US3583829A

US3583829A - Getter-ion pump for producing and maintaining a high vacuum

Info

Publication number: US3583829A
Application number: US871933A
Authority: US
Inventors: Max-Josef Schonhuber
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-11-01
Filing date: 1969-10-28
Publication date: 1971-06-08
Anticipated expiration: 1988-06-08
Also published as: DE1954441A1; FR2022353A6; GB1284290A; DE1954441B2; DE1954441C3

Abstract

A getter-ion pump for producing and sustaining a high vacuum in a vessel includes a pump housing in communication with the vessel. The pump housing includes spaced anode and cathode electrodes between which an arc is struck and maintained and the electrodes are in the form of coaxial cylinders one of which is constituted at least by two interconnected parts of different diameters such that along an axial extension which is at least greater than the spacing between the cylinders and at least 1.1fold increase in spacing between the cylinders is achieved.

Description

United States Patent GETTER-ION PUMP FOR PRODUCING AND MAINTAINING A HIGH VACUUM 23 Claims, 3 Drawing Figs.

0.8. CI 417/49 Int. Cl. F04b 37/02 Field otSearch 4l7/48,49,

[56] References Cited UNITED STATES PATENTS 3,100,274 8/1963 Luftman et al.

3,394,874 7/l 968 Marshall Primary Examiner-Robert M. Walker Attorney- Pierce. Schefiler and Parker 31 7/49X 4 l 7/49X ABSTRACT: A getter-ion pump for producing and sustaining a high vacuum in a vessel includes a pump housing in communication with the vessel. The pump housing includes spaced anode'and cathode electrodes between which an arc is struck and maintained and the electrodes are in the form of coaxial cylinders one of which is constituted at least by two interconnected parts of different diameters such that along an axial extension which is at least greater than the spacing between the cylinders and at least LI-fold increase in spacing between the cylinders is achieved.

PATENTEDJUN BIB/l 35 3529 sum 2 or 3 Fig.2

INVENTQR MJ. SCHONHUBER ATENIED JUN 8 mm SHEET 3 BF 3 INVENTOI? M. J. SCHONHUBER GETTER-ION PUMP FOR PRODUCING AND MAINTAINING A HIGH VACUUM This invention relates to a getter-ion pump for the production and maintenance of a high vacuum by means of electrodes between which an electric discharge occurs.

The invention is related from a standpoint of general subject matter to the getter-ion pump structure disclosed in my copending application Ser. No. 750,442 filed Aug. 5, 1968, now Pat. No. 3,489,336, and in which means are provided, which on switching on the pump, cause an arc to be struck between a first electrode and a second electrode at a different potential for the purpose of forming at least one cathode spot,

in the region of which the surface of the cathodic getter material is molten, said means including either an ignition pin and a starting device which momentarily short circuits the electrodes on switching on, or a switching device for producing a striking voltage between the electrodes and in which further means are provided for maintenance of the are produced, so that the latter wanders about in the space formed between the electrodes and simultaneously the cathode spot on the surface of the electrode moves about, said further means including a switching device for the application of a low DC voltage to the electrode, the space between the electrodes being connected with the receiver via at least one opening allowing the passage of gas.

This getter-ion pump can be still further improved and then enables an actual pump housing to be dispensed with and enables wandering of the cathode spot to be kept within bounds in a reliable manner and also enables any atomization of the electrode insulating material to be inhibited in a reliable manner and at the same time inhibits to a considerable extent any atomization of the electrode itself into the receiver, in addition to which the arrangement is made independent of any coolant supply.

It is consequently proposed in accordance with the present invention that the electrodes shall consist mainly of at least approximately coaxial cylinders, the outer surface of the one and the inner surface of the other cylinder forming electrode surfaces, one cylinder at least also constituting the main portion of the pump housing, and that one cylinder at least shall consist of at least two interconnected portions of different diameters, so that an at least l.lfold increase in spacing is achieved at least along an axial extension greater than the remaining spacing between the approximately coaxial cylinders.

In the accompanying drawings, FIGS. 1 to 3 show different embodiments of the invention:

FIG. 1 shows an embodiment in which the main electrode acting as cathode and having two interconnected cathodic cylinder portions of different diameters is coaxially located within the main electrode or the appropriate cylinder acting as anode.

FIG. 2 shows an embodiment in which the main electrode connected as an anode and having two interconnected anodic cylinders of different diameters is located coaxially with the cathodic main electrode also functioning as the pump housing and in which the gas passage or passages leading to the cylinder is/are in the form of a pump connection or connections in the cathode cylinder.

HO. 3 shows an appropriate electrical circuit for striking the are between the electrodes of the pump and subsequently maintaining it.

ln FIG. 1, 1 is the vacuum vessel-receiver for short. The getter-ion pump is mounted on this receiver. Said pump is built into the main electrode-the anode-consisting mainly of the cylinder 9 (or its outer wall 2 as the case may be) and of the disc 5 provided with gas passages, said electrode being sealed with a metal cover 3. lnto this vessel functioning as anode is built the cathodic main electrode having a cathode cylinder 8 having two interconnecting

portions

12, 13 of different diameters and the sealing disc 4 therefor. The are is in tended to burn between these two main electrodes.

An auxiliary electrode 6 insulated electrically from the main electrode by means of insulation 7 is also provided. Said auxiliary electrode consists partly at least of a very refractory metal, whereas, the

main electrodes

4, 8 or 5, 9 respectively consist at least partly of getter material or of a layer of getter material at least 0.5 mm. in thickness applied to a previously degasified base metal.

Part of the anode 5,9 is in a form of a screen, in order to facilitate passage of gas residues from the receiver 1 into the pump. A part at least of the cathode 4,8 is closely spaced to the anode 5, 9. The auxiliary electrode 6 at this place is located close to the main electrode 4, 8 functioning as the cathode. A high voltage pulse is first impressed on the auxiliary electrode so that an arc is struck between said auxiliary electrode and the cathode 4, 8 even when a high vacuum obtains in the pump, with the result that at least one cathode spot is formed on the main cathode 4,8. The rectifier circuit 31 (FIG. 3) is closed via the cathode spot already existing on the cathode 4, 8 owing to the auxiliary are through the vapor thus evolved from the electrode and its consequent ionization and the existing ionization of the space between the

main electrodes

4, 8 and 5, 9 and a heavy current of several hundred amperes can flow from the low voltage source, but which must be suitably energized, in order to sustain a powerfullow voltage arc. This procedure increases the number of cathode spots at least in the highand ultrahigh vacuum range, since if the current strength exceeds the value set by the electrode material, a cathode spot will divide up into two or more spots. At the same time, migration of the cathode spot into part of the electrode with increased electrode spacing will increase the length of the individual arc plasma columns. Consequently, the volume of the are which can be sustained and the strength and the current strength of which becomes increased exceeds the value of the are originally struck and consequently also the volume of the gas flowing through the are, so that an adequately large pumping speed can be achieved even in a high vacuum.

Since the getter-ion arc pump can also continue to act even in the intervals when switched off as a sorption pump and can effectively pump nonrare gases by means of the active surface films deposited from the vaporization of the electrode, the surfaces facing the cathode should for this purpose be as large as possible, by for example designing the anode 5, 9 which is provided partly at least with gas passages and is partly at least in the form of a screen 5 with oblique slots and having stays 10 with optional liquid cooling, the gas passages being fitted with a system of cooled baffles 11 on the side facing the receiver.

As a condition determining adequacy of pumping capacity, it is of quite decisive importance that on the one hand as large as possible an electrode surface should be available over which the cathode spot can wander, which is achieved according to my aforesaid copending application by combining the disc-shaped electrode4, 5 with the coaxial cylinders 8, 9 and that on the other hand means are available for reliably limiting the wandering of the cathode spot, in order without fail to keep vapors arising from the electrode away from the electrode insulation 17.

Consequently, in accordance with the invention, the electrode surface formed by the coaxial cylinders 8, 9 is to be limited by the fact that at least one of the two cylinders, for example, cylinder 8 in FIG. 1, consists of at least two interconnected parts of

different diameter

12, 13, so that along an axial extension at least, which is greater than the remaining spacing between the coaxial cylinders, at least a l.lfold increase in spacing 14 between the cylinders is achieved. More precisely this increase in spacing is achieved in such a manner that the total voltage consisting of the voltage drop at the cathode plus the product of the arc voltage gradient and electrode spacing is greater than the rated voltage of the low voltage source less the DC voltage drop when the pump is operating at its rated current discharge in the feed circuit. The effect thereof is the automatic extinguishing of any cathode spot which might wander over the cylindrical portion 13 of. reduced diameter for the purpose of such increased spacing or within the corresponding zone 14 respectively of the pump, and the prevention of any wandering of the cathode spot into the gap 15 and labyrinth 17 protecting the electrode insulation, which would destroy the functioning of the getter-ion pump. Other cathode spots still remaining within the permitted

electrode area

4, 12 subdivide automatically at the same rate as cathode spots wander off said permitted area, so that by this means, given constant current strength, the total number of cathode spots remains constant and continuous pump operation is assured.

A flanged projection 20 is provided on the inner electrode cylinder 8 or 13 as the case may be facing the active electrode area for the purpose of producing the narrow gap 15 or the labyrinth l6 and thus reliably screening off the electrode insulation 17.

If it is desired to intensify the pumping action of a getter-ion arc pump, the cylindrical electrode 8, 9 can be cooled, for example, by circulating a liquid coolant in the interior of the electrode. In many cases, however, such circulation of liquid coolant is either undesirable or complicated. Consequently, a mode of cooling is proposed in FIGS. 1 and 2, according to which a portion at least of the interior of cylindrical electrodes 8, 9 forms a

sealedoff cavity

18, 19 containing a coolant in both liquid and vapor phase, a portion at least of said cavity having a surface structure producing a capillary action.

Known examples of surface structures having a capillary action for the internal walls of such an electrode cavity are fine grooves, a porousv layer or a fine mesh screen. This surface structure is not depicted in FIGS. 1 or 2. If now a quantity ofa liquid coolant which is sufficient to fill the capillaries is charged into the cavity and the boiling point thereof lies between 50 C. and 350 C, the electrode temperature can in the main be maintained below the boiling point of the liquid coolant even when large quantities of heat are evolved from the cathode spots, and once gases are occluded, absorbed or absorbed on the surfaces of the electrodes said gases remain trapped on the electrode surfaces 4 and 8 or in the interior thereof. Examples of suitable liquid coolants are water or organic liquids, for example, the suitability of which can be enhanced by adding a wetting agent to the liquid coolant. A lowering of the boiling point of the coolant may be achieved by partly evacuation of the

cavities

18, 19 in the electrode. The coolant evaporating in the active surface regions of the electrodes recondense in the zones of the cavity remote from these regions and the effect of the surface structure with capillary action is to cause the condensate returned to the portions of the electrode to be cooled independent of the position and manner in which the getter-ion pump has been fitted up.

The portions indicated as 21, 22 constitute cooling ribs, which dissipate the heat evolved during the condensation of the liquid coolant to the ambient atmosphere.

In the embodiment according to FIG. 1, a low voltage electrical insulator 24, is provided between the receiver 1 and the connecting flange 23 of the getter-ion pump similar to that between the

flanges

3 and 25. The connections between the

flanges

3 and 25 and between flange 23 and the receiver 1 is made in a vacuum-tight manner. Moreover, the insulator 7 for the lead-in 26 of the auxiliary electrode, which may, for example, consist of an alumina tube metallized on both sides, is bonded in a vacuum-tight manner-on the one side to the connecting flange 26 for the auxiliary electrode and on the other side to the cathode cylinder 8. In order to screen the auxiliary electrode insulator from atomized metal deposits, provision is made for a gap between the insulator surface and the auxiliary electrode, but this is not shown in FIGS. 1 and 2.

FIG. 2 shows an embodiment of pump, in which the anodically connected main electrode 9 consisting mainly of two

part cylinders

12, 13 of different diameters, is located coaxially within the cathodically connected substantially cylindrical main electrode 8, which forms a large part of the pump housing. The

circular plates

4, 5 closing the front ends of cylinders 8, 9 form the remaining portion of the main electrodes. The gas passage or passages leading to the receiver 1 is/or are mounted in the cathode cylinder electrode 8, at a place to which wandering of a cathode spot is precluded by the increase in spacing between cylinders 8, 9 according to the invention. The flanged projection 20, on the anodic cylinder electrode 9 forms an arrangement which does not impede the passage of gas from the receiver for achieving a narrow gap 15 or labyrinth l6 and consequently reliable screening of the electrode insulation 17 from any atomized metallic deposits. An auxiliary electrode 6 electrically insulated by insulators 7 is mounted with close spacing in the wall of the cathodic cylinder electrode 8, the short are first struck immediately on ignition of the pilot arc being drawn out as it finally passes over and burns between the main electrodes.

This embodiment according to FIG. 2 can also be provided with a movable ignition pin instead of the auxiliary electrode. This means for stroking the pilot arc can, with advantage, also be mounted on the disc-shaped part electrode 4.

In order to facilitate the striking of the arc, the point of the auxiliary electrode or the opposite main electrode may consist at least partly of a radioactive isotope, which emits aor B rays.

However, the arc may be struck in simple manner in the case of this embodiment without the aid of the auxiliary electrode 6 shown in FIG. 2 (or an ignition pin as the case may be) for example, by mounting the disc-shaped cathodic electrode 4 so as to be movable within the cylinder 8 so that at least when switching on the pump the electrodes are at least partly brought in contact with one another, and a starting device enables the electrodes to be brought into contact and then separated, and allows the spacing between them to be increased.

FIG. 3 shows the electrical circuit. A switching device for striking the arc includes an impulse transformer 34, a condenser 36 and a blocking rectifier 39. A further switching device as a means for sustaining the arc comprises a rectifier transformer 30, and a rectifier 31. An auxiliary electrode 6-, serves as a means for decoupling between the high tension source serving to strike the arc and the low voltage source serving to sustain the are, said auxiliary electrode being mounted in closely spaced relationship to the cathodic main electrode 4, 8 of the getter-ion pump. i

The mode of operation is as follows: Switches 29 and 38 are first closed, whereupon condenser 36 is charged from the mains via the rectifier 39. On depressing the switch button 35, condenser 36 discharges through the primary winding of the ignition coil 34, which furnishes a high tension pulse at the auxiliary electrode 6 and the cathodic main electrode 4, 8 of the getter-ion pump for the striking of an are or the production of a cathode spot at least. By this means, the space between the

main electrodes

4, 8 and 5, 9 is preionized, so that the circuit of the rectifier 31 is closed via the cathode spot already existing at the cathode due to the pilot arc and a heavier current for a powerful arc discharge including a plurality of cathode spots can be produced.

At the end of the pumping operation, switch 29 is opened again. Opening and closing of switch 29 and the operation of the push button 35 can also be carried out automatically by using a pressure monitoring device which comes into operation when the vacuum in the apparatus deteriorates and switches off when the desired vacuum is reestablished. This automatic device is not shown in FIG. 3.

Iclaim:

I. In a getter-ion pump for the production and maintaining of a high-vacuum in a receiver and having main electrodes between which an electric discharge occurs and in which means are provided which on switching on the pump strike an are between two electrodes at a different potential for the purpose of the production of at least one cathode spot in the region of which the surface of the cathode consisting of getter material is molten, wherein further means including a switching device for applying a low DC voltage to the main electrodes are provided for sustaining the are so produced so that the arc wanders in the space formed between the main electrodes and simultaneously the cathode spot wanders over the surface of the cathode, and wherein the space between the main electrodes is connected by way of at least one gas passage with the receiver, the improvement wherein said main electrodes are comprised substantially of at least approximately coaxial cylinders, the outer surface of one and the inner surface of the other cylinder constituting electrode surfaces, wherein one cylinder at least also forms a major part of the pump housing, and wherein at least one of said cylinders is constituted at least by two interconnected parts of different diameters such that along an axial extension at least which is greater than the residual spacing of said coaxial cylinders an at leastl.l--fold increase in spacing between said cylinders is achieved.

2. A getter-ion pump as defined in claim 1 wherein said gas passage is established by a passage through at least one of said electrodes.

3. A getter-ion pump as defined in claim 1 wherein at least one of said electrodes is constituted at least partly in the form of a screen.

4. A getter-ion pump as defined in claim 3 wherein the screen portion of said electrode is formed with oblique slots.

5. A getter-ion pump as defined in claim 1 and which further includes a baffle system located in front of at least one gas passage at the side of the receiver.

6. A getter-ion pump as defined in claim 5 and which further includes means for liquid-cooling of said baffie system.

7. A getter-ion pump as defined in claim 1 wherein said means for striking the arc comprises a starter having an optionally used coil which moves at least one of said electrodes at least on switching on towards said second electrode having a counter potential, during which a connection and separation and an increase in electrode spacing is achieved.

8. A getter-ion pump as defined in claim 1 and which further includes at least one auxiliary electrode closely spaced to the cathodic main electrode as a means for decoupling between the high voltage which serves to strike the arc and the low DC voltage which serves to maintain the are.

9. A getter-ion pump as defined in claim 8 wherein said auxiliary electrode or the main electrode facing said auxiliary electrode is constituted at least in part by a radioactive isotope.

10. A getter-ion pump as defined in claim 1 and which further includes a switching device for striking an are between one of said main electrodes and at least one auxiliary electrode, said device serving to strike a pilot arc with at least one cathode spot on the main electrode by way of an impulse transformer between the electrode connected as a cathode both in the main and also in the pilot discharge paths, said auxiliary electrode being located in the immediate vicinity of the cathode, said cathode being molten within the range of said cathode spot and said pilot are having a current strength such that the arc is caused by way of a further switching device to burn between said main electrodes and there be maintained.

11. A getter-ion pump as defined in claim 1 and which further includes means for cooling at least one of said main electrodes by a liquid coolant from a cooling device connected to said main electrode by way of supply and discharge pipes for the coolant.

12. A getter-ion pump as defined in claim 1 wherein a surface of at least one of said main electrodes forms a wall portion of a sealed off cavity which contains both a cooling fluid and also the vapor phase thereof, at least one portion of said surface being structured to establish a capillary action.

13. A getter-ion pump as defined in claim l2 wherein the surface of said main electrode defining said sealed-off cavity is provided with fine grooves to establish the capillary action.

14. A getter-ion pump as defined in claim 12 wherein the surface of said main electrode defining said sealed off cavity is constituted by a porous layer to establish the capillary action.

15. A getter-ion pump as defined in claim 12 wherein the surface of said main electrode defining said sealed-off cavity is constituted by a fine mesh screen to establish the capillary action.

16. A getter-ion pump as defined in claim 12 wherein said cooling fluid is a liquid having a boiling point between 50 C. and 300 C. at atmosphere pressure.

17. A getter-ion pump as defined in claim 16 wherein said cooling liquid is constituted by water.

18. A getter-ion pump as defined in claim 16 and-wherein said cooling liquid includes a wetting agent added thereto.

19. A getter-ion pump as defined in claim 16 wherein said sealed-off cavity defined by said main electrode also contains an extraneous gas which is noncondensable at ambient temperature and the partial pressure of which is less than atmospheric at ambient temperature.

20. A getter-ion pump as defined in claim 1 wherein a surface of at least one of said main electrodes forms a wall portion of a sealed-off cavity which contains both a cooling fluid and also the vapor phase thereof, at least one portion of said surface being structured to establish a capillary action, and wherein said main electrode which forms the wall portion of said sealed-off cavity is provided with cooling ribs.

21. A getter-ion pump as defined in claim 1 wherein at least one of said main electrodes is constituted at least partly by getter material.

22. A getter-ion pump as defined in claim 1 wherein at least one of said main electrodes is constituted by a thermally conductive base metal to which is applied a layer of getter material.

23. A getter-ion pump as defined in claim 22 wherein said getter material has a thickness of at least 0.5 mm.

Claims

1. In a getter-ion pump for the production and maintaining of a high-vacuum in a receiver and having main electrodes between which an electric discharge occurs and in which means are provided which on switching on the pump strike an arc between two electrodes at a different potential for the purpose of the production of at least one cathode spot in the region of which the surface of the cathode consisting of getter material is molten, wherein further means including a switching device for applying a low DC voltage to the main electrodes are provided for sustaining the arc so produced so that the arc wanders in the space formed between the main electrodes and simultaneously the cathode spot wanders over the surface of the cathode, and wherein the space between the main electrodes is connected by way of at least one gas passage with the receiver, the improvement wherein said main electrodes are comprised substantially of at least approximately coaxial cylinders, the outer surface of one and the inner surface of the other cylinder constituting electrode surfaces, wherein one cylinder at least also forms a major part of the pump housing, and wherein at least one of said cylinders is constituted at least by two interconnected parts of different diameters such that along an axial extension at least which is greater than the residual spacing of said coaxial cylinders an at least1.1-fold increase in spacing between said cylinders is achieved.

6. A getter-ion pump as defined in claim 5 and which further includes means for liquid-cooling of said baffle system.

8. A getter-ion pump as defined in claim 1 and which further includes at least one auxiliary electrode closely spaced to the cathodic main electrode as a means for decoUpling between the high voltage which serves to strike the arc and the low DC voltage which serves to maintain the arc.

10. A getter-ion pump as defined in claim 1 and which further includes a switching device for striking an arc between one of said main electrodes and at least one auxiliary electrode, said device serving to strike a pilot arc with at least one cathode spot on the main electrode by way of an impulse transformer between the electrode connected as a cathode both in the main and also in the pilot discharge paths, said auxiliary electrode being located in the immediate vicinity of the cathode, said cathode being molten within the range of said cathode spot and said pilot arc having a current strength such that the arc is caused by way of a further switching device to burn between said main electrodes and there be maintained.

13. A getter-ion pump as defined in claim 12 wherein the surface of said main electrode defining said sealed-off cavity is provided with fine grooves to establish the capillary action.

16. A getter-ion pump as defined in claim 12 wherein said cooling fluid is a liquid having a boiling point between 50* C. and 300* C. at atmosphere pressure.

18. A getter-ion pump as defined in claim 16 and wherein said cooling liquid includes a wetting agent added thereto.