Systems and methods for cryogenic refrigeration

Abstract

Systems and methods for improving the performance of dilution refrigeration systems are described. Filters and traps employed in the helium circuit of a dilution refrigerator may be modified to improve performance. Some traps may be designed to harness cryocondensation as opposed to cryoadsorption. A cryocondensation trap employs a cryocondensation surface having a high thermal conductivity and a high specific heat with a binding energy that preferably matches at least one contaminant but does not match helium. Multiple traps may be coupled in series in the helium circuit, with each trap designed to trap a specific contaminant or set of contaminants. Both cryocondensation and cryoadsorption may be exploited among multiple traps.

1 . A dilution refrigeration system comprising:
 a dilution refrigerator including a helium circuit;   a secondary cold source that in operation provides cooling power at temperatures between about 4K and about 77K; and   at least a first trap coupled in series with the helium circuit, wherein the first trap comprises a first trap volume and at least one cryocondensation surface inside the first trap volume, and wherein the at least one cryocondensation surface is thermally coupled to the secondary cold source.   
     
     
         2 . The dilution refrigeration system of  claim 1  wherein the first trap volume includes multiple cryocondensation surfaces to provide a large surface area in the first trap volume. 
     
     
         3 . The dilution refrigeration system of  claim 1  wherein the secondary cold source includes a pulse tube cryocooler. 
     
     
         4 . The dilution refrigeration system of  claim 1 , further comprising:
 a second trap coupled in series with the helium circuit, wherein the second trap comprises a second trap volume and an adsorptive material inside the second trap volume.   
     
     
         5 . The dilution refrigeration system of  claim 4  wherein the second trap is thermally coupled to the secondary cold surface. 
     
     
         6 . The dilution refrigeration system of  claim 4 , further comprising:
 a tertiary cold source that in operation provides cooling power at temperatures between about 4K and about 77K, wherein the second trap is thermally coupled to the tertiary cold source.   
     
     
         7 . The dilution refrigeration system of  claim 6  wherein the tertiary cold source includes a pulse tube cryocooler. 
     
     
         8 . The dilution refrigeration system of  claim 6  wherein the tertiary cold source includes a bath of liquid cryogen. 
     
     
         9 . The dilution refrigeration system of  claim 1  wherein the dilution refrigerator is thermally coupled to the secondary cold source. 
     
     
         10 . A cryogenic trapping system comprising:
 a cryoadsorption trap including an adsorption material and a plurality of thermalization surfaces interposed throughout the adsorption material, wherein the thermalization surfaces form a circuitous route through the adsorption material through which gas flows; and   a cryocondensation trap coupled in series with the cryoadsorption trap, wherein the cryocondensation trap includes a length of tubing that is at least partially filled with a high surface area cryocondensation material.   
     
     
         11 . The cryogenic trapping system of  claim 10  wherein the cryoadsorption trap and the cryocondensation trap are both thermally coupled to a first temperature stage in a cryogenic refrigeration system. 
     
     
         12 . The cryogenic trapping system of  claim 11 , further comprising:
 at least two parallel trapping subsystems both coupled in series with the cryoadsorption trap, wherein the at least two parallel trapping subsystems are each controllably thermally coupleable to a second temperature stage in the cryogenic refrigeration system via a respective heat switch, and wherein the second temperature stage of the cryogenic refrigeration system is warmer than the first temperature stage of the cryogenic refrigeration system.   
     
     
         13 . The cryogenic trapping system of  claim 12  wherein the at least two parallel trapping subsystems each employ at least one of cryoadsorption and/or cryocondensation. 
     
     
         14 . The cryogenic trapping system of  claim 10  further comprising at least one gauge connected in series with the cryogenic trapping system, the at least one gauge selected from a group consisting of: flowmeters, pressure gauges, and contaminant sensors.