Gridded electron gun

Claim 2

In a gridded electron gun: thermionic cathode emitter means having a concave cathode emitting surface for providing a copious supply of electrons; anode electrode means spaced from said concave cathode emitting surface and having a central aperture in axial alignment with said concave cathode emitting surface for drawing a beam of electrons from said cathode through said central aperture in said anode; concave control grid means interposed between said concave cathode emitting surface and said anode means, said concave control grid means including a plurality of beam passageways therethrough of generally uniform cross-sectional area defining electrostatic focusing lenses for focusing said electrons into individual beamlets passable therethrough, said individual focusing lenses of said control grid increasing in length from the outer periphery toward the center of said control grid, said control grid means being operative at a varying control grid potential relative to said cathode emitter means.

Claim 3

The apparatus of claim 1 wherein said control grid means includes first and second axially spaced concave apertured control grids, said control grids being disposed adjacent each other with their respective apertures in axial registration, means for interconnecting said first and second control grids to be operated at the same control grid potential, and wherein the axial spacing between said first and second control grids increases from the outer periphery toward the center of said control grids to provide the increase in length for the individual electrostatic lenses formed by the respective beam passageways through said aligned apertures in said control grids.

Claim 4

The apparatus of claim 1 wherein said central aperture in said anode means has a lesser transverse cross-sectional area than said emitting surface of said cathode emitter for producing a convergent flow of electrons from said cathode emitter through said central aperture in said anode electrode means.

Claim 5

The apparatus of claim 1 including, concave shadow grid means interposed in the space between said control grid means and said concave cathode emitting surface of said cathode emitter means, said shadow means having beam apertures in alignment with the respective beam apertures in said control grid means, and means for operating said shadow grid means at the same potential as said cathode emitter means.

Claim 6

The apparatus of claim 4 wherein said concavE cathode emitting surface of said concave cathode emitter means is constituted of a plurality of dimpled regions in alignment along the beam path with respective beam passageways in said shadow and control grid means, said dimpled regions being curved in mutually orthogonal directions and having radii of curvature substantially less than that of said composite concave cathode emitting surface.

Claim 7

In a gridded electron gun: thermionic cathode emitter means having a concave cathode emitting surface for providing a copious supply of electrons; anode electrode means spaced from said concave cathode emitting surface and having a central aperture in axial alignment with said concave cathode emitting surface for drawing a beam of electrons from said cathode through said central aperture in said anode; concave control grid means interposed between said concave cathode emitting surface and said anode means, said concave control grid means including a plurality of beam passageways therethrough of generally uniform cross-sectional area, said control grid means including first and second axially spaced concave apertured control grid portions, said control grid portions being disposed adjacent each other with their respective apertures in axial registration, means for interconnecting said first and second control grid portions to be operated at the same control grid potential, whereby the second control grid portion closest to said anode is thermally shielded from the cathode by said first control grid portion to reduce thermionic emission from said composite control grid structure to reduce undesired interpulse noise.

Claim 8

In a gridded electron gun: thermionic cathode emitter means having a concave cathode emitting surface for providing a copious supply of electrons; anode electrode means spaced from said concave cathode emitting surface and having a central aperture in axial alignment with said concave cathode emitting surface for drawing a beam of electrons from said cathode through said central aperture in said anode; concave control grid means interposed between said concave cathode emitting surface and said anode means, said concave control grid means including a plurality of beam passageways therethrough of generally uniform cross-sectional area, said control grid means including first and second axially spaced concave apertured control grid portions, said control grid portions being disposed adjacent each other with their respective apertures in axial registration, means for interconnecting said first and second control grid portions to be operated at the same control grid potential, whereby the second control grid portion closest to said anode is thermally shielded from the cathode by said first control grid portion to reduce thermionic emission from said composite control grid structure to reduce undesired interpulse noise.