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Superconducting magnets serve as pivotal components in advanced rail transportation, next-generation power systems, Magnetic Confinement Fusion, and other critical infrastructure. They find extensive applications across various sectors including industry, energy, medicine, large scientific apparatuses, and semiconductors. Superconducting magnets are typically cooled through coolant immersion or cryocooler heat conduction methods. For low-temperature superconducting magnets made by NbTi and Nb3Sn, while direct cooling via cryocoolers reduces the consumption of liquid helium, it necessitates additional auxiliary equipment like compressors and water coolers. Consequently, for applications requiring high system integration and flexibility, liquid helium immersion remains the preferred cooling method for superconducting magnets. Nevertheless, the substantial consumption of liquid helium renders testing prohibitively expensive for both experimental and engineering applications, particularly in regions with limited helium resources. Therefore, developing a closed-cycle helium cooling cryogenic system is crucial, which is the focus of this study.
The proposed closed-cycle helium circulation system consists of two cryocoolers, a cryogenic fan, high-efficiency heat exchangers, flexible adiabatic transmission tubes, and quick-connect interfaces compatible with superconducting magnets. The cryogenic fan drives the helium flow, while a single-stage GM cryocooler and a hybrid GM/JT cryocooler serve as cold sources. Specifically, the single-stage GM cryocooler cools the cryogenic fan, cold shields, and other components, functioning as a pre-cooling source for helium gas. Meanwhile, the hybrid GM/JT cryocooler provides cooling for superconducting magnets across two temperature ranges: rapid pre-cooling at 30K and minimum operating temperature at 4K.
The heat exchanger efficiency exceeds 95%, and all connections utilize bayonet quick-connect interfaces. The inlet and return vacuum adiabatic pipes for the superconducting magnet are independent conduits, ensuring heat loss along the path remains below 1W/m, facilitating long-distance cold helium transmission. This paper details the thermodynamic parameter calculations within the circulation system and presents the overall layout design for the coupled superconducting magnet system. The system is capable of providing continuous cooling for superconducting magnets from 300K down to either 30K or 4K, making it suitable for both high-temperature and low-temperature superconducting applications. During normal operation, the superconducting magnet requires either no liquid helium or only a minimal amount, thereby reducing its costs and complexity.
