No abstract

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.

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 µm at the first stage and ±14.6 µm 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 second stage when the compressor is operated at 50 Hz, and 22.3 K and 2.39 K when the compressor is operated at 60 Hz. A typical cooling capacity of the prototype unit is 35 W at 41.8 K on the first stage and 0.9 W at 4.05 K on the second stage when the compressor is operated at 50 Hz and 35 W at 41.8 K on the first stage and 0.9 W at 4.07 K when the compressor is operated at 60 Hz.

No abstract

Synopsis: 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.