Pressed-oxide nickel-matrix cathode below apertured electrodes

Carbonyl-nickel powder pressed and sintered with alkaline-earth triple carbonates serves as an experimental emitter. The general behaviour of this dispenser-type cathode under the severe field and ion-focusing conditions below closely spaced and apertured electrodes is investigated. Locally confined ionization processes in the alkaline vapour components will develop. The ion-focusing ability of the aperture, particularly if the surface-protecting space charge is removed, enhances evaporation. A spontaneous rise in cathode temperature accompanies this effect, leading to more vapour generation. Deep pit formations will invalidate the advantage believed to exist in a well-determinable surface profile. Negative grid control produces similar ionization effects because of the large centre field below the aperture. The self-sustaining discharge, starting just beyond the saturation bend, will last as long as sufficient alkaline metal is available on the surface. Three discharge peaks were measured with gradually increased anode voltage, indicating the replenishing ability from within the matrix. A faster recovery from the discharge state at higher temperatures is explained by a higher deionization rate, owing to a more intense vaporization of nickel. Under the severe aperturing conditions the cathode is inferior to oxide-coated cathodes and also to dispenser-type cathodes with built-in chemical reaction and vapour controls.