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 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 with cooler returning gas;   a pulse tube cooler including a pulse tube compressor and 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 2.5 K;   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 to achieve 2.5 K.   
     
     
         2 . The cryo-cooler of  claim 1  wherein the JT cooler is further configured to cool the pre-cooled gas to 2.2 K. 
     
     
         3 . The cryo-cooler of  claim 2  wherein the JT cooler is further configured to cool the pre-cooled gas to 1.7 K and wherein a JT expansion element within the JT cooler is surrounded by a heat sink and thermally isolated from a return tube for returning 1.7K gas. 
     
     
         4 . The cryo-cooler of  claim 1  wherein the cryo-cooler requires less than 250 W of power. 
     
     
         5 . The cryo-cooler of  claim 1  wherein the input pressure to the JT cooler is on the order of a few hundred kPa and the output pressure from the JT cooler is on the order of a few kPa. 
     
     
         6 . The cryo-cooler of  claim 5  wherein the flow from the JT cooler is on the order of half a mg/sec. 
     
     
         7 . 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. 
     
     
         8 . The cryo-cooler of  claim 1  wherein the gas is 4He. 
     
     
         9 . 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. 
     
     
         10 . The cryo-cooler of  claim 1  wherein the pulse tube stages have regenerators and pulse tube walls comprising standard sized stainless-steel tubing. 
     
     
         10 . The cryo-cooler of  claim 1  wherein the last 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