Performance Measurement And Optimization Of A Compact Two-Stage GM Refrigerator

Cryopump is an efficient equipment to obtain vacuum environment by condensation and adsorption under cryogenic surroundings. Because it has advantages of high extraction velocity, reliability, convenient application, and especially it can obtain the clean and high vacuum environment, the application of cryopump is more and more. Gifford-Mcmahon refrigerator (GM refrigerator) is widely applied as the cooling source of cryopump, because of its simple structure, large cooling power, high reliability and long lifetime. The development of semi-conductor industry and coating and filming industry demands the efficient types of two-stage GM refrigerators with lower cooling temperature and higher cooling power. Based on previous GM refrigerator, the compact type of two-stage GM refrigerator has been designed and fabricated to meet the demands of cooling performance (4W@12K). The theoretical analysis and experimental investigation have been carried out. The compact two-stage GM refrigerator can reach the lowest temperature of 7.2K and achieve the cooling capacity of 4.3W at 12K at the second-stage cold head with 41.8K no-load cooling temperature at the first-stage cold head. The main content and result are as follows:(1) In order to improve the cooling performance of GM refrigerator, the refrigeration principle and theoretical refrigeration cycle have been introduced and analyzed, and the state of Helium during the cycle has been discussed. Based on the original refrigerator, the heat balance of GM refrigerator has been calculated. The theoretical cooling power and the main heat loss caused by the actual refrigeration cycle, including P-V diagram loss, heat loss in regenerator and shuttle heat loss, have been calculated. The parameters which affect the cooling performance have been discussed and the size of cylinders and pistons of GM refrigerator have been confirmed, which prepares for experimental study.(2) The experimental set-up of the two-stage GM refrigerator has been designed and constructed, which consists of cooling temperature and cooling power measurement systems. Using this experimental system, the cooling temperature and cooling power of different refrigerators were measured precisely.(3) The effects of different sizes of 2nd-stage regenerator and cylinder, inlet and exhaust pressure, structure of condensation and adsorption on the cold heads have been investigated. The different regenerative materials, such as Pb and magnetic material, have been used to improve the cooling performance. At last, a compact GM refrigerator filled with ErNi in the 2nd-stage regenerator has achieved the acquired cooling performance. Because of the advantages of high cooling performance and compact structure, the developed two-stage GM refrigerator can be used in many inducstrial applications.