Closed cycle cryogen recirculation system and method

Abstract

There is provided refrigeration system ( 1 ) and method for remote cooling of a thermal load having a first portion ( 27 ) and a second portion ( 25 ). The system comprises a cold source ( 4 ) having a first cooling stage ( 5 ) and a second cooling stage ( 6 ), the temperature of the first cooling stage being higher than the temperature of the second cooling stage. The system also comprises a cryogen circuit for circulation of a cryogen flow in a closed cycle, the closed cycle being thermally coupled to the cold source. The system further comprises a compressor ( 7 ) for compressing and circulating the cryogen flow in the cryogen circuit. The cryogen circuit comprises a first conduit for thermally connecting the first cooling stage of the cold source to the first portion of the thermal load so as to cool said first portion towards the temperature of the first cooling stage, and a second conduit for thermally connecting the second cooling stage of the cold source to the second portion of the thermal load so as to cool said second portion to wards the temperature of the second cooling stage. The cryogen flow in the system is a sub-cooled or saturated liquid, two phase, saturated or overheated, supercritical gas helium flow.

1 . A refrigeration system ( 1 ) for remote cooling of a thermal load having a first portion ( 27 ) and a second portion ( 25 ), the system comprising:
 a cold source ( 4 ) having a first cooling stage ( 5 ) and a second cooling stage ( 6 ), the temperature of the first cooling stage being higher than the temperature of the second cooling stage;   a cryogen circuit for circulation of a cryogen flow in a closed cycle, the closed cycle being thermally coupled to the cold source; and   a compressor ( 7 ) for compressing and circulating the cryogen flow in the cryogen circuit,   wherein the cryogen circuit comprises a first conduit for thermally connecting the first cooling stage of the cold source to the first portion of the thermal load so as to cool said first portion towards the temperature of the first cooling stage, and a second conduit for thermally connecting the second cooling stage of the cold source to the second portion of the thermal load so as to cool said second portion towards the temperature of the second cooling stage, and   wherein the cryogen flow is a sub-cooled or saturated liquid, two phase, saturated or overheated, supercritical gas helium flow.   
     
     
         2 . A refrigeration system ( 1 ) according to  claim 1 , wherein the first portion ( 27 ) of the thermal load is a thermal shield. 
     
     
         3 . A refrigeration system ( 1 ) according to  claim 1 , wherein the second portion ( 25 ) of the thermal load is a superconducting magnet. 
     
     
         4 . A refrigeration system ( 1 ) according to  claim 1 , wherein the system further comprises a transfer line ( 24 ) in which one or both of the conduits are located, and wherein the transfer line has low thermal loss. 
     
     
         5 . A refrigeration system ( 1 ) according to  claim 1 , wherein the first ( 5 ) and second ( 6 ) cooling stages and the first and second conduits of the closed cycle cryogen circuit are all connected in series. 
     
     
         6 . A refrigeration system ( 1 ) according to  claim 1 , wherein the cold source is a cryocooler. 
     
     
         7 . A refrigeration system ( 1 ) according to  claim 1 , wherein the cold source is contained in a cryostat that is separate and independent from a cryostat of the thermal load. 
     
     
         8 . A refrigeration system ( 1 ) according to  claim 7 , wherein the cryostat comprises an actively cooled thermal shield ( 3 ). 
     
     
         9 . A refrigeration system ( 1 ) according to  claim 1 , wherein the system further comprises at least one heat exchanger. 
     
     
         10 . A refrigeration system ( 1 ) according to  claim 1 , wherein the system comprises means for performing a Joule-Thompson expansion step ( 18 ). 
     
     
         11 . A refrigeration system ( 1 ) according to  claim 1 , wherein the system can also act as a liquefier. 
     
     
         12 . A method for cooling remotely a thermal load using a refrigeration system ( 1 ), the method comprising:
 selecting the temperature of a first cooling stage ( 5 ) of a cold source ( 4 ) of the system to be higher than the temperature of a second cooling stage ( 6 );   circulating a cryogen flow in a closed cycle around the cryogen circuit of the refrigeration system, the closed cycle being thermally coupled to the cold source, the cryogen circuit comprising a first conduit for thermally connecting the first cooling stage of the cold source to a first portion ( 27 ) of the thermal load so as to cool said first portion towards the temperature of the first cooling stage, and a second conduit for thermally connecting the second cooling stage of the cold source to a second portion ( 25 ) of the thermal load so as to cool said second portion towards the temperature of the second cooling stage; and   compressing the flow in the cryogen circuit using a compressor ( 7 ) of the refrigeration system,   wherein the cryogen flow is a sub-cooled or saturated liquid, two phase, saturated or overheated, supercritical gas helium flow.