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;   first and second passive stages, wherein the first passive stage is operatively coupled to the active first stage, and the second passive stage is operatively coupled to the first passive stage; and   a manifold coupled between the first passive stage and the second passive stage,   wherein the active first stage includes a compressor and an active expander, and   wherein at least one of the passive stages comprises a concentric pulse tube expander.   
     
     
         2 . The cryocooler of  claim 1 , wherein both of the first and second passive stages comprise a concentric pulse tube expander. 
     
     
         3 . The cryocooler of  claim 1 , wherein the concentric pulse tube expander includes a vacuum gap. 
     
     
         4 . The cryocooler of  claim 3 , wherein the concentric pulse tube expander comprises a pulse tube and a regenerator, and wherein the vacuum gap is between the pulse tube and the regenerator. 
     
     
         5 . The cryocooler of  claim 1 , wherein the manifold is a second stage manifold, and further comprising a first stage manifold coupled between the active first stage and the first passive stage. 
     
     
         6 . The cryocooler of  claim 5 , further comprising a third stage manifold coupled to the second passive stage opposite the first passive stage. 
     
     
         7 . The cryocooler of  claim 6 , further comprising respective surge volumes mechanically coupled to the respective second and third stage manifolds. 
     
     
         8 . The cryocooler of  claim 5 , wherein the second stage manifold includes a passage for diverting flow, to bypass the second passive stage. 
     
     
         9 . The cryocooler of  claim 1 , wherein the first passive stage includes the concentric pulse tube expander, and wherein the second passive stage includes a U-shaped pulse tube expander. 
     
     
         10 . The cryocooler of  claim 1 , wherein the cryocooler provides three different temperature outputs, and wherein one of the temperature outputs is below 10 K. 
     
     
         11 . The cryocooler of  claim 2 , wherein the concentric pulse tube expanders of the first and second passive stages are oriented at a nonzero angle relative to one another. 
     
     
         12 . The cryocooler of  claim 1 , further comprising a microelectromechanical system (MEMS) flow controller fluidically coupled to at least one of the active first stage, the first passive stage, or the second passive stage, for controlling flow of a working fluid within the cryocooler. 
     
     
         13 . The cryocooler of  claim 12 , wherein the MEMS flow controller is located in a bypass line between the active first stage and the first passive stage. 
     
     
         14 . The cryocooler of  claim 12 , wherein the MEMS flow controller is located in a bypass line between the first passive stage and the second passive stage. 
     
     
         15 . The cryocooler of  claim 12 , further comprising respective first and second surge volumes mechanically coupled to the respective first and second passive stages, and wherein the MEMS flow controller is located in a fluid line coupled to one of the first or second surge volume. 
     
     
         16 . The cryocooler of  claim 1 , wherein the cryocooler operates at a frequency of at least about 20 Hertz. 
     
     
         17 . A multi-stage cryocooler comprising:
 an active first stage comprising a compressor and an active expander coupled to the compressor, the active expander including a piston;   a first passive stage comprising a first concentric pulse tube expander including a pulse tube and a regenerator; and   a second passive stage comprising a second concentric pulse tube expander including a pulse tube and a regenerator,   wherein the first passive stage is coupled to the active first stage at a first stage manifold, and   wherein the second passive stage is coupled to the first passive stage at a second stage manifold.   
     
     
         18 . The multi-stage cryocooler of  claim 17 , wherein the first and second passive stages are cantilevered from the active first stage. 
     
     
         19 . The multi-stage cryocooler of  claim 17 , wherein the second concentric pulse tube expander is coupled at a nonzero angle relative to the first concentric pulse tube expander. 
     
     
         20 . A multi-stage cryocooler comprising:
 an active first stage comprising a compressor and an active expander coupled to the compressor, the active expander including a piston;   a first passive stage comprising a first pulse tube and a first regenerator that surrounds the first pulse tube, and a first vacuum gap between the first pulse tube and the first regenerator;   a second passive stage comprising a second pulse tube and a second regenerator that surrounds the second pulse tube, and a second vacuum gap between the second pulse tube and the second regenerator,   wherein the first passive stage is coupled to the active first stage at a first stage manifold,   wherein the second passive stage is coupled to the first passive stage at a second stage manifold, and   wherein the first and second passive stages are cantilevered from the active first stage.