GB813840A - Improvements relating to electron discharge devices - Google Patents

Abstract

813,840. Electron guns. GENERAL ELECTRIC CO. Dec. 29, 1955 [Jan. 12, 1955], No. 37268/55. Class 39(1). An electron gun, particularly for a travelling wave tube comprises a hollow cylindrical cathode 2 having a tapered conical end 4 which end is truncated to provide an aperture 5, an electron emissive coating 6 on at least part of the interior surface of the cathode, means such as heater wires 7 for heating the cathode, and an accelerating anode 15 having an aperture 17 aligned with the cathode aperture 5 so as to produce a hollow beam of electrons. As shown the heater wires 7 are embedded in refractory insulating material 9 in a heat conserving shield 8 and an apertured screen 18 is provided between the anode and the cathode to minimize electron emission from the external surface of the cathode, the opening 19 being slightly larger than the opening 5 to minimize heat conduction to the screen 18. The screen is operated at cathode potential. The electron beam is collimated by the field from a magnetic coil 24 which also co-operates with the cathode in producing a hollow beam. For this reason the shield 8 and cathode body are made of tantalum or of other metals which are non-magnetic at operating temperatures.