Abstract A cryostat is disclosed which includes a liquid helium chamber for cooling an object such as a superconducting solenoid to cryogenic temperatures. A vent tube is connected in gas communication with the liquid helium chamber and extends outwardly therefrom for venting vaporized helium. An elongated plug partially closes off the vent tube and defines an annular gas passageway in the space between the plug and the inside wall of the vent through which the evolved gaseous helium is vented for cooling the inside wall of the vent tube. The plug includes a liquid nitrogen chamber and thermal insulation is interposed in the plug between the liquid nitrogen and liquid helium chambers to provide a thermal barrier therebetween. The use of liquid nitrogen in the plug improves the thermal isolation of the liquid helium chamber from the surrounds and reduces the liquid helium consumption.
The apparatus of claim 1 including a plurality of ribbon shaped electrically conductive leads disposed about the periphery of said plug means in heat exchanging relation with the vented evolved cryogenic gas for cooling said leads.
Claim 2
Dependent Claim
71 words
The apparatus of claim 1 including a pair of concentric evacuated chambers surrounding said first cryogenic chamber for thermally insulating said first cryogenic chamber from the surrounds, said pair of evacuated chambers having a common partitioning wall therebetween, and said common partitioning wall being made of a thermally conductive material to form a radiation shield and being connected in heat exchanging relation to said vent tube for cooling said radiation shield.
Claim 3
Dependent Claim
47 words
The apparatus of claim 3 wherein said common partitioning wall is made of copper, and said thermally conductive connection from said vent tube to said partitioning wall includes an arcuate member interposed between said vent tube and said partitioning wall to form the thermally conductive connection therebetween.
Claim 4
Dependent Claim
24 words
The apparatus of claim 4 wherein said arcuate thermally conductive member is axially coextensive with at least a portion of said second cryogenic chamber.
Claim 5
Dependent Claim
82 words
The apparatus of claim 1 including at least one thermally conductive plate disposed intermediate the length of said thermally insulative means in said plug, said thermally conductive plate being mounted with the plane of the plate generally transverse to the longitudinal axis of said plug and vent tube to provide an isothermal plane in said plug, and means providing a thermally conductive path from said plate to said annular gas passageway such that said plate is cooled by the vented cryogenic gas.
Claim 6
Dependent Claim
32 words
The apparatus of claim 6 wherein said thermally conductive path interconnecting said gas passageway and said plate includes a thermally conductive wire connected to said plate and extending into said gas passageway.
Claim 7
Dependent Claim
34 words
The apparatus of claim 6 including a plurality of said thermally conductive plates spaced at intervals along the axis of said plug, and including thermal insulative means interposed between adjacent ones of said plates.