Method for reconfiguring a cryostat configuration for recirculation cooling
A method for converting a cryostat configuration ( 1 ) having a first container ( 2 ) with a liquid helium bath ( 3 ) and a second container ( 6 ) which is filled with liquid nitrogen ( 7 ) is characterized in that a cooling medium ( 12 ) which is in a gaseous state at a temperature of 60K and a pressure of 1 bar, is introduced into the second container and is cooled by a refrigerator ( 16 ) by means of a cooling circuit ( 11 ), the coolant lines of which are guided into the second container, to an operating temperature of ≦60K. With this retrofit for existing cryostat configurations that utilize both liquid helium and also liquid nitrogen for cooling a superconducting coil, use of liquid nitrogen can be completely avoided and the evaporation rate of the liquid helium can also be considerably reduced without having to re-liquefy the cryogens used.
1. A method for converting a cryostat configuration having a room temperature vacuum container housing a first container structured for holding a liquid helium bath at an operating temperature which is kept below 5K by means of helium evaporation, wherein the room temperature vacuum container also contains a second container structured to hold liquid nitrogen for thermally shielding the first container and to keep that liquid nitrogen at an operating temperature of between 75 and 80K by means of nitrogen evaporation, the method comprising the steps of:
a) introducing a fluid cooling medium into the second container, the fluid cooling medium being gaseous at a temperature of 60K and a pressure of 1 bar; and
b) cooling the cooling medium to an operating temperature of ≦60K using a refrigerator and a cooling circuit, the cooling circuit having coolant lines which are guided into the second container.
2. The method of claim 1 , wherein helium or neon is used as the fluid cooling medium.
3. The method of claim 1 , wherein a heat exchanger is arranged in the second container and is connected to the coolant lines of the cooling circuit, the cooling medium being cooled to an operating temperature of ≦60K by means of the heat exchanger.
4. The method of claim 1 , wherein the coolant lines of the cooling circuit are open inside the second container such that the cooling medium is guided from the second container into the coolant lines of the cooling circuit and cooled to an operating temperature of ≦60K.
5. The method of claim 1 , wherein prior to step a), the second container is filled with liquid nitrogen which is supplemented or replaced by the introduced cooling medium during conversion of the cryostat configuration.
6. The method of claim 1 , wherein an amount of nitrogen is left in or introduced Into the second container in addition to the fluid cooling medium, the nitrogen occupying a volume of at least 5 l at an operating temperature of ≦60K.
7. A cryostat configuration for carrying out the method of claim 1 , the cryostat configuration comprising:
a room temperature vacuum container housing a first container, said first container being disposed, structured and dimensioned to hold a liquid helium bath at an operating temperature which is held below 5K by means of helium evaporation, said vacuum container also housing a second container, said second container being disposed, structured and dimensioned to hold liquid nitrogen for thermally shielding said first container and for maintaining the liquid nitrogen at an operating temperature of 75 to 80K by means of nitrogen evaporation; and
a cooling circuit, said cooling circuit comprising a refrigerator as well as cooling lines communicating with said refrigerator and extending into said second container, wherein said refrigerator and said cooling lines are disposed, structured and dimensioned to cool a fluid cooling medium to an operating temperature of ≦60K and to pass that cooling medium into said second container, said fluid cooling medium being gaseous at a temperature of 60K and at a pressure of 1 bar.
8. The cryostat configuration of claim 7 , wherein the cryostat configuration is structured within a nuclear magnetic resonance apparatus to cool a superconducting magnet configuration.
9. The cryostat configuration of claim 7 , wherein a damping element is provided in said coolant lines of said cooling circuit for insulating mechanical vibrations.
10. The cryostat configuration of claim 7 , further comprising a cooling medium tank that is arranged outside of said room temperature vacuum container and by means of which said second container or said cooling circuit can be supplied with cooling medium in order to counteract pressure fluctuations.
11. The cryostat configuration of claim 7 , further comprising a nitrogen reservoir for a residual amount of liquid and/or solid nitrogen.
12. The cryostat configuration of claim 7 , wherein said second container has a volume of at least 50 l.
13. The cryostat configuration of claim 7 , wherein said refrigerator is a pulse tube cooler, a Gifford-McMahon cooler or a Stirling cooler.
14. The cryostat configuration of claim 7 , wherein said cooling circuit has a compactor which is designed as a compressor for said refrigerator, as a cold gas compressor or as a pump operated at ambient temperatures, said compactor being integrated in said cooling circuit using a counter flow heat exchanger.
15. The cryostat configuration of claim 7 , wherein said cooling circuit has a Joule-Thomson expansion stage.