High capacity closed-cycle 1 K cryocooler

A low vibration 1 K closed-cycle cryocooler, precooled by a 4 K pulse tube cryocooler (Cryomech model PT415), has been developed to provide high cooling capacities at temperatures of ∼45 K, ∼4 K and <1.8 K. The closed loop of the 1 K refrigeration system includes a vacuum pump with peak pumping speed of 35 m3/h, precooling heat exchangers and a condenser thermally attached to the pulse tube cold head, a JT valve and a 1 K pot. The vibration from the PT cold head are significantly reduced by using flexible thermal connections. The adjustable JT valve in the 1 K loop gives flexibility to obtain either the lowest temperature or highest cooling capacity on the 1 K cooling station. A thermal switch installed between the 4 K stage and 1 K stage reduces system cool-down time from 12.8 h to 3.2 h. The 1 K cryocooler can reach the minimum temperature of 1.32 K for low temperature operation, and provide cooling capacities of 400 mK at 1.78 K on the 1 K stage and 1.24 W at 4.3 K on the 4 K stage simultaneously for high capacity operation. The temperature of the 1 K stage is stable within 0.33 mK peak-to-peak.