Thermal Packaging of High Temperature Superconductor Bulk for Superconducting Flywheel Energy Storage

This paper describes thermal packaging issues of YBCO high-temperature superconductor (HTS) bulk for SFES (superconducting flywheel energy storage) system. For stable operation of the superconducting bearing, the temperature of HTS bulk needs to be maintained below 70 K by a cryocooler system where thermal radiation from room temperature environment is a dominant heat load. The thermal radiation heat flux must be reduced to avoid temperature nonuniformity inside HTS bulk and fully utilize the limited cooling capacity of the cryocooler. This paper investigates the various silver coating methods for HTS bulk of SFES. The effective silver coating and postprocessing methods of HTS bulk surface diminish the radiation heat load substantially, which enables a much smaller cryocooler to be equipped for SFES than before. Additionally, a change of thermal conductivity and thermal contact conductance of HTS bulk is investigated according to the various silver coating methods.