EXPERIMENTAL INVESTIGATION OF 4-K PULSE TUBE REFRIGERATOR

To investigate how to reach 4 K using a pulse tube and the best multiple staging configuration for the pulse tube, experiments were performed on several types of single-stage pulse tube refrigerators coupled with a Gifford-McMahon cryocooler. The minimum temperature obtained at the cold end of the pulse tube using this unit was 3.5 K, when the hot end of the pulse tube was located at room temperature. The hot end of the final stage regenerator was precooled at almost-equal-to 15-20 K. The optimum operating conditions involved a mean pressure of almost-equal-to 1.0-1.5 MPa and a frequency of almost-equal-to 1-2 Hz. Heat flow and loss analysis, as related to the phase shift effect, as well as the arrangement of the multi-stage pulse tube refrigerator for reaching 4 K, are briefly discussed.