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 .- 13 . (canceled) 
     
     
         14 . A dilution refrigeration system comprising:
 a dilution refrigerator comprising a helium fluid circuit;   a pulse tube cryocooler comprising a cold head thermally coupled to the dilution refrigerator, the pulse tube cryocooler further comprising a first and a second temperature stage, the first temperature stage operable to provide cooling power at a first temperature, the second temperature stage operable to provide cooling power at a second temperature, the second temperature lower than the first temperature, each of the first and the second temperatures having a value in a range between about 4K and about 77K; and   a cryocondensation trap coupled in series with the helium fluid circuit, the cryocondensation trap comprising a cryocondensation trap volume formed by a segment of tubing in the helium fluid circuit, and a first and a second cryocondensation surface positioned inside the cryocondensation trap volume, wherein the first cryocondensation surface is thermally coupled to the first temperature stage of the pulse tube cryocooler, and the second cryocondensation surface is thermally coupled to the second temperature stage of the pulse tube cryocooler.   
     
     
         15 . The dilution refrigeration system of  claim 14 , wherein the helium fluid circuit comprises a segment of tubing at a third temperature, the third temperature higher than the first and the second temperature. 
     
     
         16 . The dilution refrigeration system of  claim 15 , wherein the third temperature is room temperature. 
     
     
         17 . The dilution refrigeration system of  claim 14 , further comprising:
 an adsorptive trap coupled in series with the cryocondensation trap, the adsorptive trap comprising an adsorptive trap volume, and an adsorptive material inside the adsorptive trap volume.   
     
     
         18 . The dilution refrigeration system of  claim 17 , wherein the adsorptive material comprises at least one of charcoal, activated charcoal or zeolite. 
     
     
         19 . The dilution refrigeration system of  claim 17 , wherein the adsorptive trap is at room temperature. 
     
     
         20 . The dilution refrigeration system of  claim 17 , wherein the adsorptive trap is thermally coupled to the pulse tube cryocooler. 
     
     
         21 . The dilution refrigeration system of  claim 17 , further comprising:
 a bath of liquid cryogen, wherein the adsorptive trap is immersed in the bath of liquid cryogen.   
     
     
         22 . The dilution refrigeration system of  claim 14 , wherein the cryocondensation trap volume comprises a plurality of cryocondensation surfaces to provide a large surface area in the cryocondensation trap volume. 
     
     
         23 . The dilution refrigeration system of  claim 14 , wherein the cryocondensation trap comprises a length of tubing that is at least partially filled with a high surface area cryocondensation material. 
     
     
         24 . The dilution refrigeration system of  claim 14 , further comprising:
 a heat switch thermally coupled between one of the first and the second cryocondensation surface and the respective first and second temperature stage of the pulse tube cryocooler, the heat switch operable to provide controllable thermal coupling.   
     
     
         25 . The dilution refrigeration system of  claim 14 , further comprising:
 at least one valve and a segment of bypass tubing, hydraulically coupled between the cryocondensation trap and the helium fluid circuit, the at least one value operable to cause the helium fluid circuit to bypass the cryocondensation trap.