Compact Low-power Cryo-Cooling Systems for Superconducting Elements

Abstract

A compact, low power cryo-cooler for cryogenic systems capable of cooling gas to at least as low as 2.5 K. The cryo-cooler has a room temperature compressor followed by filtration. Within the cryostat, four counterflow heat exchangers precool the incoming high-pressure gas using the outflowing low-pressure gas. The three warmest heat exchangers are successively heat sunk to three stages of a pulse tube to absorb residual heat from the slight ineffectiveness of the heat exchangers. The pulse tube cold head also absorbs loads from instrumentation leads and radiation loads. The pulse tube stages operate at around 80 K, 25 K, and 10 K. The entire system—cryo-cooler, drive and control electronics, and detector instrumentation, fits in a standard electronics rack mount enclosure, and requires around 300 W or less of power.

What is claimed is: 
     
         1 . A compact, low-power cryo-cooler system for cryogenic systems comprising:
 a cryo-cooler compressor for providing a flow of hot high-pressure gas and receiving a return flow of cool low-pressure gas;   a series of counterflow heat exchangers configured to cool hotter incoming gas from the compressor with cooler gas returning to the compressor;   a pulse tube cooler including a series of closed-cycle pulse tube cooling stages configured to interact with the counterflow heat exchangers to pre-cool the high-pressure gas to at least as low as 10 K; and   a Joule-Thomson (JT) cooler configured to cool the pre-cooled gas to at least as low as 1.7 K, the JT cooler including an expansion capillary having a warm end and a cold end, wherein the warm and cold ends of the expansion capillary are physically separated enough to achieve sufficient thermal isolation between the warm and cold ends to achieve the 1.7K;   wherein the cryo-cooler and associated drive and control electronics fit within a 7U electronics rack and the cooler and associated drive and control electronics require less than about 300 W of power.   
     
     
         2 . The cryo-cooler of  claim 1  wherein the cryo-cooler requires less than 250 W of power. 
     
     
         3 . The cryo-cooler of  claim 1  wherein the input pressure to the JT cooler is between 0.1 MPa and 0.2 MPa and the output pressure from the JT cooler is between 0.2 MPa and 1.3 kPa and wherein the output pressure is lower than the input pressure. 
     
     
         4 . The cryo-cooler of  claim 3  wherein the flow from the JT cooler is on the order of half a mg/sec. 
     
     
         5 . The cryo-cooler of  claim 1  having three pulse tube cooling stages, the three stages pre-cooling the gas to about 50-100K, 20-30K, and 6-10K in turn. 
     
     
         6 . The cryo-cooler of  claim 5  wherein the three cooling stages are implemented with a 3-stage linear compressor pulse tube operating at 35 Hz. 
     
     
         7 . The cryo-cooler of  claim 1  wherein the gas is 4He. 
     
     
         8 . The cryo-cooler of  claim 1  wherein the gas is 3He and the JT cooler is configured to cool the gas to around 1.25 K. 
     
     
         9 . The cryo-cooler of  claim 1  wherein the pulse tube stages have regenerators and pulse tube walls comprising stainless-steel tubing. 
     
     
         10 . The cryo-cooler of  claim 1  wherein the coldest pulse tube cooling stage utilizes erbium-nickel spheres. 
     
     
         11 . The cryo-cooler of  claim 1  wherein the counterflow heat exchangers are tube-in-tube. 
     
     
         12 . The cryo-cooler of  claim 1  wherein a JT expansion element within the JT cooler is comprises a 1 m-3 m long, 40 μm-60 μm inner-diameter stainless steel capillary 
     
     
         13 . The cryo-cooler of  claim 1  wherein the cold end of the expansion capillary is housed in copper block and the warm end of the expansion capillary is spaced apart from the copper block.