Thermal and electrical stabilities of GdBCO magnets impregnated with epoxy composites using surface-treated carbon nanotube fillers

This study investigates the thermal and electrical stabilities of superconducting coils encapsulated with an epoxy/acid-treated carbon nanotube (CNT)composite through cool-down, over-current, and repetitive-cooling tests. Carboxylic acid groups were successfully attached to CNT surfaces by acid treatment, which facilitated uniform CNT dispersion within the epoxy resin, forming preferential paths for heat conduction. The coil encapsulated with the epoxy/acid-treated CNT composite showed a fast cooling rate in a bath of liquid nitrogen (LN2)and high endurance under over-current conditions. This contrasts with its counterpart encapsulated with untreated CNTs, because heat was easily dissipated in the epoxy/acid-treated CNT composite owing to its higher thermal conductivity. Moreover, the difference in the thermal expansion coefficients of the epoxy and the superconducting tape decreased. Therefore, using an epoxy composite containing acid-treated CNTs is recommended for developing a mechanically dense superconducting coil with enhanced thermal and electrical stabilities.