Abstract: A cryogenic system includes a housing of a cryogenic chamber, a cold source in the cryogenic chamber, and a circulation loop for circulating cryogenic fluid between the cold source and a component to be cooled in the cryogenic chamber. The component has an elongated thermally conductive structure extending to a warmer environment. For adjustable cooling of the structure, an incoming stream of the cryogenic fluid is directed along a length of the structure extending from the component, and this stream is split into a first outgoing stream at a first location from the component and a second outgoing stream at a second location further from the component, and an adjustable valve adjusts the fraction of the incoming stream that becomes the second outgoing stream.

Abstract: A cryogenic system includes a housing of a cryogenic chamber, a cold source in the cryogenic chamber, and a gas circulation loop for circulating cryogenic gas between the cold source and material to be cooled in the cryogenic chamber. The circulation loop includes a gas pump, and a counter-flow heat exchanger connecting the gas pump to the cold source for cooling an in-flow of the cryogenic gas from the gas pump to the cold source with an out-flow of the cryogenic gas from the material to be cooled to the gas pump. In a preferred construction, the heat exchanger includes an outer tube and an inner tube nested within the outer tube, and a pair of three-port connector fittings attached to respective ends of the tubes.