Computer simulation of a 360° field-of-view ‘‘top-hat’’ electrostatic analyzer

Via computer simulation, we have studied the characteristics of the ‘‘top-hat’’ electrostatic analyzer, which has in principle a 360° field of view in the acceptance plane. Explicit details are given on how the simulation calculations were done. A finite-difference method employing a polar mesh was used for the computation of the electrostatic field inside the analyzer. A three-dimensional ray-tracing technique was used for computation of the particle trajectories. The analyzer was found to have the following properties: (1) the exit angular response is extremely sharp (±1°) and can be made sharper by truncating the turn angle of the analyzer to an angle ≂90°θ0/2, where θ0 is the half-angle subtended by the top-hot; (2) there is no energy-angle skewing for particle beams parallel to the acceptance plane; (3) transmission can be maximized for normal incidence with respect to the analyzer axis; (4) the exit velocity distribution is peaked fairly sharply in one direction and can be made sharper by imposing an entrance mask; (5) the analyzer has a large geometric factor.