The effect of anode-aperture on a dense beam

The effect of an aperture in the anode of a diode or electron gun can be treated by first- or higher-order calculations of the perturbation of simple diode beams. A first-order calculation of the effect of a slit in the anode of a Langmuir planar diode gives a percentage loss of perveance 11 times the ratio of aperture-width to diode-spacing, the loss being due to trajectory divergence. Trajectory divergence can be prevented by modified Pierce electrodes, but this nearly quadruples the loss of perveance, the loss then being due to lowering of the effective anode potential. The possible bearing of these results on anode-aperture effect in converging beams is discussed.