Thermal contact conductance of ceramic AlN and oxygen-free high-conductivity copper interfaces under low temperature and vacuum for high-temperature superconducting cryocooler cooling

In this article, a device for measuring thermal contact conductance under low temperature and vacuum for cryocooler cooling in high-temperature superconducting (HTS) system is presented. Such device may be used to simulate the real running condition of HTS equipments cooled by cryocooler. It is also convenient for temperature controlling. The thermal conductivity of ceramic AlN and the thermal contact conductance (TCC) between AlN and oxygen-free high-conductivity copper for the temperature range of 45–140 K and the vacuum range of 10^-3–10^-4 Pa have been measured using axial steady heat-flow method on the Giffard-McMahon cryocooler with 5 W (20 K) capacity. Investigation shows that the TCC of the AlN/Cu interface increases as the temperature and the pressure load of contact interface increase, and the conductivity of ceramic AlN increases as temperature rises. An analysis based on micro- and nanocryogenic concepts is made to explain the behaviors of thermal conductivity for AlN and thermal contact conductance for the AlN/Cu interface.