

Abstract

A 0.4m I.D. × 1m O.D. superconducting coil for the DOE 12 Tesla Coil Program was tested at the LLNL High Field Test Facility (HFTF). Cabled NbTiTa conductor bath-cooled with liquid helium was employed. Three operating modes, defined by the coolant state, were planned: Case I - 4.2 K, saturated at 1 atm; Case II - 1.8 K, saturated at 12.5 torr; and Case III - 1.8 K at 1 atm. Due to limited lHe capacity of the LLNL refrigerator/reservoir system relative to the LLNL HFTF cryostat boiloff rate, only two cases were tested. Without the background field coils, the GA coil was energized to 10 kA without a quench. At 4.2 K and a background field of 8 tesla, the GA coil quenched at 4 kA at a maximum field of 9.15 T. In Case III (1.8 K) with a background field of 8.5 tesla, the GA coil quenched at 8 kA, at a maximum field of 10.75 T. The conductor development background, coil structure, coil test setup, test results and analysis are presented and discussed. The cause of the quench at less than 12 T appears to be incomplete mixing of the NbTiTa alloy during the crucible melt.