Design and development of a cryogenic J-T valve for a 2K cryostat with a single cryocooler

A cryogenic Joule-Thomson (J-T) valve for a 2K cryostat cooled with a G-M cryocooler has been developed to continuously supply superfluid helium. Saturated liquid helium flowing through the valve transitions to superfluid helium below 2K because of the J-T effect. The heat leak, sealing performance and the J-T effect of the valve were tested experimentally and analyzed. To reduce heat leak in the 2K range, two thermal anchors were installed in the first and second cooling stages, respectively, resulting in 89.93% reduction of useful work loss. A unique sealing structure was developed for the J-T valve and was tested at both room temperature and liquid nitrogen temperature, yielding leak rates of 3 x 10(-9) Pa . m(3)/s and 3 x 10(-4) Pa . m(3)/s, respectively. The corresponding valve needle and seat structure were designed based on the flow resistance equation. The J-T effect of the valve in 2K cryostat was tested at various valve openings. The cryostat can operate at 1.64K with no load and provide 0.143W cooling power at 2 K.