Modelling of a two-stage-compression Joule-Thomson cryocooler using mixed refrigerants at 50 K

This study aims to develop and numerically characterise a two-stage-compression Joule–Thomson (J-T) cryocooler developed for 50 K cooling using neon–oxygen–nitrogen mixed refrigerants and linear compressors. The target temperature range is critical for applications such as trapped ion quantum chips, which require compact, vibration-free cooling. Linear compressors provide low-vibration and oil-free operation, while the two-stage configuration enables high-pressure compression with adequate mass flow rate. A buffer tank between the stages mitigates pressure wave fluctuations and phase mismatch. The mixed refrigerants are used to achieve the 50 K temperature and optimised to enhance overall cooling capacity. Thermodynamic and exergy analyses are conducted to assess system performance and identify loss mechanisms. Operating between 2 and 50 bar, the system achieves 6.3 W cooling at 51 K with a mass flow rate of 0.65 g/s and an exergy efficiency of 52 %. A buffer tank stabilises the intermediate pressure at 6.48 bar, eliminating phase couple between stages. Exergy loss is mainly found in the J-T valve (12.9 %) and CFHX1 (11.3 %). The results demonstrate the feasibility of compact, oil-free, and vibration-free cryocooling for quantum computing and related applications. This work forms a theoretical basis for prototype development and future experimental validation of low-vibration 50 K cryogenic systems.