US3112863A

US3112863A - Ion pump

Info

Publication number: US3112863A
Application number: US60818A
Authority: US
Inventors: Wilson M Brubaker; Clifford E Berry
Original assignee: Consolidated Vacuum Corp
Current assignee: Consolidated Vacuum Corp
Priority date: 1960-10-06
Filing date: 1960-10-06
Publication date: 1963-12-03
Anticipated expiration: 1980-12-03

Description

DeC- 3, 1963 w. M. BRUBAKER ETAL 3,112,863

10N PUMP Filed oct. s. 1960 ,fla

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A- A 4A 2 '111111111111'111111111111111111111 k 42 a 42 i United States Patent O Consolidated Vacuum Corporation, a corporation of New York Filed Get. 6, 196i?, Ser. No. 60513 8 Claims. (Cl. 239-69) The present invention relates to ion pumps of the coldcathode discharge type, and more specifically to an irnproved coldcathode discharge ion pump.

This application is a continuation-in-part of US. latent application Serial No. 815,352 tiled May 25, 19159. in that application, various embodiments of an improved cold-cathode discharge ion pump are described. The present application describes additional embodiments of such an improved cold-cathode discharge ion pump.

A cold-cathode discharge device for measuring the pressure in an evacuated space is described in US. Patent No. 2,197,079, issued April 16, 194i), to Frans Michel Penning. The Penning device consists essentially of a ring anode contained between two dat-surfaced cathodes disposed within an evacuated envelope. The anode and cathodes are immersed in a strong magnetic field. A high positive potential with respect to the cathode is applied to the anode. The gas between the anode and cathodes is ionized, allowing a current flow therebetween. The magnitude of the ionization current is related to the pressure existing between the anode and cathodes. Such a vacuum measuring device has the disadvantage of disturbing the vacuum to be measured, as ions are driven from the evacuated space into the surface of the cathode of the device, ywhere they are collected. The vacuum to be measured is thereby increased over the vacuum which would otherwise exist.

A practical vacuum pump can be made by combining a number of such Penning cold-cathode discharge devices into a single unit. A pump comprised simply of a plurality of Penning coldcathode discharge devices often suti'ers from a poor noble gas evacuation characteristic, in that the evacuation pressure obtained by use of such a pump `oscillates instead of remaining constant. This poor noble gas evacuation characteristic results from the inability of the pump surfaces to getter the ions of gases driven thereinto. By getter is meant to establish physical or chemical bonds between atoms and molecules of the pump surfaces and the ions removed from the gas.

`lons driven into the collector which are not gettered are `often freed from entrapment by a process known as spilt-tering. By sputtering is meant the ejection of particles of a surface in lvarious directions from the surface. Sputtering is caused by the bombardment of the surface being sputtered by ions traveling at a high velocity.

s the pump surfaces are sputtered, the molecular layers of surface material entrapping the particles not gettered are worn away. These particles thereupon escape back into the evacuated area.

According to the present invention, an improved ion pump oi the cold-cathode discharge type is comprised by a cellular anode and an ion collector, between which a plurality of replacement material elements are disposed. In one embodiment of the invention, the replacement material elements are connected to the ion collector, so as to present a rough or irregular collector surface by having raised portions which extend toward the anode from the base portion of the collector. ln a second embodiment of the invention, the replacement material elements are similarly disposed and are connected to a source of negaltive potential, so las to provide fthe advantages described fin the aforementioned application Serial No. 815,352. ln a third embodiment of the invention, the connection 3,112,853 Patented Dec. 3, :3

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of the replacement material elements may be switched between the previously described connection to the ion collector and to the source oi negative electrical potential. rIhus, operation with an irregular collector surface or operation with a separate replacement material element, as appropriate for the sputtering required for operation, may' be selected. By utilizing replacement material elements disposed between the anode and collector which have a configuration such las to present a comparatively large obstructing surface in the ion path between the anode and collector, a high sputtering rate is insured together with a large reservoir of material for sputtering onto the main ion collector surface is available to continuously provide a fresh ion collector surface.

The invention may be more readily understood by referring to the accompanying drawing in which:

FIGURE l is a cross-section of an improved ion pump according to the invention;

FIGURE 2 is a cross-section of an alternate embodiment of the invention; and

FlGURE 3 is a cross-section of a different configuration of the alternate embodiment of the invention.

Referring now to FlG. l, an envelope 3, having an inlet 9, contains an improved ion pump 1u of the invention. The ion pump 1li includes a plurality of anode cells 11 which form a cellular anode 12. A pair or" ion collectors 13% are disposed on either side of the anode cells 11. A plurality of replacement material elements 14 are di,- posed between the anode cells 11 and the collectors '13, so as to obstruct the passage of ions from the anode to the collector. rthe collectors 13 have apertures 15' therein, through which extend leads 1d, one end of which is connected to the replacement material elements 142'. At the opposite end, leads 16 are connected to a common connection 17. The common connection 17 is connected to a contact arm 1li of a switch 19 by a lead 2u. extending through an insulator 21. The switch has a pair of contacts 22A, 221B. The contact 22A is grounded. rl`he contact 22B is connected by a lead 23 to the negative terminal connected to a source of a negative electrical potential illustrated as a battery 24, the positive terminal of which is connected to a ground by a lead 2d. The collectors 13 are connected to ground by a lead 26 which extends through an insulator 2.7. The anode cells 11. are connected to a source of positive electrical potential 28 by means of a lead 29 extending through an insulator 30. The source of positive electrical potential 2S` has its negative terminal connected to ground by a lead 31.

The ion pump 1d is disposed between the poles of a magnet A during pump operation. The magnet provides the magnetic iield required for pump operation. The operation of the pump is initiated by an application of the magnetic field coincident with an application to the anode of the positive potential. Anode potentials in the range of three thousand volts have been found to be pan ticularly appropriate. The switch 19 is set either to connect the replacement elements to the collector 13 through the lead Ztl, switch 19, and ground, or to the source of negative electrical potential 24 by the switch 19 and lead 23. ated, or noble gases are not to be pumped, the replace` ment material elements 14 are connected to the collectors 13 through ground. The passage of ions from the anode 12 to the collectors 13 is now obstructed by the replacement material elements 14S. Ions then strike the replacement material elements 14, sputtering material therefrom for deposition upon the collectors 13 to provide the fresh collector surface previously referred to. It will be noted, however, that when the replacement material elements 1d are connected to ground and, through ground, to the collectors 13, the replacement material elements 14 function as collectors also, so that the collector now consists lf a moderate oscillatory characteristic can be toleraliases of a collector base 13 and projections 14 extending therefrom toward the anode 12. If such a oscillatory characteristic cannot be tolerated, or hicher pumping rates are required, the switch 19 is Switched so that the negative electrical potential from the battery 24 is applied to the replacement material elements 14. This negative potential increases the rate of sputtering, so that the rate of deposition of material on the collectors 13 are greatly increased. By increasing the rate of deposition of material, a fresh collector surface of layer is always available, so as to provide for the elimination of the oscillatory characteristic and more etiicient gettering. A negative potential of two thousand volts has been found to be appropriate for application to the replacement material elements 14. Other negative potentials can, of course, be used.

FIGURE 2 is a sectional view of an alternate embodiment of the invention. An ion pump 4t? has anode cells 11 which are the same as previously referred to with respect to FIG. 1. Collectors i1 are disposed on either side of the anode cells 11. Replacement material elements i2 are disposed on the collectors d1. The anode cells 11 are connected by a lead 43 to a positive terminal of a battery 44. The collectors il are connected together by a lead 45 and are connected to ground by a lead 46.

It will be readily apparent that the embodiment of FIG. 2 is simply a modification of the embodiment of FIG. l when operating with the replacement material elements 14 connected to the collectors 13 through ground. Thus, each of the collectors 13 has an irregular surface extending toward the anode 12, the irregularities being formed by the replacement material elements 14. Of course, both the collectors 13 and replacement material elements 14 can be made of the same material, or different materials can be used. Furthermore, the irregularities can take a variety of shapes, and need not be of the conical conguration shown. In the embodiment of FIG. 2, the alternate modes of the pump operation have been eliminated, so that the pump is only suitable for pumping when some oscillatory characteristic, if present, can be tolerated, or noble gases are not to be pumped.

The pump is put into operation by disposing the pump 4G between poles of a magnet (not shown), so that the pump is immersed in an appropriate magnetic field. The positive potential applied to the anode initiates the pumping action, and ions are driven into the collectors 41. Thus, ions striking the replacement material elements, now forming collector projections, sputter material therefrom, which is deposited on the collectors 41, now forming the collector base, from which the projections extend, so as to provide a fresh collector surface.

Referring now to FiG. 3, a modification of the pump Of FIG. 2 is shown. A pump Sti has a collector 51 with a plurality of replacement material elements 52 projecting therefrom toward an anode 12. The replacement material elements 52 of FIG. 3 are more closely spaced than are replacement material elements 32 of FIG. 2. Thus, the elfective collector surface, which consists of the collector 51 and replacement material elements 52, is more irregular or rough than is the collector surface of the embodiment of FIG. 2. Obviously, a further extension of the modification of FIG. 3 would be to place the replacement material elements 52 still closer together so that, using the conical replacement element configuration, the ultimate configuration would be a saw-tooth surface for the collector. By providing the irregular or rough collector surface, additional sputtering surface is made available for ion contact. Thus, the effective collector surface is increased and the rate of sputtering is likewise increased, so that both the pump capacity is increased and the pressure oscillation characteristic is improved.

The use of conically-shaped replacement material clements provides a sloping surface for ion Contact so as t0 i maximize the rate of sputtering of material from the replacement material elements. This maximization is a result of ions striking the surface of the elements with a glancing blow, rather than striking perpendicular to the ion surface.

It is, of course, to be understood that the practice of the invention is not limited to the use of conical-shaped replacement material elements. Any one of a variety of shapes may be selected for use with the replacement material elements, the important feature in the embodiments of FIG. 2 and FIG. 3 being that a rough or irregular collector surface exists in the direction of the anode. For example, the replacement material elements configuration could be rectangular, either in vertical or horizontal cross-section. Any other geometrical shape which might be selected which provides for the replacement material elements to project towards the anode, thus insuring the presence of an irregular or rough collector surface.

The invention claimed is:

l. An ion pump of the cold-cathode discharge type comprising an anode, a collector having an irregular surface extending toward the anode, means for initiating a voltage gradient in the space between the anode and the collector and extending in a direction from the anode toward the collector so as to cause ions to strike the irregularities in the collector surface, means for enclosing said anode and said collector so as to provide a sealed enclosure during pumping operations, and means for producing magnetic lines of force through the enclosure wherein the lines extend in a direction from said anode toward said collector.

2. The combination of claim 1 in which the irregularities consist of raised portions of replacement material extending from the collector toward the anode.

3. The combination of claim l in which the anode is formed with a plurality of Cells and said irregularities are symmetrically aligned with said anode cells.

4. The combination of claim 1 in which the raised portions are substantially triangular in vertical cross-section.

5. The combination of claim 1 in which the raised portions are substantially rectangular in vertical cross-section.

6. In an ion pump of the cold-cathode discharge type, the combination of an anode, a collector, a plurality of replacement material elements disposed on the collector adjacent the anode so as to provide an irregular surface extending toward the anode, means connecting the replacement material elements to the collector means for enclosing said anode and said collector so as to provide a sealed enclosure during pumping operation, means for initiating a voltage gradient in the space between the anode and the collector and extending in a direction from the anode toward the collector and means for producing magnetic lines of force through said enclosure wherein the lines extend in a direction from said anode toward said collector.

7. In an ion pump of the cold-cathode discharge type, the combination of an anode, a collector, a plurality of replacement material elements disposed between the collector and the anode and having a configuration so as to obstruct a substantial portion of the ion passage between the anode and collector, means connecting the replacement material elements to the collector means for enclosing said anode and said collector so as to provide a sealed enclosure during pumping operation, means for initiating a voltage gradient in the space between the anode and the collector and extending in a direction from the anode toward the collector, and means for producing magnetic lines of force through said enclosure wherein the lines extend in a direction from said anode toward said collector.

8. In an ion pump of the cold-cathode discharge type, the combination of an anode, a collector, a plurality of replacement material elements disposed between the anode and collector and having a configuration so as to obstruct a substantial portion of the ion passage between the anode and the collector, a source of negative electrical potential, switching means connected between the replacement material elements, source of negative electrical potential and collector, said switching means being switchable between a rst state and a second state, means connecting the negative electrical potential, collector and replacement material elements to the switching means so that the replacement material elements are connected to the collector when the switching means is in its first state and the replacement material elements are connected to the negative electrical potential when the switching means is in its second state, means for enclosing said anode and said collector so as to provide a sealed enclosure during 6 pumping operation, means for initiating a voltage gradient in the space between the anode and the collector and extending in a direction from the anode toward the collector, and means for producing magnetic lines of force through said enclosure wherein the lines extend in a direc- 5 tion from said anode toward said collector.

References (Iited in the file of this patent UNITED STATES PATENTS 10 2,636,664 Hertzler Apr. 28, 1953 FOREIGN PATENTS 797,232 Great Britain June 25, 1958

Claims

1. AN ION PUMP OF THE COLD-CATHODE DISCHARGE TYPE COMPRISING AN ANODE, A COLLECTOR HAVING AN IRREGULAR SURFACE EXTENDING TOWARD THE ANODE, MEANS FOR INITIATING A VOLTAGE GRADIENT IN THE SPACE BETWEEN THE ANODE AND THE COLLECTOR AND EXTENDING IN A DIRECTION FROM THE ANODE TOWARD THE COLLECTOR SO AS TO CAUSE IONS TO STRIKE THE IRREGULARITIES IN THE COLLECTOR SURFACE, MEANS FOR ENCLOSING SAID ANODE AND SAID COLLECTOR SO AS TO PROVIDE A SEALED ENCLOSURE DURING PUMPING OPERATIONS, AND MEANS FOR PRODUCING MAGNETIC LINES OF FORCE THROUGH THE ENCLOSURE WHEREIN THE LINES EXTEND IN A DIRECTION FROM SAID ANODE TOWARD SAID COLLECTOR.