IL42916A - An electron gun - Google Patents

Claims (3)

1. In an electron gun: thermionic cathode emitter means having, a base member with a concave emitting surface, said concave emitting surface being constituted ©f a plurality of lesser individual concave oxide coated cathode emitter surfaces, said lesser oxide coated emitter surfaces being concave in each of two orthogonal directions with radii of curvature substantially less than that of said composite cathode emitter surface; an accelerating electrode means having a central aperture of substantially smaller cross-sectional area than ttxe area of said emitting surface of said cathode emitter, said central aperture being disposed in axial alignment with the center of said concave emitting surface of said cathode emitter for accelerating and converging a stream of electrons through said central aperture of said accelerating electrode into a unitary beam of electrons? control grid means comprising a multiapertured concave control grid structure disposed overlaying, but not in contact with the concave emitting surface of said cathode emitter with the centers of individual apertures in said control grid structure being disposed in alignment along the convergent beam path with the centers of individual lesser concave cathode emitting surfaces to form a plurality of individual convergent beam electron guns projecting the beam through said control grid in a plurality of nonlntercepting beamlets which converge into the unitary beam after passage through said control grid? shadow grid means comprising a second multiapertured grid structure of substantially Identical hole pattern to that of said control grid structure wherein the web portion of said shadow grid is disposed in nominal contact with the concave surface of said cathode emitter in the web-like regions thereof defined between adjacent lesser concave emitting surfaces, whereby a relatively poor thermally conductive path is provided between said shadow grid and said cathode emitter to allow said shadow grid to operate at a lower temperature than said cathode emitter in use, said shadow grid structure being operated at the same potential as said cathode emitter for inhibiting thermionic emission from the underlying regions of said cathode emitter shadowed by said shadow grid and for focusing the lesser beamlet through the respective aligned apertures in said control grid structure, and said, shadow-grid being made of a material having essentially the same coefficient of thermal expansion as that of said cathode emitter.

2. The apparatus of claim 1 wherein said shadow grid and said cathode base members are made of nickel.

3. The apparatus of claim 2 wherein the web portion of said shadow grid is disposed in nominal contact with the concave surface of said cathode emitter in the web-like regions thereof defined between adjacent lesser concave emitting surfaces, whereby a relatively poor thermally conductive path is provided between said shadow grid and said cathode emitter to allow said shadow grid to operate at a lower temperature than said cathode emitter in use.