Yoshiaki Kanazawa

A miniature pulse tube refrigerator for temperatures below 100K

Abstract A miniature pulse tube refrigerator reaching temperatures below 100K has been developed. In this paper the test results of the refrigerator are reported. The refrigerator is a orifice pulse tube refrigerator. It is based on a miniature Stirling refrigerator. It consists of a compressor, a cold head and. a reservoir. The features are high operating frequency and compact size. The lowest temperature is achieved to 98K.

Development of 1.5W 4K G-M Cryocooler with Magnetic Regenerator Material

A two-stage 4K Gifford-McMahon (G-M) cycle cryocooler with magnetic regenerator material which has cooling capacity 1.5W at 4.2K has been developed. The hybrid structural second regenerator composed of lead and ErNi0.9Co0.1 was used in the cryocooler. ErNi0.9Co0.1 has a large specific heat peak at lower temperature than 10K and lead has a larger specific heat in the. higher temperature region. The intake/exhaust valve timing was optimized to improve the cooling capacity not only of the second stage but also of the first stage. A larger size second cylinder in diameter than the former one was used to get a larger pressure-volume (PV) work.

Temperature Stabilization on Cold Stage of 4 K G-M Cryocooler

A simple method of temperature stabilization on cold stage of 4 K Gifford-McMahon (GM) cryocooler has been proposed. A copper pot connected to compressor unit by a stainless steel capillary tube is mounted on the 4 K stage of a GM cryocooler. Depended on the temperature of pot, pressurized helium can naturally go into or out of the pot. The utilization of high volumetric specific heat of pressurized helium in the pot at 4 K region produces a good temperature stability on the 4 K stage. The periodic temperature fluctuation of the 4 K stage is ∼ 0.5 K (peak-to- peak) typically, but the high pressure pot described in the present paper reduces the temperature fluctuation effectively down to ∼ 0.05 K (peak-to-peak). The method is safe to deal with, and the system is easy to operate. This paper shows the experimental details, and discusses the temperature stabilization effect of the pot and other advantages of the method.

Improvement of Two-Stage GM Refrigerator Performance Using a Hybrid Regenerator

To improve the performance of two-stage GM refrigerators, a hybrid regenerator with magnetic materials of Er3Ni and ErNi0.9Co0.1 was used in the 2nd stage regenerator because of its large heat exchange capacity. The largest refrigeration capacity achieved with the hybrid regenerator was 0.95W at helium liquefied temperature of 4.2K. This capacity is 15.9% greater than the 0.82W refrigerator with only Er3Ni as the 2nd regenerator material. Use of the hybrid regenerator not only increases the refrigeration capacity at 4.2K, but also allows the 4K GM refrigerator to be used with large 1st stage refrigeration capacity, thus making it more practical.

INFLUENCE OF VALVE OPEN TIMING AND INTERVAL ON PERFORMANCE OF 4 K GIFFORD-McMAHON CYCLE CRYOCOOLER

The influence of intake/exhaust valve timing on performance of a 4 K Gifford-McMahon(GM) cycle cryocooler has been investigated. The 4 K GM cryocooler is one of the standard two-stage types with magnetic regenerator material, ErNi0.9Co0.1, in its second stage regenerator, and delivers more than 1 W cooling at 4.2 K. A reasonably early open timing of intake/exhaust valves not only brings about a cooling capacity above 1 W at 4.2 K on the second stage, but also produces a much larger cooling capacity at the first stage. Under the optimum conditions, 39.4 W cooling at 40 K on the first stage, as well as 1.18 W at 4.2 K on the second stage, was obtained with an input electric power of 7.05 kW. This paper discusses the results of cooling capacity with P-V diagrams, and indicates that the reduction in pressure drop at intake/exhaust valves is important for a 4 K GM cryocooler.

A four-valve pulse tube cryocooler with a cooling power over 30 W at 80 K

A single stage four-valve pulse tube cryocooler with a large cooling power at 80 K has been built and tested. The cryocooler has a regenerator stacked with stainless steel screen disks of 250 mesh, and a pulse tube of 200 mm long. A rotary valve unit is employed to control the mass flow at the hot ends of regenerator and pulse tube. Because the size of pulse tube is an important parameter of the cryocooler, three kinds of pulse tube, 18, 28 and 38 mm in diameter, were prepared for investigating the influence of pulse tube size on cooling performance. Initial test demonstrated that the cryocooler with the pulse tube of 28 mm in diameter delivers a cooling power of 33.5 W at 80 K. Cycle frequency also shows a great effect on cooling performance, and the cryocooler reached its terminal temperature of 20.5 K with a cycle frequency of 1.8 Hz. This paper describes details of the cryocooler design and the experimental results.

A Simple Method of Temperature Stabilization for 4 K GM Cryocooler

Publisher Summary This chapter develops a simple method of temperature stabilization for 4 K GM cryocooler. It applies the high volumetric specific heat of pressurized helium at 4 K region to reduce the temperature fluctuation of the 4 K stage. It describes the experimental details and the results. In a proposed simple method of temperature stabilization for 4 K G M cryocooler a copper pot connected to compressor unit by a capillary tube is mounted on the 4 K stage of a GM cryocooler. The utilization of high volumetric specific heat of pressurized helium in the pot at 4 K region produces good temperature stability on the 4 K stage. The periodic temperature fluctuation of the 4 K stage is, 43.5 K (peak-to-peak) typically, but the helium pot reduces the temperature fluctuation effectively down to, 43.05 K (peak-to peak). The system can be operated continuously, and is easy to cool down, furthermore it is safe to use.

Improvement of a 1.5W-class 4K Gifford-McMahon cryocooler

Publisher Summary This chapter discusses the effect of cylinder size for the cooling capacity. Various sizes of cylinders and displacers are tested, and drastic effects of the size on the cooling capacity are obtained. When these cylinders are tested with same compressor, certain relation is found between the data of the first stage cooling capacity and the second stage cooling capacity. But when the compressor was changed, the newly obtained data formed another relation. The maximum cooling capacity of the first stage at 40K is 53.7W, and that of the second stage at 4.2K is 1.74W. The results of this work are in the work on 1.5W-class 4K-GM cryocooler, performance of four cylinders having different size is tested. Comparing with data obtained by using same compressor, the larger the ratio of the second cylinder volume to tile first cylinder volume of the cylinder, the larger cooling capacity is produced, Owing to extend the length of the first cylinder, cooling capacity of the first stage rose up about 15W. The maximum data of the first stagecooling capacity at 40K is obtained 53.7W by using cylinder No.4 and compressor No.2, and that of the second stage cooling capacity at 4.2K is obtained 1.74W by using cylinder No.2 and compressor No.2.

New Magnetic Regenerator Materials with Broad Peaks of Magnetic Specific Heat

The materials of the Er1-x Dyx Ni system are proposed as new magnetic regenerator materials for use in a 2-stage Gifford-McMahon refrigerator. We produced a series of solid solutions, Er1-x Dyx Ni, by mixing two substances, ErNi and DyNi. These two substances have the same crystal structure and their easy axes of magnetization are perpendicular to each other. The peak in the temperature dependence curve of the magnetic specific heat was observed to broaden, as the concentration, x, of the Dy ions increased above x=0.075. We have demonstrated that mixtures of ErNi and DyNi, which have different easy axes of magnetization, lead to materials with broad peaks in the temperature dependence curve of the magnetic specific heat.

Optimization of Intake and Exhaust Valves for 4 K Gifford-McMahon Cryocooler

Publisher Summary Intake and exhaust valves are key components of Gifford-McMahon (GM) cryocooler, and include several important factors, such as valve type, valve structure and valve timing. This chapter focuses on the influence of intake and exhaust valve timing on performance of 4 K GM cryocooler at various cooling temperatures in order to optimize the intake and exhaust valves. The 4 K GM cryocooler is a standard two-stage type one with a rotary valve for intake and exhaust. The second stage regenerator in the cryocooler has both lead spheres and spherical magnetic regenerator material with the latter arranged at the colder end. The cooling capacities of the first stage and the second stage are measured in wide temperature ranges. The results indicate that the optimum intake and exhaust valve timing is dependent on the cooling temperature and is possible to be different for each stage. The optimum intake and exhaust valve timing is dependent on the cooling temperature, and is possible to be different between the first stage and the second stage. In other words, the cooling temperature is important for the optimization of the intake and exhaust valves. The 4 K GM cryocooler delivers great cooling capacities not only at 4.2 K but also at much higher temperatures.