Temperature Field Simulations of a ReBCO Pancake Coil Under Pulsed Overcurrent Conditions

Abstract

Under pulsed overcurrent conditions, some of the superconducting layers inside a ReBCO pancake coil are quenched and very high ac losses are generated due to nonlinear quenching resistances. Transient ac loss of each ReBCO layer is modeled in this paper by using an electromagnetic-superconducting coupled finite-element-modeling (FEM) method. Temperature field distributions inside and around the whole ReBCO pancake coil caused by the distributed ac losses are further discussed to investigate the thermal operating characteristics under pulsed overcurrent conditions. For a ReBCO pancake coil having 20 coil turns, the maximum ac loss value locates in the sixth coil turn from inner wall to outer wall of the whole coil. By considering the solid-to-solid and solid-to-fluid heat transfer behaviors, local overheated point having the highest operating temperature appears inside the middle and lower part of the sixth coil turn. A current-dependent power function for the highest temperature estimation is also concluded to depict the nonlinear relations between the operating temperatures and currents inside the ReBCO pancake coil. These electromagnetic superconducting thermal coupled characteristics lay some technical bases to design and evaluate proper overcurrent and overheating schemes for various ReBCO pancake coils and magnets.