GB1146546A - Improvements in or relating to electrostatically focussed travelling wave tubes - Google Patents

Abstract

1,146,546. Velocity-modulated tubes. SIEMENS A.G. 14 July, 1966 [15 July, 1965], No. 31574/66. Heading H1D. In an E-type travelling wave tube, in which a strip-shaped electron beam is projected on to a helical path along a delay line in the electrostatic field provided by a cylindrical capacitor, the electron gun includes an apertured accelerating anode 5; a cathode 1 having an emitting surface positioned perpendicular to the anode and to one side of the aperture; a deflecting electrode 7 positioned parallel to the cathode surface but on the opposite side of the beam path; and a set of beam-forming electrodes, a first one of which, 9, is positioned between the cathode surface and the anode, and a second of which, 10, is positioned between the cathode surface and the deflecting electrode 7. The strip beam is formed by a slot aperture 3 in the modulating electrode 2, the additional electrode 11 permitting fine adjustment of the beam path, and variation of the potential of the deflecting electrode 7 permitting adjustment of the exit angle of the beam from the gun. In modified arrangements, the angled electrode portions 6 and 8 may be replaced by separate electrodes, and the cathode may have a concave emissive surface. Disturbance of the beam by the transitional electric field between the gun and the drift space field produced by the cylindrical capacitor, of which one electrode (16, Fig. 2, not shown) is in the form of a slow wave structure, is reduced by the provision of a parallel plate capacitor (14) through which the beam passes after its emergence from the gun. The relative potentials applied to the various electrodes are given.