Development of High Efficiency 4 K Two-Stage Pulse Tube Cryocooler
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Sumitomo Heavy Industries has been continuously improving the efficiency of our 4K pulse tube cryocooler in order to make it exchangeable with our 4K GM cryocooler. In order to improve the performance, three development model pulse tube cryocoolers have been built and tested. On the latest unit, the cooling capacity of the 4K pulse tube cryocooler has been improved to be equivalent to that of the 4K GM cryocooler. A typical cooling capacity of the latest pulse tube cryocooler is 40 W at 37.0 K on the first stage and 1.0 W at 3.86 K on the second stage when the compressor is operated at 50 Hz, and 40 W at 36.8 K on the first stage and 1.0 W at 3.82 K at 60 Hz. The input power is about 6.4 kW at 50 Hz and 7.7 kW at 60 Hz at steady state with 40 W heat load on the first stage and 1.0 W on the second stage. In addition, performance in a helium atmosphere has been measured and has been improved significantly by reducing the temperature difference between regenerator and pulse tube. The experimental results are described.