Development of a turbine cryocooler for high temperature superconductor applications

For high temperature superconductor (HTS) applications such as a power cable, a motor, and a transformer, a refrigerator enough to cool them below liquid nitrogen temperature is required to attain the HTS system stable operation. Since no refrigerator matched for the HTS application both in temperature and in cooling power is available up to now, a neon turbo-Brayton cycle refrigerator of 2 kW at 70 K was developed. Neon gas was used as the working fluid in the refrigerator. Although hydrogen and helium could be selected as a working fluid for the refrigerator, neon is better energy carrier since it has higher heat capacity and larger molecular weight than hydrogen and helium at a temperature around 70 K in order to make a refrigerator smaller in size. Neon has an advantage in using a small turbo-expander with an impeller of 25 mm in diameter. The turbine rotated at a maximum speed of 100,000 rpm. The information for developing a suitable refrigerator for HTS applications was collected and a new type of neon refrigerator was proposed.