Thermal properties of NbTi superconductor wire and its heat release performance over quench

The cryostability of superconducting magnet is mainly dependent on the heat release performance between superconductor (SC) and coolants as well as superconductor material properties. The heat balance between that generated in solid and that cooled by coolant in the vicinity of quench is studied in this paper. Various cooling media (normal liquid, saturated superfluid and subcooled superfluid helium) and different surface materials on SC (lacquer, porous and its bare form) are examined. Measurements show that the varnish layer working as the electrical insulator is a barrier of heat release, which allows quench to happen immediately just when current shares in matrix. It is also found that the thermal properties are obviously developed by coating a porous layer on wire instead of varnish layer, even better than the bare wire. The current transported is thus greatly increased and also the thermal performance of porous coated wire in HeIIs expresses the characteristics in HeIIp. A reasonable explanation is given in this paper and verified by experiments.