Thermal Management of High-Speed Drive Motors for Fusion Engineering Cryogenic Systems Under Extreme Asymmetric Temperature Span Boundaries

Clean and reliable integrated air refrigerators are essential for the cryogenic systems of Tokamak devices. However, the high-speed drive motors in these systems are subjected to severe axial asymmetric temperature span boundaries. The axial temperature difference between the compressor and expander ends can reach a maximum value of 180 °C. To mitigate the risk of localized thermal accumulation under such extreme conditions, this paper proposes a switchable cooperative thermal management strategy. The approach integrates internal cooling using self-produced cryogenic air from the expander with a dynamically switchable multi-channel water-cooling network. A segmented switching logic is implemented for the water-cooling channel and the cold-air channel at the bearing near the expander to adapt to variable thermal boundaries. A multi-source thermal network (MSTN) model was established, and the cooling parameters were optimized using a genetic algorithm (GA). Experimental results at 35,000 rpm under a −85.4 °C deep-cooling condition demonstrate that the strategy successfully maintains the peak motor temperature at 126.2 °C. The measured system cooling capacity of 17 kW surpasses the initial design target (15 kW), confirming the engineering feasibility and robustness of the proposed strategy for clean cryogenic cooling in fusion engineering applications.