Dynamic acoustic impedance matching for cryocoolers

Abstract

This disclosure describes systems, methods, and apparatus for improving the cooldown time, or efficiency of cooling systems, for a low-frequency one or multi-stage pulse-tube refrigerator. More specifically, actuation is performed on the driving frequency of the oscillating pressure and flow, on flow resistance of valves in the acoustic network that terminate the LF-OPTR or LF-DIPTR, and/or on the asymmetric flow resistance of the bypass valves in a LF-DIPTR's flow network. The actuation of these parameters is informed by measurements of the output pressure or output-input differential pressure at the steady flow compressor, the temperature of each stage of the refrigerator, and the temperature difference between the final stage and upper stages of the refrigerator, to name a few non-limiting examples.

1 . A multi-stage cryocooling system comprising:
 a compressor configured to be driven at a drive frequency;   a refrigerator coupled to the compressor and receiving an oscillatory fluid flow therefrom, the refrigerator comprising:   a first stage having an input coupled to the compressor via a first fluid path, and further having a first regenerator, a first cold heat exchanger, a first thermal buffer tube, and a first-stage output;   a second stage having an input coupled to the first cold heat exchanger, and further having a second regenerator, a second cold heat exchanger, a second thermal buffer tube, and a second-stage output;   a second fluid path between the first-stage output and a first-stage reservoir, a first-stage orifice valve controlling fluid flow along the second fluid path;   a third fluid path between the second-stage output and a second-stage reservoir, a second-stage orifice valve controlling fluid flow along the third fluid path; and   a controller configured to adjust (i) the first-stage orifice valve and the second-stage orifice valve in order to optimize a cooling characteristic of the second stage and (ii) the first-stage orifice valve and the second-stage orifice valve based on monitoring a cooling characteristic of the first stage,   the cooling characteristic of the second stage being a rate of cooling at the second cold heat exchanger or a pressure in the compressor of the second stage.   
     
     
         2 .- 3 . (canceled) 
     
     
         4 . The multi-stage cryocooling system of  claim 1 , wherein the cooling characteristic of the first stage is a rate of cooling at the first cold heat exchanger or a pressure in the compressor of the second stage. 
     
     
         5 . The multi-stage cryocooling system of  claim 4 , wherein the compressor is a linear compressor. 
     
     
         6 . A multi-stage cryocooling system comprising:
 a compressor configured to be driven at a drive frequency;   a refrigerator coupled to the compressor and receiving an oscillatory fluid flow therefrom, the refrigerator comprising;   a first stage having an input coupled to the compressor via a first fluid path, and further having a first regenerator, a first cold heat exchanger, a first thermal buffer tube, and a first-stage output;   a second stage having an input coupled to the first cold heat exchanger, and further having a second regenerator, a second cold heat exchanger, a second thermal buffer tube, and a second-stage output;   a second fluid path between the first-stage output and a first-stage reservoir, a first-stage orifice valve controlling fluid flow along the second fluid path;   a third fluid path between the second-stage output and a second-stage reservoir, a second-stage orifice valve controlling fluid flow along the third fluid path; and   a controller configured to adjust the first-stage orifice valve and the second-stage orifice valve in order to optimize a cooling characteristic of the second stage,   wherein the controller is further configured to adjust the first-stage orifice valve and the second-stage orifice valve based on monitoring a cooling characteristic of both the first stage and the second stage.   
     
     
         7 . A multi-stage cryocooling system comprising:
 a compressor configured to be driven at a drive frequency;   a refrigerator coupled to the compressor and receiving an oscillatory fluid flow therefrom, the refrigerator comprising;   a first stage having an input coupled to the compressor via a first fluid path, and further having a first regenerator, a first cold heat exchanger, a first thermal buffer tube, and a first-stage output;   a second stage having an input coupled to the first cold heat exchanger, and further having a second regenerator, a second cold heat exchanger, a second thermal buffer tube, and a second-stage output;   a second fluid path between the first-stage output and a first-stage reservoir, a first-stage orifice valve controlling fluid flow along the second fluid path;   a third fluid path between the second-stage output and a second-stage reservoir, a second-stage orifice valve controlling fluid flow along the third fluid path; and   a controller configured to adjust the first-stage orifice valve and the second-stage orifice valve in order to optimize a cooling characteristic of the second stage,   wherein the controller is further configured to adjust the drive frequency of the compressor based on monitoring the cooling characteristic of the second stage.   
     
     
         8 . The multi-stage cryocooling system of  claim 7 , wherein the compressor is a dual valve compressor. 
     
     
         9 . The multi-stage cryocooling system of  claim 1 , wherein a ratio of the maximum to the minimum drive frequency is at least 1.5:1. 
     
     
         10 . The multi-stage cryocooling system of  claim 7 , wherein the controller is configured to adjust a first-stage asymmetric bypass valve and a second-stage asymmetric bypass valve based on the monitoring of the cooling characteristic of the second stage. 
     
     
         11 . A multi-stage cryocooling system comprising:
 a compressor configured to be driven at a drive frequency;   a refrigerator coupled to the compressor and receiving an oscillatory fluid flow therefrom, the refrigerator comprising;   a first stage having an input coupled to the compressor via a first fluid path, and further having a first regenerator, a first cold heat exchanger, a first thermal buffer tube, and a first-stage output;   a second stage having an input coupled to the first cold heat exchanger, and further having a second regenerator, a second cold heat exchanger, a second thermal buffer tube, and a second-stage output;   a second fluid path between the first-stage output and a first-stage reservoir, a first-stage orifice valve controlling fluid flow along the second fluid path;   a third fluid path between the second-stage output and a second-stage reservoir, a second-stage orifice valve controlling fluid flow along the third fluid path; and   a controller configured to adjust the first-stage orifice valve and the second-stage orifice valve in order to optimize a cooling characteristic of the second stage,   wherein the controller is configured to acoustically impedance match the compressor to the refrigerator at a first time with a first impedance, and to acoustically impedance match the compressor to the refrigerator at a second time later than the first time with a second impedance, the second impedance being larger than the first impedance.   
     
     
         12 . A multi-stage cryocooling system of comprising:
 a compressor configured to be driven at a drive frequency;   a refrigerator coupled to the compressor and receiving an oscillatory fluid flow therefrom, the refrigerator comprising;   a first stage having an input coupled to the compressor via a first fluid path, and further having a first regenerator, a first cold heat exchanger, a first thermal buffer tube, and a first-stage output;   a second stage having an input coupled to the first cold heat exchanger, and further having a second regenerator, a second cold heat exchanger, a second thermal buffer tube, and a second-stage output;   a second fluid path between the first-stage output and a first-stage reservoir, a first-stage orifice valve controlling fluid flow along the second fluid path;   a third fluid path between the second-stage output and a second-stage reservoir, a second-stage orifice valve controlling fluid flow along the third fluid path; and   a controller configured to adjust the first-stage orifice valve and the second-stage orifice valve in order to optimize a cooling characteristic of the second stage,   wherein the controller is configured to acoustically impedance match the compressor to the refrigerator with a variable impedance that increases on average as the temperature of the second-stage cold heat exchanger decreases.   
     
     
         13 .- 25 . (canceled) 
     
     
         26 . A cryocooling system comprising:
 a compressor configured to be driven at a drive frequency;   a refrigerator coupled to the compressor and receiving an oscillatory fluid flow therefrom, the refrigerator comprising;   an input coupled to the compressor via a first fluid path, a regenerator, a cold heat exchanger, a thermal buffer tube, and an output;   a second fluid path between the output and a reservoir, an orifice valve controlling fluid flow along the second fluid path; and   a controller configured to adjust the orifice valve based on optimizing a cooling characteristic of the refrigerator,   wherein the cryocooling system is configured to adjust a bypass valve between the first fluid path and the second fluid path based on the optimizing the cooling characteristic of the refrigerator.   
     
     
         27 . The cryocooling system of  claim 26 , wherein the cooling characteristic of the refrigerator is (1) a rate of cooling at the cold heat exchanger, (2) a pressure in the compressor, or (3) a pressure in the regenerator. 
     
     
         28 . The cryocooling system of  claim 26 , wherein the controller is further configured to adjust the drive frequency of the compressor based on the optimizing the cooling characteristic of the refrigerator. 
     
     
         29 . The cryocooling system of  claim 28 , wherein the compressor is a dual-valve compressor. 
     
     
         30 . The cryocooling system of  claim 29 , wherein a ratio of a maximum to a minimum drive frequency is at least 1.5:1. 
     
     
         31 . The cryocooling system of  claim 26 , wherein the compressor is a linear compressor. 
     
     
         32 . (canceled) 
     
     
         33 . The cryocooling system of  claim 26 , wherein the refrigerator comprises two or more cooling stages and wherein the cooling characteristic is optimized in one or more of the two or more cooling stages.