A REBCO Persistent-Current Switch, Immersed in Solid Nitrogen, Operating at Temperatures Near 10 K

We present design and test results for a thermally-activated persistent-current switch (PCS) applied to a double pancake (DP) coil (151-mm ID, 172-mm OD), wound, using the no-insulation (NI) technique, from a 120-m-long, 76-mu m-thick, 6-mm-wide REBCO tape. For the experiments reported in this paper, the NI DP assembly was immersed in a volume of solid nitrogen (SN2), cooled to a base temperature of 10 K by conduction to a two-stage cryocooler, and energized at up to 630 A. The DP assembly operated in quasi-persistent mode, with the conductor tails soldered together to form a close-out joint with resistance below 6 n Omega. The measurements confirm PCS activation at heating powers below our 1-W design target, and a field decay time constant in excess of 900 h (i.e., 0.1% h(-1) field decay rate), limited by the finite resistance of the close-out joint.