Recondensing service neck for cryostat

1. A service neck and refrigerator assembly for a cryostat, comprising:

a service neck tube for providing access to the interior of the cryostat;

a recondensing surface for recondensing liquid cryogen boiled off from a liquid cryogen within a cryostat;

a refrigerator for cooling the recondensing surface to below the boiling point of the cryogen; and

a thermal link provided between a cooling surface of the refrigerator and a part of the service neck tube; wherein

an interior surface within said part of the service neck tube forms the recondensing surface; and

a surface of the thermal link is exposed within the service neck tube, said exposed surface being the interior surface that forms recondensing surface.

2. A service neck and refrigerator assembly according to claim 1 , wherein the recondensing surface is ribbed.

3. A service neck and refrigerator assembly according to claim 1 , wherein:

the recondensing refrigerator is a two-stage refrigerator;

a first stage cooling surface of the recondensing refrigerator is thermally connected to an upper part of the service neck tube; and

a second stage cooling surface is thermally connected to the thermal link.

4. A service neck and refrigerator assembly according to claim 1 , wherein:

the cooling surface is thermally connected to the thermal link by a recondensing interface;

the recondensing interface itself comprises a closed recondensation chamber containing a cryogen exposed to the cooling surface of the refrigerator and also exposed to the thermal link, whereby heat may be transferred from the thermal link to the cooling surface by repeated evaporation and recondensation of the cryogen within the closed recondensation chamber.

5. A cryostat comprising a service neck and refrigerator assembly according to claim 1 , housed within a single turret structure.

6. A cryostat according to claim 5 wherein the turret structure is located substantially on a side of the cryostat.