Abstract
The authors feel that Stirling coolers are much suitable for use at ultra-low temperatures between -200℃ and -50℃ in the field of refrigeration, and have developed a Stirling cooler and a cooling unit using the single Stirling cooler for ultra-low temperature use. In this paper, the new cooling unit with double Stirling coolers is presented to meet a demand in cooling equipment market. The secondary refrigerant circulates in series between the both Stirling coolers. The cooling capacity increases about two times as much as the single cooling unit mentioned above.