High Efficiency Operation of a 4K-Gifford-McMahon Cryocooler without Rotary Valve with a Metal Bellows Compressor

Traditional Gifford-McMahon cryocoolers are operated with an integrated rotary valve which regulates the compressed Helium supply and return into and from the cold head. Theory predicts that about 50% of the input energy is lost in this rotary valve [1]. In this work we removed the rotary valve from a Sumitomo RDK-101G cold head and drove the Gifford-McMahon cryocooler in Stirling-mode directly with a slow-moving metal bellows compressor at around 1.2Hz. We could demonstrate that the energy efficiency of the cryocooler system improves by almost 50%. As a result, we were able to operate this cold head with 650W of total electrical input power with a cooling power of 140mW at 4.2K on the second stage and no-load temperatures of below 40K on the first stage. This corresponds to a COP of 215mW/1000W which one of the highest COPs reached for small and medium size 4K GM and pulse tube cryocoolers.