Enhancement of Thermal Properties of HTS Magnets Using Built-in Cryogenic Oscillating Heat Pipes

Enhancement of the thermal properties of high- $T_{\rm c}$ superconducting (HTS) magnets has been investigated using built-in cryogenic oscillating heat pipes (OHPs). A cryogenic OHP is built into windings of an HTS magnet to improve the thermal properties of windings and to protect them from damage caused by a large temperature gradient. It is rather difficult for an HTS magnet to quickly remove the heat generated in windings, especially, in a protection operation when a magnet quenches, because the thermal diffusivities of component materials of windings decrease with an increase of temperature. Therefore, a local hot spot can be formed in a magnet, and there are possibilities of having degradation of superconducting properties and/or mechanical damages by thermal stresses. A flat-plate cryogenic OHP has been developed that is suitable for imbedding in magnet windings as a high-performance heat transportation device in order to increase the thermal conductivity and the thermal diffusivity at the same time. By using hydrogen, neon, and nitrogen as working fluid, its excellent thermal transport properties have been proved in the operating temperature range of 18–84 K.