GB1103890A - Improvements in or relating to electron beam-generating systems for electric discharge tubes - Google Patents

Abstract

1,103,890. Discharge apparatus. SIEMENS A.G. 29 June, 1966 [30 June, 1965], No. 29162/66. Heading H1D. In an electron beam generating system, e.g. for a travelling wave tube, comprising a main dispenser cathode having at one end a porous emitter substance carrier disc 2 which forms the closure of a shallow cylindrical dispenser vessel 3, the main dispenser cathode is heated by the impact of electrons on the bottom of vessel 3 in an auxiliary discharge which is coaxial with the main beam and is formed between an auxiliary indirectly heated dispenser cathode 8 and the bottom of vessel 3 and has an associated Wehnelt cylinder control electrode 10, the voltage on which controls the main beam cathode temperature. An anode 5 is disposed coaxially within main beam-forming electrode 1 to accelerate the electrons and has one or more coaxial apertured diaphragms 6, 7 one of which, e.g. 7, may be coated with a getter material to act as a getter pump for residual gases. This diaphragm 7 has a smaller aperture than that of entry diaphragm 6 to ensure that, by electron bombardment, the getter is raised to an operable temperature and diaphragm 7 may gradually decrease in thickness towards the rim. The main dispenser cathode may be supported by a tantalum, foil cylinder 4 secured to cathode body 3, which may be of molybdenum, and the junction of support 4 and body 3 may form a thermoelectric junction. The thermo e.m.f. produced, which is related to the main cathode temperature, may be fed into a temperatureregulating arrangement which controls the voltage on the Wehnelt cylinder to maintain the main cathode emission temperature at a predetermined value. An additional foil cylinder 11 may be provided to increase thermal shielding.