Theory and experiment of a capillary-type emitter
The theory for a capillary emitter structure in which cesium vapor is caused to diffuse through an ordered, uniform matrix is presented For the dimensions being considered it is shown that surface diffusion is negligible Although no detailed theory is formulated to explain the mechanism by which ions and electrons are extracted from the capillary cavities, a qualitative model, which assumes the electrons, ions, and neutrals in thermal equilibrium within the cavity form a plasma, appears to agree with the experimental data Two experimental devices are described; a monocapillary and a multicapillary Experimental electron currents from the multicapillary devices are shown to be in good agreement with the random current predicted from a thermal plasma However, ion currents measured at low collector temperature are somewhat higher than predicted by the random current theory From the results discussed, it is concluded that the emission of ions and electrons from the capillary structure studied does not appear to depend upon the continuous circulation of cesium