Medium-size pulse tube coolers with linear compressor

Abstract

We have designed and constructed two medium-size U-shaped pulse tube coolers for potential future replacement of Stirling cold fingers. The pressure oscillation in the coolers is generated by means of commercial linear compressors (Leybold Polar or AIM SL200) operated at a frequency of 40 Hz. Adjustment of phase shift between pressure and mass flow oscillation is accomplished by means of an inertance tube with buffer volume and a second-inlet flow impedance that are connected to the warm end of the pulse tube. The pulse tube cold head PT 01 operated with Polar compressor reached a lowest temperature of 34.3 K, and a cooling power of 5.2 W at 80 K has been achieved so far at a compressor input power of 180 W. A cooling power of 2.8 W at 60 K has been obtained with 200 W input power. At 100 W compressor input power, the two tested units, consisting of PT01 with Polar compressor and PT02 with SL200 compressor, produced more than 2.5 W of cooling at 80 K. The above results data were obtained with the pulse tube in horizontal position. Measurements of the cold tip temperature as function of the cold head orientation showed a convection-induced temperature variation of several percent. The minimum temperature is achieved with the cold end facing downwards.