US3197122A

US3197122A - Ion pump

Info

Publication number: US3197122A
Application number: US291649A
Authority: US
Inventors: Allen R Hamilton; Harmon G Redmond
Original assignee: Consolidated Vacuum Corp
Current assignee: Consolidated Vacuum Corp
Priority date: 1963-07-01
Filing date: 1963-07-01
Publication date: 1965-07-27
Anticipated expiration: 1982-07-27

Description

July 27, 1965 A, R HAMlLTON ETAL 3,197,122

ION PUMP Filed July 1, 1963 2 Sheets-Sheet 1 pmi AW /M l.

July 27, 1965 A, R. HAMILTON ETAL 3,197,122

ION PUMP Filed July l, 1963 2 Sheets-Sheet 2 United States Patent C) 3,197,122 IGN PUB/ll Allen R. Hamilton, Rochester, NX., and Harmon G.

Redmond, Castro Valley, Calif., assignors to Consolidated Vacuum Corporation, Rochester, NY., a corporation of New York Filed .luly 1, 1963, Ser. No. 291,649 13 Claims. (Si. 23d-69) The present invention relates to -ion pumps, and more particularly to an improved anode structure for ionic vacuum pumps.

Ionic vacuum pumps have been known for a number of years. More recently, an ion pump has been developed which consists essentially of a pair of spaced collector plates of a suitable getter material, such as titanium, a cellular anode structure located between the collector plates, a housing for the collector plates and the anode structure and means for establishing a magnetic iield through the collector plates and the anode structure. In this well known type of prior art pump, the anode structure is composed of a plurality of open-ended cells which are deiined by solid cell walls that extend at right angles to the ion collector plates. During operation of the pump, the above-mentioned housing is connected to a space to be evacuated. Space and housing are then pre-evacuated and the anode structure is biased positively with respect to the collector plates so that an electric discharge takes place inside the housing. This discharge causes gas molecules and atoms in the housing to be ionized and driven to the collector plates. ln this manner, getter material is sputtered from each collector plate.

This type of prior art pump is capable'of pumping gases which are able to form chemical bonds with the getter material. Difficulties are, however, encountered if chemically inert gas atoms are to be removed from the vacuum space. lnert gases can, of course, not be retained by chemical bonds, but have to be physically entrapped or embedded by sputtered material. To a certain extent, inert gas atoms are entrapped by the sputtered material in this type of prior art pump. However, it has been found that a large portion of these inert gas atoms is re-liberated as the sputtering of getter material proceeds, so that the degree of evacuation is limited if an inert gas or, for that matter, ordinary air which always contains certain amounts of inert gases, is pumped. The reason for this limitation resides primarily in the presence of the solid cell walls of the anode structure between the collector plates. These cell walls intercept a large portion of the sputtered getter material and gas atoms before they can reach the adjacent collector plate. Significant portions of each collector plate are therefore prevented from being reached by sputtered getter material and gas atoms.

The book Scientiic Foundations of Vacuum Technique, SecondV Edition, 1962, by Saul Duschman, published by lohn Wiley & Sons, Inc., shows on page 681 thereof a radiograph which illustrates the latter fact. This radiograph was obtained by pumping radioactive lrrypton S5 with a pump of the above-mentioned type and placing a collector electrode of this pump on a photographic ulm. The radiograph shows the regions on which krypton was deposited and also the significant spaces between these regions on which no deposition of krypton took place.

The present invention overcomes these disadvantages by providing a cellular anode structure that, while retaining significant features of the cellular anode structure of the above-mentioned prior art pump, enables a substantially uniform distribution of sputtered getter material and gas atoms on the collector plates. From one aspect thereof, the invention resides in an anode structure for an ion pump, which anode structure is composed of a plurality of open-ended cellular or prismatic elements that are defined by perforated cell walls.

From another aspect thereof, the invention resides in an anode structure for an ionic vacuum pump; which anode structure is composed of a plurality of prismatic sections delined by an array of spaced wires, as will be more fully apparent from the following description.

An ionic vacuum pump according to a preferred embodiment of the subject invention comprises an envelope for confining an evacuated space containing residual gas molecules, means for said envelope in a predetermined direction, a cellular anode structure within said envelope composed of open-ended cellular elements extending with their longitudinal axes in the general direction of said magnetic field and having perforated lateral cell walls, a cathode structure within said envelope for releasing electrons to said anode structure to cause, with the assistance of said magnetic field, ionization of residual gas molecules present in said envelope, and means for removing the ionized gas molecules from the space adjacent said anode and cathode structures.

Preferably, the perforations in the perforated lateral cell wall parts are larger in area than the cell wall parts between such perforations, so that the majority of gas molecules and sputtered material particles may travel through the anode structure without being intercepted by parts thereof.

An ionic vacuum pump according to a further preferred embodiment of the subject invention comprises a magnet structure having a pair of substantially parallel, spaced pole faces, a pair of spaced electrodes extending between said pole faces substantially parallel thereto, at least three mutually spaced wire arrays extending between said spaced electrodes substantially parallel thereto, each wire array being composed of a first plurality of mutually spaced wires extending in a lirst direction and a second plurality of mutually spaced wires extending perpendicularly to said first plurality of wires, and said wire arrays being mutually aligned with respect to the wires thereof, means for connecting said electrodes to the negative terminal of a source of electrical direct-current, and means for jointly connecting said wire arrays to the positive terminal of said source.

The invention, together with further objects and embodiments thereof, will become more readily apparent from the following detailed description and the accompanying drawings, in which:

FIG. l is aV sectional elevation of a prior art ionic vacuum pump device;

FIG. 2 is a sectional plane view taken along line ll-ll of FIG. l of the device shown therein;

FlG. 3 is a sectional elevation of an ionic vacuum pump .device according to a preferred embodiment of the sub` Ject invention; Y f

FIG. 4 is a sectional plane view taken along ine IV-lV of FIG. 3 of the device shown therein; and y FIG. 5 is a perspective view on a larger scale of'a detail of the device shown in FIGS. 3 and 4, taken within line V indicated in FIG. 4.

Considering first FlGS. l and 2, marked Prior Art, it will be apparent that an ionic vacuum pump device of the type described in the above-mentioned Review article is shown therein. This prior art device comprises a sealed envelope l having an inlet or nipple portion 2 for connection of the envelope 1 to a space tobe evacuated. A magnet structure 4 having spaced pole pieces 5 and 6 is used to establish through envelope l a magnetic field extending in the general direction of arrow 8l symbolically indicating such magnetic field. A pair of electrodes 1t) and l1 having confronting surfaces 12 and 13 is disposed in envelope 1 and extends substantially perpendicularly to Y E, the general direction of the magnetic iield indicated by arrow 8. An anode structure is disposed between surfaces 12 and 13 of electrodes 10 and 11 and is spaced therefrom.

Anode structure 15 is composed of a plurality of cellular elements 16; twenty-live such elements 16 being shown in FIG. 2. Each cellular element 16 has a pair of oppositely disposed, open ends 17 and 18 and is dened by solid lateral cell walls 19 extending in the direction of the magnetic eld indicated by arrow S. An anode terminal 22, sealably extending through a nipple 23* in envelope 1, serves to connect anode structure 15 to the positive terminal of a high-voltage source (not shown), and, in the device shown, serves also as a means for mounting anode structure 15 in envelope 1. Terminals 24 and 25, sealably extending through envelope 1, serve to connect electrodes 1) and 11, respectively, to the negative side of the latter high-voltage source (not shown). A disk 26 disposed on anode terminal 22 prevents the formation of a leakage path between anode terminal 22 and electrodes 1t) and 11. Y

The potential and current supply capabilities of the high-voltage source just mentioned are such that electrical discharge is established in the space between anode structure 15 and electrodes 1@ and 11. Since electrodes 1t? and 11 are negatively biased, they will, with respect to anode structure 15, assume the role of cathodes and will therefore, release electrons to the anode structure 15. The magnetic field indicated by arrow 8 will cause the released electrons to travel along substantially helical paths, so that the probabilitythat they will Strike and ionize gas molecules present in the discharge area is largely increased. Ionized gas molecules are driven toward electrodes 1t) and 11. These electrodes 10 and11 are of a material, such as titanium, capable of releasing sputtered material particles upon ion impact.

Let us now consider the ion pumping function of the device shown in FIGS. l and 2 by means of an isolated impact:

lf an'ionized gas molecule (not shown) hits at point 27 the surface 13 of electrode 11, sputtered particles are released from surface 13 and follow trajectories indicated by an array of dotted lines 29'. The majority of these particle trajectories lead to the solid lateral cell Walls 12 of anode structure 15. Y

While the trajectories of sputtered particles released by `a single ion haverbeen indicated in FIGS. '1 and 2, it is,

. of course, clear that electrodes 10 and 11 are simultafour mutually spaced crossvirc arrangements composed of Wires 39 are mounted in a vtrarne member 48 connected to `anode terminal 22. The meshes 50 of the four cross-wire arrangements are mutually aligned.

lt should, of course, be understood that the prismatic anode sections or cellular elements 37 need not necessarily be defined by wires. Thus, lateral cell or prismatic section walls having perforations similar to the mutual spacings between the shown wire larrangements may be employed.

An electrical discharge is set up between anode structure 3:5 and electrodes 10 and 11 in the manner indicated above in connection with FIGS. l and 2. l

Let us now consider the ion pumping action of the def vice according to the invention shown in FIGS. 3 to 5, by means of an isolated ion impact:

It an ionized gas molecule (not shown) hits, for instance, the surface 13 of electrode 11 at point 52, the

vast majority'ot' sputtered particles released by electrodeV 11 follows trajectories 54 which lead directly to the surface 12. of the opposite electrode 19, since the Vanode structure 35, owing to its above-mentioned design, will not intercept an appreciable number of sputtered particles. Gas molecules will, of course, also no longer be intercepted by the .positively charged anode structure 35, but will reach the electrodes 1@ and 11.

Thus, ionized gas molecules not only will be securely held by collector electrodes 10 `and 11 but Will be vigorously entrapped on the exposed surfaces 12 and 13 by an unimpededly ilowing stream of sputtered particles bombarding such surfaces 12 and 13.

It will, therefore, be appreciated, that the subjectV anode structure design and arrangement which defines cellular elements having their lateral portions extending in the direction of the above-mentioned magnetic eld serves a very significant purpose and results in an ultraL high vacuum pump which achieves significantly improved results over prior art devices.

' It will, of course, be appreciated that various modications and alternative variations may be made in the device sho-vn in FIGS. 3 to 5 without departing from the scope of `the invention.

Thusgvhile an envelope 1 for connection to an evacuated space has been shown, it will of course be understood that the pump device according to the invention may also be manufactured Without a sealed envelope, if it is intended to insert the device directly into the `space Within a vacuum vessel. Y

The magnetic ield indicated in FIGS. 3 and 4 by arrow Smay be established by a permanent magnet or an electrornagnetic structure.

YThe present invention will also be applicablerto those pumping systems which employ a source of vaporizable magnet structure 4 having pole pieces 5 and 6 for establishing `a magnetic field in a direction indicated by arrow 3, a pair of electrodes 1t) and 11, having confronting surfaces 12 and 13 andterminals'Zl and 25, and anode terminal and mountingmeans 22, all of the general type shown in FIGS. 1 and 2.

The device of FIGS. 3 and 4 comprises, however, an anode structure 35 composed of a plurality of prisrnatic sections 37. One such prismatic sectionr37 is perspectivematerial, such a titanium, and means for vaporizing such material onto ion collector surfaces. In such case, the anode structure according to the invention Will permit substantially unimpeded llow of the vaporized material Vto the ion collector surfaces.

tion will result Yin-lsubstantially unimpeded gas moleculeV and embedding material iiow, so that gas, molecules are securely removed from the space to be evacuated. As a rule, the latter space is pre-evacuated by a conventional pre-pumping device, so that the operation of lon pump' according to the invention is primarily directed to the removal of residual gasmolecules.

Between pumping operations, the ion collector electrodes of the .devices of the subject invention may be subjected to high temperatures or baked out.

Additional modilications and variations within the scope o the subject invention will become apparent to those skilled in the art.

We claim:

l. An ionic vacuum pump comprising an envelope for conining an evacuated space containing residual gas molecules, means for establishing a magnetic field extending through the space within said envelope in a predetermined direction, a cellular anode structure within said envelope composed of open-ended cellular elements extending with their longitudinal axes in the general direction of said magnetic eld and having lateral cell Walls, means in said envelope for releasing electrons to said anode structure to cause, with the assistance of said magnetic field, ionization of residual gas molecules in said envelope, and for releasing sputtered particles in said envelope for the entrapment of ionized gas molecules, said lateral cell walls of the cellular anode structure delining a plurality of spaced perforations being larger in area than the cell Wall portions between said perforations and being arranged and dimensioned to permit travel of said sputtered particles through the cell walls from one cellular element to another.

2. An ionic vacuum pump comprising an envelope for conning an evacuated space containing residual gas molecules, means for establishing a magnetic tield extending through the space within said envelope in a predetermined direction, a cellular anode structure Within said envelope composed of cellular elements having oppositely located open ends deined by lateral cell Walls extending in the general direction of said magnetic iield, a pair of cathode electrodes Within said envelope having said anode structure arranged therebetween for releasing electrons in the general direction of said magnetic field to cause ionization or" residual gas molecules present in said envelope, said cathode electrodes having surface areas facing said anode structure and extending substantially perpendicularly to the general direction of said magnetic lield to present target areas to the ionized gas molecules and each of said cathode electrodes comprising a material capable ot releasing, when hit at its target area surface by ionized gas molecules, sputtered particles traveling from such target area through said cellular anode structure elements to the other one of said cathode electrodes for the entrapment of gas molecules present on the target area surface thereof, said lateral cell walls of the cellular anode structure defining a plurality of spaced perforations being larger in area than the cell Wall portions between the perforations and being arranged and dimensioned to permit travel of sputtered particles from either one of said cathode electrodes through said cell walls and to the other one ot' said cathode electrodes.

3. An ionic vacuum pump for removing residual gas molecules from an evacuated space, comprising a pair ot substantially parallel, spaced electrodes, a plurality of mutually spaced cross-wire arrays having mutually aligned meshes and extending between said spaced electrodes substantially parallel thereto, terminal means for connecting said electrodes to the negative terminal of a source of electrical potential, and terminal means for connecting said cross-wire arrays to the positive terminal of said source.

il. An ionic vacuum pump for removing residual gas molecules from an evacuated space, comprising a pair of substantially parallel, spaced electrodes, a plurality of mutually spaced cross-Wire arrays having mutually aligned meshes and extending between said spaced electrodes substantially parallel thereto, terminal means for connecting said electrodes to the negative terminal of a source of electrical potential, terminal means for connecting said cross-wire arrays to the positive terminal of said source and means for establishing a magnetic field having lines of ilux extending between said spaced electrodes substantially perpendicularly thereto.

5. An ionicvacuum pump for removing residual gas molecules from an evacuated space, comprising a magnet structure having a pair of substantially parallel, spaced pole faces, a pair of spaced electrodes extending between said pole faces substantially parallel thereto, a plurality of mutually .spaced cross-wire arrays having mutually aligned meshes and extending between said spaced electrodes substantially parallel thereto, means -for connecting said electrodes to the negative terminal of a source of electrical energy, and means'for connecting said cross-wire arrays to the positive terminal of said source.

6. An ionic vacuum pump for removing residual gas molecules from an evacuated space, comprising a magnet structure having a pair of, substantially parallel spaced pole faces, a pair of spaced electrodes extending between said pole faces substantially parallel thereto, a plurality of mutually spaced wire arrays extending between said spaced electrodcs substantially parallel thereto, each -wire array being composed of a first plurality of mutually spaced Wires extending in a first direction and a second plurality of mutually spaced Wires extending perpendicularly to said irst plurality of Wires, and said plurality of Wire arrays being mutually aligned with respect to the wires thereof, means for connecting said electrodes to the negative terminal of a source of electrical direct-current, and means for jointly connecting said wire arrays to the positive terminal of said source.

7. An ionic vacuum pump for removing residual gas molecules from an evacuated space, comprising a magnet structure having a pair of substantially parallel, spaced pole faces, a pair of spaced electrodes extending between said pole faces substantially parallel thereto, at least three mutually spaced wire arrays extending between said spaced electrodes substantially parallel thereto, cach wire array being composed ot a lirst plurality of mutually spaced Wires extending in a rst direction and a second plurality of mutually spaced wires extending perpendicularly to said first plurality of wires, and said wire arrays being mutually aligned with respect to the wires thereof, means for connecting said electrodes to the negative terminal of a source of electrical directcurrent, and means for jointly connecting said wire arrays to the positive terminal of said source.

3. An ionic vacuum pump for removing residual gas molecules from an evacuated space, comprising an anode structure composed of a plurality of mutually spaced cross-wire arrays having mutually `aligned meshes, an electrode structure in the vicinity or said anode structure and spaced therefrom for releasing electrons to said anode structure to cause ionization of residual gas molecules present in the vicinity thereof, said electrode structure comprising elements presenting target areas to ionized gas molecules, said elements being of a material releasing sputtered particles when hit by ionized gas molecules, and a collector structure in the vicinity of said electrode structure for collecting ionized gas molecules and receiving said sputtered particles for entrapment of said collected ionized gas molecules.

9. An ionic vacuum pump for removing residual gas molecules from an evacuated space, comprising an anode structure composed of a plurality of substantially parallel, mutually spaced wire arrays, each wire array comprising a rst plurality of mutually spaced wires extending in a irst direction and a second plurality of mutually spaced Wires extending perpendicularly to said first plurality of Wires, with said plurality of Wire arrays being mutually aligned with respect to the wires thereof, means for establishing a magnetic field extending substantially perpendicularly to said wires, means for releasing electrons to said anode structure in the general direction of said magnetic lield to cause residual gas molecules present in the vicinity of said anode structure to be ionized, means for causing said ionized gas molecules to move substantially vin a predetermined direction, means for intercepting part of said moving ionized gas molecules to provided particles of sputtered material, and means for ultimately receiving said ionized gas molecules and said particles of sputtered material and for permitting said particles of sputtered material to form a layer having said gas molecules entrapped therein.

it?. An electrode assembly for an ionic vacuum pump, comprising a iirst electrode structure providing a pair of spaced, substantially parallel, confronting surfaces, and a second electrode structure comprising a plurality of mutually spaced cross-wire arrays having mutually aligned meshes and extending between said spaced surfaces substantially parallel thereto.

i1. An electrode assembly for an ionic vacuum pump, comprising aiirst electrode structure providing a pair of spaced, substantially parallel confronting surfaces, and a second electrode structure comprising a plurality of mutually spaced wire arrays extending between `said spaced surfaces, each of said wire arrays comprising a first plurality of mutually spaced wires extending parallel to `said spaced surfaces and a second plurality of mutually spaced wires extending perpendicularly to said irst plurality of Wires.

t@ Y l2. An anode structure for an ionic vacuum pump, comprising an array of spaced wires arranged to deiinc a plurality of laterally perforated prismatic anode cell sections.

13. An anode structure for an ionic vacuum pump, comprising at least three spaced cross-wire arrangements having mutually aligned'wire meshes arranged to define a plurality of prismatic ano-:le cell sections, two of said cross-wire arrangements fixingk the longitudinal dimen.

sions of the prismatic sections and the third Ycross-wire arrangement `being located between said two cross-wire arrangement for xing the lateral dimensions of the prismatic sections between said two cross-wire arrangements.

References Cited by the Examiner Y UN TED STATES PATENTS 2,993,638 7/61 Hall et al. 2SC-69 ROBERT M. WALKER, Primary Examiner.

VJARREN E. COLEMAN, Examiner.

Claims

1. AN IONIC VACUUM PUMP COMPRISING AN ENVELOPE FOR CONFINING AN EVACUATED SPACE CONTAINING RESIDUAL GAS MOLECULES, MEANS FOR ESTABLISHING A MAGNETIC FIELD EXTENDING THROUGH THE SPACE WITHIN SAID EVELOPE IN A PREDETERMINED DIRECTION, A CELLULAR ANODE STRUCTURE WITHIN SAID ENVELOPE COMPOSED OF OPEN-ENDED CELLULAR ELEMENTS EXTENDING WITH THEIR LONGITUDINAL AXES IN THE GENERAL DIRECTION OF SAID MAGNETIC FIELD AND HAVING LATERAL CELL WALLS, MEANS IN SAID EVELOPE FOR RELEASING ELECTRONS TO SAID ANODE STRUCTURE TO CASE, WITH THE ASSISTANCE OF SAID MAGNETIC FIELD, IONIZATION OF RESIDUAL GAS MOLECULES IN SAID ENVELOPE, AND FOR RELEASING SPUTTERED PARTICLES IN SAID ENVELOPE FOR THE ENTRAPMENT OF IONIZED GAS MOLECULES, SAID LATERAL CELL WALLS OF THE CELLULAR ANODE STRUCTURE DEFINING A PLURALITY OF SPACE PERFORATIONS BEING LARGER IN AREA THAN THE CELL WALL PORTIONS BETWEEN SAID PERFORATIONS AND BEING ARRANGED AND DIMENSIONED TO PERMIT TRAVEL OF SAID SPUTTERED PARTICLES THROUGH THE CELL WALLS FROM ONE CELLULAR ELEMENT TO ANOTHER.