Performance of G-M Cryocooler with Oil-Free Linear Compressor

A completely oil-free compressor for use with GM cryocoolers has been designed, built, and tested. The compressor uses two, fully-balanced, STAR linear motors together with friction-free reed valves. This arrangement eliminates all possibility of oil contamination in the helium working fluid, and therefore also eliminates the regular servicing that is required by conventional GM compressors. The compressor delivers high-pressure flows comparable to those delivered by well-developed conventional compressors, and is designed to match the operating point pressures and flow for a Sumitomo model 408 cold head. The design of the compressor is briefly reviewed. The measured performance of the compressor when integrated with a Sumitomo model 408 GM cold head is presented. The performance is mapped as a function of the refrigeration load and temperature at both the first and second stage heat exchangers and is compared with the both the manufacturer specified performance and separate baseline tests for the same cold head integrated with a conventional oil-flooded GM compressor.