Study on the Effect of Metal Protection Rings in No-Insulation HTS Coils

In this study, we propose the installation of multiple metal protection rings on the outermost turn of no-insulation (NI) coils to improve thermal, mechanical, and electrical stability. The current bypass characteristics in the transverse direction within an NI test coil wound with 10 turns of GdBCO wire and wrapped with 8 turns of Cu tape around the outermost layer were experimentally investigated for various amounts of heating by a heater and various heater positions. To confirm the electrical effectiveness of the metal protection rings, 8-turn Cu tape was used as the rings. A bypass current from the outermost part of the test coils to the Cu tape was observed. The local temperature increase due to thermal disturbance was suppressed.