Cryostat system for temperatures on the order of 2{20 K or less

摘要

A cryostat system for cooling a device to a temperature on the order of 2 DEG K or less includes a dewar, in which helium, in other than the superfluid state, is stored. Helium flows from the dewar through a heat exchanger tube and a restrictor tube, which controls the helium flow rate, into the cavity of a heat exchanger, to whose outer wall the device to be cooled is attached. A pressure regulator valve controls the pressure in the cavity to be very low, e.g., on the order of 30 Torr. As the helium exits the restrictor tube into the cavity, due to low pressure cavity, it becomes an aerosol mixture of helium gas and superfluid helium droplets at the desired temperature. The latter form a thin layer or film of superfluid helium on the inner side of the heat exchanger wall and thereby cool the device, which is attached to the wall to the desired temperature. The helium gas, formed during the exit of the helium into the cavity and the helium gas, formed from the superfluid helium, which is evaporated by absorbing heat from the device being cooled, are evacuated from the cavity. As they flow around the heat exchanger tube, through which helium flow from the dewar, heat is absorbed by the helium gas from the helium in the tube, so that the helium entering the cavity is at a lower temperature than the helium entering the tube from the dewar. The evacuated helium gas may be used for one or more purposes, including reducing the amount of radiated heat reaching the dewar, as well as serve as the propellant for spacecraft attitude control. The cryostat may be used to cool different devices to different temperatures on the order of 2 DEG K or less during an entire mission or during selected independent periods for each device.