Ionizing pump stage

Abstract

The invention relates to an ionizing pump stage, in particular for a vacuum pump, comprising an inlet for gas entering into the pump stage; an ionizing section communicating with the inlet in a gas-conductive manner and an ionizing device for ionizing the gas entered into the ionizing section; an acceleration device for accelerating the ionized gas present in the ionizing section in the conveying direction; and a neutralizing section following the ionizing section in the conveying direction and communicating with the ionizing section in a gas-conductive manner and a neutralizing device for the electrical neutralizing of the ionized gas entering into the neutralizing section.

Claims

1. A vacuum pump, comprising at least one ionizing pump stage (10); and at least one turbomolecular pump stage (28) following the ionizing pump stage (10) in a conveying direction, wherein the ionizing pump stage (10) has: an inlet (12) for gases entering into the pump stage (10); an ionizing section (14) communicating with the inlet (12) in a gas-conductive manner and an ionizing device for ionizing the gas entered into the ionizing section (14); an acceleration device (20) for accelerating the ionized gas present in the ionizing section in a conveying direction of the gas; and a neutralizing section (18) following the ionizing section (14) in the conveying direction and communicating with the ionizing section (14) in a gas-conductive manner and a neutralizing device (24) for the electrical neutralizing of the ionized gas entering into the neutralizing section (18), and wherein the ionizing device comprises an ionizing structure for ionizing the gas, and wherein the ionizing section extends, least at one point, over at least approximately a total gas-conductive cross-section of a conveying space for the gas and which is formed by the ionizing path, and the ionizing structure bounds the ionizing section of the conveying space.

2. The vacuum pump in accordance with claim 1, wherein the vacuum pump comprises a plurality of ionizing pump stages (10).

3. The vacuum pump in accordance with claim 1, wherein a plurality of ionizing pump stages (10) are connected in series or in parallel with respect to a gas flow conveyed in the conveying direction of the gas.

4. The vacuum pump in accordance with claim 1, wherein the neutralizing section (18) is substantially separated from the inlet (12) by the ionizing section (14).

5. The vacuum pump in accordance with claim 1, wherein the acceleration structure (20) is arranged in an acceleration section (16) or bounds the acceleration section (16) which is arranged in the conveying direction between the ionizing section (14) and the neutralizing section (18) and connects the ionizing section (14) and the neutralizing section (18) to one another in a gas-conductive manner.

6. The vacuum pump in accordance with claim 1, wherein the acceleration structure (20) is configured for producing an electrical acceleration field, and/or wherein the acceleration structure (20) can be acted on by an electrical acceleration potential.

7. The vacuum pump in accordance with claim 1, wherein the neutralizing structure (24) can be acted on by a neutral electrical potential.

8. The vacuum pump in accordance with claim 1, wherein gas molecules (32, 32) to be conveyed are selected from the group comprising molecules of H.sub.2, O.sub.2, N.sub.2, CO and CO.sub.2.

9. The vacuum pump in accordance with claim 1, wherein the ionizing pump stage (10) has a cylindrical basic shape.

10. The ionizing pump stage in accordance with claim 9, wherein the ionizing section (14) and the neutralizing section (18) follow one another in an axial direction or in a radial direction.

11. The vacuum pump in accordance with claim 1, wherein an outlet (26) for leading off the gas from the neutralizing section (18) is provided following the neutralizing section (18) in the conveying direction and connected to the neutralizing section (18) in a gas-conductive manner.

12. A vacuum pump stage according to claim 1, wherein the acceleration device (20) has an acceleration structure formed by a grid-shaped electrode and having a plurality of channel-shaped or tunnel-shaped openings (22), each channel-shaped or tunnel-shaped opening (22) having a length larger than both width and height of the channel-shaped or tunnel-shaped opening (22).

13. The vacuum pump stage in accordance with claim 12, wherein each channel-shaped or tunnel-shaped opening (22) has a ratio of a length thereof to a height or width thereof from 2 to 5.

14. A vacuum pump, comprising at least one ionizing pump stage (10); and at least one turbomolecular pump stage (28) following the ionizing pump stage (10) in a conveying direction, wherein the ionizing pump stage (10) has: an inlet (12) for gases entering into the pump stage (10); an ionizing section (14) communicating with the inlet (12) in a gas-conductive manner and an ionizing device for ionizing the gas entered into the ionizing section (14); an acceleration device (20) for accelerating the ionized gas present in the ionizing section in a conveying direction of the gas; and a neutralizing section (18) following the ionizing section (14) in the conveying direction and communicating with the ionizing section (14) in a gas-conductive manner and a neutralizing device (24) for the electrical neutralizing of the ionized gas entering into the neutralizing section (18), wherein the ionizing device comprises an ionizing structure for ionizing the gas, and wherein the ionizing structure can be acted on by an electrical DC voltage potential or by an electrical AC voltage potential, and wherein the electrical DC or AC voltage potential is adapted to ionize the gas molecules to be pumped once or a multiple of times, with the gas molecules being selected from the group consisting of hydrogen, oxygen, nitrogen, carbon monoxide or carbon dioxide molecules.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The drawings are show in:

(2) FIG. 1 a vacuum pump having an ionizing pump stage in accordance with the invention in accordance with an embodiment of the invention;

(3) FIG. 2 a schematic representation of a flow model of the ionizing pump stage of FIG. 1; and

(4) FIG. 3 exemplary characteristic lines of two vacuum pumps in accordance with a respective one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) FIG. 1 shows a vacuum pump having an ionizing pump stage 10 in accordance with an embodiment of the invention.

(6) The ionizing pump stage 10 comprises an inlet 12 through which the gas can enter from a volume to be evacuated into the conveying space of the ionizing pump stage 10. A plurality of gas molecules are shown by way of example and as exaggeratedly large in FIG. 1 and are provided with the reference numeral 32 and 32 respectively. A gas molecule 32, 32 is in principle also to be understood as a single gas atom. Accordingly, an ionized gas molecule 32, 32 is to be understood both as an ionized gas molecule, i.e. a gas molecule electrically charged once or a multiple of times, comprising a plurality of atoms and also as an ionized gas atom.

(7) Following the inlet 12 in the conveying direction, a baffle 13 is provided with which the cross-section of the conveying space and thereby the amount of the gas can be regulated which enters into the sections of the conveying space of the pump stage 10 following the baffle 13, i.e. into the ionizing section 14, into the acceleration section 16 and into the neutralizing section 18.

(8) The ionizing section 14 follows the baffle 13 in the conveying direction and is arranged such that the gas molecules 32, 32 present in said ionizing section are ionized by a corresponding ionizing device not shown in FIG. 1, with the gas molecules 32, 32 being positively charged in the present case, i.e. emitting electrons on the ionizing. The ionizing device can, for example, comprise an electrode arranged in or bounding the ionizing section 14 and being able to be acted on by an electrical DC voltage potential or AC voltage potential.

(9) The acceleration section 16 is provided following the ionizing section 14 in the conveying direction. An acceleration structure 20 is arranged in the acceleration section 16. The structure 20 is formed by a grid-shaped electrode which has an electrical charge opposite to the electrical charge of the ionized gas molecules 32, 32, i.e. negative in the present case, so that the ionized gas molecules 32, 32 are attracted by the acceleration structure 20 and are accelerated in the conveying direction.

(10) The acceleration structure 20 has channel-like openings 22 which extend in parallel with one another in the conveying direction and which have a relatively large aspect ratio, i.e. a ratio of length L to the cross-sectional diameter d. The channels 22 connect the ionizing section 14 in a gas-conductive manner to the neutralizing section 18 following the acceleration section 16 in the conveying direction so that the ionized gas molecules 32, 32 enter through the acceleration section 16 into the neutralizing section 18 as is indicated in FIG. 1 for the example of two ionized gas molecules 32.

(11) The wall 24 of the pump stage 10 surrounding the neutralizing section 18 and its surface 36 bounding the conveying chamber are acted on by an electrically neutral potential. When the gas molecules 32, 32 entering into the neutralizing section 18 come into contact with the surface 36, they are electrically neutralized, i.e. they reabsorb previously emitted electrons. In the region of the surface 36, the wall 24 can at least regionally have a material which admittedly electrically neutralizes the conveyed gas molecules 32, 32, but does not adsorb them or only adsorbs them with a small probability.

(12) While the ionized gas molecules 32, 32 present in the ionizing section 14 are accelerated in the direction of the neutralizing section 18, the movement of the neutralized gas molecules 32, 32 present in the neutralizing section 18 is essentially determined by their thermal movement and is consequently substantially undirected. The thermally induced back diffusion of neutralized gas molecules 32, 32 in the direction of the ionizing section 14 is thus much smaller than the electrically accelerated conveying of gas molecules 32, 32 from the ionizing section 14 into the neutralizing section 18 so that an efficient pumping effect results.

(13) Following the neutralizing section 18 in the conveying direction, an outlet 26 is arranged which is connected to the neutralizing section 18 in a gas-conductive manner and which is connected in a gas-conductive manner to the inlet of a further pump 28 connected downstream of the ionizing pump stage 10. In particular when the pump stage 28 is a turbomolecular pump stage, an extremely high-power vacuum pump is provided in this manner. The conveying effect of the total vacuum pump is illustrated by arrows 37, 39 in FIG. 1.

(14) FIG. 2 shows a schematic representation of a flow model of the ionizing vacuum pump stage 10 of FIG. 1 with reference to which the pumping effect and the power properties of this pump stage 10 are explained in the following.

(15) The arrows in FIG. 2 indicate the flow direction of the gas. The gas to be pumped out which enters via the inlet 12 of the pump stage 10 has an inlet pressure p1. This pressure p1 produces a gas flow Q through the inlet 12 and the baffle 13 (FIG. 1) which depends on an admittance value LB which can be varied by varying the opening cross-section of the baffle 13, with the gas entering through the inlet 12 and the baffle 13 having an intermediate pressure p1.

(16) The pumping effect performed by the ionization, acceleration and neutralizing mechanism described above is represented in FIG. 2 by an idealized ionizing pump stage 38 which conveys an ionizing gas flow Q.sub.i to the neutralizing section of the pump stage 10 and in so doing compresses the gas to the outlet pressure p2. The back diffusion from the neutralizing section back to the inlet or to the ionizing section is modeled in FIG. 2 by the backflow conduction value L.sub.r which produces a back diffusion gas flow Q.sub.i. In stationary operation of the pump stage 10, the gas flow Q.sub.aus led off through the outlet of the pump corresponds to the incoming gas flow Q of the pump stage 10.

(17) The gas flow Q entering through the inlet 12 and the baffle 13 is related to the inlet pressure p.sub.1, the intermediate pressure p.sub.2 and the admittance value LB in accordance with the equation Q=(p.sub.1p.sub.2).Math.L.sub.B. A portion Q.sub.i(i) of the gas flow Q dependent on the degree of ionization i of the ionizing section (i=0 . . . 100%) is, as described above, ionized, is accelerated toward the acceleration structure, flies through the acceleration structure and is neutralized again in the neutralizing section. The back diffusion of the electrically neutral gas molecules is no longer subject to the electrical movement laws, but rather to the thermal movement laws and results as Q.sub.r=(p.sub.2(1i).Math.p.sub.1).Math.Lr.

(18) Starting from the above flow equations, the maximum suction capacity S0 and the idling compression k.sub.0 of the pump stage 10 can be determined, wherein the H.sub.o factor H.sub.0 results from the suction capacity S.sub.0 and the admittance value LB in accordance with the equation H.sub.0=S.sub.0/L.sub.B, where H.sub.0<100&%.

(19) The H.sub.o factor can be calculated, starting from the above-described model, as H.sub.o=(k.sub.01)/(k.sub.0+g), where g is a pump stage-specific constant whose value can e.g. be 2 and k.sub.o gives the idling compression of the pump stage 10. The idling compression k.sub.o can be determined according to the equation k.sub.o=1+i/(i1).Math.a.Math.22,4.Math.(U/V).sup.1/2. Here is a geometrical factor which depends on the length of the channels 22 (see FIG. 1) and is approximately equal to 1. The factor a in this respect increases for larger lengths L of the channels 22 here (FIG. 1) so that a larger length L of the channels 22 produces a larger idling compression k.sub.0 and a larger H.sub.o factor H.sub.0. U designates the amount of the acceleration voltage or of the acceleration potential which is applied to the acceleration structure and which can be selected independently of the degree of ionization.

(20) A high H.sub.o factor can in this respect in particular be achieved with high acceleration voltages U and high degrees of ionization i. The ionizing pump stage 10 can be configured such that an idling compression K.sub.0>30 is reached and simultaneously an H.sub.o factor H.sub.0>90% is reached. For example, with an acceleration voltage U of 17 kV/1.9 kV/0. kV or 0.2 kV and a degree of ionization i of 1%/3%/5% or 10%, an Ho factor H.sub.0>90% can be achieved. A degree of ionization of at least 3% is advantageously realized to be able to achieve an H.sub.o factor>90% even with moderate acceleration voltages U.

(21) The H.sub.o factor of the total vacuum pump shown in FIG. 1, i.e. the effective H.sub.o factor H.sub.0eff determined while taking account of the further pump stage 28, depends on the suction power of the further pump stage 28 as well as on the admittance value and accordingly on the inlet size or flange size of the further pump stage 28 in comparison with the admittance value and accordingly with the inlet size or flange size of the ionizing pump stage 10, with a greater effective H.sub.o factor H.sub.0eff being achieved with a larger flange size of the further pump stage 28.

(22) FIG. 3 shows for comparison two exemplary characteristic lines 40, 42 which each give the effective Ho factor H.sub.0eff of an exemplary vacuum pump in accordance with FIG. 1 in dependence on the relative molecular mass m of the gas molecules conveyed by the pump, with both cases starting from an acceleration voltage U of 2 kV and a degree of ionization i of 10% of the ionizing pump stage 10 of the same design for both pumps. In both pumps, the further pump stage 28 (FIG. 1) is in each case formed by a turbomolecular pump stage. The characteristic line 40 describes a pump having a larger turbomolecular pump stage 28 in which the flange size of the turbomolecular pump 28 corresponds to the flange size of the ionizing pump stage 10. The characteristic line 42 describes a pump having a smaller turbomolecular pump stage 28 in which the flange size of the turbomolecular pump stage 28 is smaller by one size than the flange size of the ionizing pump stage 10.

(23) As can be seen with reference to the characteristic lines 40, 42 in FIG. 3, a very high effective H.sub.o factor H.sub.0eff is achieved with both pumps, in particular also with small molecular masses m, with the effective H.sub.o factor H.sub.0eff being larger than 90% over a wide range of the molecular mass m, in particular with the pump having the larger turbomolecular pump stage (characteristic line 40).

(24) Though the present invention was shown and described with references to the preferred embodiments, such are merely illustrative of the present invention and are not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is, therefore, not intended that the present invention be limited to the disclosed embodiments or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.