NI (no-insulation) winding method have been widely used to develop high field superconducting magnets using REBCO wires due to excellent mechanical and electromagnetic stability. When REBCO magnets are operated in a bath of cryogens such as liquid helium and liquid nitrogen, sufficient cooling is achieved by pool boiling of the cryogen. However, conduction-cooled REBCO magnets must ensure sufficient thermal paths from cryocoolers to the magnets. When the NI REBCO magnets are not impregnated by epoxy, radial heat transfer, which is perpendicular to the wire surface, is limited due to the dry contacts between the REBCO wires. To solve this problem, thin metal conduction plates, attached by epoxy to the wound surface of the coil, are usually used to enhance radial thermal conductance as additional thermal path. In the case of REBCO magnets with large mechanical stress, vacuum impregnation is applied using epoxy with thermal contraction similar to the magnet to avoid well-known delamination problem of REBCO wires.
In this study, two kinds of REBCO DPCs (Double Pancake Coil) were fabricated: 1) DPC with conduction plates which are attached to the wound surface of the coil by epoxy; 2) Vacuum impregnated DPC with conduction plates. The coils were installed in a conduction cooling test apparatus to compare the thermal characteristics during charging and discharging operations. In addition, AC loss, eddy current loss and leak-current loss were quantified by analyzing the measured temperature variations. The results will be used to develop mechanically robust and thermally stable REBCO magnets of maglev trains and large wind power generators.
This research was supported by "Core technology development of subsonic capsule train" of the Korea Railroad Research Institute (Grant number: PK1901A1) and by Korea Electric Power Corporation (Grant number: R18XA03).