Development of small size Claude cycle helium refrigerator with micro turbo-expander

In the field of small size helium refrigerators, need for a maintenance free and vibration free system is rapidly increasing, especially for the application to cryoelectronic devices such as NMR-CT and Josephson computers. To meet this need, we have been developing a Claude cycle helium refrigerator (5W at 4.5 K) with two-stage expansion micro-turbines. Other than the micro-turbines, compact size perforatedplate heat exchangers and a single-stage screw type compressor have been developed for the system. This paper describes design and test results of the major components of the system with an emphasis on the microturbine performance