Numerical Simulation of Unbalanced Forces on NI REBCO TF Coils During Quench Event

Rare-earth barium copper oxide (REBCO), which has high superconducting performances under a high magnetic field, attracts attention in the field of compact fusion reactor and so on. Compact fusion reactors consist of several magnets including D-shaped toroidal-field (TF) magnets arranged in a circle to create a toroidal field. Considering the use of no-insulation (NI) REBCO TF magnets for compact fusion reactors, there are a few points to note. One of them is unbalanced forces during the event of quench. The equilibrium state of the electromagnetic forces is disrupted by quench of one NI REBCO TF magnet. Since the NI technique is applied, the current remains in TF magnets with a time delay even when an operating current is cut off externally. Therefore, it is impossible to immediately stop the operation after the detection of quench; it is difficult to control the REBCO-tape-longitudinal currents. In addition, the TF magnets next to the quenched TF magnet have large induced currents. Thus, for NI REBCO TF magnets in compact fusion reactors, unbalanced forces in the overturning directions occur between TF magnets while the currents in the TF magnets decay after the sudden shut-down of current. For this reason, it is necessary to investigate such unbalanced forces working to NI REBCO TF magnets in compact fusion reactors when a quench event happens. In this research, unbalanced overturning forces on NI REBCO TF magnets during quench is numerically investigated.