Experimental study of a pulse tube cold head driven by a low frequency thermal compressor.

Cryocoolers operating at liquid helium temperature span a number of application domains, such as cooling of superconducting magnets, SQUID devices etc. GM type cryocoolers are widely used at liquid helium temperature but with shortcomings of using an oil-lubricated compressor that require regular maintenance and rotary valves that reduces the efficiency of the cryocooler. We are developing an alternative system that makes use of a Vuilleumier type thermal compressor. The system consists of a Stirling type pulse tube cryocooler that provides a cold heat sink to a thermal compressor. The thermal compressor generates pressure wave to drive a second pulse tube cold head. We experimentally studied the influence of pre-cooling temperature and frequency on the performance of the pulse tube cold head. The lowest recorded temperature is 24.3 K with a pressure ratio of 1.18 and a frequency of 3 Hz. In this paper, the design of the cooling system and preliminary experimental results are presented.