Energy and exergy analysis of the cryogenic system for HTS magnets based on an open-cycle G-M/J-T cryocooler

High-field magnets have been developed for a broad range of research applications. High-temperature superconducting magnets have received considerable attention due to their potential use in high-field applications. The High Magnetic Field Laboratory of the Chinese Academy of Sciences (CHMFL) is currently designing and constructing high-temperature superconducting (HTS) magnets which need the cooling capacity about 5 W to 10 W at 4.5 K in order to ensure the stability of the system. To meet their operational requirements, a miniature cryogenic system based on the Gifford-McMahon/Joule-Thomson (G-M/J-T) cryocooler has been designed and analyzed. In this research, the performance of the cryogenic system for HTS magnets is investigated systematically by employing both energy analysis and entropy analysis techniques. The results highlight the importance of several key factors, including high pressures, precooling temperature at cooling stages, and J-T exchanger efficiency, for improving the cooling capacity of the cryogenic system. Lowering the precooling temperature can enhance the system cooling capacity and also cause an increase in the precooling capacity. As the pressure increases, the cooling capacity of the system reaches its maximum point at 11.31 bar The J-T heat exchanger accounts for the largest exergy loss rate, 35.2–43.7%. The findings provide technical guidelines for the subsequent experiments and performance optimization of cryogenic system.