Abstract: In order to bring a high power vacuum tube to full power in a few seconds, it is necessary to heat the cathode quickly to 1100.degree. C. In large tubes, prior art structures cannot be simply enlarged. A novel cathode structure in which the heater element is anisotropic pyrolytic graphite coated with anisotropic pyrolytic boron nitride for insulation and then sintered to the cathode avoids these problems.

Abstract: A very fine-mesh, non-emissive shadow grid is formed on the smooth emissive surface 16 of a thermionic cathode 12 by deposition from a vapor a continuous layer 22 of non-emissive conductive material. Between the elements 24 of the grid the non-emissive material is removed by bombardment through an apertured mask to restore emissivity between the elevated grid elements 24.

Abstract: A gun for generating a multiple sheet beams 50 of electrons has a flat surfaced cathode 10 with parallel protruding ridges 12 of non-emitting material forming parallel focus electrodes for the sheet beamlets. A control grid of parallel bars 14 is aligned with the ridges 12 to reduce grid interruption. The beamlets may be focussed between support bars 54 of a foil anode 52 for passing the beam into a high-pressure volume such as a gas laser 48. The ridges are formed by inserting non-emissive bent sheets into grooves 58 in the cathode, which are dovetailed to hold them.

Abstract: Disclosed are a method and apparatus for rapidly heating a thermionic vacuum tube cathode, thereby enabling the vacuum tube to be placed in useful operation shortly after the tube is switched on. Rapid heating of the cathode is achieved by passing current through the cathode, thereby directly heating it. Simultaneously, the cathode is also heated by an indirect radiant heater and by electron bombardment by electrons emitted from the heater. When the cathode reaches its operating temperature, the direct heating current and the electron bombardment are stopped and the cathode is maintained at its operating temperature by the indirect heater alone. Cathode warm-up times of less than 1 second may be attained using this invention.

Abstract: A permanent-magnet-focused linear-beam high power millimeter-wave tube is externally adjustable for optimum electron beam optics during initial tube operation. The adjustment is made possible by providing an enlarged cavity within the cathode polepiece within which is housed a confined-flow magnetically-focused electron gun, and a cylindrical insert of magnetic material axially symmetrically disposed about the gun and in spaced relationship to and adjacent the gun insulator envelope. The insert may comprise iron or a radially magnetized permanent magnet, either alone or in combination, and more than one insert of magnetic material may be concentrically employed. In this manner, and by movement of the insert axially within the cavity toward and away from the gun, a finely controllable smooth adjustment of the beam diameter in the beam-microwave interaction region of the tube is effected over a wide range during initial operation.

Abstract: A gun for a linear-beam electron tube has a control grid for modulating the beam current which consists of an array of conductive web elements whose spacing from each other is much larger than their spacing from the concave emissive surface of the cathode. It was found that when this condition is met the grid can be operated at cathode potential while beam current is being drawn without distorting the electric accelerating field enough to ruin the focusing of the beam. Thus, when the grid is used to pulse the beam current on and off, it can have zero bias in the "on" condition, whereby the pulse modulator can be greatly simplified.

Abstract: A gun for a linear-beam electron tube has a control grid for modulating the beam current which consists of an array of conductive web elements whose spacing from each other is much larger than their spacing from the concave emissive surface of the cathode. It was found that when this condition is met the grid can be operated at cathode potential while beam current is being drawn without distorting the electric accelerating field enough to ruin the focusing of the beam. Thus, when the grid is used to pulse the beam current on and off, it can have zero bias in the "on" condition, whereby the pulse modulator can be greatly simplified.

Abstract: The electron gun includes a spherically concave cathode emitter with a pair of axially spaced spherically concave focus and control grids closely spaced overlaying the cathode emitter for controlling the beam current. The grids are supported from a common thermally conductive tubular grid support structure via the intermediary of first and second annular members one of which is a thermally conductive insulator. One or more of the grids are serrated about their peripheries to define a plurality of radially directed fingers bonded to the end of a respective annular grid support member. In an alternative embodiment, the end of the annular grid support member, as bonded to the serrated grid, is castellated to accommodate differences in thermal expansion between the grid and the annular grid support member.

Abstract: A grid-controlled electron source comprises an apertured grid spaced in front of a thermionic cathode. Areas of the cathode directly behind the grid conductors are made non-emissive by a bonded surface layer of non-emissive material such as zirconium. On porous metal cathodes impregnated with active emitting material the metal surface may be sealed with a dense layer of inactive metal under the non-emissive layer to prevent chemical reaction of the latter with the emitting material.Methods of depositing the surface layers in the desired pattern include coating the cathode's entire large-scale surface contour, followed by machining small concave dimples into the surface, thereby removing the non-emissive layer from the dimpled surfaces from which small beamlets of electrons are focused between the grid conductors without grid interception.Another method is to mask the desired non-emissive areas with an apertured mask having solid elements registered with the desired positions of the grid conductors.

Abstract: A method and apparatus for preventing oscillations in high-current electron guns. Spurious oscillations frequently occur as a result of interaction of the electron stream with the fields of resonant modes of the gun structure. The resonant impedances of the modes are lowered by damping with lossy dielectric or resistive materials which are suited to the high temperature and vacuum environment of electron guns. The lossy materials are located in places shielded from high electric fields applied to the gun. Lossy dielectric materials which are D.C. insulators may be used as insulating supports for gun electrodes.