Abstract: A cryogenic refrigerator (10) which generates a cryogenic temperature by compressing and expanding a working gas in a closed loop (11). The cryogenic refrigerator comprises a bypass line (22) allowing a high-pressure portion and a low-pressure portion to communicate with each other, a gas storage tank (24) located midway in the bypass line and having pressure regulation valves (23a, 23b) on the high-pressure side and the low-pressure side, respectively, and a pressure control unit (26) controlling the pressure regulation valves. The pressure control unit (26) controls the pressure regulation valves (23a, 23b) so that the pressure in the gas storage tank (24) is equal to the pressure in the closed loop at room temperature and in a stopped state and so that the pressure in the gas storage tank (24) is between the pressures in the high-pressure portion and in the low-pressure portion and is close to the pressure in the low-pressure portion in an operating state.

Abstract: An adiabatic expansion apparatus 22 with a built-in turbine impeller 12 adiabatically expands gas at a cryogenic temperature when the impeller rotates. A control device 24 is connected coaxially with the turbine impeller to control the impeller. A variable nozzle mechanism 30 is provided for varying the throat area for the gas at a cryogenic temperature to be introduced into the turbine impeller. The adiabatic expansion apparatus is installed in a vacuum vessel 14, and a control device is disposed outside the vacuum vessel. The variable nozzle mechanism comprises a nozzle component 32 built into the adiabatic expansion apparatus, and a driving component 34 installed outside the vacuum vessel. The nozzle component and the driving component are connected to the turbine impeller with a coaxial, thin cylindrical component 36, and drive the nozzle component when the cylindrical component rotates about the axis Z of the turbine impeller.

Abstract: Method and apparatus for manufacturing superfluidity helium (He II). The method includes the steps of (a) providing .sup.3 He gas (b) providing liquid .sup.4 He, (c) compressing the .sup.3 He gas to produce compressed .sup.3 He gas, (d) indirectly cooling the compressed .sup.3 He gas with liquid .sup.4 He to produce cryogenic .sup.3 He gas (e) adiabatically expanding the cryogenic .sup.3 He gas to produce cryogenic .sup.3 He gas having a temperature of less than about 1.18.degree. K., preferably less than 1.8.degree. K., and (f) indirectly cooling the liquid .sup.4 He with the cryogenic .sup.3 He gas produced in step (e) to produce superfluidity helium. The apparatus includes a first container for liquid helium and a second container for containing superfluidity helium, and a first line for connecting the first and second containers. A .sup.3 He refrigeration circuit is provided to cool the .sup.4 He in directly with cryogenic .sup.3 He to produce superfluidity helium.