A high capacity completely closed-cycle 250 mK 3He refrigeration system based on a pulse tube cooler Original Research Article

We present the design of a completely closed-cycle refrigeration system. The system consists of four stages; the first two, 40.5 and 2.7 K, are provided by a pulse tube cooler, the third and fourth stages by helium adsorption refrigerators. The adsorption refrigerators use 4He and 3He with base temperatures of 700 and 250 mK, respectively. Performance tests including some with the cooler rotated from the vertical showed that with a load of 15 μK, a temperature below 286 mK can be maintained for 72 h.