Electron optic modeling starting trajectories from a planar cathode

The paper describes a method for defining the initial electron beam conditions for a planar cathode which is subject to space charge limited emission in an axially symmetric field. The method, a refinement of J. E. Boers\´ technique for describing cathode conditions, has improved the correlation with empirical results. Features described are: a) noniterative computation of the space charge density factor; b) current density limit based upon empirical data from production cathodes; c) Monte Carlo assignment of thermal speed; and d) correction for "captured" trajectories at the beam periphery.