Cryostat assembly

Abstract

A cryostat assembly includes a thermal shield, a cooling system including a cold member maintained in use at a temperature lower than that of the thermal shield, a first adsorption pump assembly located at least partly within the thermal shield, a first switch thermally connecting the adsorption pump to the thermal shield, a second switch selectively, thermally connecting the adsorption pump to the cold member, and a first thermal link. The first adsorption pump includes a pumping chamber containing a working fluid and an adsorption pump in fluid communication with the pumping chamber. The first thermal link couples the pumping chamber to the cold member. During adsorption of the working fluid by the adsorption pump, a portion of the working fluid evaporates so as to cause the temperature within the pumping chamber to fall below the temperature of the cold member.

1 . A cryostat assembly comprising:
 a thermal shield;   a cooling system including a cold member which is maintained in use at a temperature lower than that of the thermal shield;   a first adsorption pump assembly located at least partly within the thermal shield, the assembly comprising a pumping chamber containing a working fluid, and an adsorption pump in fluid communication with the pumping chamber;   a first switch for selectively, thermally connecting the adsorption pump to the thermal shield so as to cause the working fluid to desorb from the adsorption pump;   a second switch for selectively, thermally connecting the adsorption pump to the cold member so as to cause the working fluid to be adsorbed by the adsorption pump; and   a first thermal link coupling the pumping chamber to the cold member so as to condense at least a portion of the working fluid desorbed from the adsorption pump,   wherein during adsorption of the working fluid by the adsorption pump, a portion of the working fluid evaporates so as to cause the temperature within the pumping chamber to fall below the temperature of the cold member.   
   
   
       2 . An assembly according to  claim 1 , wherein the cooling system comprises a mechanical cooler. 
   
   
       3 . An assembly according to  claim 2 , wherein the mechanical cooler comprises a pulse-tube refrigerator, Gifford-McMahon refrigerator, Joule-Thomson refrigerator, or Stirling refrigerator. 
   
   
       4 . An assembly according to  claim 3 , wherein the mechanical cooler comprises at least two stages, a first stage being coupled with the thermal shield and a second stage defining, or being coupled to, the cold member. 
   
   
       5 . An assembly according to  claim 1 , wherein the cooling system comprises a liquid cryogen containing vessel. 
   
   
       6 . An assembly according to  claim 5 , wherein the liquid cryogen comprises liquid helium. 
   
   
       7 . An assembly according to  claim 5 , wherein the liquid cryogen containing vessel is cooled by a mechanical cooler. 
   
   
       8 . An assembly according to  claim 5 , wherein the liquid cryogen containing vessel is coupled to a boil off path which passes adjacent the thermal shield so as to cool the shield. 
   
   
       9 . An assembly according to  claim 1 , wherein the pumping chamber comprises a pipe extending downwardly from the adsorption pump. 
   
   
       10 . An assembly according to  claim 1 , wherein a lower end of the pumping chamber comprises a heat exchanger which is cooled by evaporation of a liquid phase of the working fluid in the pumping chamber. 
   
   
       11 . An assembly according to  claim 10 , wherein the heat exchanger is thermally coupled to a system to be cooled. 
   
   
       12 . An assembly according to  claim 11 , wherein the system to be cooled comprises a working volume in which a sample can be removably located. 
   
   
       13 . An assembly according to  claim 12 , wherein the system is adapted to receive a sample in the working volume for dynamically nuclear polarizing the sample. 
   
   
       14 . An assembly according to  claim 1 , further comprising
 a second adsorption pump assembly located at least partly within the thermal shield, the assembly comprising a pumping chamber containing a working fluid, and an adsorption pump in fluid communication with the pumping chamber;   a third switch for selectively, thermally connecting the adsorption pump to the thermal shield so as to cause the working fluid to desorb from the adsorption pump;   a fourth switch for selectively, thermally connecting the adsorption pump to the cold member so as to cause the working fluid to be adsorbed by the adsorption pump; and   a second thermal link coupling the pumping chamber to the cold member so as to condense at least a portion of the working fluid desorbed from the adsorption pump, wherein during adsorption of the working fluid by the adsorption pump, a portion of the working fluid evaporates so as to cause the temperature within the pumping chamber to fall below the temperature of the cold member.   
   
   
       15 . An assembly according to  claim 14 , wherein a lower end of the pumping chamber of the second adsorption pump assembly comprises a heat exchanger which is cooled by evaporation of a liquid phase of the working fluid in the pumping chamber. 
   
   
       16 . An assembly according to  claim 15 , wherein a heat exchanger is thermally coupled to a system to be cooled. 
   
   
       17 . An assembly according to  claim 16 , wherein the first and second pump assemblies are coupled via their respective heat exchangers to a system to be cooled, the switches being operable so as to achieve substantially continuous cooling of the system to be cooled. 
   
   
       18 . An assembly according to  claim 11 , wherein the heat exchanger is coupled to the system to be cooled via a cryogenic fluid which in use condenses on the heat exchanger and falls onto the system to be cooled. 
   
   
       19 . An assembly according to  claim 11 , wherein the system to be cooled comprises a magnet. 
   
   
       20 . An assembly according to  claim 19 , wherein the magnet is located in a coolant containing vessel. 
   
   
       21 . An assembly according to  claim 1 , wherein the first thermal link is permanently connected between the pumping chamber and the cold member. 
   
   
       22 . An assembly according to  claim 1 , further comprising a control system for controlling operation of the switches. 
   
   
       23 . An assembly according to  claim 1 , wherein the thermal shield at least partly surrounds the cold member. 
   
   
       24 . (canceled) 
   
   
       25 . An assembly according to  claim 14 , wherein the second thermal link is permanently connected between the pumping chamber and the cold member.