Study on the Persistent Current Switch in HTS Coils Wound with 2G Wire for Compact NMR Magnets

High temperature superconducting (HTS) magnets wound with REBCO wires are used in many applications, and the superconducting magnet which is operated in persistent current mode has many advantages. Therefore, we have been developing compact NMR relaxometry devices using HTS coils operated at liquid nitrogen temperature. The required strength and homogeneity of magnetic field of proposed NMR relaxometry devices are 1.5 T and 150 ppm/cm³ respectively. The proposed HTS magnet for NMR relaxometry device consists with stacked HTS double pancake coils wound with REBCO wires and operated by persistent current mode (PCM) using superconducting joint between REBCO wires. In PCM operation, the ability of persistent current switch (PCS) is very important, so, in this study, the thermal properties of YBCO wire against the various thermal inputs by heater were investigated experimentally to design the PCS for PCM HTS magnets. The thermal behaviors of the YBCO wires were measured as functions of amount of heat input using two types of epoxy resin. The current bypassing properties on the YBCO loop coil with developed PCS were studied experimentally.