Ultra-low-temperature refrigeration is a key enabling technology for advanced physics experiments and space science missions. The superfluid vortex cooler (SVC) employs superfluid helium-4 (He II) as the working medium and offers several advantages, including low mechanical vibration, compact structure, gravity-insensitive operation, and continuous cooling capability.
In this work, the cooling principle of the SVC is investigated, and an experimental SVC system is designed and constructed. The driving mechanism based on the fountain effect is analyzed, and a thermal-driven refrigeration cycle is established using a superfluid fountain pump.
To ensure the experimental environment temperature is below the superfluid transition temperature, a ⁴He evaporation refrigerator precooled by a Gifford–McMahon cryocooler is implemented. Based on this cooling system, sub-kelvin refrigeration is successfully achieved with the SVC. The minimum temperature reaches 0.936 K, and the specific cooling power is 50 μW@1 K.
Experimental results show that the cooling performance of the SVC is affected by parasitic heat loads. These include heat leakage due to thermal conduction within the system and thermal effects caused by non-ideal superleaks that fail to fully block the normal component of He II. In particular, the competition between the enhanced superfluid mass flow driven by the fountain effect and the associated increase in heat leakage plays a critical role in determining both the achievable cooling power and the minimum temperature.
The successful integration and operation of the fountain pump demonstrate its potential as a low-temperature circulation driver for closed-cycle dilution refrigerators operating in space. This work provides experimental validation of superfluid vortex cooling in the sub-kelvin regime, clarifies the key physical factors limiting its performance, and highlights its potential as a cost-effective alternative for future ultra-low-temperature applications.