Electron gun structure

Claim 2

An electron gun system comprising: a cathode means, positioned on an electron gun axis, for emitting an electron beam along a beam path; a plurality of grid electrodes arranged along said electron gun axis, a first voltage source coupled to at least one of said grid electrodes for forming a plurality of electrostatic lenses on said electron gun axis for focusing said electron beam; a focus control means coupled to a first voltage source for controlling said focusing; and wherein at least three of said grid electrodes comprise asymmetric deflecting means for forming at least two asymmetric electrostatic lenses along said electron gun axis for deflecting said electron beam.

Claim 3

The electron gun structure of claim 1 wherein said asymmetric electrostatic lenses comprise a first asymmetric lens positioned near said cathode and a second asymmetric lens positioned along the electron gun axis downstream from said first asymmetric lens, wherein said first asymmetric lens, in response to said focus control means, deflects the beam at a first differential angle and said second asymmetric lens deflects the beam at a second differential angle to compensate for said first differential angle deflection caused by said first asymmetric lens.

Claim 4

The electron gun structure according to claim 1 wherein said plurality of grid electrodes comprises a first, second and third grid electrode, said second grid electrode positioned between said first and third grid electrodes and wherein said asymmetric deflecting means forms two asymmetric electrostatic lenses, one of said asymmetric lenses positioned between said first grid electrode and said second grid electrode and the other of said asymmetric lenses positioned between said second grid electrode and third grid electrode, said first voltage source is coupled to said second grid electrode whereby, in response to said focus control means, said other asymmetric lens compensates for a differential deflection caused by said one asymmetric lens.

Claim 5

The electron gun structure according to claim 3, further comprising a second voltage source coupled to said first grid electrode and a third voltage source coupled to said third grid electrode, wherein said first voltage source is greater than said second voltage source but lower than said third voltage source.

Claim 6

The electron gun structure according to claim 1 wherein at least one of said asymmetric electrostatic lenses comprises two spaced grid electrodes, each having an aperture, wherein the center of one aperture is offset from the center of the other aperture.

Claim 7

The electron gun structure according to claim 1 wherein at least one of said asymmetric electrostatic lenses comprises two spaced grid electrodes each having an aperture defining a plane, wherein the plane of the aperture of one electrode is disposed at an angle with respect to the plane of the aperture of the other electrode.

Claim 8

The electron gun structure according to claim 1 wherein said grid electrodes comprises a first electrode positioned near said cathode, a third electrode positioned along said electron gun axis downstream from said first electrode, a second electrode positioned between said first and third electrode, a fourth electrode positioned along said electron gun axis downstream from said third electrode, a sixth electrode positioned along said electron gun axis downstream from said fourth electrode, and a fifth positioned between said fourth and sixth electrode.

Claim 9

The electron gun structure according to claim 7 wherein said second electrode and said third electrode form a first asymmetric lens, and said fifth electrode and said sixth electrode form a second asymmetric lens.

Claim 10

An electron gun system comprising: a cathode means comprising first, second and third cathode for emitting first, second and third initially-parallel electron beams, respectively, having a general common direction; wherein said first electrode is positioned on a first gun axis, said third electrode is positioned on a third gun axis and second electrode is positioned on a center gun axis; a plurality of grid electrodes, each comprising a plate-like grid having three apertures therethrough in a line incluing two side apertures and a center aperture; and a voltage means for supplying voltages to said grid electrodes; wherein said center aperture of each of said grid electrodes is aligned with said center gun axis for forming a plurality of symmetric lenses for focusing said second beam, said one side aperture of each of said grid electrodes is disposed along said first gun axis for forming at least two asymmetric lenses for deflecting and focusing said first electron beam; and said other side aperture of each of said grid electrodes is disposed along said second gun axis for forming at least two asymmetric lenses for deflecting and focusing said third electron beam.

Claim 11

An electron gun system comprising: a cathode means comprising first, second and third cathode for emitting first, second and third initially-parallel electron beams, respectively, having a general common direction; wherein said first electrode is positioned on a first gun axis, said third electrode is positioned on a third gun axis and second electrode is positioned on a center gun axis; a plurality of grid electrodes, each comprising a plate-like grid having three apertures therethrough in a line incluing two side apertures and a center aperture; and a voltage means for supplying voltages to said grid electrodes; wherein said center aperture of each of said grid electrodes is aligned with said center gun axis for forming a plurality of symmetric lenses for focusing said second beam, said one side aperture of each of said grid electrodes is disposed along said first gun axis for forming at least two asymmetric lenses for deflecting and focusing said first electron beam; and said other side aperture of each of said grid electrodes is disposed along said second gun axis for forming at least two asymmetric lenses for deflecting and focusing said third electron beam.