A fast thermal-triggered PCS with high switching-off resistance suitable for MI HTS magnets

In this paper, a fast thermal-triggered persistent current switch (PCS) for metal-as-insulation (MI) high-temperature superconducting (HTS) magnets was developed. To enhance the switching-off resistance of the PCS, we removed the copper and silver layers of the HTS tape by chemical etching. The critical current test results verified that the method did not lead to a decrease in the critical current of the HTS tape, confirming its reliability. In addition, to reduce joint resistance, we designed a special joint welding device that applies pressure and heat uniformly. Experimental results show that the switching-off resistance of the PCS can achieve up to 0.21 Ω with less than 50 s of trigger time. The charging experimental results of the MI coil with PCS show that the PCS has little effect on the magnetic field delay. Meanwhile, the closed-loop operation results show that the magnetic field decays by only 2.6% at 8 h, corresponding to a joint resistance of only 20 nΩ. The PCS is suitable for MI HTS magnets with high characteristic resistances to shorten the excitation time.