Torque Simulation on NI REBCO Pancake Coils during Quench

Abstract

This paper presents the unbalanced torque generated in No-Insulation (NI) REBa2Cu3Ox (REBCO, RE = Rare Earth) pancake coils after a normal-state transition. The NI REBCO pancake coil has a high thermal stability, and it is desired to apply to ultra-high field magnets. When an NI REBCO pancake coil locally transitions into a resistive state, the operating current bypasses a normal-state-transitioned turn to adjacent turns in the coil-radial direction, and the amount of heat generation can be reduced. That is an inherent feature of NI REBCO pancake coils. However, when a radial current flows in a magnetic field, a Lorentz force is generated toward the coil-circumferential direction, i.e. torque. In case that the coil radius and the external magnetic field are very large, the extremely large torque is generated, and it could damage the magnet itself and/or the joints to terminals with a mechanical factor. Therefore, it is necessary to investigate the behavior of the torque generated in the NI REBCO pancake coil after the quench. In this paper, we present the numerical simulation results of the behaviors of the torque generated in the NI REBCO double pancake coil after quench. Their current, thermal, and mechanical behaviors are simulated by a partial element equivalent circuit (PEEC) method and 2-D thermal finite element method (FEM). The behaviors are different depending on the coil size. In addition, the behavior is presented when the operating current is suddenly shut down after quench.