Sudden Discharging Tests and Overcurrent Tests of a 3T HTS Model Magnet for MRI Systems Equipped With Electrically Conductive Epoxy Resin

A 3 T HTS MRI model magnet equipped with conductive epoxy resin for quench protection was designed and fabricated in 2021 and the REBCO multicoil generated 3 T with 143 A stably with no abnormal voltages. In this coil, the electrically conductive epoxy resin is attached to the edge of the winding as a bypass circuit between turns so that the excessive current can flow across turns in the radial direction to suppress local heat generation automatically. However, when the voltage of the coil rises as a start point in a quench protection process, the DC power supply is shut down by a quench detector and the magnet is suddenly discharged. Then, part of the magnetic stored energy is consumed in the coil and the coil temperature increases, which suggests the load factor increases during the sudden discharging operation. In this study, the sudden discharging tests were performed, and the behavior of the coil voltages and temperatures was evaluated at 30 K and 40 K using the middle-scale REBCO coil that had large inductance and high stored energy (3 T, 91 H, 1 MJ). After that, the overcurrent tests were performed for the verification of the quench protection at 50 K. The coil temperature reached 72 K at maximum, however, thermal runaway was avoided and the REBCO coil was protected.