Numerical modeling of space-charge-limited charged-particle emission on a conformal triangular mesh

Orbit tracing is a numerical technique to design high-current charged particle guns and transport systems. Although most available programs use the finite-difference approach to calculate electric fields, the finite-element method has advantages for accuracy and versatility. This paper describes an effective algorithm to model space-charge-limited emission and a procedure to apply it to variable-resolution conformal triangular meshes with multiple emission regions. Improved tabulations of space-charge solutions for sharply curved emission surfaces are given. In a benchmark Pierce diode simulation, the procedure gives an absolute current prediction within 0.2% of the analytic value and particle orbits within 0.1 degrees of the predicted exit angle. (C) 1996 Academic Press, Inc.