Design of quick start, high current density electron guns

This paper presents two designs for dispenser cathodes in electron guns which attain operating temperature and emission within one and three seconds after the initial application of heater power. Fast warm-up times are achieved by the use of low thermal mass components. The cathode is a very thin concave button made of tungsten matrix material. After brazing and impregnation the result is a practical, low thermal mass cathode for use in production guns. The three second design uses a filament heater cataphoretically coated with alumina. The filament is surged by as much as twice the normal operating voltage to achieve the required warm-up time. However, to achieve emission in one second another method must be used. The cathode button is heated by electron bombardment. In this arrangement a potential difference of several hundred volts is applied between the cathode and a thoriated tungsten heater, which is itself a thermionic emitter.