Numerical Investigation on Current Behaviors of NI Multi-Tape-Bundled REBCO Coils Wound With Dump Resistance for Sudden Discharge Test

Progress in the field of applied superconductivity, such as MRI, NMR, and compact fusion reactors, relies on improvements in material developments and winding techniques. The no-insulation (NI) winding technique enables rare-earth barium copper oxide (REBCO) coils to show high electromagnetic characteristics, while having a high current density. The multi-tape-bundled winding technique improves charging delays on large-scale NI REBCO coils. Meanwhile, previous research has suggested several disadvantages of these techniques. Especially in the NI multi-tape-bundled REBCO coils, rapid discharging is reported due to the influence of a small coil inductance, which makes coil protection harder. In this paper, several D-shaped multi-tape-bundled REBCO coils with dump resistor are modeled. Sudden discharging tests are simulated for each model with a different number of bundled tapes and turn-to-turn contact resistivities. The simulation results show that REBCO-tape-longitudinal currents are concentrated on one side, meanwhile the opposite-directional currents are observed on the other side. The concentration is larger as the number of bundled tapes increases. In addition, the Joule heat simulation shows that the energy stored in a coil is discharged faster on the more-tapes-bundled NI REBCO coil, although the energy extracted into the dump resistor is smaller due to the low turn-to-turn/tape-to-tape contact resistance. Further investigations will be needed, especially for a thermal simulation.