Gas gap heat switch configuration
View Patent ↗A cryogenic cooling system that includes a cooled plate thermally coupled to a cryogenic refrigerator, a target assembly that includes a target refrigerator configured to achieve a lower base temperature than the cryogenic refrigerator, and a heat switch assembly with one or more gas gap heat switches. The heat switch assembly has a first end thermally coupled to the cooled plate and a second end thermally coupled to the target assembly. A sorption pump is configured to control thermal conductivity across the heat switch assembly based on the temperature of the sorption pump. The sorption pump is thermally coupled to the cryogenic refrigerator by a thermal link extending from the cooled plate to the heat switch assembly, with the sorption pump positioned along the thermal link between the cooled plate and the heat switch assembly.
1. A cryogenic cooling system comprising:
a cooled plate thermally coupled to a cryogenic refrigerator;
a target assembly, wherein the target assembly comprises a target refrigerator configured to obtain a lower base temperature than the cryogenic refrigerator;
a heat switch assembly comprising one or more gas gap heat switches, the heat switch assembly having a first end thermally coupled to the cooled plate and a second end thermally coupled to the target assembly; and
a sorption pump configured to control the thermal conductivity across the heat switch assembly in accordance with the temperature of the sorption pump, wherein the sorption pump is thermally coupled to the cryogenic refrigerator by a thermal link extending from the cooled plate to the heat switch assembly, wherein the sorption pump is arranged at a position along the thermal link between the heat switch assembly and the cooled plate;
wherein the thermal link comprises a first connecting member and a second connecting member, wherein the first connecting member extends between the heat switch assembly and the sorption pump, and wherein the second connecting member extends between the sorption pump and the cooled plate; and
wherein the first connecting member comprises a conduit for conveying gas between the sorption pump and one or more gas gap heat switches of the heat switch assembly.
2. A cryogenic cooling system according to claim 1 , wherein the sorption pump is configured to close one or more gas gap heat switches of the heat switch assembly in response to the temperature of the sorption pump exceeding a nominal transition temperature, and wherein the sorption pump is thermally coupled to the cooled plate so as to cool the temperature of the sorption pump below the nominal transition temperature during operation of the cryogenic refrigerator.
3. A cryogenic cooling system according to claim 2 , wherein the sorption pump is thermally coupled to the cooled plate so as to maintain the temperature of the sorption pump below the nominal transition temperature independent of the temperature of the target assembly.
4. A cryogenic cooling system according to claim 2 , wherein the nominal transition temperature is between 4 and 30 kelvin.
5. A cryogenic cooling system according to claim 2 , wherein the target assembly comprises a target plate thermally coupled to a target heater and the target refrigerator, wherein the sorption pump is thermally coupled to the cooled plate so as to maintain the temperature of the sorption pump below the nominal transition temperature during operation of the target heater.
6. A cryogenic cooling system according to claim 5 , wherein said operation of the target heater raises the temperature of the target plate above the nominal transition temperature.
7. A cryogenic cooling system according to claim 1 , wherein the target assembly comprises a target plate thermally coupled to a target heater and the target refrigerator.
8. A cryogenic cooling system according to claim 1 , wherein the sorption pump is configured to open and close each said gas gap heat switch of the heat switch assembly.
9. A cryogenic cooling system according to claim 1 , further comprising a sorption heater configured to apply localised heating to the sorption pump.
10. A cryogenic cooling system according to claim 1 , wherein the second connecting member has a thermal conductance between 1 and 50 milliwatts per kelvin.
11. A cryogenic cooling system according to claim 1 , further comprising one or more stages arranged between the cooled plate and the target assembly, wherein each stage is thermally coupled to one or more gas gap heat switches of the heat switch assembly.
12. A cryogenic cooling system according to claim 1 , wherein the cryogenic refrigerator is a mechanical refrigerator selected from the group comprising: a pulse tube refrigerator, a Stirling refrigerator and a Gifford-McMahon refrigerator.
13. A cryogenic cooling system according to claim 1 , wherein the target refrigerator comprises any of a helium-3 refrigerator, a still or a mixing chamber of a dilution refrigerator, or a 1 kelvin pot.
14. A method of operating a cryogenic cooling system comprising a cooled plate thermally coupled to a cryogenic refrigerator, a target assembly comprising a target refrigerator configured to obtain a lower base temperature than the cryogenic refrigerator, a heat switch assembly comprising one or more gas gap heat switches and having a first end thermally coupled to the cooled plate and a second end thermally coupled to the target assembly, and a sorption pump configured to control the thermal conductivity across the heat switch assembly in accordance with the temperature of the sorption pump, wherein the sorption pump is thermally coupled to the cryogenic refrigerator by a thermal link extending from the cooled plate to the heat switch assembly, wherein the sorption pump is arranged at a position along the thermal link between the heat switch assembly and the cooled plate, wherein the sorption pump is configured to thermally couple the cryogenic refrigerator with the target assembly in response to the temperature of the sorption pump exceeding a nominal transition temperature, the method comprising the following step:
a) raising the temperature of the target assembly from a first temperature below the nominal transition temperature to a second temperature above the nominal transition temperature;
wherein the sorption pump is thermally coupled to the cryogenic refrigerator using the thermal link so as to maintain the temperature of the sorption pump below the nominal transition temperature during step (a).
15. A method according to claim 14 , wherein the cryogenic cooling system further comprises a sorption heater thermally coupled to the sorption pump, the method further comprising performing the following step after step (a):
b) operating the sorption heater so as to raise the temperature of the sorption pump above the nominal transition temperature, thereby thermally coupling the cryogenic refrigerator to the target assembly.
16. A method according to claim 14 , wherein the target assembly further comprises a target heater, and wherein step (a) is performed by operating the target heater.
17. A method according to claim 14 , wherein the first temperature is below 5 kelvin.
18. A method according to claim 14 , wherein the second temperature is above 20 kelvin.