Cooling apparatus comprising a thermal interface and method for recondensing a cryogen gas

1. Cooling apparatus comprising:

a removable cryogenic refrigerator mounted within a sleeve, wherein a volume within the sleeve surrounding the refrigerator forms a closed recondensing chamber; and

a thermal interface between the removable cryogenic refrigerator and a cryogen vessel to be cooled by the cryogenic refrigerator; wherein,

the thermal interface is a non-contact thermal interface between a cooling stage of the refrigerator and a base of the closed recondensing chamber and includes: a gas held in thermal contact with the cooling stage of the refrigerator, the base of the closed recondensing chamber, and a pool of liquid in contact with the base but not the cooling stage;

the cryogen vessel is cooled by thermal conduction through the base of the closed recondensing chamber; and

the cooling stage does not make mechanical contact with the base of the closed recondensing chamber,

wherein the base of the closed recondensing chamber is in direct thermal contact with a further recondensing chamber, arranged for the recondensation of a cryogen gas and sealed from the closed recondensing chamber of the thermal interface,

wherein the base forms part of a wall of the cryogen vessel and forms part of a wall of the sleeve.

2. The cooling apparatus according to claim 1 , wherein the gas condenses to the liquid on the cooling stage and falls under gravity into contact with the base of the closed recondensing chamber.

3. The cooling apparatus according to claim 1 , wherein the cooling stage is provided with fins.

4. A cryostat comprising the cryogen vessel containing a liquefied cryogen, and being connected for cooling by the cooling apparatus according to claim 1 .

5. An MRI system comprising superconducting windings contained within a cryostat as claimed in claim 4 .

6. A thermal interface, comprising a closed recondensing chamber that is disposed around a recondensing refrigerator and is in thermal contact with a cryogen vessel that is to be cooled, through a base of the closed recondensing chamber, wherein:

the closed recondensing chamber is formed by a volume within a sleeve surrounding the recondensing refrigerator, the closed recondensing chamber filled with a gas which is recondensed into a liquid by the recondensing refrigerator, the liquid forming a pool that is in contact with the base but not the recondensing refrigerator,

thermal contact between the recondensing refrigerator and the cryogen vessel is provided by recondensation of the gas and through the base of the closed recondensing chamber,

the thermal interface is a non-contact thermal interface between a cooling stage of the refrigerator and the base of the closed chamber,

the cooling stage does not make mechanical contact with the base of the closed recondensing chamber, and

the base of the closed recondensing chamber is in direct thermal contact with a further recondensing chamber, arranged for the recondensation of a cryogen gas and sealed from the closed recondensing chamber of the thermal interface,

the base forms part of a wall of the cryogen vessel and forms part of a wall of the sleeve.

7. A method for recondensing a cryogen gas within a cryostat comprising the steps of:

providing a recondensing surface exposed to the cryogen gas within the cryostat and arranged in thermal contact with a wall of a closed recondensing chamber of the thermal interface as recited in claim 6 ; and

cooling the recondensing surface by cooling the component through the wall of the closed recondensing chamber of the thermal interface,

wherein the wall of the closed recondensing chamber is in direct thermal contact with a further recondensing chamber, arranged for the recondensation of a cryogen gas and sealed from the closed recondensing chamber of the thermal interface.

8. A cooling apparatus comprising:

a cryogenic refrigerator mounted within a sleeve, wherein a volume within the sleeve surrounding the refrigerator forms a closed recondensing chamber;

a thermal interface that is in thermal contact with a cooling stage of the refrigerator, and with a cryogen vessel that is to be cooled; wherein

said thermal interface comprises the closed recondensing chamber, at least a portion of which is in thermal contact with said cooling stage of the refrigerator;

the closed recondensing chamber is filled with a cryogen gas, and is separated and sealed from a cryogen fluid contained in the cryogen vessel, by a base of the closed recondensing chamber that is in thermal contact with said cryogen fluid in said cryogen vessel;

said recondensing chamber is configured such that, in an operating state, gas that is liquefied in said recondensing chamber accumulates adjacent said base but does not contact the cooling stage, and is boiled off by heat transferred from gaseous cryogen fluid in said cryogen vessel; and

the cooling stage does not make mechanical contact with the base of the closed recondensing chamber,

wherein the base of the closed recondensing chamber is in direct thermal contact with a further recondensing chamber, arranged for the recondensation of a cryogen gas and sealed from the closed recondensing chamber of the thermal interface,

wherein the base forms part of a wall of the cryogen vessel and forms part of a wall of the sleeve.

9. A cryogenic cooling apparatus comprising:

a cryogenic refrigerator mounted within a sleeve, wherein a volume within the sleeve surrounding the refrigerator forms a first recondensing chamber that is filled with a gas and is in thermal contact with a cooling stage of said cryogenic refrigerator; and

a second recondensing chamber that is in thermal contact with a base of said first recondensing chamber and with a cryogen vessel that is to be cooled; wherein,

said first recondensing chamber is separated from said second recondensing chamber by said base which forms a heat transfer path between said first and second recondensing chambers, and which seals and isolates said first recondensing chamber from said second recondensing chamber;

said second recondensing chamber is in thermal contact with a cryogenic fluid in said cryogen vessel; and

said gas in said first recondensing chamber forms a non-contact thermal interface between said cooling stage and said base, wherein said cooling stage does not make mechanical contact with said base, wherein said gas condenses to form a liquid pool in contact with the base but not the cooling stage,

wherein the base of the first recondensing chamber is in direct thermal contact with a second recondensing chamber, arranged for the recondensation of a cryogen gas and sealed from the first recondensing chamber of the thermal interface,

wherein the base forms part of a wall of the cryogen vessel and forms part of a wall of the sleeve.

10. The cryogenic cooling apparatus according to claim 9 , wherein said second recondensing chamber is in fluid communication with cryogenic fluid that is contained in an interior of said cryogen vessel.