Secondary electron emission from barium dispenser cathodes

Abstract

Measurements of the total secondary electron emission coefficient under electron bombardment δ have been made at room temperature on "L" cathodes and porous tungsten cathodes impregnated with barium calcium aluminates. For "L" cathodes δ decreases with increasing porosity due to the increased surface roughness but δ is always above that for clean tungsten, due to the activation of the surface by adsorbed layers. For the impregnated cathode, δ increases with increasing porosity due to the larger contribution from the impregnant in the pore ends which has a larger value of δ than the surrounding activated tungsten. δ for the impregnated cathode is above that for the "L" cathode and comparable with that for bulk barium oxide. Decay of δ under electron bombardment is observed in the case of the impregnated cathode but the initial value can always be recovered by heating.