This paper describes the basic structure of a two-stage pulse tube refrigerator. A novel phase shifter termed a double-orifice is introduced. The machine was driven by a valved compressor and the on-off timing was controlled by a computer and solenoids. The lowest temperature of 3.1 K at the cold end of the second stage was achieved.

Experiments have been made on the onset and damping behavior of the oscillation in a thermoacoustic prime mover with nitrogen as the working

Based on review and analysis of thermodynamic efficiency e of the Carnot cycle and the cycle with two isothermal and two polytropic processes, another thermodynamic cycle with two isentropic and two polytropic processes, which can achieve the Carnot value of thermodynamic efficiency, is testified theoretically. Thermodynamic efficiency expressions of a number of ideal regenerative refrigeration cycles are derived, including the ideal pulse tube refrigeration cycle. A classified branch chart and a plot of ideal thermodynamic efficiency of regenerative refrigeration cycles are given for the purpose of comparison.

Based on the discussion of the matching problems between the prime mover and pulse tube, a self-made standing-wave ther-moacoustic prime mover is used to drive a coaxial single-stage pulse tube refrigerator A lowest refrigeration temperature of 138 K was obtained from the preliminary tests in 1999 Then, some improvements have been made to the heat exchangers and the con-nection between prime mover and pulse tube The minimum cooling temperatures of ll9.7 and ll7.6 K have been obtained from therecent experiments with helium andhelium-argon mixture filling of 2.0 MPa as the working fluids, respectively Itis a great progress for the standing-wave machine and provides the possibility of liquefying natural gas of 0.2 MP.