Numerical analyses of space charge and surface field of a point cathode electron gun

The space charge effects of a point cathode thermionic emission gun have been studied with a numerical method. The method is based on the integral form of Poisson's equation. The space charge distribution was approximated with many coaxial charged-rings and their charges were estimated by using a large number of electron trajectories traced with random emitting conditions considering the energy and angular distributions. Iterative procedure provided the self-consistent result giving the emission current near the measured value. Using the method, the space charge distribution and the surface field were analyzed for different cathode temperatures and bias conditions. The variations of the space charge distribution and the surface field were shown, and the influence of the space charge on the surface field was discussed. (C) 2008 Elsevier B.V. All rights reserved.