Hybrid cryocooler with multiple passive stages

Abstract

A multi-stage cryocooler has three or more stages, including an active first stage and passive second and third stages. The active stage may include a Stirling expander, and the passive second and third stages may be pulse tube coolers. The cryocooler may provide cooling at three different temperatures. The coldest cooling temperature may be at or below 10 K, and may be at or below 5 K. The system may provide cooling at such low temperatures while still operating at a relatively high frequency, for example, at a frequency of at least about 20 Hertz.

1 . A multi-stage cryocooler comprising: 
 an active first stage; and    plural passive stages operatively coupled to the active first stage.    
   
   
       2 . The cryocooler of  claim 1 , wherein the passive stages include a pulse tube second stage and a pulse tube third stage.  
   
   
       3 . The cryocooler of  claim 2 , wherein at least one of the pulse tube stages is a concentric pulse tube.  
   
   
       4 . The cryocooler of  claim 3 , wherein the concentric pulse tubes each include a vacuum gap between parts of the pulse tube.  
   
   
       5 . The cryocooler of  claim 2 , wherein at least one of the pulse tube stages is a U-shape pulse tube stage.  
   
   
       6 . The cryocooler of  claim 2 , wherein the passive stages include respective manifolds allowing fluid flow therethrough.  
   
   
       7 . The cryocooler of  claim 6 , further comprising respective surge volumes mechanically coupled to the respective manifolds.  
   
   
       8 . The cryocooler of  claim 7 , wherein the surge volumes are located in an ambient temperature portion of the cryocooler.  
   
   
       9 . The cryocooler of  claim 6 , 
 wherein the manifolds include a second-stage manifold; and    wherein the second-stage manifold includes a passage for diverting flow, to bypass the pulse tube third stage.    
   
   
       10 . The cryocooler of  claim 9 , wherein the second stage manifold includes a flow plug.  
   
   
       11 . The cryocooler of  claim 10 , 
 wherein first openings of the flow plug allow incoming flow to pass from the pulse tube second stage to the pulse tube third stage; and    wherein second openings of the flow plug divert incoming flow to bypass the pulse tube third stage.    
   
   
       12 . The cryocooler of  claim 2 , wherein the pulse tube stages are oriented at a nonzero angle relative to one another.  
   
   
       13 . The cryocooler of  claim 1 , wherein the active first stage is a Stirling cycle stage.  
   
   
       14 . The cryocooler of  claim 1 , further comprising one or more microelectromechanical systems (MEMS) flow controllers for controlling flow of a working fluid within the cryocooler.  
   
   
       15 . The cryocooler of  claim 14 , wherein the output is at three different temperatures.  
   
   
       16 . The cryocooler of  claim 15 , wherein one of the temperatures is below 10 K.  
   
   
       17 . The cryocooler of  claim 16 , wherein the one of the temperatures is below 5 K.  
   
   
       18 . The cryocooler of  claim 16 , wherein the cryocooler operates at a frequency of at least about 20 Hertz.