Thermal and Electromagnetic Simulation of Multistacked No-Insulation REBCO Pancake Coils on Normal-State Transition by PEEC Method

This paper presents the thermal and electromagnetic behaviors of multistacked no-insulation (NI) REBa₂Cu₃O_{7- x} (REBCO, RE = rare earth) pancake coils. The NI winding technique gives a high enough thermal stability not to damage REBCO coils even though a normal-state transition occurs. The high thermal stability has been verified through overcurrent tests. Moreover, the numerical simulation of multistacked NI REBCO pancake coils has been performed to investigate the electromagnetic behaviors in detail. The simulation results also confirmed the high thermal stability of NI REBCO pancake coils. However, it does not mean that an NI REBCO magnet never quenches. In experiments, it was observed that a quench in one of the pancake coils propagated to the other pancake coils sequentially. The above sequential quench from pancake to pancake has not been confirmed in the numerical simulation since the thermal behavior is not considered. For the more reliable verification, we have developed a numerical simulation to investigate the thermal and electromagnetic behaviors by the partial element equivalent circuit method and the two-dimensional thermal finite-element method. In this paper, the six-stacked NI REBCO pancake coil is simulated with several operating temperatures, and the sequential quench is reproduced. The velocity of the sequential quench is also shown.