An intense electron beam source

High emission currents were achieved from a line electron thermionic source. The cathode was heated by electron bombardment from a secondary filament. Cathodes were built from massive strip made of tantalum or tungsten. Current densities were further increased by focusing the secondary electrons on to a narrow strip at the bottom of the cathode. The focus was achieved following a numerical model calculation. The design permitted the emitting surface temperature to be further increased, by keeping the cathode partially molten, in a reliable, continuous mode of operation.