Development of a 4K Two-stage Pulse Tube Cryocooler

Sumitomo Heavy Industries, Ltd. (SHI) has been developing 4K pulse tube cryocoolers for cooling MRI Magnet Systems, Small Superconducting Magnets, SQUIDs, X-ray detectors, etc. The valve unit of the cryocoolers is separated from the cold head by a self-sealed coupling. With this configuration, the maintenance for the valve unit becomes much easier and faster than that with a unified one since it is not necessary to warm up the cold head and cool down again. The vibration from the compressor and valve unit can be reduced by this configuration with some simple techniques. A typical cooling capacity is of 0.9W at 4.23 K at the second stage and 40W at 45.9 K at the first stage, simultaneously. The results of the influence on the performance by filling pressure, operating frequency are reported. The vibration of a SHI 4K pulse tube cryocooler is measured with a laser displacement sensor.