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

We describe the design, operation, and performance of a high capacity, single stage, ³He refrigerator optimized for balloon-borne payloads. A temperature of ∼0.2 K is routinely maintained for more than seven days at ∼100 μW 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.