Electron gun with masked cathode and non-intercepting control grid

Claim 1

An electron beam vacuum tube comprising: anode means having an electron beam permeable aperture, electron beam permeable current-density control grid means adjacent said aperture having a predetermined pattern of radially extending grid forming vane elements subject to damage by electron bombardment, concave dispenser cathode electron beam emitting means formed of plural sectoral emitter elements comprising porous sintered refractory metal having a surface facing said electron beam permeable current-density control grid means, and masking element means composed of non-electron-emitting hafnium metal having a pattern of centrally joined radial arm elements embedded at said electron emitting surface, said predetermined pattern and said masking element means pattern being in aligned orientation for preventing electrons from bombarding said grid forming elements, said masking element means embedded at said electron emitting surface extending above said electron emitting surface for cooperating with said electron beam permeable current-density control grid means in directing electrons arising adjacent said masking element means away from said grid forming element, said radial arm elements being welded to said electron beam emitting cathode means at the periphery of said electron beam emitting surface.