Development of 4K Pulse Tube Cryocooler

Sumitomo Heavy Industries, Ltd. (SHI) has been continuously improving the efficiency and reducing the vibration of a 4K pulse tube cryocooler. Recently, the efficiency of a 4K pulse tube cryocooler has been competitive with a 4K GiffordMcMahon (GM) cryocooler. Owing to its low vibration and high reliability, pulse tube cryocooler has been widely used for cooling superconducting magnets and pre-cooling ultra-low temperature cryocoolers. In many cases, pulse tube cryocoolers are used to directly recondense helium. In a helium atmosphere, the performance degradation of a pulse tube cryocooler is larger than that of a GM cryocooler because of extra convection losses, which are caused by the temperature difference between the pulse tube and regenerator tube. In order to reduce this degradation, the temperature profiles are shifted with several novel concepts. Firstly, the configuration of the holes, which are drilled on the second stage heat station to increase the recondensing surface area, is investigated. The performance degradation is reduced by 0.04 W by replacing the holes from go-through holes to one-end-close holes. Then, a spacer is inserted at the cold end of the second stage regenerator to shift the temperature profile. Accordingly, after these improvements, the temperature difference between the second stage pulse tube and the regenerator tube is reduced and the performance degradation is reduced from 0.39 to 0.24 W, which is almost the same as that of a GM cryocooler.