A New Low-Temperature Gas Expansion Cycle

Abstract

In the past decade, experimentation at extremely low temperatures has brought to light several physical phenomena which show considerable promise of practical applications, provided a simple, reliable refrigerator can be developed to maintain the required low temperature. The solid statemaser [1,2], a low-noise microwave amplifier, may require temperatures as low as 1.5°K. Superconductive devices such as the cryotron [3], will probably require temperatures In the vicinity of the boiling point of helium (4.2°K); and there are a variety of infrared detectors which are benefited considerably by cooling below the temperature of liquid air [4]. A refrigeration system of the required simplicity and with sufficient flexibility to meet the broad spectrum of foreseeable applications will necessarily be based on a closed-cycle, adiabatic-expansion system using helium gas as the refrigerant. The use of helium is inevitable because it is the only substance which remains fluid at the lower temperatures, and it is highly desirable to have a closed-cycle device because of the necessity of conserving helium. Finally, it is necessary to use adiabatic expansion because Joule-Thomson expansion does not result in cooling of helium gas until the gas is first cooled to below 30°K by some other means.