Some Notes on the Design of Electron Guns

A method is outlined for the design of electron guns based on the simple theory first published by J. R. Pierce. This method assumes that the electrons are moving in a beam according to a known solution of the space-charge equation, and requires that electrodes exterior to the region of space charge be shaped so as to match the boundary conditions at the edge of the beam. An electrolytic tank method is used to obtain solutions for cases which are not amenable to direct calculation. Attention is given to some of the complications ignored by the simple theory and to some of the practical difficulties which are encountered in constructing guns according to these principles. An experimental check on the theory is described, together with some information as to the actual current distribution in a beam produced by a gun based on this design procedure.