Development of helium liquefiers and refrigerators for nuclear fusions

New helium liquefiers and refrigerators for nuclear fusion reactors were developed. The system consists of a helium liquefying refrigerator, a recovery and refining system, and a liquid helium container. The refrigerator consists of a cold box and a circulating compressor. In the cold box, an expansion turbine, a heat exchanger, valves and pipings are contained. A gas bearing system is used in the turbine, and the rotating rate is 230000 rpm. The heat exchanger in the cold box was made small by using aluminum plate fins. The compressor is of rotating screw type, and can be operated for long period continuously. A microcomputer system is used for the automatic control of start-up, operation and stop. This refrigerator can make liquid helium of 100 litre per one hour. (Kato, T.)