Kyosuke Nakano

Study of low vibration 4 K pulse tube cryocoolers

Sumitomo Heavy Industries, Ltd. (SHI) has been continuously improving the efficiency and reducing the vibration of a 4 K pulse tube cryocooler. One advantage of a pulse tube cryocooler over a GM cryocooler is low vibration. In order to reduce vibration, both the displacement and the acceleration have to be reduced. The vibration acceleration can be reduced by splitting the valve unit from the cold head. One simple way to reduce vibration displacement is to increase the wall thickness of the tubes on the cylinder. However, heat conduction loss increases while the wall thickness increases. To overcome this dilemma, a novel concept, a tube with non-uniform wall thickness, is proposed. Theoretical analysis of this concept, and the measured vibration results of an SHI lowvibration pulse tube cryocooler, will be introduced in this paper.

Development of high efficiency 4 K two-stage pulse tube cryocoolers with split valve unit

SHI has been continuously improving the efficiency and reducing the vibration of a 4 K pulse tube cryocooler. A high-efficiency 4 K pulse tube cryocooler with a split or a remote valve unit has been developed. The valve unit of the cryocooler is split from the cold head by one flexible gas line and two stainless pipes. The experimental data of a highefficiency pulse tube cryocooler with a split or a remote valve unit is reported in this paper. The diameter of the gas lines between the valve unit and the cold head is optimized. The wall thickness of the tubes on the cylinder is optimized for low vibration with minimum impact on cooling performance. The typical vibration displacement is ±10.3 im at the first stage and ±14.6 im at the second stage when the compressor is operated at 50 Hz. When the valve unit is split with 1 m lines, the cooling capacity is reduced because of increased pressure drop and dead volume. The minimum temperature of a prototype unit is 23.0 K at the first stage and 2.30 K at the sec...