EP0803687B1 - Cryostat for cryogenic refrigerator and refrigerators comprising such a cryostat - Google Patents

Description

The present invention relates to the design and production of cryogenic coolers which works a working gas following a thermodynamic cycle in closed circuit between a compression chamber and a expansion chamber, through a thermal accumulator said regenerator, which ensures a recovery exchange between compressed hot gas and expanded cold gas.

These coolers conventionally include a pressure oscillator controlled to vary the volume of the compression chamber, and a cold finger ending with the expansion chamber, in thermal contact with an element to be cooled, placed at the bottom of an envelope thermal insulation. The element to be cooled is commonly an electronic component that must be kept in operation at temperatures between 60 ° K and 200 ° K, in particular to improve the signal to noise.

In such a context, which involves many areas of the industry where electronic components are used or optoelectronics, cryogenic coolers of the type in question are successful each growing day, mainly when they are designed to be manufactured at low cost in forms incorporating the pressure oscillator with the cold finger in one mechanical assembly no longer needing external pipes to close the working gas circuit.

But, moreover, the variety of their applications industrial has led to the development of different technological configurations of chillers in operation of the work cycle best suited to the circumstances. We will find them described in principle in an article by Damien Feger entitled "Cooling of optoelectronic detectors" published in "Engineering techniques, treated Electronics "pages E4070-1 to 11.

This article already describes the particularities specific to each configuration and presiding criteria at the choice of one or the other. In connection with this invention, it should be emphasized in particular that, in general, tube type coolers pulsed gas (TGP) fish by a lower yield than that Stirling cycle configurations, when when the notion of efficiency loses importance, chillers with pulsed gas tube take precedence over coolers Stirling cycle. If only for cost issues they have the advantage of involving a number of more limited parts and a lower requirement in the realization of seals. From this last point of view, we recall that Stirling cycle coolers have a piston called "displacer" which is mounted to slide in the cold finger finished by the chamber of trigger, hence the need for gas tightness of the type dynamic.

US patents 3,220,201, US 4,858,442, and 5,293 748, describe examples of a cycle cooler Stirling.

In order to further reduce the cost and provide greater flexibility in the use of coolers in all kinds of applications, the present invention is mainly offers to make available to users a cryostat which is not limited to an envelope insulating capable of receiving the cold finger from the cooler, but which incorporates part of its essential organs, in a form allowing their interchangeable adaptation to different configurations.

More specifically, a cooler cryostat cryogenic produced according to the invention adapts easily, in accordance with its interchangeable character, both at a pulsed gas tube configuration than a Stirling cycle, and that driving the oscillator of pressure goes through a rotary type drive to crankshaft or linear type, according to the expressions used by those skilled in the art, as they are repeated in particular in the article already cited.

By its different characteristics as they will be described and claimed below, the invention allows also to make significant improvements to the construction chillers incorporating such a cryostat and their driving style. The resulting benefits relate in particular to the combination of the cryostat with a pressure oscillator in a relevant embodiment of a pulsed gas tube configuration.

In addition, the special features proposed for different components of cryostats according to the invention have the advantage of being particularly suitable well to the respective operating modes of two types of coolers and improve their clean performance. This is particularly the case with the provisions recommended for the regenerator, which is responsible to absorb and release heat, alternatively, by compared to the gas passing through it. This is also the case an exchanger advantageously provided in a cold zone, at level of the relaxation room, to favor the transfer towards the component to be cooled, as well as for a exchanger located in hot zone and under pressure which is especially useful in gas type coolers pulsed, to favor a heat loss towards outside.

Thus, the invention more specifically relates to a cryostat for cryogenic cooler using a closed working gas circuit between a compression located in a pressure oscillator housing associated and a relaxation room located at the bottom of the cryostat, in heat exchange situation with a component to be cooled, comprising inside an envelope thermal insulation, integral with a mounting base on said housing, a thermal regenerator interposed on the working gas circuit. This regenerator is in annular arrangement around an extending axial volume between a cold exchanger which is in thermal contact with the component to be cooled and makes the regenerator communicate with said axial volume at the bottom of the cryostat. The cryostat also has a gas distribution ring in said regenerator, at the head of the cryostat, from a conduit drilled through the base for connection to the chamber compression. The timing ring is formed by a central piece mounting through said base axially at its center. Said central part is mounted removably in said base, in particular by tight screwing. This makes it easily interchangeable between a first model for operating the axial volume as a gas piston in a gas tube type cooler pulsed, and a second model, with an axial bore suitable for being traversed by a displacement piston Stirling cycle cooler, sliding introduced watertight in the same axial volume. So we can use the same cryostat, built according to the invention, with nothing change other to its dimensioning or its manufacture, to integrate it with a pressure oscillator adapted from so as to constitute a cooler corresponding to one or the other of these major configurations.

In the central room following the model intended for a cooler operating on the principle of the pulsed gas, at least one channel is advantageously provided passage of gas under controlled flow between a tank gas buffer formed inside the oscillator housing pressure, and the internal axial volume of the cryostat which works in gas tube. It is also advantageous to add one or more other flow-controlled channels allowing hot gas to be drawn directly at the outlet compression, at the timing ring to the regenerator.

In the alternative case of a cooler works a Stirling cycle, the internal volume is at the contrary occupied by the displacer piston, which is preferably solid, made of a weak material thermal conductivity, and which leaves only the volume of the expansion chamber at the bottom of the cryostat.

Preferably, the central piece, with its crown distribution, is made integral with a central tube limiting said axial volume. This tube is then advantageously of the same internal diameter as the axial bore of the model intended for connection of the cryostat to a cooler Stirling cycle. It can therefore constitute either the tube containing the pulsed gas in the first model, namely the guide tube of the cooler displacement piston in the second case.

According to another characteristic of the invention, it is associated with the cryostat a hot exchanger, positioning in the internal volume at the top of the cryostat. Its role is located in the evacuation of calories which takes place by heat loss to the outside through the base and the casing of the compressor part of the cooler, made for this purpose of thermally conductive material. It is especially useful in the cooler variant with pulsed gas tube, taking into account the heat to be evacuated in gas tube outlet, which adds to the stored heat by the gas back from the regenerator.

Regarding at least the cold exchanger, but where appropriate also the hot exchanger, the invention foresees, according to a secondary characteristic, that one can apply advantageously with others in any operating combination, to use a geometry structure of revolution, alternating around the axis of the cryostat, in a daisy arrangement, massive areas in material good thermal conductor and void areas open to the passage of gas. As a result, these areas are in particular on horseback, on both sides, in relation to a centering shoulder at the end of the central tube.

It is often advantageous to combine such a cold exchanger with a laminate of perforated grids having the effect of ensuring a tranquilization of the gas flow at passage of the exchanger.

Note again that in a next cooler the invention built to operate on the principle of the pulsed gas tube, it is advantageous to save the volume gas buffer supplying the gas piston inside a compression piston, which for this purpose on the side opposite the compression chamber, is directly opened in a guide sleeve of said piston which is connected to the appropriate center piece of the cryostat.

For driving the piston in such a cooler, preferably a single piston, it is generally desirable to have recourse to means of piloting linear motor, as far as the cost is more lower than for rotary control.

In some applications, a configuration of the type with rotary engine can however prove useful. The preferred solution then goes through piloting means comprising a crankshaft actuating a transmission mechanism of movement by movable ball bearing in a groove formed transversely outside said piston.

Whatever the embodiment chosen for the cooler according to the invention, the arrangement ring of the regenerator lends itself particularly well to a manufacture from a sheet wound on itself. In addition, the invention makes it possible to significantly improve the efficiency of the heat exchanges sought, compared to stacks of conventional grids or balls, in using for this a sheet of suitable material, which has been previously machined, in particular by photolithographic process, so as to form longitudinal strips with smooth surfaces and transverse bars in extra thickness occasionally joining the strips successive.

Preferably, the different bands are succeed the length of the regenerator. They form annular smooth surface layers intersected by intervals between bands and bars inserted between the layers help to distribute the flow in all directions at each cross section level.

• La figure 1 représente en coupe longitudinale un cryostat suivant l'invention, vu dans ses spécificités plus particulièrement destinées à un accouplement avec un oscillateur de pression de sorte à constituer un refroidisseur cryogénique appliquant un cycle à tube à gaz pulsé ;
• La figure 2 montre les organes principaux du même cryostat, dans une vue éclatée, en s'intéressant au contraire à sa constitution pour accouplement avec l'oscillateur de pression d'un refroidisseur de type à cycle de Stirling ;
• La figure 3 schématise une forme de réalisation préférée du régénérateur thermique, valable dans l'un et l'autre cas ;
• La figure 4 montre une coupe transversale du cryostat au niveau de l'échangeur thermique disposé en zone froide du circuit de gaz de travail, dans la chambre de détente ;
• La figure 5 illustre le montage du cryostat de l'invention, avec sa pièce de distribution interchangeable suivant la figure 2, dans un cas d'application pratique où il sert à constituer un refroidisseur cryogénique à cycle de Stirling suivant l'invention, qui est ici du type à pilotage rotatif ;
• La figure 6 illustre, quant à elle, un autre mode de réalisation de l'invention, fournissant au total un refroidisseur à cycle TGP (tube à gaz pulsé), et elle montre en plus comment se concrétise préférentiellement, conformément à l'invention, un pilotage rotatif dans cette configuration de refroidisseur cryogénique.
• La figure 7 illustre en vue éclatée une conception particulière de l'échangeur froid associé à un feuilleté de grilles de tranquilisation de gaz.
• La figure 8 représente, dans une coupe schématique partielle, une variante de l'échangeur froid faisant appel à une réalisation en deux parties concentriques.

The invention will now be more fully described in the context of preferred characteristics which best meet the aims of the invention by their advantages, with reference to the figures of the appended drawings which illustrate them and in which:

• FIG. 1 represents in longitudinal section a cryostat according to the invention, seen in its specificities more particularly intended for coupling with a pressure oscillator so as to constitute a cryogenic cooler applying a cycle with pulsed gas tube;
• Figure 2 shows the main organs of the same cryostat, in an exploded view, looking instead to its constitution for coupling with the pressure oscillator of a Stirling cycle type cooler;
• Figure 3 shows schematically a preferred embodiment of the thermal regenerator, valid in both cases;
• FIG. 4 shows a cross section of the cryostat at the level of the heat exchanger arranged in the cold zone of the working gas circuit, in the expansion chamber;
• FIG. 5 illustrates the assembly of the cryostat of the invention, with its interchangeable distribution part according to FIG. 2, in a case of practical application where it serves to constitute a cryogenic cooler with a Stirling cycle according to the invention, which is here of the rotary pilot type;
• FIG. 6 illustrates, for its part, another embodiment of the invention, providing a total cooler with a TGP cycle (pulsed gas tube), and it also shows how preferentially takes shape, in accordance with the invention, rotary control in this cryogenic cooler configuration.
• FIG. 7 illustrates in exploded view a particular design of the cold exchanger associated with a laminate of gas stilling grids.
• Figure 8 shows, in a partial schematic section, a variant of the cold exchanger using an embodiment in two concentric parts.

According to the invention, the cryostat of the figure 1 is used in combination with a pressure oscillator either to constitute a cryogenic cooler of the pulsed gas according to Figure 6, or alternatively to constitute a Stirling cycle type cooler as shown in Figure 5. In all cases, the cooler thus constituted is of compact construction, the cryostat and pressure oscillator being integrated in one same mechanical assembly.

From Figure 1, we can see that the cryostat according to the invention is not limited, as in the embodiments known, to a thermal insulation envelope intended to receive a cold finger previously formed in all its functional organs necessary for the implementation work of the thermodynamic cycle of the working gas. At on the contrary, the passive functional organs, which are not subject to displacement during operation, are permanently installed in the cryostat, the latter being constructed so that it can be connected alternately at the user's choice, at the housing of an oscillator pressure either from a specific cooler for implementation of a Stirling cycle, ie of a cooler of the pulsed gas tube type.

This is how in the cryostat we find, at inside a thermal insulation envelope 1 mounted integral with a base 4 used for its connection mechanical and pneumatic with the oscillating part of cooler pressure, two concentric tubular ferrules, namely a central tube 3 and an internal wall 2 of envelope 1, which delimit between them a space ring occupied by a thermal regenerator 5. The regenerator 5 is thus constructed in an annular arrangement around an axial volume 6, limited on its periphery by the central tube 3 from the two previous ferrules.

In practice the other ferrule, which limits externally the thermal regenerator, so here is directly formed by the inner wall 2 of the envelope thermal insulation 1. This is indeed, so in itself classic, of the double wall type. Between his two walls it is either filled with a low inerting gas condensation point, or subjected to a high vacuum, this for which it is provided with a loading port 25.

In other embodiments, however, but generally less advantageous, we prefer build regenerator 5 with its own envelopes, including an outer envelope which is then separate from the inner wall 2 of the thermal insulation envelope and / or an internal envelope which is then added against the tube central 3.

At the bottom of the cryostat, beyond the regenerator and its internal envelope constituted by the tube 3, it is disposed an exchanger 8, which constitutes in operation the cold exchanger of the cooler. For this, this exchanger is designed and arranged to facilitate the transfer of cooling capacity resulting from the expansion of the work towards a component to be cooled 21, while ensuring pneumatic communication allowing the passage of gas of work between the bottom of the axial volume 6 and the space ring occupied by the regenerator 5.

The intermediate shell of the cryostat of the invention, constituted by the wall 2, is closed at its end lower, at the bottom of the cryostat, by a transverse plate 22 against which the cold exchanger 8 is affixed. On its opposite side to this exchanger is mounted the component 21, generally by simple bonding.

When the element to be cooled is constituted, as illustrated, by an electronic component 21, for example a optoelectronic detector, it is necessary to provide its connection to an electrical circuit carrying the signals that it receives or that it transmits. So we made appear on the Figure 1, an electrical distribution ring 23, of which the conductive parts pass through watertight bushings through the outer wall of the insulation jacket thermal 1, as well as conductive wires 24 which then connect to component 21.

The envelope 1 as a whole has the function of limit heat losses by radiation or convection to level of organs involved in the thermodynamic cycle of the complete cooler in the cold zone thereof.

As it appears in Figure 1, its wall outer is welded on the underside of the base 4, while its internal wall 2 is monolithic therewith. One and the other can be made of stainless steel.

However, we can also choose, for the wall internal 2, a quality of stainless steel corresponding to a alloy with low thermal conductivity, adapted to be compatible with the working gas used, which is preferably helium in the case of the regenerator at metallic foil rolled up as described below.

The outer wall of the envelope 1 is produced also in stainless steel, or possibly in one appropriate quality of glass, for economic reasons.

Depending on the material chosen, it can therefore be necessary to use glass / metal junctions for sealing of welds and bushings electric, which will however pose all the less problems to those skilled in the art that this need lies in places under static pressure.

At the head of the cryostat, at the upper end of the thermally insulating envelope 1 and of the regenerator 5, the base 4 is on the contrary in the hot zone of the cooler in operation, where there is also pressure working gas dynamics, subjected to pulsations of periodic pressures, printed by the moving parts of the cooler when the cryostat is connected to the housing 50 an associated pressure oscillator.

In this hot zone, the calories from gas returning from trigger after recovery performed in regenerator 5. For this, it is planned to make the base 4 in a material of good conductivity thermal, usually stainless steel, under a shape favoring the losses towards the outside.

In the base 4 there is a collar circular 16, pierced with holes for the passage of screws 48 fixing to the casing 50 of the cooler, which is connected by pressing on the upper face of the flange 16, opposite the thermal envelope 1. On also distinguishes a ring 17, forming part of the base 4, which ensures the centering of the two elements one inside the other. The tight connection of these two elements (cryostat and pressure oscillator) vis-à-vis the outside is ensured by a seal 19, housed in an annular groove on the face upper part of the collar 16.

The base 4 delivers passage, in the axis of the system, to a central part 10, tightly screwed into the ring 17, which is internally threaded. A throat hexagonal 41, formed in its upper planar face, serves to handling during assembly.

As already explained, this central piece of the cryostat is designed in two different models which, by their external geometry, their dimensioning, and their functional design, are interchangeable in one same construction of cryostat. Both models are illustrated by FIG. 1 and by FIG. 2, depending on whether the cryostat 30 is mounted to be coupled with housings 50 or 60 from either of the two pressure oscillators in the two cooler variants shown on the Figures 6 and 5 respectively.

In any case, this central part, therefore in in particular that bearing the reference 10 in FIG. 1, here consists of a single piece with the inner tube 3 cryostat.

On the other hand, it forms a distribution crown 71, for the annular distribution of the gas at the top of the regenerator 5. Consequently, this crown is placed above of it (in the vertical arrangement shown, cryostat under the casing 50), and more precisely at center of the base 4 in its main part formed by the flange 16.

In the illustrated embodiment, the crown of distribution 71 has a circular groove 45, hollowed out in its underside, which abuts the regenerator 5. This groove communicates through orifices 46 with an annular chamber 43, extended upwards at 42, which is arranged externally in the part of the room central 10 located at the flange 16, between this part and the face opposite the base 4.

This is where a channel 39 opens, pierced through this collar of the base 4 until communicating, once the assembly of the cooler finished, with a conduit 61 by which takes place the pneumatic connection with the compression located in the pressure oscillator.

For the rest, the central part 10 is shown in Figure 1 in the model suitable for a cooler TGP type illustrated in Figure 6.

The second model of central part of the cryostat, intended for a Stirling cycle cooler, is shown on the schematic representation in exploded layout of Figure 2. In this case, the central part 20 is identical to the previous one externally, but internally, it simply comprises an axial bore 72, formed all along through it, at the same diameter as the tube 3 of which it extends the central volume.

Returning to Figure 1, we observe the constitution means for supplying the occupying gas piston the internal volume 6 of the cryostat. At the entrance of it opens a channel 11, which is drilled axially in the room central 10 to its upper face, where it ends with a calibrated orifice 13 imposing a controlled gas flow.

Another pneumatic connection, involving one or several channels, is ensured through room 10, with the annular chamber 43 of the gas distribution ring towards the regenerator 5. there has thus appeared a calibrated orifice 14, on a channel 12 opening into the channel axial 11.

The calibrated orifices of channels 11-12 are working, in a conventional manner in itself, like valves introducing pneumatic impedances. Main channel 11 as well equipped in operation provides the useful phase shift between the pressure wave generated by the pressure oscillator and the resulting flow variations in the container tube pulsed gas. Secondary impedance (channel 12) allows to bring a fraction of the periodic feed rate of the tube by taking it directly out of compression, by diversion of the circulation passing to through the regenerator and the tube. This decreases the load thermal on the regenerator and helps to improve the efficiency of the chiller, in the case of a gas cycle pulsed.

FIG. 1 finally shows an exchanger 9, located at hot zone in the central volume, at the crown distribution 71. This hot exchanger can possibly be performed analogously to what will be described more far for the cold exchanger, the main thing being that in this variant embodiment of the cryostat of the invention, it complete the removal of excess calories from the thermodynamic cycle by completing, starting from the zone hot of the pulsed gas tube, heat losses outwardly occurring through the base 4, and incidentally from the associated pressure oscillator housing.

For either of the two types of coolers, the thermal regenerator 5 is advantageously constituted, as it appears from Figures 1 and 3, so to fully play its role of thermal accumulator for the recovery taking place, in a conventional manner, between the working gas passing from the compression phase to the expansion phase and the working gas passing from the expansion during the compression phase.

In the preferred embodiment of the invention described here and illustrated by FIG. 3, such regenerator comes in the form of a leaf continuous which is wound in a series of turns around the central tube 3 which limits the internal volume 6 of the regenerator, so as to fill, as completely as it is possible in industrial practice, the annular space between this tube 3, which forms its envelope ferrule internal, and its associated external envelope shell, constituted by the internal wall 2 of the insulating envelope 1.

Machining processes by photolithography, which are known in themselves, are particularly interesting in this sense, insofar as they represent means particularly simple to implement for a limited cost price, when it comes to driving to the configuration illustrated by the detail in FIG. 3.

According to this configuration, the sheet which is thus wound in contiguous consecutive turns, forms a succession of separate longitudinal bands 27, which are oriented perpendicular to the axis of the cryostat and which are separated from each other by intervals 28. Bars 26 are formed in excess thickness of the strips and across them in a perpendicular direction. They are evenly distributed over the entire length and leaf height and staggered, each joining two successive bands over the interval that separates them.

In this way, we realize both layers smooth surfaces which will be licked by the working gas according to its overall direction of circulation under the effect of pressure differences but which are periodically interrupted by intervals 28, and barriers oriented transversely to the bands and to the intervals between two consecutive turns of the sheet. this allows to obtain a good distribution of the gas between the layers, balanced in all directions of a section transverse of the regenerator, as well as avoiding the appearance of instabilities detrimental to efficiency exchanges, while creating significant pressure drop which is necessary for the phase shift in the control of certain coolers.

Regarding the geometric design of a regenerator thus constructed, we can cite as an example the case of a sheet 100 to 200 microns thick, hollowed out halfway through each side, for a regenerator from 2 to 3 millimeters in radial thickness. The tapes and intervals between them can, for example, be of a same width, of the order of 50 to 100 microns. The length transverse of the bars 26 can correspond, here again for example, at 1.5 times the repetition step of longitudinal strips 27, with a width of about half lesser and a distance between two successive bars offset, equivalent to about three times the width of each.

The invention thus makes it possible to take advantage of a relationship between local convective exchange and losses of longitudinal loads which, in the case of plates parallel to the axis of the cold finger, would be greater than the value that can be obtained by the usual stacks of grids or balls, however that in this form of practical realization, it ensures better distribution of the gas flow between the parallel layers of smooth surfaces.

In this way, we manage to balance the flow of working gas flowing between the annular layers at surface parallel to the axis of the cryostat of the invention, and the gas flow circulating transversely, in all radial directions of the regenerator at the different levels between successive bands. As a result, we avoid differences that exist in known regenerators between the radial flow and the axial flow, while we can find that such a difference in distribution results unbalanced heat transfers which degrade performance of regenerators.

The presence of barriers 26, which remain low dimensions compared to the length and thickness of the regenerative, also allows the introduction of an interrupt of the longitudinal flow between the strip layers successive from one end to the other of the regenerator, and thereby to stabilize the overall gas flow. Simultaneously, like these bars adjoin two adjacent layers of bands, we thanks to them a reduction in energy losses thermal by conduction in the longitudinal direction. Simultaneously, this ensures a reduction in energy losses thermal by conduction in the longitudinal direction.

In this way, we solve the problems which, in the known coolers, are linked to variations in the viscosity of the working gas as a function of the temperature local, and which cause variations causing instability intrinsic gas flow, and thus a low efficiency of the regenerator.

Such an embodiment of the regenerator 5 allows, particularly advantageously in the context of the present invention to obtain a relationship between the exchange local convective and longitudinal pressure drop very advantageous, while improving the flow distribution of gas between the parallel layers oriented longitudinally, up to recovery performance thermal at least equivalent, if not greater than those that we know get in known achievements by regenerators with stacked transverse grids or balls.

Another characteristic common to both variants of coolers described here, by way of example, relate the realization of the cold exchanger 8 installed at the bottom of the thermal insulation envelope 1 of the following cryostat the invention, as more particularly illustrated by figure 4.

It will be noted first of all that, when setting place of the central part 10 or 20 in the cryostat, its centering is ensured at the level of the timing ring 71, directly in the axis of the base 4 and on the wall internal 2 of casing 1, until pushing the regenerator 5 in abutment on the cold exchanger 8. Insofar as it carries with it the central tube 3, this central part is also centered, at the end of the latter, thanks to a shoulder 34 formed on the upper face of the exchanger 8.

This cold exchanger is produced in accordance with this which emerges from Figures 1, 2 and 4, in a form called Daisy. It is constituted by a structure with geometry of revolution, which is made of a material strongly conductor such as copper or aluminum.

This structure alternates in a star around a central core 31, empty areas 32 hollowed out through its longitudinal thickness and massive zones 33 ensuring the thermal conduction. Both extend radially astride the shoulder 34, in part and from the end of the central tube 3. They leave therefore the gas circulate freely between the central volume 6 of the cryostat (or at least the expansion chamber remaining at the bottom of the cryostat in the case of a cooler according to the figure 5 applying a Stirling cycle), bypassing the lower end of the central tube 3 received in shoulder 34.

Such a miniature exchanger, for example under 5 mm diameter and 3 mm thick, can be manufactured easily by electrochemical machining of a cylindrical bar, which is then cut into sections.

It provides an exchange surface important for a small footprint, and without creating disruptive pressure losses, while ensuring beneficial tranquilization at the bottom of tube 3 in the event that it receives pulsed gas. In order to better calm the gas flow of laminated perforated grids are interposed between the tube 3 and the lobes of the exchanger. They have not been shown in Figure 3.

The same benefits are found if the areas alternately full and empty radiant are inverted. The core 31 can also be pierced with a empty passage in its center, and there is no need to leave a peripheral crown of material, contiguous continuously with the central tube 3. The zones massive form lobes of exchanger material, here again in a configuration astride the diameter of the tube 3, in which the void areas between the lobes ensure the passage of gas between the regenerator and either the expansion chamber of a Stirling cycle cooler, i.e. the bottom of the gas piston of a gas tube cooler pulsed.

FIG. 5 illustrates the combination of the cryostat of the previous figures, using the central part 20 of the Figure 2, with a pressure oscillator corresponding to the configuration of a Stirling cycle cooler, in which the piloting is with rotary motor.

We have schematically represented a system classic drive by a crankshaft 51 of which the eccentric is linked to two connecting rods 53, 54, arranged at 90 degrees from each other. Inside the housing 60, the connecting rod 53 is articulated on the end of the displacing piston 55, while the connecting rod 54 is articulated on the piston of compression 56 which limits the compression chamber 57. The compressed gas is conveyed through conduits 58, 59 to channel 39 of the cryostat supplying the distribution chamber 71 of the cryostat, and from there the regenerator 5.

The displacement piston 55 is axially movable in the internal volume 6 of the cryostat 30. It occupies almost everything volume, leaving no room at the bottom of the tube 3 which constitutes his guide, that the thickness of the expansion chamber, considerably enlarged in the figure compared to the practical reality.

It therefore passes through the axial bore 72 of the part central 20. Its sliding in it is ensured under gas tightness by a suitable coating applied to its peripheral surface.

Figure 6 on the contrary uses an oscillator of pressure designed for a TGP type cooler including the casing 50 is connected to the cryostat around the central part 10 of the model in FIG. 1.

We therefore see in this figure 6 that the exchanger hot 9 is present and the internal volume 6 of the cryostat remained empty to be occupied by the pulsed gas and function as a gas piston.

In the particular case illustrated, the mode of piloting is of rotary type. The motor shaft is perpendicular to the axis of the system and, by an axis crankshaft off center 66, it involves an oscillating movement, a single piston 74.

The piston 74 is movable, vertically on the figure, in the axis of the cryostat, in a jacket formed at inside the housing 50.

On the offset axis 66 is mounted the internal cage 68 a ball bearing, the outer cage 67 of which is trapped in a rectilinear groove 75 dug laterally in the peripheral surface of the piston 74, perpendicular to its axis and to the plane of the figure. This provision ensures the reciprocating movement of the piston while immobilizing it in rotation.

The compression chamber 63 is formed between the upper end face of the piston and the casing 60. It is connected, as in the previous case, by a hole 62 and a conduit 61 to channel 39 opening into the chamber distribution of the cryostat.

The opposite side of the piston is hollow. we clean thus, on the side opposite to the compression chamber, a tank 65, of large volume relative to the volume of gas in circulation. The pressure in this tank therefore remains practically constant in operation.

This is how the piston 74 spares there, inside of its guide jacket, a tank which is directly open on the central part of the cryostat and which fulfills the buffer volume function for the valve under controlled flow constituted by the calibrated orifice 13 of the Figure 1, to the supply of the gas piston occupying the central volume 6.

According to a practical variant remaining within the scope of the invention, it is advantageously possible apply the same arrangement, sparing the buffer tank, directly open on the free surface of the central part 10 at the head of the cryostat, inside the compression piston, in the case of a type TGP whose piloting is ensured by linear motor rather than by rotary motor.

In Figure 7 we have shown a variant of particularly advantageous for the bottom of the cryostat. Exploded representation, used for more than clarity, schematically shows the regenerator 5 between the tube 3 of pulsed gas and the tubular wall 2, which leaves place the cold exchanger 8 against the plate 22.

The exchanger 8 here consists of lobes 77 of massive material in radiating arrangement around a core central 34. Between these lobes 77 are the passages of gases 78 which connect the lower end of the regenerator with the axial volume of the tube 3.

The gas flow tranquilization laminate, which has already been discussed, is represented by a stack of perforated grids 81 mounted in section transverse of the tube 3 at this lower end. These grids can be retained by legs of tube 3, as shown, or just stuck between the end of the tube and the exchanger 8 in its central part limited by a tube centering shoulder 79 3. In all cases, the gas passing between the exchanger lobes is found to have cross the stack of grids.

This circulation is indicated by arrows in FIG. 8, which relates to another embodiment particularly advantageous especially since it facilitates a tranquilization of the gas flow as close as possible to the cold plate 22. The cold exchanger is produced there in two parts 83 and 84 concentrically embossed one in the other; Each has its own material lobes heat exchange alternating with empty areas free to gas circulation. In other words, functionally the exchanger is therefore pierced with channels dividing into two crowns, one under regenerator 5, the other at the end of the tube 3. We can also see that the internal part 83 of the exchanger is shorter than the external part 84 which surrounds it and so that the end of the tube 3 comes center in the part 84 in abutment on the part 83.

A stack of grids 82 constitutes the laminated to calm the gas flow. These grids are interposed directly against the cold plate 22 between this and the two parts 83 and 84 of the exchanger. In case if necessary, they could be blocked in the exchanger on the outskirts, providing for this purpose a shoulder in the part 84 forming the annular ring of this exchanger.

Claims (15)

1. Cryostat for a cryogenic cooler using a closed working-gas circuit between a compression chamber located in an associated pressure oscillator casing and an expansion chamber located at the bottom of the cryostat, in a situation of heat exchange with a component to be cooled, comprising, inside a thermal insulation envelope (1), secured to a mounting baseplate (4) on the said casing (50, 60), a heat regenerator (5) inserted on the circuit of the working gas, in an annular arrangement around an axial volume (6) lying between a cold exchanger (8) which is in thermal contact with the component to be cooled (21) and which makes the regenerator (5) communicate with the said axial volume at the bottom of the cryostat (30), characterized in that it comprises a ring (71) for distributing gas in the said regenerator (5), at the top of the cryostat, from a pipe (39) drilled through the baseplate (4) for connection to the compression chamber, the said distribution ring (71) being formed by a central part (10, 20) mounted detachably and through the said baseplate (4) axially at its centre, and interchangeable between a model suitable for a cooler of the pulsed-gas type in which the axial volume (6) operates as a gas piston and a model suitable for a cooler of the Stirling cycle type in which a displacer piston moves in the said axial volume.
2. Cryostat according to Claim 1, characterized in that the said central piece, with the said distribution ring (71), is secured to a tube (3) limiting the said axial volume (6).
3. Cryostat according to either of Claims 1 and 2, characterized in that the said central part has, in the model suitable for a cooler of the Stirling cycle type, an axial bore capable of being traversed by a displacer piston of the cooler, inserted so that it can slide in a sealed manner in the said axial volume (6).
4. Cryostat according to any one of Claims 1 to 3, characterized in that the said cold exchanger (8) has a structure with axisymmetric geometry, making solid regions (33) made of a good thermal conductor alternate around the axis of the cryostat with empty regions (32) open to the passage of the gas.
5. Cryostat according to Claim 4, characterized in that the said empty regions (33) lie on each side of a shoulder (34) for centring a central tube (3) limiting the said axial volume.
6. Cryostat according to any one of Claims 1 to 5, characterized in that the said thermal insulation envelope (1) has an inner tubular wall (2) contiguous with the regenerator, closed by a plate (22) accommodating the component to be cooled, to which the cold exchanger (8) is fixed.
7. Cryostat according to any one of Claims 1 to 6, characterized in that the said regenerator consists of a sheet wound over itself in the annular space between an inner wall (2) of the said envelope (1) and a central tube (3) limiting the said axial volume, in alignment with the said distribution ring, the said sheet being machined, in particular by a photolithographic process, so as to form distinct strips (27) with smooth surfaces parallel to the axis of the cryostat and transverse bars (26) in the form of an overthickness bringing together the successive strips at discrete points.
8. Cryostat according to any one of Claims 1 to 7, characterized in that the said distribution ring has a lower face for stopping on the said regenerator, in which face a circular groove (45) is hollowed out, communicating via regularly spaced orifices with an annular chamber (42, 43) made externally around the said central part at the level of the baseplate (4) of the cryostat, in communication with the said channel (39).
9. Cryostat according to any one of Claims 1 to 8, characterized by a lamination of grids for calming the gas stream inserted at the bottom of the said axial volume against the cold exchanger.
10. Cryostat according to any one of Claims 1 to 9, characterized in that the said baseplate (4) forms a ring (17) for mounting the said central part (10, 20), in alignment with the said axial volume (6).
11. Cooler, characterized in that it comprises a cryostat according to any one of Claims 1 to 10 corresponding to the model suited for a Stirling cycle cooler, connected to the casing (60) of a pressure oscillator comprising a displacer piston driven in a synchronized manner so that it is out of phase with a compression piston and in that the said displacer piston (55) is able to move axially in the said inner volume (6) of the cryostat (30) and then changes to sliding in a sealed manner in an axial bore (72) provided for this purpose in the said central part (20) mounted in the said baseplate of the cryostat.
12. Cooler, characterized in that it comprises a cryostat according to any one of Claims 1 to 10 corresponding to the model suited for a pulsed-gas cooler, connected to the casing (50) of a pressure oscillator comprising means for periodically driving a piston for compressing the gas causing the volume of the compression chamber and a buffer reservoir of gas at constant pressure to vary, and in that the said central part (10) mounted in the baseplate (4) of the cryostat comprises means for pneumatic connection at a controlled flow rate with the said reservoir (65).
13. Cooler according to Claim 12, characterized in that the said central part comprises, in addition to a channel (11) for the passage of the gas at a controlled flow rate between the said buffer reservoir of gas at constant pressure made inside the casing (50) of the pressure oscillator, and the said internal axial volume (6) of the cryostat, the latter being filled with gas in operation in order to form a gas piston out of phase with respect to the periodic compression, at least one other channel (12) with a controlled flow rate, opening out into an annular chamber (42, 43) formed by the said central part (10) made according to Claim 8.
14. Cooler according to Claim 12 or 13, characterized in that the said buffer volume of gas is made inside a compression piston controlled by the said drive means, which is for this purpose directly open, in a liner for guiding the said piston, on the said central part (10) of the cryostat.
15. Cooler according to any one of Claims 12 to 14, characterized in that, in a configuration of the rotary engine type, the said drive means comprise a crankshaft actuating a mechanism for transmitting movement by means of ball bearings which is able to move in a groove made transversely outside the said piston.

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