US3217974A

US3217974A - Dual surface ionic pump with axial anode support

Info

Publication number: US3217974A
Application number: US239430A
Authority: US
Inventors: Knauer Wolfgang
Original assignee: Hughes Aircraft Co
Current assignee: Raytheon Co
Priority date: 1962-11-23
Filing date: 1962-11-23
Publication date: 1965-11-16
Anticipated expiration: 1982-11-16

Description

Nov. 16, 1965 w. KNAUER 3,217,974

mm. summer: IONIC PUMP WITH AXIAL ANODE SUPPORT Filed Nov. 23, 1962 2 Sheets-Sheet 1 Nov. 16, 1965 w. KNAUER 3,217,974

DUAL SURFACE IONIC PUMP WITH AXIAL ANODE SUPPORT Filed Nov. 23, 1962 2 Sheets-Sheet 2 the anode cylinder.

United States Patent 3,217,974 DUAL SURFACE IONIC PUMP WITH AXIAL ANODE SUPPORT Wolfgang Knauer, Malibu, Calif., assignor to Hughes Aircraft Company, Culver City, Calif, a corporation of Delaware Filed Nov. 23, 1962, Ser. No. 239,430 8 Claims. (Cl. 230-69) This invention relates to electrical vacuum pumps and more specifically to ionic vacuum pumps of the Penning discharge type.

Vacuum pumps of the Penning discharge type for creating high vacuums of the order of l0 torr are known and in general comprise a pair of parallel disks composed of a reactive cathode material and an openended hollow cylinder suitable for use as an anode. The cathode disks are slightly greater in diameter than the anode cylinder, and are placed at the respective extremities of and normal to the anode cylinder. The entire device is immersed in a magnetic field parallel to the axis of the anode, and enclosed in an envelope connected to the apparatus to be evacuated. When a high electric potential difference is applied between the cathode and anode members a discharge strikes. Positive ions from this discharge continuously bombard the reactive cathode elements, and sputter off some of the reactive material thereon. The sputtered material is deposited on other exposed surfaces within the envelope to be evacuated, particularly surfaces of the anode element. These deposits act as a getter; i.e., they remove gas molecules from within the envelope by adsorption. This adsorption is the primary pump action; however, some gases such as the noble gases and hydrogen are removed by direct ion burial in the cathode elements.

Investigation of the discharge mode in such ion pumps has revealed that the active discharge area is confined to a thin plasma layer which lines the inside surface of The present invention is based upon the discovery that under proper conditions such a discharge may also be made to occur on the out-side surface of the anode. With simultaneous discharges on both the in and outside surfaces of the anode, the total discharge current, and, hence, also the bombardment rate and the pump speed is greatly increased. Furthermore, the fact that the discharge is in the form of a thin plasma layer at the anode surface means that the anode cylinder need not be restricted to either round or rectangular cross sections as used in conventional pumps but may have any desirable shape which may produce a maximum pumping rate.

It is therefore an object of the invention to provide an improved ion pump.

Another object of the invention is to provide an ion pump of increased pumping speed for a given physical size by establishing simultaneous discharges on more than one surface of the anode member.

Another object of the invention is to provide an ion pump with anode and/or cathode members whose geometric configurations optimize the rate of pumping and simplify the mechanical construction.

These and other objects and advantages of the invention are realized by the providing of a connection and/ or support for an anode member which does not disrupt the electron motion within the plasma layer. This is achieved according to invention by providing the anode with a support rod and/ or connecting lead which extends axially along the direction of the major surfaces of the anode and is fastened to the anode at an edge rather than on a wall or major surf-ace. In this way, the discharge path on the wall surfaces of the anode remains completely unobstructed. The anode may also be pro- 3,217,974 Patented Nov. 16, 1965 vided with meander-type cross-section in order to provide maximum anode surface to obtain maximum discharge current and pumping speed. Unlike anode structures of the conventional multi-cellular pumps, the meander-type anode of the invention can be manufactured from a single mold.

These and other features of the invention will be described in greater detail by reference to the drawings in which:

FIGURE 1 is a sectional view of an ion pump according to invention wherein the anode support rod is oriented to extend parallel to the major surfaces of the anode;

FIGURE 2 is an orthogonal View of a corrugated cathode configuration having ridges and valleys extending radially to the major surfaces of the anode;

FIGURE 3 is a sectional view of a corrugated cathode with ridges and valleys extending parallel to the major surfaces of the anode; and

FIGURE 4 is an orthogonal view of a corrugated anode which provides maximal surface area for the total volume occupied by a given anode element.

Referring now to FIGURE 1, a Penning discharge pump employing the invention is shown wherein an anode cylinder 2 is mounted between two

cathode plates

4 and 4, which may be circular. T heseanode and cathode members are disposed within an envelope 6 which is adapted to be connected to apparatus to be evacuated by means of a connecting tube 8. Magnetic means 10 are provided outside and adjacent the envelope 6 for establishing a magnetic field within the envelope parallel to the major surfaces of the anode cylinder 2. The anode cylinder 2, the envelope 6, and the connecting tube 8 may be of any desirable metal, for example, stainless steel. The

cathode plates

4 and 4 may be of a reactive material such as tantalum, for example. Anyone of a number of suitable materials may be employed for the cathode members such as molybdenum, titanium, tungsten, niobium, zirconium, barium, thorium, magnesium calcium and strontium. In practice it may be desirable to provide a film of reactive material on a base metal, such as stainless steel.

In the embodiment of FIGURE 1 electrical connection is made to the anode cylinder 2 in such a manner as to not disrupt the electron motion of the plasma sheet formed adjacent the anode Walls during operation. This is achieved in this embodiment by extending the electrically conductive rod 12 parallel along the direction of the major surfaces of the anode cylinder 2. The rod 12 extends to the outside of the envelope 6 through a hole in the cathode disk 4 and thence through a hole in the envelope 6. The rod 12 may be used to support the anode cylinder if desired. The rod is electrically isolated from the envelope 6 by means of a glass member or plug 14 which is hermetically sealed in the hole of the envelope 6 and to the rod 12. The edge 16, constituting a minor surface of the anode cylinder 2, may be welded or otherwise secured to the end of the rod 12 so as to be in good electrical conducting relationship therewith and preferably supported thereby.

In operation the pump 1 is connected to the apparatus to be evacuated by means of the connecting tube 8. A high electric potential is imposed between the

cathode members

4 and 4 and the anode 2. A suitable potential for this purpose may be of the order of 3,000 volts. At the same time a magnetic field of the order of 1-2 kilogauss may be imposed across the pump in a direction parallel to the axis of the anode cylinder. A Penning discharge sheath will be established on both sides (inside and outside) of the anode member 6 to enhance the pumping speed as described heretofore.

In FIGURES 2 and 3 embodiments are shown wherein the inner surface of the envelope constitutes or provides a reactive cathode surface. The anode cylinder 2 is disposed between end cathode members 4 and 4' and within a cylindrical type cathode portion 5 which may be integral with or otherwise connected to the

end cathode members

4 and 4. This cathode configuration is designed to effect maximum pumping speed by the discharge action along the outer anode surface. In FIGURE 2 the cathode portion 5 is corrugated with relatively sharp folds extending parallel with the major surfaces of the anode cylinder 2. In FIGURE 3 the folds extend toward the major surfaces of the anode. These corrugated cathode surfaces may be employed to effect greater sputtering action (and therefore greater pumping speed) by providing a high angle of incidence of ions from the discharge along the outer anode surface. The anode may be supported or connected to a source of potential by the arrangements shown in FIG- URE '1 and described in connection therewith. The cylindrical cathode portion may be provided with an outlet 22 for connectionlo the apparatus to be evacuated so that the gas to be pumped may be introduced into the space between the anode and cathode members.

In the embodiments described thus far the anode has been shown as a round cylinder. Since the anode current is proportional to the total anode area, an increase in the anode area as by a meander-type surface will result in an increase of the discharge current and therefore the pump speed as well. The only requirements are that the anode surface be closed or continuous and parallel to the magnetic field. In FIGURE 4 a corrugated type anode cylinder 2 is shown satisfying these requirements for use in the ion pump of FIGURES 1, 2, or 3. In order to permit the discharge to develop properly on both inside and outside surfaces of the anode cylinder the surface should not come closer to each other than twice the sheath width and the radii of curvature of the anode should not be smaller than one sheath width.

There thus has been shown and described an improved ion pump in which the Penning type discharge may be established and maintained on both sides of an anode member. In addition alternatives have been shown and described which in combination with the dual surface discharge capability of the anode permits an even greater pumping action.

What is claimed is:

1. An ionic pump comprising an envelope adapted to be connected to apparatus to be evacuated, means for establishing a magnetic field within said envelope, an anode member within said envelope and having at least two major surfaces parallel to said magnetic field and an end portion constituting a minor surface, connection means for said anode member secured to said end portion only and extending parallel to said magnetic field, and reactive cathode means diposed in said envelope at an angle with respect to said major surfaces.

2. An ionic pump comprising an envelope adapted to be connected to apparatus to be evacuated, means for establishing a magnetic field within said envelope, a cylindrical anode member having inner and outer major surfaces and an end portion constituting a minor surface, said major surfaces being parallel to said magnetic field, connection means for said anode member secured to said end portion only and extending parallel to said magnetic field, and reactive cathode means disposed in said envelope at an angle with respect to said major surfaces.

3. The invention according to claim 2 wherein said reaction cathode means is disposed adjacent and across said end portion.

4. An ionic pump comprising an envelope adapted to be connected to apparatus to be evacuated, means for establishing a magnetic field within said envelope, an open-ended cylindrical anode member having inner and outer major surfaces parallel to said magnetic field, reactive cathode means disposed adjacent the ends of said cylindrical anode member and at an angle with respect to said major surfaces, connection means for said anode member secured only to an end portion thereof and extending parallel to said magnetic field through said reactive cathode means and electrically isolated therefrom.

5. An ionic pump comprising an envelope adapted to be connected to apparatus to be evacuated, means for establishing a magnetic field within said envelope, an anode member within said envelope and having a plurality of major surfaces parallel to said magnetic field and an end portion constituting a minor surface, connection means for said anode member secured to said end portion only and extending parallel to said magnetic field, and reactive cathode means disposed in said envelope at an angle with respect to said major surfaces.

6. The invention according to claim 5 wherein said anode member contains a plurality of folds extending parallel to said magnetic field thereby providing said plurality of major surfaces.

7. An ionic pump comprising a corrugated envelope adapted to be connected to apparatus to be evacuated, the inner surface of said envelope constituting a reactive cathode member, means for establishing a magnetic field within said envelope, an anode member within said envelope having at least two major surfaces parallel to said magnetic field and an end portion, and connection means for said anode member secured to said end portion only and extending parallel to said magnetic field.

8. The invention according to claim 7 wherein said anode member contains a plurality of folds extending parallel to said magnetic field thereby providing said plurality of major surfaces.

References Cited by the Examiner UNITED STATES PATENTS 2,032,179 2/1936 Lowry 313205 2,993,638 7/1961 Hall et al 23069 3,070,283 12/1962 Hall 23069 3,112,863 12/1963 Brubaker et al. 23069 GEORGE N. WESTBY, Primary Examiner,

Claims

1. AN IONIC PUMP COMPRISING AN ENVELOPE ADAPTED TO BE CONNECTED TO APPARATUS TO BE ELEVATED, MEANS FOR ESTABLISHING A MAGNETIC FIELD WITHIN SAID ENVELOPE, AN ANODE MEMBER WITHIN SAID ENVELOPE AND HAVING AT LEAST TWO MAJOR SURFACES PARALLEL TO SAID MAGENTIC FIELD AND AN END PORTION CONSTITUTING A MINOR SURFACE, CONNECTION MEANS FOR SAID ANODE MEMBER SECURED TO SAID END PORTION ONLY AND EXTENDING PARALLEL TO SAID MAGNETIC FIELD, AND REACTIVE CATHODE MEANS DISPOSED IN SAID ENVELOPE AT AN ANGLE WITH RESPECT TO SAID MAJOR SURFACES.