US3596123A

US3596123A - Anode structure for a magnetically confined glow discharge getter ion pump

Info

Publication number: US3596123A
Application number: US859004A
Authority: US
Inventors: Nathan D Levin
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1969-09-18
Filing date: 1969-09-18
Publication date: 1971-07-27
Anticipated expiration: 1988-07-27

Abstract

A magnetically confined glow discharge getter ion pump is disclosed. The pump includes a pump housing containing an anode electrode having a glow discharge passageway therethrough and with a pair of cathode electrodes disposed on opposite sides of the anode for establishing the glow discharge. The anode structure is formed by a collapsible coiled sheet metal spring member which is collapsed for insertion into the pump housing through a constricted access passageway and then allowed to expand into place within the housing due to the spring action of the collapsible anode structure.

Description

United States Patent UN l l Inventor Nathan D. Levin Los Altos Hills, Calfl. Appl No 859,004 Filed Sept. 18, I969 Patented July 27, 1971 Auignee Vnrlan Allociates Palo Alto, Cnlil.

ANODIZ STRUCTURE FOR A MAGNETICALLY CONFINED GLOW DISCHARGE GET"!!! [ON PUMP 7 Claims, 3 Drawing Figs.

U.S. CL 313/7. 417/49 Int. Cl .r not 6/17 M Search 313/7; 417/48, 49, 5t

[56] References Cited UNITED STATES PATENTS 3,217,971 I l [965 Knauer H317 X 3,460,745 8/1969 Lamont, .lr 313/7 X Primun bmmim'r Roy l ake Assistant Examiner- Lawrence J Dahl AnorneysStanley Z Cole and Gerald L Moore ABSTRACT: A magnetically confined glow discharge getter ion pump is disclosed. The pump includes a pump housing containing an anode electrode having a glow discharge passageway therethrough and with a pair of cathode electrodes disposed on opposite sides of the anode for establishing the glow discharge. The anode structure is formed by a collapsible coiled sheet metal spring member which is collapsed for insertion into the pump housing through a constricted access passageway and then allowed to expand into place within the housing due to the spring action of the collapsible anode structure.

PATENYEU JULZHSTI INVENTOR. NATHAN D. LEVIN BY ATTORNEY ANODE STRUCTURE FOR A MAGNETICALLY CONFINED GLOW DISCHARGE GETTER ION PUMP DESCRIPTION OF THE PRIOR ART Heretofore, hollow cylindrical anode structures for magnetically confined glow discharge getter ion pumps have been employed. However, in such anodes the anode cylinder was relatively rigid such that the access passageway through which the anode cylinder was inserted into the pump housing had to have dimensions equal to or larger than the dimensions of the anode cylinder. The problem with this type of construction is that for a given size constriction in the passageway through which the anode is inserted, the anode can be no bigger than the constriction. Oftentimes the optimum anode diameter for a given magnetic field intensity is larger than the size of the constriction and therefore less than optimum pumping speed is obtained with a rigid anode that must pass the restricted access passageway.

SUMMARY OF THE PRESENT INVENTION The principal object of the present invention is the provision of an improved anode structure for a magnetically conlined glow discharge getter ion pump.

One feature of the present invention is the provision of an anode structure for a magnetically confined glow discharge getter ion pump which comprises a collapsible spring structure, whereby the anode is collapsible for insertion into the pump housing through a constricted access passageway and thereafter allowed to expand into place with the housing due to the spring action of the collapsible anode structure.

Another feature of the present invention is the same as the preceding feature wherein the collapsible anode is formed by a curved sheet of spring hardened metal.

Another feature of the present invention is the same as any one or more of the preceding features wherein the pump housing includes a hollow cylindrical dielectric section surrounding the anode electrode and wherein the collapsible anode includes a plurality of outwardly directed projections for contacting the inside walls of the dielectric section of the housing to space the anode from the inside wall thereof, thereby increasing the current leakage path between the cathode electrodes and the anode.

Another feature of the present invention is the same as any one or more of the preceding features wherein the anode is formed by a single turn coil spring of sheet metal.

Other features and advantages of the present invention become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side elevational view of an image intensifier tube incorporating a getter ion pump of the present invention as an appendage thereto.

FIG. 2 is a longitudinal sectional view of a portion of the structure of FIG. I delineated by the line 2-2, and turned 90 counterclockwise, and

FIG. 3 is a sectional view of the structure of FIG. 2 taken along the line 33 in the direction of the arrows DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, there is shown an image intensifier tube 1 which includes an evacuated envelope structure 2, as of glass, having a central cylindrical portion and an outwardly domed faceplate portion 3 through which photon images to be intensified pass to a scintillator. A photocathode in contact with the scintillator produces an emitted electron image which is accelerated to a fluorescent screen via other electrodes disposed inside the envelope 2. The opposite end of the envelope 2 includes a constricted neck portion 4 connected to the central cylindrical portion 2 via an outwardly domed portion 5. A magnetically confined getter ion appendage pump 6 is sealed into the domed portion 5 for evacuating the tube I after the tube is sealed off during processing.

Referring now to FIGS. 2 and 3, the appendage pump 6 is shown in greater detail. The appendage pump 6 includes a hollow cylindrical pump housing 7 having a hollow cylindrical central section 8, as of glass, the outer end of which is closed off by means ofa Kovar disk 9, as of l/l6-inch thick, sealed by glass-to-metal seals across the end of the central section 8. The other end of the central section 8 includes an annular pole piece II, as of )-inch thick Kovar sealed to the central dielectric section 8 via glass-to-metal seals. A tubulation 12, as of glass, seals the pump housing 7 to the image intensifier tube I, to be evacuated.

A centrally disposed constricted access 13 is provided in the Kovar plate 11 and the access passageway 13 is plugged by means of a perforated cylindrical magnetic plug 14, as of cold rolled steel. The plug 14 includes a plurality of axially directed gas access passageways 15 providing gas communication between the interior of the pump housing 7 and the intensifier tube 1 via the tubulation I2.

A pair of cathode electrode structures 16 and 17 are disposed at opposite ends of the pump housing 7 and are carried from the plug 14 and the end closing plate 9, as by spot welding at 18 and 19, respectively. Cathode electrode structures l6, 17 comprise disks 2] and 22 of a getter material such as titanium of tantalum with centrally disposed axially directed

posts

23 and 24, respectively, as of titanium or tantalum.

An annular anode electrode 25 is disposed intermediate the cathode electrode structures I6 and I7 to provide a glow discharge passageway defined by the space between the cathode electrodes [6 and 17 and bounded at the outer perimeter by the anode cylinder 25, as of stainless steel.

The anode electrode 25 is fixed in position and supplied with operating anode potential, as of 2 to 5 kv. relative to the grounded cathode structures 16 and 17, via a support lead 26, as of stainless steel, spot welded to the anode cylinder 25 at 27. The anode lead 26 is supported at its other end from an electrode structure 28, as by spot welding thereto, such elec trode structure 28 being disposed inside the intensifier tube 1. A dielectric insulator tube 29, as of glass, is disposed surrounding support lead 26 at the position that the lead 26 passes through one of the bores 15 in the magnetic plug 14. The glass insulator tube 29 is held in position on the anode lead 26 via crimped portions 3| of the lead 26, such crimped portions being provided at both ends of the insulator tube 29.

The anode electrode 25 comprises a single turn coil of spring hardened sheet metal, as of 0.010 inch thick stainless steel, which forms a coil spring structure. The coil spring structure is radially collapsible for insertion through the constricted access passageway I3 into the pump housing 7. Once positioned inside the pump housing 7 the coil spring anode 25 is allowed to expand outwardly against the cylindrical central section 8 of the pump housing.

The sheet metal anode electrode 25 includes a plurality of outwardly directed projections 32 formed by indentations 33. The projections 32 thus serve to space the anode electrode 25 from the inside wall of the pump housing 7 to increase the current leakage path between the cathode electrode structures I6 and I7 and the anode electrode 25 along the inside walls of the housing 7. In a typical example, the projections 32 have a radial extent of approximately 0.010 inch. Such projections 32 are shielded from the sputtered cathode material by being positioned away from the axial end portions of the cylindrical anode 25.

A ring-shaped permanent magnet 35, as of alnico V or VIII, is disposed surrounding the pump housing 7. The magnet 35 abuts the lower Kovar disk II to provide one pole of the magnet structure and a magnetically permeable disk 36 abuts the opposite end of the magnet 35 and the end plate 9 of the housing 7 to provide the second pole structure for the magnetic circuit. The magnet 35 and its magnetic circuit produces an axially directed magnetic field B, as of l,000 gauss, centrally of the anode 2.5 for magnetically confining the glow discharge within the glow discharge passage within the anode 25.

The anode electrode structure 25 together with its support lead 26 and insulator sleeve tube 29 is first assembled to the plug structure l4 along with the cathode electrode 16 and then the spring anode 24 is collapsed such that the plug together with the anode may be inserted through the constricted access passageway 13. The spring anode structure is then allowed to expand into position within the pump housing and the plug I4 is spot welded to the plate II at 37 and then lead 26 is spot welded to the support 28 at 38.

The advantage of the collapsible spring anode electrode 25 is that the anode can expand to a larger diameter than the diameter of the access passageway 13 such that the anode may assume dimensions more nearly those of an optimum sized anode for the magnetic field intensity being employed for the pump. in this manner, the pumping speed of a pump can be substantially increased as compared to a similar construction wherein the anode is not expandable once located inside the pump and thus limited in transverse dimensions to the size of the access passageway 13.

In use, a magnetically confined glow discharge is established within the glow discharge passageway within the anode 25 to produce sputtering of cathode material from the cathode electrodes l6 and 17. The getter material sputtered from the cathode electrodes deposits upon the anode and other surfaces within the pump housing including the opposed cathode electrodes to getter gases coming in contact therewith. In this manner, the appendage pump 6 pumps the envelope structure 2 by flow of gas from the envelope 2 via tubulation l2 and gas passageways to the pump housing 7.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What I claim is:

1. In a magnetically confined glow discharge ion pump, means forming a pump housing for connection to a structure to be evacuated, an anode electrode structure having a glow discharge passageway therethrough disposed in said housing, a pair of cathode electrode structures disposed on opposite sides of said anode within said housing for establishing a glow discharge in said glow discharge passageway, THE lM- PROVEMENT WHEREIN, said anode electrode structure comprises a collapsible spring structure, whereby the anode electrode is collapsible for insertion into said pump housing through a constricted access passageway and allowed to expand into place within said housing due to the spring action of said collapsible anode structure.

2. The apparatus of claim 1 wherein said collapsible anode is a curved sheet of spring hardened metal.

3. The apparatus of claim 2 wherein said spring hardened metal is stainless steel.

4. The apparatus of claim 2 wherein said pump housing includes a hollow cylindrical dielectric section surrounding said anode electrode, and therein said sheet metal anode includes a plurality of outwardly directed projections for contacting the inside wall of said hollow cylindrical dielectric section for spacing said anode from said cylindrical wall.

5. The apparatus of claim 2 wherein said curved sheet metal anode is formed into a single turn coil.

6. The apparatus of claim 4 wherein said curved sheet metal anode is formed into a single turn coil.

7. The apparatus of claim 1 including, means forming a magnetic circuit for producing a magnetic field axially directed through said glow discharge passageway in said anode for magnetically confining the glow discharge.

Claims

1. In a magnetically confined glow discharge ion pump, means forming a pump housing for connection to a structure to be evacuated, an anode electrode structure having a glow discharge passageway therethrough disposed in said housing, a pair of cathode electrode structures disposed on opposite sides of said anode within said housing for establishing a glow discharge in said glow discharge passageway, THE IMPROVEMENT WHEREIN, said anode electrode structure comprises a collapsible spring structure, whereby the anode electrode is collapsible for insertion into said pump housing through a constricted access passageway and allowed to expand into place within said housing due to the spring action of said collapsible anode structure.