Apparatus and method for controlling the cooling power of a cryogenic refrigerator delivered to a cryogen vessel

摘要

The present invention provides a cryostat comprising a cryogen vessel 1, a thermal radiation shield 2, and a sleeve 5 for accommodating a cryogenic refrigerator. Also provided is a first thermal contact for thermally and mechanically connecting a first stage of the cryogenic refrigerator to the radiation shield for cooling thereof. A secondary recondensing chamber 8 is provided for accommodating a second stage of the cryogenic refrigerator. Means 10, (24, fig.5) are provided for thermally connecting the secondary recondensing chamber to a recondensing surface 11a, (44, fig.5) exposed to the interior of the cryogen vessel. The cryostat further comprises a pressure control arrangement 100 for controlling the pressure of a gas within the secondary recondensing chamber. Preferably, the pressure control arrangement comprises an inlet valve 106 for admitting gas, so as to increase the chamber pressure, and a vent valve 104 for releasing gas, so as to reduce the chamber pressure. In use, by controlling the gas pressure in the secondary recondensing chamber, the cooling power delivered into the cryogen vessel by the refrigerator may be controlled.