Abstract: A cryostat has a cryogen vessel retained within an outer vacuum container, the cryogen vessel being provided with a vent path allowing cryogen gas to escape from the cryogen vessel, the cryostat further having a thermal radiation shield interposed between the cryogen vessel and the outer vacuum container. The vent path is arranged such that escaping cryogen gas is directed through a conduit, which forms an integral part of a thermal radiation shield.

Abstract: 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 a cryogenic refrigerator to the radiation shield for cooling thereof. A secondary recondensing chamber is provided (8) for accommodating a second stage of a cryogenic refrigerator, and means (10; 24) are provided for thermally connecting the secondary recondensing chamber to a recondensing surface (11a; 44) 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.

Abstract: 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 a cryogenic refrigerator to the radiation shield for cooling thereof. A secondary recondensing chamber is provided (8) for accommodating a second stage of a cryogenic refrigerator, and means (10; 24) are provided for thermally connecting the secondary recondensing chamber to a recondensing surface (11a; 44) 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.

Abstract: A compressor (1) including a compressor mechanism; an input line (12) for providing gas to the compressor; and an output line (14) for providing compressed gas from the compressor. The compressor may supply gas at a first pressure or at a second pressure, by variation of the charge pressure within a gas circuit. A buffer volume and arrangement of valves, contained within the compressor, facilitate the change in static charge pressure. The electrical power drawn by the compressor is reduced when the charge pressure is reduced. Changing the charge pressure in the compressor also varies the cooling power delivered by the refrigerator. Therefore, this variable charge compressor can be used to reduce the electrical power drawn by an MRI system when it is in standby, and the full refrigeration capability is not required. Also, this has the effect of reducing wear and increasing the life of certain components within the refrigerator and compressor.

Abstract: A cryostat has a cryogen vessel retained within an outer vacuum container, the cryogen vessel being provided with a vent path allowing cryogen gas to escape from the cryogen vessel, the cryostat further having a thermal radiation shield interposed between the cryogen vessel and the outer vacuum container. The vent path is arranged such that escaping cryogen gas is directed through a conduit, which forms an integral part of a thermal radiation shield.