Advanced Electromagnetic Analysis for Electron Source Geometries

One of the challenging issues for analytically modeling electron sources, such as rf photoinjectors, is calculating time-dependent electromagnetic fields generated by the electron beam within a complicated conductor boundary. This problem can be handled self-consistently using a time-dependent Green’s function method. We demonstrate this approach for a simplified electron source geometry, namely a semi-infinite circular pipe with a cathode. Following similar Lorentz gauge approaches that were used for computing electromagnetic potentials in low frequency (< 1 GHz) photoinjectors [1,2], we present a compact Green’s function solution for this simplified geometry. As an application, we show the electromagnetic potentials for a disk bunch of charge emanating from the cathode wall with acceleration parameters corresponding to the BNL 2.856 GHz 1.6 cell photocathode gun. [3]