GB1046639A - Improvements in dispenser cathode - Google Patents

Abstract

1,046,639. Thermionic cathodes; electron beam tubes. GENERAL ELECTRIC CO. July 30, 1965 [Aug. 17, 1964], No. 32794/65. Heading H1D. A miniature dispenser cathode for producing an intense electron beam comprises an openended capsule 1 filled with a sintered electronemissive material 2 providing an exposed emitting surface 4, and conductive supports 5, 6 secured to spaced points on the capsule for conducting heating current therethrough. The capsule 1 may be of W, Re or a 75% W-25% Re alloy. A powder mix of 63% W, 17% tungsten carbide and 20% Th is lubricated and pressed into the capsule in stages, and sintered by passing a heating current through the capsule or by vacuum firing, after which the open end of the capsule may be ground flat. Specific dimensions and sintering temperatures are given. Alternatively, the emissive material may comprise stable compounds of U, La or rare earth metals The conductive supports 5, 6 of Re, W or Ta are semi-circular to establish a heat-retaining cavity 9 around the capsule, and may be mounted in metal bushes extending through a ceramic plate of an electron gun support. The cathode may be used in an electron beam tube for writing charge patterns, e.g. the lines of a 3-colour diffraction grating on a deformable light-valve medium, i.e, a deformable oil or a thermoplastic tape. The electron beam may be continuously deflected transversely across a moving tape 30 by magnetic deflection coils 31, while input signals are fed to auxiliary electrostatic deflection plates 27 to modulate the velocity of this transverse deflection and so produce a varying charge density and deformation of the tape, Fig. 5 (not shown). The cathode is unharmed by the presence of carbonaceous vapours evolved from the tapes, suitable materials for which are given.