Evaluation of a Two-stage Mixed Refrigerant Cascade for HTS Cooling Below 60 K

A mixed refrigerant cascade presents a potential solution for cooling of high-temperature superconductors between 55 K and 70 K. The envisioned process consists of a pre-cooling and a low-temperature stage, where pre-cooling to 120 K is achieved by a conventional mixed refrigerant cycle. The low-temperature stage operates with a mixture of neon, nitrogen and oxygen at high pressure. Process simulation predicts an overall efficiency of about 8% of Carnot at 55 K. Simulation results for the pre-cooling stage were validated by experiments with an existing test stand.