Abstract: To improve cooling efficiency of a pulse tube refrigerator, it is found that creating two conditions in the refrigerator, particularly in a regenerator is effective. In a first condition, working fluid in the regenerator should be compressed or expanded without having any displacement thereof, while it should be displaced without compression or expansion in a second condition. In order to realize this idea, a fluid displacement control valve assembly including two relief valves is disposed between a pulse tube and a buffer tank. Each of the relief valves is a normally closed one-way valve, and the valves open in opposite directions to one another when a pressure difference between the pulse tube and the buffer tank reaches a predetermined value, thus allowing the working fluid to be displaced after its compression from the pulse tube to the buffer tank and after its expansion from the buffer tank to the pulse tube.

Abstract: To improve refrigerating efficiency by preventing working fluid flowing into a pulse tube from a high-temperature end side thereof from reaching a cooling part in a cryogenic refrigerator, a ball-shaped travel member which has almost the same cross-section as the cross section of the pulse tube is inserted into the pulse tube and moves together with the working fluid therein. In this arrangement, when the working fluid begins to flow into the pulse tube from a flow rate regulation part on the high-temperature end side of the pulse tube, the travel member located within the pulse tube moves toward a cooling part together with the working fluid flowing in the pulse tube. Since the travel member has almost the same cross-section as the cross-section of the pulse tube, there is no possibility that the working fluid flows through between the inner wall of the pulse tube and the travel member.