Design and Testing of GM Cryocooler for a Large Capacity Cryopump

Cryopump, which is the removal of gas from a system by solidification onto a cold space, is an ideal form of ultra high vacuum pump due to its contamination-free operation at its highest pumping speed. With high crossover capability and high throughput, the cryopump can provide clean vacuum environment. Since the cryopump creates a vacuum state by condensation and adsorption mechanisms, a multi-stage cryocooler is imperative. This research focuses on the development of a 2-stage GM (Gifford-McMahon) cryocooler utilized for a large capacity cryopump. By taking simple computation on two different regenerator, it is possible to predict the cooling performance of the GM cryocooler. As a working fluid, helium is supplied by a helium compressor with the electric consumption of 2.4 kW. The operational frequency of GM cryocooler is set to be 1.2 Hz (72 rpm). Although the second stage regenerator has a little bit more thermal loss than expected, the experiment results show that the design methodology is able to adequately explain the thermal characteristic of the GM cryocooler. The developed 2-stage GM cryocooler can exert the cooling power of 40.04 W at 80 K and 5.36 W at 20 K, simultaneously.