Development and Experimental Investigations on Two Stage GM Type Pulse Tube Refrigerator for 20 K Applications

Because of the absence of any moving components at the cold region, low vibration and high reliability, two stage GM type pulse tube refrigerator (PTR) is nowadays preferred compared to conventional GM refrigerator for cooling of superconducting magnets, SQUIDS, and cryopumping applications. The second stage regenerative material plays an important role in achieving low temperature below 20 K. Leads balls with 0.2 mm to 0.4 mm average diameter was selected as second stage regenerator matrix material while 200 mesh of SS 304 material was filled in the first stage. A two stage GM type PTR was developed. A rotary valve was fabricated and the valve timing effects on cooling performance of PTR were also studied. The valve timings were varied by the different width of rotor slit forming the flow area with stator ports. The lowest no-load temperature of 18.52 K and cooling capacity of 7 W at 29.58 K were obtained with an optimum frequency of 1.6 Hz, charging pressure of 16.5 bar.