Developments on gm-type pulse tube cryorefrigerators with large cooling power

Over the past several years the authors have participated in basic and prototype developments of four valve pulse tube refrigerators (FVPTR) [1,2]. Systematic studies have been carried out to characterize the basics of energy transport mechanisms, the flow distribution and loss mechanisms of this type of pulse tube refrigerator (PTR) [3] with its active type of phase shifting. Based on the comprehension of these phenomena, several prototypes have been built and optimized for various applications. Recently a single-stage PTR in coaxial arrangement has been designed for maximum refrigeration power in the temperature range between 20 and 80 K limited by an available electrical input power of 7 kW. To reach this goal we used lead screens in the coldest part of the regenerator instead of spheres in order to decrease the pressure drop. The improvement of the regenerator prevents the reported fact that at higher temperatures the performance of a pulse tube with a regenerator partially filled with lead spheres can even be worse than a regenerator totally made of stainless steel [4]. At the moment the cooler provides a cooling power of 120 W@74 K and 40 W@34 K. The minimum no-load temperature achieved is 18.6 K.