Method For Fabricating A Dimpled Concave Dispenser Cathode Incorporating A Grid

Abstract

Methods for fabricating concave dimpled dispenser cathodes are disclosed. A multicell groove pattern is formed in the concave face of the cathode blank. An array of concave dimples are formed in the cellular regions of the concave emitter face bounded by the cells of the groove pattern. A multicell grid structure is incorporated into the groove pattern. The groove pattern is formable by photoetching, electrical discharge machining or by milling. The grid structure may be brazed into the grooves or merely supported therein in noncontacting relation therewith.

Description

DESCRIPTION OF THE PRIOR ART

Heretofore, it has been proposed to provide a multicell grid structure on or in the surface of a concave and dimpled cathode emitter with the cells of the grid structure being in alignment with apertures in a control grid. Such a cathode is disclosed and claimed in copending U.S. Pat. application Ser. No. 650,893 filed July 3, 1967 and assigned to the same assignee as the present invention. Such cathodes are especially useful in electron guns of high-convergence high-power linear beam tubes since control grid current interception is greatly reduced. This follows since the grid structure in or on the cathode helps to focus the electron beamlets through the aligned apertures of the control grid. Moreover, the focusing grid structure helps to inhibit electron emission from the regions of the cathode in registration with the webs of the control grid. However, heretofore practical production methods for fabricating dispenser cathodes incorporating such focusing grid structures have not been known.

SUMMARY OF THE PRESENT INVENTION

The principal object of the present invention is the provision of an improved method for fabricating a concave dimpled dispenser cathode having a grid structure incorporated therein.

One feature of the present invention are the steps of forming a multicell groove pattern in the concave face of a dispenser cathode blank to accommodate a multiapertured grid structure and forming an array of dimpled facets in the concave face of the cathode blank, such facets each being bounded by individual cells of the multicell groove pattern.

Another feature of the present invention is the same as the preceding feature wherein the step of forming the groove pattern comprises the step of milling the grooves in the concave face of the cathode blank.

Another feature of the present invention is the same as the first feature wherein the step of forming the groove pattern comprises chemically etching the groove pattern in the concave face of the cathode blank.

Another feature of the present invention is the same as the first feature wherein the step of electrically discharge machining the groove pattern with a discharge defining electrode having a pattern conforming to at least a portion of the groove pattern to be formed.

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

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is fragmentary longitudinal sectional view of an electron gun fabricated by methods incorporating features of the present invention;

FIGS. 2 and 4 are enlarged detail views of alternative embodiments to that portion of the structure of FIG. 1 delineated by lines 2-2 and 4-4,

FIGS. 3 and 5 are enlarged detail views of portions of FIGS. 2 and 4 delineated by lines 3-3 and 5-5, respectively,

FIG. 6 is a perspective flow diagram depicting a method of the present invention for fabricating dispenser cathodes,

FIG. 7 is a flow diagram in block diagram form depicting a cathode-fabricating method of the present invention;

FIG. 8 is flow diagram in block diagram form depicting certain steps in a method of the present invention; and

FIG. 9 is a sectional view of a tool of an electrical discharge machine depicting how it is employed in a method of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, there is shown an electron gun 1 employing a concave dispenser cathode emitter 2. The emitter is of the type disclosed in the aforecited U.S. Pat. application Ser. No. 650,893 and briefly is a spherical section of barium-impregnated porous tungsten having a multitude of closely packed dimpled facets 3 in the concave face 4 of the emitter 2. A centrally apertured anode electrode 5 faces the concave face 4 of the emitter 2. A multiapertured control grid 6 is disposed closely overlying and conforming to the shape of the concave surface 4. The apertures 7 of the control grid 6 are preferably hexagonal and disposed in registration with the dimpled facets 3, i.e., center of grid openings 7 falls on an electron trajectory leaving the center of facet 3. The facets 3 may be of circular or hexagonal boundary configuration with spherically concave surfaces of substantially lesser radius of curvature than the radius of curvature for the composite concave face 4.

A focus grid structure 8, having a configuration substantially identical to that of control grid 6, is incorporated into the concave surface 4 of the emitter 2 such that the web portions of focus grid 8 are in alignment with the similar web portions of the control grid 6. The focus grid 8 is positioned within a grid shaped groove pattern 9 in the concave surface 4 of the emitter. The grid 8 may be supported in noncontacting relation with respect to the grooves or it may be affixed, as by brazing, to the grooves. These two alternatives are depicted in greater detail in FIGS. 2--5 below. The focus grid serves to focus the individual electron beamlets through the corresponding aperture 7 in control grid 6 in a substantially nonintercepting manner. The focus grid 8, as of molybdenum, is coated with an electron-emission-inhibiting material, such as, carbon, titanium, zirconium, iridium, etc., to prevent current interception on the control grid 6 because the coating inhibits emission from those portions of the cathode surface 4 which would have electron trajectories to intercept the web members of grid 6.

After the beamlets pass through apertures 7 they converge into a unitary beam which passes through the central opening in anode 5. In a typical example, the gun 1 produces a beam of 1 amp at 10 kv. with a microperveance of 1.0 and cathode loading current density of 1.2 amps/cm. 2. Grid interception was 0.8 percent of the beam current.

Referring now to FIGS. 2 and 3, there is shown one embodiment of the dispenser cathode 2. In this embodiment, focus grid structure 8 is supported at its periphery from a relatively heavy tubular thermally conductive support 11 for heat sinking and cooling the grid 8. The grid 8 is supported in noncontacting relation within the groove pattern 9 to inhibit thermal conduction from the cathode 2, which normally operates within the range of 900.degree. to 1,100.degree. C, to the grid 8. The noncontacting relation also serves to inhibit migration of barium impregnant from the cathode 2 to the grid 8. In a typical example, the grooves 9 have a width of 0.016 inch and a depth of 0.005 inch and the grid 8 has a web width of 0.010 inch and a depth in the direction of the beam of 0.009 inch and is separated from the bottom of the groove 9 by 0.001 inch.

Referring now to FIGS. 4 and 5, there is shown a second embodiment of the dispenser cathode 2 wherein the grid 8 is supported from the cathode body via brazed joints 12 between the bottom of the grooves 9 and the abutting surface of the grid 8. Suitable braze materials include molybdenum-nickel or molybdenum-ruthenium mixes.

Referring now to FIG. 6, there is shown a flow diagram depicting the steps of the present invention for fabricating dispenser cathodes having grid structures incorporated therein. In the method, a spherically concave dispenser cathode blank 2, such as porous tungsten impregnated with a malleable material such as copper or plastic has its concave surface 4 grooved, in step (a), with a multicell hexagonal pattern of grooves 9 such groove pattern conforming to the grid pattern of the control grid 6 and to the pattern of the focus grid 8 to be located in the grooves 9. The grooves 9 may be formed as by chemical etching, milling, or by electrical discharge machining in the manner more fully described below with regard to FIGS. 7--9.

After the grid pattern of grooves 9 is formed, the dimpled facets 3 are formed, in step (b), in each of the cells of the groove pattern 9. The dimples 3 are formed either by machining or by electrical discharge machining.

In step (c), the focus grid structure 8 is incorporated into the groove pattern 9 either in noncontacting relation, as described above with regard to FIGS. 2 and 3, or in contacting relation as described with regard to FIGS. 4 and 5.

Referring now to FIG. 7, the general method of FIG. 6 is described in greater detail as employing chemical etching to form the grid-shaped pattern of grooves 9 in the cathode blank 2.

More specifically, in step (a), a masking grid structure substantially identical to grid 8, in fact it can be grid 8, is affixed to the concave surface 4 of the cathode blank 2, as by an adhesive or by clamping. In step (b), an acid resistant emulsive coating, such as A--Z 111 photo resist coating manufactured by Shipley Company, is applied to the concave surface 4 of the cathode blank 2 through the openings in the masking grid. In step (c), the masking grid is removed leaving the exposed grid pattern in the cathode blank surface 4.

In step (d), the surface 4 is treated with a chemical acid etch such as potassium ferrocyanide and caustic for etching the groove pattern 9 into the concave surface 4. In step (e) the surface 4 is dimpled as above described. In step (b), the malleable impregnant of the porous tungsten body is removed, as by chemical etching or heating to boil out the impregnant.

In step (g), the porous tungsten body is impregnated with electron emissive material, such as barium, ferrocyanide conventional manner. In step (h), the grid structure 8 with its electron-emission-inhibiting coating is incorporated in the grid pattern of grooves 9 either in the noncontacting manner, as described above with regard to FIGS. 2 and 3, or in contacting relation, as described above with regard to FIGS. 4 and 5. The dimpling step (e) can be performed either before or after incorporation of the grid 8. If it is performed after incorporation of the grid 8, the dimpling tool is merely inserted through the respective aperture in grid 8.

Referring now to FIG. 8, there is shown the steps in an alternative method for forming the pattern of grooves 9 in the cathode blank 2. More specifically, steps (a--d) replace steps (a--d) in the process of FIG. 7. In step (a), a masking grid is affixed to the cathode blank 2, as in step (a) of the method of FIG. 7. In step (b), a marking dye or paint is applied through the holes in the masking grid to indicate the desired grid pattern for the grooves 9 by the unpainted web pattern in the painted surface. In step (c), the masking grid is removed to expose the desired grid pattern markings. In step (d), the concave surface 4 is milled by a milling machine along the unpainted lines of the desired grid pattern. The remainder of the process of manufacture remains the same as described with regard to FIG. 7.

Referring now to FIG. 9, there is shown an alternative method for forming the grid pattern of grooves 9 in the cathode surface 4. In this method, steps (a--d) of the method of FIG. 7 are replaced by the step of electrically discharge machining the pattern of grooves 9 in the concave surface 4 of the cathode blank 2. The electrical discharge defining electrode tool 15 has a spherically curved surface 16 conforming to the surface 4 of the cathode blank 2. Formed on the surface 16 of the tool 15 is a raised grid pattern 17 conforming to the grid pattern of the grooves 9 to be formed in the cathode blank 2. The electrical discharge machining tool 15 is then moved into the surface 4 of the cathode blank 2 to machine the grid pattern of grooves 9 therein. The remainder of this method is the same as that previously described above with regard to FIG. 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 drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

What we claim is:

1. In a method for fabricating a dimpled dispenser cathode for a convergent stream electron gun the steps of, forming a multicell groove pattern in the concave face of a dispenser cathode blank, such multicell groove pattern conforming generally to the web pattern of a multiapertured control grid to be employed over the concave emissive surface of the dispenser cathode, forming an array of concave dimpled emissive facets in the concave face of the cathode blank, each of the individual facets being located such as to be bounded by an individual cell of the multicell groove pattern, and incorporating a multiapertured grid structure in the groove pattern, such grid structure having a web pattern conforming generally to the groove pattern and to the web pattern of the control grid.

2. The method of claim 1 wherein the step of forming the multicelled groove pattern in the concave face of the dispenser cathode blank comprises the step of marking the concave face to be grooved to indicate the pattern of the desired grooves, and milling the grooves in the concave face according to the marked pattern.

3. The method of claim 1 wherein the step of forming the multicelled groove pattern in the concave face of the dispenser cathode blank comprises the step of electrically discharge machining the concave face with a tool having a discharge defining electrode pattern conforming to at least a portion of the desired groove pattern to be formed in the concave face of the dispenser cathode blank.

4. The method of claim 1 wherein the step of forming the multicelled groove pattern in the concave face of the dispenser cathode blank comprises the step of, chemically etching the groove pattern in the concave face of the dispenser cathode blank.

5. The method of claim 1 wherein the cathode blank into which the groove pattern is to be formed comprises a porous tungsten body with the pores infiltrated with a malleable material, and including the steps of removing the malleable material from the grooved cathode blank to leave a porous metal blank, and infiltrating the pores of the metal blank with electron emissive material to form a dispenser cathode body.

6. The method of claim 5 wherein the step of incorporating the grid structure into the groove pattern includes the steps of, locating the web of the grid structure in the groove pattern, and brazing the grid structure to the grooved cathode body.

7. The method of claim 5 including the step of, coating the grid structure to be incorporated in the groove pattern of the dispenser cathode blank with an electron-emission-inhibiting coating.

8. The method of claim 4 wherein the step of chemically etching the groove pattern includes the steps of, positioning a masking grid structure, having the desired grid pattern to be formed in the cathode, adjacent the concave face of the cathode blank, coating the grid structure and exposed positions of the masked concave face of the cathode blank with an acid-resistant emulsion, removing the masking grid structure to expose the surface of the cathode blank masked by the masking grid structure, and chemically etching the exposed surfaces in the concave face of the cathode blank to form the desired groove pattern.

9. The method of claIm 1 wherein the individual cell pattern of the grooves formed in the concave face of the cathode blank is hexagonal.