US3327930A - Ionic getter pump electrode - Google Patents

Description

June 27, 1967 'r. A VANDERSLICE 3,327,930

IONIC GETTER PUMP ELECTRODE Filed Jan. 26, 1965 2 Sheets-Sheet l PRIOR ART INVENTOR: THOMAS A.VANDERSLICE,

AT TORNEY June 1957 T. A. VANDERSLICE ,3

IONIC GETTER PUMP ELECTRODE Filed Jan. 26, 1965 2 Sheets-Sheet 3 25 FIG.4. e

FIGT.

INVENTOR: THOMAS A. VANDERSLICE,

United States Patent 3,327,930 IONIC GETTER PUMP ELECTRODE Thomas A. Vanderslice, Scotia, N.Y., assignor to General Electric Company, a corporation of New York Filed Jan. 26, 1965, Ser. No. 432,438 18 Claims. (Cl. 23069) ABSTRACT OF THE DISCLOSURE A multicellular electrode structure for getter ion pumps wherein predetermined dimensional characteristics of the m-ulticellular configuration differ to provide increased pumping speed over a broad range of pressures.

This invention relates to an ionic pump electrode structure and more particularly to an improved electrode structure, for use in an ionic getter ion pump, having a predetermined configuration including electron transparency variations which are correlated to pumping speed and the strength and dispersion of the cooperating magnetic field passing therethrough.

Getter ion pumps are well known in the prior art and are adequately described, for example in US. Patents 2,775,014 Westendorp et a1. and 3,080,104 Vanderslice, each of which is assigned to the same assignee as the present invention. In one form an ionic getter pump may be described as an envelope or an enclosure having spaced apart coaxial cathode elements therein as an intermediate electron transparent anode, the anode and cathodes being subjected to a magnetic field having lines of force directed substantially perpendicular to and through the anode. In this type of pump a glow discharge is established between the anode and the cathode so that gas molecules in the enclosed volume are ionized with the resistant positive ions striking the cathode surfaces to be trapped or imbedcled therein. Also, where the cathode is ofa suitable metal, sputtering takes place and the sputtered metal is collected or condenses on the anode surfaces. This type of glow discharge is referred to as the Penning cold cathode discharge, described for example with respect to pressure measuring gages in US. Patent 2,197,079 F. M. Penning. Gas cleanup in the described pump occurs through gettering action of the fresh deposits of metal on the anode and other surface, and also by being entrapped or imbedded in these surfaces. A particular problem associated with these getter ion pumps relates to utilization of the anode surfaces not only :as discharge control elements but also as condensing or collecting surfaces for sputtered cathodic metal. These surfaces should be so formed and arranged that they will control the discharge for increased sputtering and, where applicable, receive sputtered metal in an optimum manner for increased gettering effect andentrapment action and also for wider ranges of pump speed in the liters/ sec. of gas which will be removed or pumped at a given pressure. At. the same time the anode surfaces should not adversely interfere with optimum electrical discharge therethrough. The usual empirical relationship previously established for the configuration and utilization of these anodes are not s-atisfactory'for pumps of increased speed, efliciency and capacity.

It is an object of this invention to provide an improved electrode configuration for a getter ion pump.

It is another object of this invention to provide an improved anode electrode configuration for a getter ion pump. 7 i

' It is still another object of this invention to provide a non-uniform anode configuration for a getter ion pump.

It is another object of this invention to provide a vari- 3,327,930 Patented June 27, 1967 ice able configuration anode electrode for a getter ion pump.

It is a still further object of this invention to provide an anode electrode configuration for a getter ion pump which is correlated to the lines of force of and their dispersion of the magnetic field passing therethrough.

It is a yet further object of this invention to provide an improved condensing or receiving surface for a getter ion pump,

Briefly described, this invention in one of its preferred forms includes a multicell-ular anode electrode structure for getter ion pumps wherein predetermined dimensional characteristics of the multicellular configuration differ to provide increased pumping speed over a wider range of pressures and where the difference is proportioned to the magnetic field passing through the multicellular structure for more elfective pumping over the increased range This invention will be better understood when taken in connection with the following description and the drawings in which FIG. 1 illustrates a prior art Penning discharge type getter ion pump utilizing a single cell anode structure.

FIG. 2 illustrates one preferred anode embodiment of this invention.

FIG. 3 illustrates a further anode ambodiment of this invention.

FIG. 4 illustrates a modification of FIG. 3.

FIG. 5 illustrates a further anode embodiment of this invention.

FIG. 6 illustrates another modification of this invention. FIG. 7 illustrates an application of this invention in a triode pump.

The particular mode of opera-tion of the getter ion pump is based upon the Penning discharge as above described. This discharge principle is incorporated in a Penning discharge type getter ion pump 10 as illustrated in FIG. 1 and as more fully described in the above mentioned Patent 2,755,014. The diode pump device of FIG. 1 includes an evacuated envelope 11 containing a pair of spaced apart disk-like cathodes 12 and an intermediate cylindrical -or ring anode 13. The anode 13 and cathodes 12 are arranged concentrically along a common axis. External to the envelope 11 there is positioned a permanent magnet14 with its pole pieces also positioned concentrically along the described axis so that the lines of force of the magnetic field are directed perpendicularly to and through the ring anode 13. When a high positive potential with respect to the cathodes 12 is applied to the anode 13, a gas in the envelope 11 between the anode and cathode is ionized, permitting a current flow therebetween. Electrons tending to flow to the anode 13 are urged into a spiral path trajectory by the presence of the described magnetic field and this greatly increases the electron pat-h which results in a higher probability of collision between free electrons and gas molecules in the pump. A collision of an electron with gas molecules provides a positive gas ion. This positive gas ion is accelerated toward one of the disk cathodes 12 and strikes the cathode with great velocity, sputtering cathode metal from the cathode, to be collected on the anode and other exposed pump surfaces. The freshly sputtered cathode metal formschemically stable compounds with active gas atoms such as oxygen and nitrogen for the pumping action. Additionally, gases are removed in the pump by being injected into the cathode material or by being covered with sputtered metal on the anode and other surfaces.

In order to increase the pumping speed or capacity of the-Penning discharge type pump as described, prior efforts have been directed to the use of a plurality of distinct Penning discharges arranged in different relationships. For example, a plurality of Penning pumps may be arranged in parallel tandem relationship so that each cathode disk becomes in effect a cathode disk for a pair of anodes, one cathode on each side thereof. This tandem relationship with its plural Penning discharge increases the pumping action because a greater anode surface area is presented as a condensing or collecting surface for the sputtered metal. One may also arrange a plurality of Penning discharge type pumps by inserting a plurality of the units as above described in lateral parallel spaced relationship so that there is in effect a plurality of anodes (cellular) between a pair of cathodes. In the latter instance particularly, increased capacity is minimized because neither the gettering action nor the magnetic field is uniform insofar as the cross-sectional configuration of the anode is concerned. An increase in surface area does not effectively increase pumping speed over a wider pres sure range. For example, it is known that the pumping speed of a pump of given geometry is constant for only a limited range of pressures. At higher and lower pressures the pump speed generally declines. An increase in surface area therefore does not solve the problem of pump speed decline at lower and higher pressures, and optimum areas of the anode for gettering purposes are, therefore, not employed to their greatest advantage.

It has been discovered that the overall pumping efficiency in liters per second of a multicellular anode structure in a Penning discharge type getter ion pump may be greatly increased when the configuration of the anode which is exposed to the cathode is correlated to the magnetic field passing through the anode. Referring now to FIG. 2 there is illustrated one embodiment of this invention as an anode member 15 which is constructed so that the pump has increased pumping speed over a wider range of pressures, and where electron transparency is cooperatively related to the magnetic field passing therethrough. As previously described, the magnetic field bridging a gap between the pole pieces of a magnet includes certain lines of force which may not be uniformly distributed transversely through the gap. In addition, different magnets will have different field uniformities or characteristics. It has been discovered that these magnetic differences have a marked effect on the pumping action of a getter ion pump utilizing multicellular anodes with cells of dimensional uniformity, and it can be seen by observation that the metallic deposits on these anodes are not uniformly distributed across the anode.

When the uniformity of anode cell dimensions is varied so that the ion transparency of the anode becomes increased or decreased in predetermined areas, an increased efficiency and higher capacity pumping is produced. One effect is that more surface area is presented at predetermined parts of the anode where more sputtering metal may be effectively collected. A mixture of cell sizes is employed where some cells of predetermined size are most effective at one pressure range while other cells of predetermined different sizes are most effective at a different pressure. Thus a pump is provided which includes a favorable pumping speed over a wider pressure range. At the same time the different cells are arranged in more advantageous positions in the anode structure so that their individual pumping effectiveness is increased, As one example an anode electrode incorporates predetermined groups of cells, each group having cells of the same size but different from cell sizes of other groups. Such elec trodes are effectively utilized in uniform or non-uniform magnetic fields and are two-fold in nature in that 1) the variation of cell size is chosen for example toincrease pumping characteristics, for example, a given large cell size provides optimum pumping at a given pressure and a given small cell size provides optimum pumping at a different given pressure, and (2) based on (1) the variation in cell size or distribution is again chosen and arranged for more effective pumping for non-uniform mag netic fields. There is accordingly a two-step predetermination involved. As a part of the two-step predetermination,

however, it will be apparent that the product of a cell opening diameter (in the case of a cylindrical cell) to the strength of the magnetic field passing therethrough will not be optimum as is usually desired. In contradistinction the product will be optimum or approaching optimum for the primary purpose of, in combination with adjacent different size cells, increasing the pumping speed over a wide range of pressures or maintaining a more constant pumping speed for a wider range of pressures.

In FIG. 2, anode 15 which may be of any desired overall cross-sectional configuration such as circular or polyhedral includes a plurality of individual cells 16 which are formed for example by bounding means in the form of slat members 17. The cooperative relationship of these slats defines individual cells 16 having a depth or dimen sion along their longitudinal axis preferably at least equal to an opening dimension. This opening may take the form of various geometric or irregular or combined perimeter designs such as for example arcuate, circular, square, polygonal, etcetera, or combinations thereof. It is an important feature of anode 15 that the electron transparency of the cells is not uniform or similar for each cell. The non-uniformity is illustrated in one manner by different cell sizes in the outer or peripheral row, although a plurality of similar cell sizes may exist in one peripheral row. In this particular embodiment, while there is an overall uniform gradation radially, i.e., cells 18, 19 and 20, other directional indications are non-uniform. It is this superimposition of one configuration over another which is important to this invention. Because of the many variations in a given magnetic field or a given pump an orderly peripheral distribution of different cell sizes is preferred as illustrated in FIG. 2 noting the perimeter row of cells. However, the distribution may be random if desirable. A variation in cell size is intended to include a difference in any dimension of the cell or walls thereof, its area or volume. The difference may be included in one or more cells with the variation among cells being regular, irregular, progressively uniform, interrupted, concentrated, localized, or random. The difference employed, however, must be effective for changing the pumping speed and capacity of the pump. In the slat type assem* bly as illustrated, minor mechanical changes of position will provide innumerable combinations of variations in cell sizes for optimum correlation with pumping speed range and applied magnetic field.

A further example of a variable cell anode is illustrated in FIG. 3, Referring now to FIG. 3, there is shown an anode 21 having a center area or group of cells 22 made up of a plurality of large cells 23 of one size and a surrounding area or group of smaller cells 24. In this embodiment the cell size may be referred tothe opening area of the individual cells. An important feature of the embodiment of FIG. 3 is the superimposition of two kinds of cells for two different purposes as described for FIG. 2. The overall configuration of anode 21 is that of a plurality of adjacent cells 23, each cell 22 having an adjacent similar cell on at least two sides. However, an outer perimeter row of cells 23 have been subdivided to provide smaller cells 24. Smaller cells 24 also have an adjacent similar cell on at least two sides. Anode 21 is thus a two-stage anode which partially compromises high capacity at a given pressure for increased pumping speed over a wider range, a more desirable mode of operation in many instnaces. The particular choice of an anode as illustrated in FIG, 2 or that as illustrated in FIG. 3 will depend on the pump configuration, magnet arrangement and configuration and magnetic field distribution. However, it is desirable that in a two-stage anode two substantial areas of similar cells are included, or as in FIG. 2, the superimposition results in substantial cell size differences in peripheral as well as radial directions.

In FIG. 4 there is illustrated an anode 25 having localized cell size variation opposite to that as illustrated in FIG. 3. In FIG. 4, anode 25 is made up of a group of similar cells 26 which are of optimum 'size for a given pump speed. Superimposed on anode 25 is a central sec tion 27 of smaller similar cells 28 which are of optimum size for a further pump speed. The particular cells of any of the anodes of this invention need not be for example polygonal as anode may contain both polygon and circular cells or various combinations of regular or irregular cells. For example, cylindrical may fit within or contain polygon cells. In connection with the FIG. 4 illustration as a reversal of the FIG. 3 illustration, the illustration of FIG. 2 may also be reversed.

FIG. 5 is an illustration of a further embodiment of this invention. In FIG. 5, electrode 29 includes a combination of concentric or non-concentric annular elements 30, 31, 32, 33 and cross slats 34. The annular elements have proportionate diameters which provide closer spacings between elements radially. The reverse configuration is also evident. The cross slats 34 are an additional superimposition on included concentric cylinder combinations and are utilized not only for support purposes but also to establish cell sizes for a given pumping speed. In FIG. 5 the electrode configuration may be provided by means of a spiral strip which is so wound to provide the desired variation.

In addition to varying the electron transparency of a multicellular electrode by changing one or more cell opening sizes, certain other modifications may be suitably employed to provide similar results. For example, the electrode structure 35 of FIG. 6 includes a forward face 36 and a rearward face 37. These faces are illustrated as inwardly outwardly tapered curved or disked. The effect of this curvature is to change the longitudinal or depth dimension of individual cells with a resultant change in the effectiveness of the cell. The curvature of the faces 36 and 37 of electrode 35 are merely exemplary of the many both smooth and interrupted configurations which may be utilized in conjunction with these faces to increase favorable pumping characteristics. Where desirable, the

magnet pole pieces utilized may have similarly shaped.

faces in apparent interfitting relationship with the anode.

One operative example of the practices of this invention is illustrated in connection with the triode ion pump of FIG. 7. Referring now to FIG. 7 triode pump 38 includes a central multicellular anode 39 and a pair of spaced multicellular cathodes 40 and 41. The practices of this invention may be applied to the cathodes 40 and 41 as well as to the anode 39. In one example one or more central cells of each electrode, i.e., anode and cathodes, is of a similar size and all are in axial alignment. Cell sizes then may be varied as illustrated in FIGS. 2 through 6. f

Accordingly, by practices of this invention a multicellular ion pump electrode structure may be specifically correlated pumping speed and to the magnetic field passing therethrough and also to concentration of sputtered metal at certain regions of the anode. The teachings of this invention as described may also be incorporated in an anode multicellular structure having means to vary the positional relationship of the anode or individual portions thereof with respect to the cathodes and to the magnetic field. For example, certain elements such as the slats may be adjusted or otherwise positionally changed so that their cross-sectional configuration directly exposed to the cathode is changed, or various parts of the anode may be mechanically adjusted to change their relative position. The mechanics involved relate to well known adjusting devices in the art such as blade and vane pitch adjusting devices and controls, irises, gates, et cetera. Such changes may be employed to adjust the speed or pumping range of the pump.

The objects of this invention are attained through the use of variation, broadly, of electrode transparency which is cooperatively correlated to pumping speed and to the applied magnetic field. In one preferred practice of this invention the. variation in cell size enables the pump to include optimum and more consistent pump speeds at diiferent pressures thus taking advantage of the different disclosure.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an ionic getter pump having an ion transparent anode electrode positioned adjacent a cathode electrode and submerged in a magnetic field passing in a direction from one of said electrodes to the other, said electrodes having a potential impressed thereon to provide a discharge therebetween so that cathode metal is sputtered for gettering action, the improvement comprising (a) one of said electrodes including a multiplicity of individual cells of at least two different sizes effective to alter the pumping characteristics of said pump,

(b) said cell sizes being predeterminedly optimumly correlated to pumping speed thereof and to the nonunifor mity of the magnetic field passing therethrough,

(c) a significant number of said cells of one size having optimum pumping characteristics in conjunction with a high intensity magnetic field being exposed'to a substantial lower intensity magnetic field,

(d) a significant number of said cells of the other size having optimum pumping characteristics in conjunction with a low intensity magnetic field being exposed to a substantial higher magnetic field,

(e) so that a favorable pumping speed of said pump is extended over a wider range of pressures.

2. The anode asrecited in claim 1 wherein said electrode is an anode electrode.

3. The invention as recited in claim 1 wherein said electrode is a cathode electrode.

4. The invention'as recited in claim 1 wherein said electrode includes an anode and a cathode electrode.

5. The invention as recited in claim 1 wherein said cell size is denoted by a cell opening dimension.

6. The invention as recited in claim 1 wherein said cell size is denoted by a cell depth dimension.

7. The invention as recited in claim '1 wherein said cells are arranged to include an interspersed order. 8. The invention as recited in claim 1 wherein said cells are arranged in distinct groupings.

9. In an ionic getter pump having an ion transparent anode electrode positioned adjacent a cathode electrode and submerged in a magnetic field passing in a direction from one of said electrodes to the other, said electrodes having a potential impressed thereon to provide a Penning discharge therebetween so that cathode metal is sputtered on said anode for gettering action, the improvement comprising (a) one of said electrodes including a multiplicity of individual cells of at least two different sizes effective to alter the pumping characteristics of said pump,

(b) said cell sizes being arranged in at least two distinct groups having the same cell size in each not found in the other,

(e) one of said groups encircling the other,

(d) said cell sizes being predeterminedly optimumly correlated to pumping speed thereof and to the nonuniformity of the magnetic field passing therethrough,

(e) so that a favorable pumping speed of said pump is extended over a wider range of pressures.

10. The invention as recited in claim 9 wherein said electrode is an anode electrode and (a) the first group of said cells being centrally arranged in a regular order of differing cell sizes,

(b) the second group of said cells encircling said first group and comprising at least a row of cells of differing sizes.

11. In an ionic getter pump having an ion transparent anode electrode positioned adjacent a cathode electrode and submerged in a magnetic field passing in a direction from one of said electrodes to the other, said electrodes having a potential impressed thereon to provide a Penning discharge therebetween so that cathode metal is sputtered on said anode for gettering action, the improvement comprising (a) one of said electrodes including a multiplicity of individual cells of at least two different sizes effective to alter the pumping characteristics of said pump,

(b) said cell sizes being predeterminedly optimumly correlated to pumping speed thereof and to the nonuniformity of the magnetic field passing therethrough,

(c) the cells of said electrodes being arranged so provide a central group of cells of similar size,

(d) an adjacent group of cells of similar cell size and (e) the cell size of one of said groups differing from the cell size of the other said group so that said electrode is operative to increase the pumping speed of said pump over a wider range.

12. The invention as recited in claim 11 wherein said electrode is an anode electrode and said adjacent group of cells comprises at least two rows of cells encircling said central group.

13. In an ionic getter pump having an ion transparent anode electrode positioned adjacent a cathode electrode and submerged in a magnetic field passing in a direction from one of said electrodes to the other, said electrodes having a potential impressed thereon to provide a Penning discharge therebetween so that cathode metal is sputtered on said anode for gettering action, the improvement comprising (a) one of said electrodes including a multiplicity of individual cells of at least two different sizes effective to alter the pumping characteristics of said pump,

(b) said cell sizes being predetermined optimumly correlated to pumping speed thereof and to the non-uniformity of the magnetic field passing therethrough,

(c) the openings of said cells having different geometrical configurations comprising the combination of arcuate and rectilinear sides,

(d) so that a favorable pumping speed of said pump is extended over a wider range of pressures.

14. The invention as recited in claim 13 wherein said electrode comprises a series of concentric cylinders and cross members.

15. In an ionic getter pump having anion transparent anode electrode positioned adjacent a cathode electrode and submerged in a magnetic field passing in a direction from one of said electrodes to the other, said electrodes having a potential impressed thereon to provide a Penning discharge therebetween so that cathode metal is sputtered on said anode for gettering action, the improvement comprising (a) one of said electrodes including a multiplicity of individual cells of at least two different sizes effective to alter the pumping characteristics of said pump,

(b) said cell sizes being predeterminedly optimumly correlated to pumping speed thereof and to the nonuniformity of the magnetic field passing therethrough,

(c) the said cell sizes having differences limited to an axial dimension thereof,

((1) so that a favorable pumping speed of said pump is extended over a Wider range of pressures.

16. The invention as recited in claim 15 wherein the said cells have uniform progressively differing depth dimensions.

17. The invention as recited in claim 15 where the said differences progress radially. p

18. In a triode ion getter pump having an ion transparent electrode positioned between spaced ion transparent cathodes Where said electrodes are submerged in a magnetic field passing in a direction generally perpendicularly through said electrodes and said electrodes having a potential impressed thereon to provide a Penning type discharge therebetween so that cathode metal is sputtered on said anode for gettering action, the improvement comprising (a) said anode and said cathodes each including a multiplicity of individual cells of at least two different sizes effective to alter the pumping characteristics of said pump,

(b) said cell sizes being predeterminedly optimumly correlated to pumping speed thereof and to the nonuniformity of the magnetic field passing therethrough,

(c) so that a favorable pumping speed of said pump is extended over a Wider range of pressures.

References Cited UNITED STATES PATENTS 3,141,986 7/1964 Lloyd 23069 ROBERT M. WALKER, Primary Examiner.

LAURENCE V. EFNER, Examiner.

Claims (1)

1. IN AN IONIC GETTER PUMP HAVING AN ION TRANSPARENT ANODE ELECTRODE POSITIONED ADJACENT A CATHODE ELECTRODE AND SUBMERGED IN A MAGNETIC FIELD PASSING IN A DIRECTION FROM ONE OF SAID ELECTRODES TO THE OTHER, SAID ELECTRODES HAVING A POTENTIAL IMPRESSED THEREON TO PROVIDE A DISCHARGE THEREBETWEEN SO THAT CATHODE METAL IS SPUTTERED FOR GETTERING ACTION, THE IMPROVEMENT COMPRISING (A) ONE OF SAID ELECTRODES INCLUDING A MULTIPLICITY OF INDIVIDUAL CELLS OF AT LEAST TWO DIFFERENT SIZES EFFECTIVE TO ALTER THE PUMPING CHARACTERISTICS OF SAID PUMP, (B) SAID CELL SIZES BEING PREDETERMINEDLY OPTIMUMLY CORRELATED TO PUMPING SPEED THEREOF AND TO THE NONUNIFORMITY OF THE MAGNETIC FIELD PASSING THERETHROUGH, (C) A SIGNIFICANT NUMBER OF SAID CELLS OF ONE SIZE HAVING OPTIMUM PUMPING CHARACTERISTICS IN CONJUNCTION WITH A HIGH INTENSITY MAGNETIC FIELD BEING EXPOSED TO AS SUBSTANTIAL LOWER INTENSITY MAGNETIC FIELD, (D) A SIGNIFICANT NUMBER OF SAID CELLS OF THE OTHER SIZE HAVING OPTIMUM PUMPING CHARACTERISTICS IN CONJUNCTION WITH A LOW INTENSITY MAGNETIC FIELD BEING EXPOSED TO A SUBSTANTIAL HIGHER MAGNETIC FIELD, (E) SO THAT A FAVORABLE PUMPING SPEED OF SAID PUMP IS EXTENDED OVER A WIDER RANGE OF PRESSURES.

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