Numerical Investigation on Current Behaviors of NI/PI REBCO Coils Wound with Many Bundled Tapes for Sudden Discharge

Abstract

Abstract For future applications such as compact fusion reactors, it is necessary to investigate some characteristics of meter-class D-shaped no-insulation (NI) REBCO coils. In recent years, several kinds of NI winding techniques, such as multi-tape-bundled REBCO tapes and a partial-insulation winding technique, have been proposed and experimented to improve the current characteristics of REBCO coils, such as an excitation delay and a large induced current. In this paper, the sudden discharging has been simulated to investigate not only the current behaviors but also the Joule heats for meter-class D-shaped REBCO coils with a few different NI winding techniques: (1) complete no-insulation between tape-to-tape/turn-to-turn for multi-tape-bundled windings and (2) partial-insulation for turn-to-turn of multi-tape-bundled windings without tape-to-tape insulation. The simulation results show that the amount of Joule heats emitted in a short time is large for many-tape-bundled NI REBCO coils. Also, the simulation result show that the greater number of tapes bundled on an NI REBCO coil, the more unbalanced current distributions are observed among the bundled tapes. Furthermore, the partial-insulation REBCO coils show a particular current distribution. These results reveal that cooling systems should be considered depending on the winding techniques.