Thermal impedance of electricaly insulated thermal joint for hybrid current leads

Hybrid current lead is one of the important parts for the development of cryogen free superconducting magnet system. The thermal stability of the NbTi magnet is greatly dependent on the performance of the hybrid current lead. Hybrid current lead, which is a combination of the metallic (copper) lead and HTS lead, has some inter-lead joints which need to be electrically insulating and thermally conducting with the different stages of the cryocooler. A thermal anchoring block of oxygen-free high-conductivity (OFHC) copper is developed for inter-lead thermal joint. A detailed experimental study is carried out using Kapton and Aluminium nitride (AlN) as interlayer insulation material in the thermal anchoring block. The thermal resistance of the interface for 19 mm² contact surface area, is found to be ∼7 K/Wand ∼15 K/W for Kapton and Aluminium nitride (AlN) respectively at 4.2 K temperature range and ∼0.6 K/W (nearly similar) for both Kapton and Aluminium nitride (AlN) at 40 K temperature range. Dependency of the thermal impedance on the contact surface area is also discussed in details.