The electron optics of high-current-density electrostatic electron guns

It is shown that for some types of electron gun of perveance about 2×10¿6amp/volt3/2 the cathode current density can be closely determined with the aid of trajectories found in the absence of space charge. Subsequent recomputation of the trajectories allowing for space-charge forces has little effect on the emission current density previously determined. Calculations have been made on two electron guns with the aid of electrolytic-tank measurements and an automatic electron-trajectory tracer. Satisfactory agreement with experimental results is obtained.