Electromagnetic and thermal characteristics of supplementary-conductor-based no-insulation REBCO pancake coils with comparison to conventional-based ones

Abstract

A no-insulation (NI) winding technique was originally developed in 2011 to enhance the thermal stability of Rare-Earth Barium Copper Oxide (REBCO) pancake coils. Thereafter, several similar techniques of controlling turn-to-turn contact resistance have been proposed, and they can be categorized as the conventional NI winding technique, named a conventional-based NI (CNI) technique in this paper. Recently, a few novel winding techniques different from the CNI winding technique but similar have been proposed: an intra-layer no-insulation technique and a conductive-epoxy-resin-coating technique. These techniques utilize supplementary conductors attached or embedded on REBCO coils as bypassing current paths, which is, in this paper, categorized as supplementary-conductor-based no-insulation (SNI) techniques. These conventional-based and supplementary-conductor-based NI techniques have high a potential for high-field applications. As of today, the applications of these NI techniques are nuclear magnet resonance and magnetic field imaging, and compact nuclear reactors. Those applications require a high performance; however, it is still uncertain which NI technique is suitable for which application since the differences in the characteristics are not clarified well. Therefore, we have systematically investigated the thermal stability of SNI REBCO pancake coils with different circuit parameters in this paper. The thermal stability simulation results of SNI REBCO coils were compared with those of CNI REBCO coils. As a result, the SNI REBCO pancake coils are able to be operated with high thermal stability without deteriorating charging performance as long as the turn-to-turn contact resistances between REBCO tapes and supplementary conductors are low.