Enthalpy improved dielectric insulation for NbTi

Abstract

Two new dielectric insulation systems applicable to NbTi are described. Both systems incorporate significant enthalpy stabilization in that the volumetric specific heats of the dielectrics are equivalent to, or much larger than, that of Pb below 10K. For one of the systems, the thermal conductivity at 5K approaches that of commercial Cu. Both coating systems can be applied to NbTi without the use of a fugitive binder: One system can be hot-extruded directly on the wire, and the other system can be dip-coated with a room-temperature cure. Both coating systems withstand demanding bend tests. For 0.13-mm thick coatings, the thermal time constants at 5K are 0.24 μs and 2.5 ms; the corresponding enthalpies per unit volume at 6K (relative to 4.2K) are 50.5 and 54.6 mJ/cm3At 8K; the enthalpies are 179 and 311 mJ/cm3respectively. The thermal properties of both systems are unaffected by intense magnetic fields.