A high capacity 0.23 K He-3 refrigerator for balloon-borne payloads

We describe the design, operation, and performance of a high capacity, single stage, He-3 refrigerator optimized for balloon-borne payloads. A temperature of similar to 0.2 K is routinely maintained for more than seven days at similar to 100 mu W total heat load. Recycling can be completed in less than 12 h. A simple design avoids valves and explicit heat switches, resulting in simplified construction and improved performance. A numerical model characterizes the operating temperature of the system over a large range of conditions. (C) 1996 American Institute of Physics.