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

Abstract

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-μm 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 nΩ. 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 field decay rate), limited by the finite resistance of the close-out joint.

A novel heater-triggered HTS semi-persistent current switch with high switching-off resistance

“…Applying 1.67 W of power to nickel-chromium wire in the semi-PCS required a hold time of about 2 min to open it. The temperature measured by thermocouples during the test was about 111 K. By soldering two voltage leads, the resistance of the semi-PCS at 111 K can be measured to be 1.18 Ω, which is much larger than the resistance in the common heatertriggered semi-PCS [8,13,17], which are normally in the mΩ level. The change of resistance exhibits a delay during both the warming-up and cooling-down stages.…”

HTS Shim Coils Energized by a Flux Pump for the MIT 1.3-GHz LTS/HTS NMR Magnet: Design, Construction, and Results of a Proof-of-Concept Prototype

“…The DFI was placed 45-cm away from the Z2 shim coil center in the orthogonal direction to the main Z2 field to minimize the field interference generated by DFI. Each PCS of REBCO tape had a 350-Ω strain gauge heater and surrounded by a 5-mm wall expanded polystyrene foam sealed with Epoxy [22]–[24]. About 0.3-W of heater power was required to open the PCS within 10 s.…”

Persistent Current Switch for HTS Superconducting Magnets: Design, Control Strategy, and Test Results

“…The PCS usually achieve above features through the transitions of the superconductor between the superconducting state (zero-resistance state) and the normal state. Thermally-controlled switches trigger the transition though heating the superconductor above its critical temperature [2][3][4][5][6]. This type of PCS can achieve a high resistance, but it usually takes several seconds or even longer to transfer between the two states.…”