Design and Test of Superconducting Persistent Current Switch for Experimental Nb3Sn Superconducting Magnet

A superconducting persistent current switch with an off-state resistance of 10 Ω for an experimental Nb 3 Sn superconducting coil has been designed, fabricated, and tested. The superconducting switch is thermal controlled, consisting of the bobbin of brass, the noninductive superconducting winding, the heater, and the support bar. A temperature sensor is fixed in the bobbin to monitor the temperature of the superconducting switch. The superconducting switch operates at 4.2-K temperature connected in parallel with the power supply and the experimental Nb 3 Sn superconducting coils. One GM cryocooler is employed to cool down the whole system. Based on the finite-element method, the numerical simulations of the switching performance of temperature distribution during heating and cooling cycles are performed. The results of the closed-loop operation show that the switch can successfully operate in the conduction-cooled magnet. The maximum closed-loop current is 170 A.