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Various embodiments are directed to pulse tube coolers having flow resistance devices that are variable within the thermodynamic cycle of the pulse tube. An example pulse tube may comprise a compressor, a regenerator, a reservoir and a pulse tube. A working fluid may be positioned within the regener

Various embodiments are directed to pulse tube coolers having flow resistance devices that are variable within the thermodynamic cycle of the pulse tube. An example pulse tube may comprise a compressor, a regenerator, a reservoir and a pulse tube. A working fluid may be positioned within the regenerator, pulse tube and reservoir. Further, a variable phase control device may be positioned in a fluid path between the pulse tube and the reservoir. The pulse tube cooler may also comprise a control circuit. The control circuit may be programmed to vary a characteristic of the variable phase control device based on the position of the pulse tube cooler in its thermodynamic cycle.

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1. A pulse tube cooler comprising: a compressor;a regenerator having a first end and a second end, wherein the regenerator is in fluid communication with the compressor at the first end;a pulse tube having a cold end and a hot end, wherein the pulse tube is in fluid communication with the regenerato

1. A pulse tube cooler comprising: a compressor;a regenerator having a first end and a second end, wherein the regenerator is in fluid communication with the compressor at the first end;a pulse tube having a cold end and a hot end, wherein the pulse tube is in fluid communication with the regenerator at the cold end;a reservoir, wherein the reservoir is in fluid communication with the pulse tube at the hot end of the pulse tube;a working fluid positioned within the regenerator, the pulse tube, and the reservoir; anda variable phase control device positioned in a fluid path between the hot end of the pulse tube and the reservoir, the pulse tube cooler having a thermodynamic cycle defined by the flow of working fluid into and out of the regenerator, pulse tube and reservoir; anda control circuit in communication with the variable phase control device, wherein the control circuit is programmed to vary a characteristic of the variable phase control device based on the position of the pulse tube cooler in its thermodynamic cycle. 2. The pulse tube cooler of claim 1, wherein the characteristic of the variable phase control device is an inertance. 3. The pulse tube cooler of claim 1, wherein the characteristic of the variable phase control device is a flow resistance. 4. The pulse tube cooler of claim 1, wherein the variable phase control device comprises a plunger positioned within a flange, wherein the plunger and flange define a gap there between and where the size of the gap is variable based on a position of the plunger with respect to the flange on an axis parallel to the direction of working fluid flow between the pulse tube and the reservoir. 5. The pulse tube cooler of claim 4, wherein the plunger and the flange have shapes that widen towards the pulse tube. 6. The pulse tube cooler of claim 4, wherein the plunger and the flange have shapes that narrow towards the pulse tube. 7. The pulse tube cooler of claim 1, wherein the variable phase control device comprises: a housing;a piston positioned within the housing, wherein the piston and the housing define a gap there between where the size of the gap is variable based on a distance between the piston and the housing on an axis perpendicular to the direction of working fluid flow between the pulse tube and the reservoir; anda motor positioned to translate the piston relative to the housing. 8. The pulse tube cooler of claim 7, wherein the variable phase control device comprises a device defining an orifice with a variable diameter. 9. The pulse tube cooler of claim 1, further comprising a sensor positioned to capture data indicative of a position of the pulse tube cooler in the thermodynamic cycle, wherein the control circuit is further programmed to determine the position of the pulse tube cooler in its thermodynamic cycle based on the data received from the sensor. 10. The pulse tube cooler of claim 9, wherein the data indicative of the position of the pulse tube cooler in its thermodynamic cycle comprises at least one of data indicating a position of a piston of the compressor and data indicating a pressure of the working fluid proximate the compressor. 11. The pulse tube cooler of claim 9, wherein the data indicative of the position of the pulse tube cooler in the thermodynamic cycle comprises data indicating at least one of a temperature, a pressure, and a mass flow at the first end of the regenerator. 12. The pulse tube cooler of claim 9, wherein the data indicative of the position of the pulse tube cooler in the thermodynamic cycle comprises data indicating at least one of a temperature, a pressure, and a mass flow at the cold end of the pulse tube. 13. The pulse tube cooler of claim 9, wherein the data indicative of the position of the pulse tube cooler in the thermodynamic cycle comprises data indicating at least one of a temperature, a pressure, and a mass flow at the hot end of the pulse tube. 14. The pulse tube cooler of claim 1, wherein the control circuit is programmed to vary a characteristic of the variable phase control device based on the position of the pulse tube cooler in its thermodynamic cycle by varying at least one of an inertance of the variable phase control device and a flow resistance of the variable phase control device according to a first period. 15. The pulse tube cooler of claim 14, wherein the first period is equal to a period of the thermodynamic cycle of the pulse tube cooler. 16. The pulse tube cooler of claim 14, wherein the first period is a multiple of a period of the thermodynamic cycle of the pulse tube cooler. 17. A method of operating a pulse tube cooler, the method comprising: varying a characteristic of a variable phase control device based on the position of the pulse tube cooler in a thermodynamic cycle of the pulse tube cooler, wherein the thermodynamic cycle is defined by the flow of a working fluid into and out of a regenerator, a pulse tube and a reservoir of the pulse tube cooler, and wherein the variable phase control device is positioned between a pulse tube of the pulse tube cooler and a reservoir of the pulse tube cooler. 18. The method of claim 17, wherein the characteristic of the variable phase control device is an inertance. 19. The method of claim 17, wherein the characteristic of the variable phase control device is a flow resistance. 20. The method of claim 17, further comprising varying the characteristic of the variable phase control device according to a first period selected from the group consisting of a period of the thermodynamic cycle of the pulse tube cooler and a multiple of the period of the thermodynamic cycle of the pulse tube cooler. 21. The method of claim 17, further comprising receiving from a first sensor data indicating a position of a pulse tube cooler in a thermodynamic cycle of the pulse tube cooler; and determining the position of the pulse tube cooler in its thermodynamic cycle based on the data. 22. A computer readable medium comprises instructions thereon that, when executed by at least one processor, cause the at least one processor to: vary a characteristic of a variable phase control device based on the position of the pulse tube cooler in a thermodynamic cycle of the pulse tube cooler, wherein the thermodynamic cycle is defined by the flow of a working fluid into and out of a regenerator, a pulse tube and a reservoir of the pulse tube cooler, and wherein the variable phase control device is positioned between a pulse tube of the pulse tube cooler and a reservoir of the pulse tube cooler. 23. The computer readable medium of claim 22, further comprising instructions thereon that, when executed by the at least one processor, cause the at least one processor to receive from a first sensor data indicating a position of a pulse tube cooler in a thermodynamic cycle of the pulse tube cooler; and determine the position of the pulse tube cooler in its thermodynamic cycle based on the data.