EP0000311B1 - Cryogenic pump - Google Patents

Description

The present invention relates to a cryopump of the kind incorporating, in a thermally insulated enclosure, trapping means comprising refrigerated trapping walls by condensation and trapping walls by adsorption covered with at least one layer of adsorbent products, such as activated carbon. or zeolites. Such adsorption trapping walls are described in US Patent 3,296,773. Thanks to the combination of these two trapping means, it is possible, at least theoretically, to descend to very deep voids, of the order of 1 ax torr, because the gases which are difficult to condense even at very low temperatures of trapping like hydrogen, neon are trapped by the trapping walls by adsorption. However, the efficiency of the adsorption trapping walls is considerably reduced by the fact that they are contaminated by the more easily condensable gases such as nitrogen, oxygen, argon. We have managed to mitigate this drawback by locating the trapping walls by adsorption downstream of the trapping walls by condensation with respect to the path of the gases which, moreover, advantageously comprise a wall in the form of a baffle protecting from the direct path of the gases. the trapping walls by adsorption.

This type of cabinet has at least three drawbacks: on the one hand it is expensive to produce, on the other hand, to be effective in molecular regime, it must be optically sealed, which results in a large decrease in the speed of pamping of the surface covered with adsorbent; finally whatever the model, it plays practically no role for the protection of the adsorbent, when the gas flow regime of the enclosure is viscous or intermediate, which can happen in certain types of use of the cryopump.

Another method of pumping by adsorption has also been proposed which consists in depositing on the cryosurface a gas which is condensable at this temperature and which has adsorbent properties for incondensable gases (for example a deposition of C0 ₂ has adsorbent properties for hydrogen. at 20 K). On the one hand, this deposition of adsorbent gas is subject to the same drawbacks described above as a solid adsorbent; on the other hand, during the injection of the adsorbent gas on the cryosurface, there is always a rise in pressure in the enclosure, either by excess of injected gas, or by surface heating of the already formed cryodeposit and this rise in pressure is generally harmful.

A first objective of the present invention is to produce an adsorption cryopump, having a high pumping efficiency, namely a maximum pumping speed in molecular regime and excellent protection of the adsorbent in viscous or intermediate regime.

A second objective of the present invention is to produce a cryopump with injection of adsorbent gas preventing pressure build-up in the enclosure during the injection of adsorbent gas.

A cryopump according to the invention is characterized by a partition delimiting a confined area and comprising at least one partition movable under the action of a control means accessible from outside of said enclosure, from a closed position isolating said confined area from a remaining part of the enclosure to a position of communication between said confined area and said remaining area of enclosure, the sheets of adsorbent product being located in said confined area in said closed position of said partitioning.

In this way, it is possible to maintain in the state of complete regeneration the trapping walls by adsorption during all the phases preliminary to their final intervention in order to capture the last residual quantities of gas which are very difficult to condense. Not being brought into contact with the more easily condensable gases which are trapped by the condensation walls, the effectiveness of the trapping walls by adsorption remains full.

• - La figure 1 est une vue schématique partielle en perspective et en partie éclatée d'une cryopompe selon l'invention, dans la phase initiale de pompage,
• - La figure 2 est une vue de la cryopompe selon la figure 1 dans la phase finale de pompage,
• - Les figures 3 et 4 sont des vues analogues aux figures 1 et 2 d'une variante de réalisation,
• - Les figures 5 et 6 sont des vues plus détaillées en élévation-coupe et de dessus du dispositif commande équipant une autre variante de réalisation de cryopompe.

The characteristics and advantages of the invention will become apparent from the description which follows by way of example with reference to the appended drawings in which:

• FIG. 1 is a partial schematic view in perspective and partially exploded of a cryopump according to the invention, in the initial pumping phase,
• FIG. 2 is a view of the cryopump according to FIG. 1 in the final pumping phase,
• - Figures 3 and 4 are views similar to Figures 1 and 2 of an alternative embodiment,
• - Figures 5 and 6 are more detailed views in elevation-section and from above of the control device fitted to another alternative embodiment of the cryopump.

Referring to Figures 1 and 2, in a pumping enclosure 1 of which a wall part has been shown 2 is placed a cryopump body consisting of a partition 3 formed of a plurality of longitudinal partitions 4 (eight in number ) extending along a polygonal contour between two bottom partitions 5 and 6. The partitions 4 are mounted along a longitudinal axis defined by the pins 7 and 8 engaging in the trunnions of the bottom partitions 5 and 6. Under the bottom partition 5 is mounted in axial rotation a ring 9 which can be controlled in rotation by a wheelhouse 10 passing through the enclosure wall 2 by a sealed junction 11. This ring 9 is secured to an axial pivot 12 which is mechanically connected to each partition 4 by an articulated link 13, so that, starting from the fully closed position as shown in FIG. 1, traction on the linkage 10 according to the arrow f ^l , which has the effect of ensuring an axial rotation movement according to the arrow f ² of the ring 9 ensures by through the connecting rods 13, an opening rotation making a confined area 20 communicating delimited by the partitions 4, 5 and 6 in the closed position with a remaining part of the enclosure 1.

The partitions 4 have this characteristic of being metallic and preferably made of thermally conductive metal. They are coated on one side only with a sheet 14 of adsorbent product generally in the form of activated carbon particles or zeolites bonded to the metal surface or embedded in the metal. Refrigeration means, for example welded tubes convey helium at 20 ° K allowing the cooling of the partitions 4. In this embodiment, the internal face (FIG. 1) of the partitions 4 with its coating in web 14 of product adsorbent constitutes the trapping wall by adsorption, while the external face of these same partitions 4, without any coating, constitutes the trapping wall by condensation 16.

• - Une chambre à évacuer (non représentée) et la cryopompe sont d'abord mises sous vide primaire (Pression inférieure à 5.10-¹ torr), au moyen d'une pompe mécanique, la cryosurface formée par le cloisonnage 3 étant en position ouverte (figure 2) pendant cette opération.
• - La cryopompe est ensuite mise en froid, le cloisonnage 3 étant amené en position fermée (figure 1). La chambre se trouve alors évacuée par la cryopompe, les gaz condensables venant se fixer sur la face externe 16 des cloisons 4, dépourvues d'adsorbant. Le vide limite ainsi obtenu est identique au vide obtenu par une cryopompe simple et dépend du taux de gaz incondensables se trouvant dans la chambre à vider. On peut alors, soit pour abaisser le taux résiduel de gaz incondensables, soit parce que l'expérience qui se déroule dans la chambre libère des gaz incondensables, agir sur la timonerie 10, de manière à faire pivoter les cloisons 4 L'adsorbant, fixé en nappe 14 sur la face primitivement interne des cloisons 4, est alors mise en communication avec l'enceinte 1 et devient le facteur essentiel de l'action de pompage. L'angle d'ouverture des cloisons 4 peut être réglé, rendant ainsi variable simultanément la vitesse de pompage pour le gaz à adsorber et le taux de contamination par les autres gaz.

The operation of the cryopump is as follows:

• - A chamber discharging (not shown) and the cryopump are first under low vacuum (pressure less than 5.10 torr ¹⁾ by means of a mechanical pump, the cryosurface formed by said partition 3 in the open position ( figure 2) during this operation.
• - The cryopump is then cooled, the partition 3 being brought into the closed position (Figure 1). The chamber is then evacuated by the cryopump, the condensable gases coming to be fixed on the external face 16 of the partitions 4, devoid of adsorbent. The limit vacuum thus obtained is identical to the vacuum obtained by a simple cryopump and depends on the rate of noncondensable gases found in the chamber to be emptied. It is then possible, either to lower the residual rate of noncondensable gases, or because the experiment which takes place in the chamber releases noncondensable gases, act on the wheelhouse 10, so as to pivot the partitions 4 The adsorbent, fixed in sheet 14 on the originally internal face of the partitions 4, is then placed in communication with the enclosure 1 and becomes the essential factor of the pumping action. The opening angle of the partitions 4 can be adjusted, thereby making the pumping speed for the gas to be adsorbed and the rate of contamination by other gases variable simultaneously.

According to the variant embodiment shown in FIGS. 3 and 4, the same geometrical arrangement of the partition 3 is found, but here the partitions 4 are devoid, on their internal face, of adsorbent product permanently fixed, and opposite these partitions 4, when they are in the closed position (FIGS. 3) there is one of the openings 30 formed at the periphery of a hollow shaft 31, the interior of which communicates with a conduit 32 connected to a source of pressurized gas not shown and located outside the cryopump.

The operation of this alternative embodiment is the same as that described above with the difference that in the final phase where the trapping walls by adsorption will intervene, but before the partitions 4 are opened, the lights 31 are delivered. puffs of adsorbent gas which immediately condense into a sheet 33 on the internal face of the trapping partitions by adsorption 4. Once the gas has been deposited, the wheelhouse 10 can then be maneuvered to cause the walls 4 to rotate as before.

According to the variant embodiment shown in FIGS. 5 and 6, there are again here partitions 50 (eight in number) arranged according to a polygonal contour, one inner face 51 of which is covered with a sheet of adsorbent product, while a outer face 52 is devoid of any coating. As before, these partitions 50 are hingedly mounted on axes 53 and are capable of being rotated by an angle of 90 ° by the linkage 10 passing through the sealed junction 11 of the partition 2 and by means of a chain. 56 meshing on pinions 57 integral with axes 53. Here, the trapping surfaces by adsorption have been considerably increased by providing an equal number of fixed radial partitions 54 extending from a central shaft 55 to the immediate vicinity of partitions 50. These radial partitions 54 are covered on both sides with sheets of adsorbent product.

The applications of the present invention are those which require a clean and high vacuum with high pumping speeds, in particular the applications generating a release of large quantities of noncondensable gases, (such as hydrogen: production of thin layers, controlled nuclear fusions , etc ...

The most well-known example of application is the use in an evaporation frame of mine layers, where release to air is frequent, therefore periods of operation in viscous regime (5.10- '- 10- ⁴ torr ) many. The invention makes it possible to almost completely overcome the drawbacks due to these releases to the air. The saturation of the adsorbent (in the case of solid adsorbent) is then due only to the quantity of noncondensable gases released during the evaporations.

Claims (7)

1. A cryopump of the type incorporating refrigerated trapping means (4) in a thermally insulated chamber (1-2), said refrigerated trapping means (4) comprising walls (16) for trapping by condensation and walls for trapping by adsorption covered by at least one layer of an adsorbing product, characterised by a partitioning (4,5,6) comprising at least one partition (4) displaceable under the action of a control means (9,10) accessible from outside said chamber (1,2) from a closed position (Fig. 1) insulating a confined zone (20) of a remain- .ing part of the chamber (1-2) to a position of communication (Fig. 2) between the said confined zone (20) and the said remaining zone of the chamber (1,2), the sheets (14) of adsorbent product being situated in said confined zone (20) in said position of closure of said partitioning (Fig. 1

2. A cryopump according to claim 1, characterized in that at least a part of the walls for trapping by adsorption (4) comprises at least in part the said partitioning (4,5,6) covered by a layer (14) of adsorbent product on its face situated on the side of the confined zone (20).

3. A cryopump according to claim 1, characterized in that the layer (33) of adsorbent product is constituted by condensed adsorbent gas and in that means for conveying said gas (30-31-32) extend from outside the cryopump chamber to within the confined adsorbtion zone (20).

4. A cryopump according to claim 1, characterized in that the partitioning is of a general cylindrical shape constituted by a plurality of longitudinal partitions (4) disposed in a polygonal formation between two partitions with a fixed base (5,6), said longitudinal partitions (4) being displaceable round a median longitudinal axis of articulation (2,8).

5. A cryopump according to claim 1, characterized in that the means (9-10) for control of a displaceable partition (4) is a push-rod (10) slidable longitudinally in a sealed passage (11) of the wall (2) of the cryopump (2-1

6. A cryopump according to claim 3, characterized in that the means for supply of the adsorbent gas extend from part to part of the confined zone (20) and present openings (31) distributed with respect to the trapping partitions (4) by adsorption of the confined zone (20).

7. A cryopump according to claim 4, characterized in that walls for trapping by adsorption comprise radial, fixed partitions (34) a confined zone (20) of the chamber (1-2).

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