Pulse tube cooler system

Abstract

A cryogenic cooling system comprising a cold finger for cooling of a transducer is preintegrated with a dewar, so that final implementation can be executed by simply adding a compressor connection and buffer inertance assembly. The transducer may be a detector such as an optical detector, and may be permanently integrated with the cold end of the cold fingen Figure 3

Description

FIELD OF THE INVENTION The present invention relates to the field of pulse tube cryogenic cooler systems including cryogenic cold finger element and / or a compressor, and methods for constructing BACKGROUND PRIORART Figure 1 shows a typical pulse tube cryogenic cooler system as known in the art. As shown in figure 1, a cooler system 100 comprises a cold finger element 110 comprising a hot end 111 and a cool end 112, with a pulse tube 113 extending therebetween. The cold finger element is coupled to a compressor 130 via a compressor transfer line 120. Pulse tube 113 is shown as enclosed in dewar 140, comprising a sealed, insulating vessel. The described elements may this typically constitute a . Such a system may be used for example to provide cooling for a sensor such as an infrared optical detector. W02009075911A1 for example presents a prior art approach along these lines, in which the dewar 30 and detector 32 are first integrated, and cold finger element then inserted into the dewar. The cryocooler is manufactured separately from the detector-dewar, and these elements are indeed often manufactured by unrelated entities. The integration is then not performed by the cryocooler manufacturer, but typically by the party that manufactures the detector-dewar assembly. As such, this complex step is to be performed by the party that is not particularly used to this step or handling cryocoolers. It is accordingly desired to develop new cryogenic cooler structures better addressing the foregoing considerations. SUMMARYOF THE INVENTION In accordance with the present invention in a first aspect there is provided a pulse tube cooled cryogenic module comprising: a pulse cooled cold finger element having a warm end and a cool end, with a pulse tube extending there between, and a regenerator volume; a transducer assembly permanently fixed to the cool end of said cold finger element in a manner adapted to thermally couple the cool end of said cold finger element to said transducer assembly; a mounting body; a dewar vessel sealingly fixed to said mounting body so as to sealingly enclose said cold finger element and said transducer assembly; said cryogenic transducer module characterized in that said mounting body comprises a first releasable coupling for removably receiving a buffer inertance assembly, said first releasable coupling providing for sealingly coupling said pulse tube at said warm end to a reservoir of working fluid contained in said buffer inertance assembly when said buffer inertance assembly is coupled to said mounting body, and a second releasable coupling for sealingly coupling said regenerator volume at said warm end to a compressor transfer line. In a development of the first aspect, the transducer assembly is a detector. 3 In a development of the first aspect, the transducer assembly is an optical detector. In a development of the first aspect, the transducer assembly is permanently fixed to the cool end of said cold finger element by means of a metallic adapter that is welded or soldered to the cool end of said cold finger element. In a development of the first aspect, the first releasable coupling comprises a circular threaded structure adapted to engage a corresponded threaded mouth of said buffer inertance assembly, and a circular port arranged concentrically with respect to said buffer inertance assembly for sealingly engaging said pulse tube. In a development of the first aspect, the second releasable coupling comprises a circular port for sealingly engaging said compressor transfer line, and a plurality of threaded openings positioned to engage a bracket member of said compressor transfer line, and to be secured with respect thereto by means of a respective plurality of threaded fixing members. In a development of the first aspect, the mounting body further comprises a flange member arranged concentrically with said first cold finger element to receive a vacuum dome or flask. In accordance with the present invention in a second aspect there is provided a pulse tube cooled cryogenic system comprising a pulse tube cooled cryogenic module according to any preceding claim, a buffer inertance assembly coupled to said mounting body at said first releasable coupling, a compressor, and a compressor transfer line coupled to said mounting body at said second releasable coupling and to said compressor. In accordance with the present invention in a third aspect there is provided a method of constructing a pulse tube cooled cryogenic module comprising the steps of providing a pulse cooled cold finger element having a warm end and a cool end, a pulse tube extending from said warm end to said cool end, and a regenerator volume; providing a transducer assembly permanently fixed to the cool end of said cold finger element in a manner adapted to thermally couple the cool end of said cold finger element to said transducer assembly; providing a mounting body; providing a dewar vessel sealingly fixed to said mounting body so as to sealingly enclose said cold finger element and said transducer; wherein said method comprises providing said mounting body with a first releasable coupling for removably receiving a buffer inertance assembly, said first releasable coupling providing for sealingly coupling said pulse tube at said warm end to a reservoir of working fluid contained in said buffer inertance assembly when said buffer inertance assembly is coupled to said mounting body, and with a second releasable coupling for sealingly coupling said a regenerator volume at said warm end to a compressor transfer line. In accordance with the present invention in a fourth aspect there is provided a method of constructing a pulse tube cooled cryogenic system, said method comprising the steps of providing a pulse tube cooled cryogenic module according to the first aspect coupling a buffer inertance assembly to said mounting body at said first releasable coupling, and coupling a compressor to said mounting body via a compressor transfer line at said second releasable coupling. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood and its various features and advantages will emerge from the following description of a number of exemplary embodiments provided for illustration purposes only and its appended figures in which: Figure 1 shows a typical as known in the art; Figure 2 presents a cold finger element with dewar for a pulse tube cryogenic cooler system in accordance with an embodiment in a plan view; Figure 3 presents a cold finger element with dewar for a pulse tube cryogenic cooler system in accordance with an embodiment in an isometric view; Figure 4 presents schematically a cryogenic cooler system in accordance with an embodiment in a plan view; Figure 5 presents a method of constructing a pulse tube cooled cryogenic module in accordance with an embodiment; and Figure 6 presents a method of constructing a pulse tube cooled cryogenic system in accordance with an embodiment. DETAILED DESCRIPTION OF THE INVENTION Figure 2 presents a cold finger element with dewar for a pulse tube cryogenic cooler system in accordance with an embodiment in a plan view. As shown, a pulse tube cooled cryogenic module 200 comprises a pulse cooled cold finger element 210 having a warm end 211 and a cool end 212, a pulse tube 213 extending from the warm end to the cool end, and a regenerator volume 214. The pulse tube cooled cryogenic module 200 further comprises a transducer assembly 220 permanently fixed to the cool end of the cold finger element in a manner adapted to thermally couple the cool end of the cold finger element to the transducer assembly; a mounting body 230, and a dewar vessel 240 (sealed, insulated vessel) sealingly fixed to the mounting body 230 so as to sealingly enclose the cold finger element 210 and the transducer assembly 220. As shown, the mounting body comprises a first releasable coupling 231 for removably receiving a buffer inertance assembly (not shown) for sealingly coupling the pulse tube at the warm end to a reservoir of working fluid contained in the buffer inertance assembly when the buffer inertance assembly is coupled to the mounting body, and a second releasable coupling 232 for sealingly coupling the regenerator volume at the warm end to a compressor transfer line (not shown). The transducer assembly detector may comprise any transducer element for example requiring cooling during operation such as an optical detector, e.g. an infrared detector or the like. The transducer assembly may be permanently fixed to the cool end of the cold finger element by means for example of a metallic adapter that is welded or soldered to the cool end of the cold finger element. The first releasable coupling (phase shifter connection) 231 may comprise a circular threaded structure adapted to engage a corresponded threaded mouth of the buffer inertance assembly, and a circular port arranged concentrically with respect to the buffer inertance assembly for sealingly engaging the pulse tube. As shown in figure 2, mounting body further comprises a flange member 234 arranged concentrically with the first cold finger element to receive a vacuum dome or flask. The latter is shown as a flanged connection but can also be made with other connection methods such as welding. As such, the critical components of the cold finger may be part of the dewar, i.e. the cold heat exchanger 221, regenerator 214, pulse tube 213, phase shifter connection 231. As such, after integrating the detector and dewar there is no additional step of integrating the critical cold finger parts. The integration of the remainder of the pulse tube cooler can thus be performed by the party providing the Detector Dewar Cooler Assembly, as there are no additional complex integration problems with the pulse tube. The process is thus less prone to errors and the thermal contact between the cold finger and dewar is improved. An integrated dewar and cold finger can be attached to the remainder of the pulse tube cooler after integrating the detector, eliminating the need for the detector manufacturer to integrate the critical parts and improving the thermal contact. This solution also offers better thermal contact between the cold finger and dewar. Figure 3 presents a cold finger element with dewar for a pulse tube cryogenic cooler system in accordance with an embodiment in an isometric view. As shown, a pulse tube cooled cryogenic module 300 comprises a pulse cooled cold finger element (not shown) substantially as described for example with reference to figure 1. The pulse tube cooled cryogenic module 300 further comprises a transducer assembly (not shown) substantially as described for example with reference to figure 1. The pulse tube cooled cryogenic module 300 further comprises a mounting body 330, a dewar vessel 340 sealingly fixed to the mounting body 330 so as to sealingly enclose the cold finger element 210 and the transducer assembly 220 e.g. as described above. As shown, the mounting body comprises a first releasable coupling 331 for removably receiving a buffer inertance assembly (not shown) for sealingly coupling the pulse tube at the warm end to a reservoir of working fluid contained in the buffer inertance assembly when the buffer inertance assembly is coupled to the mounting body, and a second releasable coupling 332 for sealingly coupling the regenerator volume at the warm end to a compressor transfer line (not shown). As shown the second releasable coupling 332 may comprise a circular port for sealingly engaging the compressor transfer line, and a plurality of threaded openings 333a, 333b positioned to engage a bracket member of the compressor transfer line, and to be secured with respect thereto by means of a respective plurality of threaded fixing members, such as bolts, screws or the like. As shown, the Dewar 340 may be provided with a region 341 transparent to energies emitted or received by the transducer. As shown, the releasable coupling 332 may in use couple with a compressor transfer line 303b which may comprise a mounting plate 303a with holes that align with holes of the cold finger. Bolts can be used for connecting the mounting plate with split pipe to the cold finger whilst the interface is sealed leak tight with a metal seal. Figure 4 presents schematically a cryogenic cooler system in accordance with an embodiment in a plan view. As shown in figure 4, there may be provided a pulse cooled cryogenic transducer system 400 comprising a pulse tube cooled cryogenic module 200 as described above, and additionally a buffer inertance assembly 401 coupled to the mounting body 230 at the first releasable coupling 231, a compressor 402, and a compressor transfer line 403 coupled to the mounting body at the second releasable coupling and to the compressor. It may be noted that the resulting system is operationally equivalent to that of figure 1 for example, however the novel structure of the pulse tube cooled cryogenic module 200 addresses the difficulties described with respect to prior art structures. With reference to figure 4, the compressor transfer line may comprise a mounting plate with holes that align with holes of the cold finger. Bolts can be used for connecting the mounting plate with compressor transfer line to the cold finger whilst the interface is sealed leak tight with a metal seal. The buffer inertance assembly 401 can be connected to or disconnected from the lower cylindrical part of the cold finger / dewar, wherein the cylindrical part is inserted into the buffer inertance assembly. As is clear from the figures, by disconnecting the compressor transfer line and thereby the compressor, and by disconnecting the buffer inertance assembly, the cold finger / dewar can be processed by itself. The cold finger / dewar can then be integrated with the detector 220. After integration the remainder of the cooler can be (re)connected with the cold finger / dewar by connecting the buffer inertance assembly to the cylindrical part and the split pipe by means of the bolts and seals as described above. Figure 5 presents a method of constructing a pulse tube cooled cryogenic module in accordance with an embodiment. As shown, the method starts at step 500 before proceeding at step 505 to provide a pulse cooled cold finger element having a warm end and a cool end, a pulse tube extending from the warm end to the, cool end, and a regenerator volume. The method then proceeds to step 510 of providing a transducer assembly permanently fixed to the cool end of the cold finger element in a manner adapted to thermally couple the cool end of the cold finger element to the transducer assembly. The method then proceeds to step 515 of providing a mounting body. The method then proceeds to step 520 of providing a dewar vessel sealingly fixed to the mounting body so as to sealingly enclose the cold finger element and the transducer. The method then proceeds to step 525 of providing the mounting body with a first releasable coupling for removably receiving a buffer inertance assembly, the first releasable coupling providing for sealingly coupling the pulse tube at the warm end to a reservoir of working fluid contained in the buffer inertance assembly when the buffer inertance assembly is coupled to the mounting body. The method then proceeds to step 530 at which the mounting body is provided with a second releasable coupling for sealingly coupling a regenerator volume at the warm end to a compressor transfer line, before terminating at step 535. It will be appreciated that the steps of figure 5 may be performed in many different sequences. For example, steps 525 and 530 are logically performed after step 515, by may be reversed or performed in parallel, and at any stage after step 515. The steps 505, 510, 515, may be performed in any desired sequence, subject to the requirement that the cold finger element, transducer element and mounting body must be assembled before the dewar is coupled to the mounting body. Figure 6 presents a method of constructing a pulse tube cooled cryogenic system in accordance with an embodiment. As shown, the method starts at step 600 before proceeding to step 605 at which a pulse tube cooled cryogenic module is received as described above, possibly manufactured in accordance with the method of figure 5. The method then proceeds to step 610 of coupling a buffer inertance assembly to the mounting body at the first releasable coupling, and then at step 615 coupling a compressor to the mounting body via a compressor transfer line at said second releasable coupling, before terminating at step 620. It will be appreciated that steps 610 and 615 may be performed in opposite sequence, or in parallel. Accordingly, there is provided a cryogenic cooling system comprising a cold finger for cooling of a transducer is pre-integrated with a dewar, so that final implementation can be executed by simply adding a compressor connection and buffer inertance assembly. The transducer may be a detector such as an optical detector, and may be permanently integrated with the cold end of the cold finger. The examples described above are given as non-limitative illustrations of embodiments of the invention. They do not in any way limit the scope of the invention which is defined by the following claims.

Claims

1. A pulse-tube cooled cryogenic module comprising: a pulse-cooled cold finger element with a warm tip and a cool tip, with a pulse tube extending between them, and a regenerator volume; a turnover assembly that is permanently attached to the cool end of the said cold finger element in a manner designed to the cool end of the said to thermally couple the thermal finger element to the aforementioned conversion assembly; a fastening body; a Dewar flask that is sealed onto the mounting body to the to seal enclose the cold finger element and the conversion assembly; where the cryogenic transducer module is characterized by the fact that it comprises the mounting body a first detachable coupling for the removable receiving of a buffer inertia assembly, where the first detachable coupling ensures sealing connecting the pulse tube at its hot end to a reservoir containing working fluid includes in the buffer inertia assembly when the buffer inertia assembly is coupled to the mounting body, and a second detachable coupling for the sealing connection of the regenerator volume at the hot end with a compressor transfer line.

2. The pulse-tube cooled cryogenic module according to claim 1 where the conversion assembly is detector is.

3. The pulse-tube cooled cryogenic module pursuant to claim 2 where the conversion assembly is optical detector is.

4. The pulse-tube cooled cryogenic module in accordance with one of the preceding conclusions whereby the turnover assembly is permanently attached to the cool end of the said cooling finger element by means of a metal adapter attached to the cool end of the The mentioned cold finger element is welded or soldered.

5. The pulse-tube cooled cryogenic module pursuant to one of the preceding conclusions whereby the first detachable coupling comprises a circular threaded structure that is designed to work with a corresponding threaded opening of the buffer inertia assembly, and a circular gate concentric with respect to the A buffer inertia assembly has been configured for the sealing engagement of the pulse tube.

6. The pulse-tube cooled cryogenic module in accordance with one of the preceding conclusions whereby the second detachable coupling includes a circular port for sealing the compressor transfer line, and a number of threaded openings that are positioned to engage a bracket member of the compressor transfer line, and at to be secured in relation to it by means of a number of fastening elements with screw thread.

7. The pulse-tube cooled cryogenic module in accordance with one of the preceding conclusions whereby the fastening body further comprises a flange element that is concentric with the first The cold finger element is set up to receive a vacuum dome or flask.

8. A pulse tube-cooled cryogenic system comprising a pulse tube-cooled cryogenic module according to one of the preceding conclusions, a buffer inertia assembly that is coupled with the fastening body via the first detachable coupling, a compressor, and a compressor transfer line connected to the mounting body via the second detachable coupling and with the compressor.

9. A method for constructing a pulse-tube cooled cryogenic module comprising the steps for providing a pulse-cooled cold finger element with a warm end and a cool end, a pulse tube extending from the warm end to the cool end, and a regenerator volume; providing a turnover assembly that is permanently attached to the cool end of the cold finger element in a manner designed for the cool end of the cold finger element to be thermally coupled to the conversion assembly; providing a fastening body; providing a Dewar flask that is sealingly attached to the mounting body for the sealing enclosure of the cold finger element and the transducer; where the method involves providing the fastening body with a first detachable coupling for the removable reception of a buffer inertia assembly, where the first detachable coupling ensures the sealing connection of the pulse tube at the hot end thereof with a reservoir of working fluid enclosed in the buffer inertia assembly when the buffer inertia assembly is coupled to the fastening body, and of a second detachable coupling for sealing connection of the regenerator volume at the hot end with a compressor transfer line.

10. A method for constructing a pulse-tube cooled cryogenic system, whereby the method the steps comprise of: providing a pulse tube-cooled cryogenic module according to one of conclusions 1 through 7, coupling a buffer inertia assembly with the fastening body via the first detachable coupling, and the coupling of a compressor with the mounting body via a compressor transfer line to the second detachable coupling.

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