Pulse tube cooler

Abstract

There is disclosed a cold head for a pulse tube cooler, comprising: a regenerator having a first end connectable to a compressor; a pulse tube having a first end and a second end; a heat exchanger connected between a second end of the regenerator and the first end of the pulse tube; and a phase control device connected at the second end of the pulse tube for controlling the flow dynamics in the pulse tube to provide cooling at the heat exchanger, thereby maintaining a negative temperature gradient between the first and second ends of the regenerator, wherein: the pulse tube comprises a wall having a porous portion for allowing a working gas to enter or leave the pulse tube directly through the porous portion, the porous portion being nearer to being parallel than perpendicular to the temperature gradient between the first and second ends of the regenerator.

1 . A cold head for a pulse tube cooler, comprising:
 a regenerator having a first end connectable to a compressor;   a pulse tube having a first end and a second end;   a heat exchanger connected between a second end of the regenerator and the first end of the pulse tube; and   a phase control device connected at the second end of the pulse tube for controlling the flow dynamics in the pulse tube to provide cooling at the heat exchanger, thereby maintaining a negative temperature gradient between the first and second ends of the regenerator, wherein:   the pulse tube comprises a wall having a porous portion for allowing a working gas to enter or leave the pulse tube directly through the porous portion, the porous portion being nearer to being parallel than perpendicular to the temperature gradient between the first and second ends of the regenerator; and   the heat exchanger coaxially surrounds the pulse tube.   
     
     
         2 . A cold head according to  claim 1 , wherein the porous portion is within  5  degrees of being parallel to the temperature gradient between the first and second ends of the regenerator. 
     
     
         3 . A cold head according to  claim 1 , wherein the pulse tube is cylindrical or has a substantially annular cross-section and the porous portion is within  5  degrees of being parallel to the axial direction of the pulse tube. 
     
     
         4 . A cold head according to  claim 1 , wherein the porous portion is a part of a shared wall that is shared between the pulse tube and one or more of the following: the regenerator, the heat exchanger, a flow distributer between the pulse tube and the phase control device. 
     
     
         5 . A cold head according to  claim 4 , wherein the regenerator coaxially surrounds the pulse tube and the porous portion is part of a shared wall that is a radially inner wall of the regenerator. 
     
     
         6 . A cold head according to  claim 1 , wherein the pulse tube is substantially cylindrical and the regenerator has a substantially annular cross-section. 
     
     
         7 . (canceled) 
     
     
         8 . A cold head according to  claim 4 , wherein the pulse tube coaxially surrounds the regenerator and the porous portion is part of a shared wall that is a radially inner wall of the pulse tube. 
     
     
         9 . A cold head according to  claim 8 , wherein the regenerator is substantially cylindrical and the pulse tube has a substantially annular cross-section. 
     
     
         10 . A cold head according to  claim 1 , wherein the porous portion extends from the second end of the regenerator along a portion of the regenerator towards the first end of the regenerator, without reaching the first end of the regenerator. 
     
     
         11 . A cold head according to  claim 1 , wherein the porosity of the porous portion of the wall decreases as a function of increasing separation from the second end of the regenerator. 
     
     
         12 . A cold head according to  claim 1 , wherein the pulse tube is orientated such that the second end of the pulse tube is further from the first end of the regenerator than the first end of the pulse tube. 
     
     
         13 . A cold head according to  claim 1 , wherein the phase control device is configured to control the flow dynamics using one or more fluid phase control components to control the flow of gas into and out of the second end of the pulse tube, the fluid phase control components being configured to operate without using any solid moving parts. 
     
     
         14 . A cold head according to  claim 1 , wherein the phase control device provides either or both of damping and inertia. 
     
     
         15 . A cold head according to  claim 1 , wherein the phase control device comprises a piston and cylinder in fluid communication with the second end of the pulse tube. 
     
     
         16 . A cold head according to  claim 1 , wherein the porous portion of the wall is formed from an electroformed sheet. 
     
     
         17 . A cold head according to  claim 16 , wherein the electroformed sheet is sandwiched between layers of mesh that act to even out and/or straighten the flow of gas passing through the porous portion of the wall. 
     
     
         18 . A cold head according to  claim 1 , wherein the cold head is configured to operate as a multi stage cooler and has a first stage pulse tube assembly comprising:
 a first regenerator having a first end connectable to a compressor;   a first pulse tube having a first end and a second end; and   a first heat exchanger connected between a second end of the first regenerator and the first end of the first pulse tube, wherein   the phase control device is connected at the second end of the first pulse tube for controlling the flow dynamics in the first pulse tube to provide cooling at the first heat exchanger, thereby maintaining a negative temperature gradient between the first and second ends of the first regenerator;   the first pulse tube comprises the wall having the porous portion for allowing the working gas to enter or leave the first pulse tube directly through the porous portion, the porous portion being nearer to being parallel than perpendicular to the temperature gradient between the first and second ends of the first regenerator; and   the cold head further comprises a second stage pulse tube assembly comprising:   an additional pulse tube directly connected to the first pulse tube in the region of the first heat exchanger and in such a way that there is a continuous fluidic connection between the first pulse tube and the additional pulse tube, the additional pulse tube being fluidically coupled to the phase control device via said continuous fluidic connection;   an additional regenerator configured to receive working gas from the first regenerator; and   an additional heat exchanger configured to provide cooling at a lower temperature than the cooling provided at the first heat exchanger.   
     
     
         19 . A pulse tube cooler comprising a cold head according to  claim 1  and a compressor connected to the first end of the regenerator. 
     
     
         20 . (canceled)