Unbalanced radial current flow simulation of no-insulation REBCO pancake coils during normal state transition

Abstract

The no-insulation (NI) winding technique greatly enhances the thermal stability of REBCO (REBa2Cu3O x , RE = Rare Earth) pancake coils by avoiding burn-out and thermal runaway. The complicated electrical behaviors in NI REBCO pancake coils produce convoluted mechanical behaviors, so that some journal papers reported that high-field NI REBCO pancake coils were mechanically damaged during quench. To apply NI REBCO magnets for practical commercial use, it is important to understand the electromagnetic and mechanical behaviors of NI REBCO pancake coils in detail with both experiments and simulations. To clarify the electrical behaviors, a few simulation methods for NI REBCO pancake coils have been proposed; such as a simple RL parallel equivalent circuit. In these previous models, the radial current paths along the top and bottom of the pancake coils are represented as one current circuit path. However, since the radial current path of the bottom of one pancake coil is actually very close to that of the top of the next lowest coil, inductive behavior between these two paths appears. The simulation results show a probability that different amounts of radial current on the top and bottom of one pancake coil are carried during quench.