Miniature Stirling cryocoolers: trends in development

Abstract

Following a lengthy period of development, Stirling refrigerators have emerged as the preferred system for the miniature cryocoolers used in infrared night-vision, missile guidance systems and other low capacity cryogenic sensors. Single stage expansion integral and split-Sterling refrigerators having capacities of 0.25-1 W at 80 K are in series volume production. They are characterized by increasing reliability (multithousand hours operation). Future preference is anticipated for split-Stirling systems with close tolerance seals replacing rubber contact seals and linear electric motors increasingly preferred as the compressor drive. Present difficulties with the cooler—sensor interface and of fluid leakage will be overcome by manufacture of integrated cooler—sensor units welded leak-proof and having no provision for field servicing. Eventual production is anticipated of throw-away, radio tube like, cryocooler-sensor units capable of plugging in to ambient temperature circuits. Control of compression speed in accordance with load demand will be routine. The use of multistage expansion Stirling cryocoolers for superconducting electronics is anticipated with the development of the high temperature superconducting materials having critical temperatures ≈ 20 K and operating temperatures ≈ 10 K. Availability of a reliable, compact, relatively low cost, 10 K refrigerator would eliminate the need for liquid helium cooling and open possibilities for application of superconducting electronics on a broad front for diverse military and civil purposes.