Effects of azimuthal and radial angular spread on e-beam focusing characteristics in the presence of space-charge forces

摘要

Abstract: A theoretical and numerical investigation of the effects of azimuthal and radial angular spread on an electron beam focused by a magnetic lens in the presence of space-charge forces is presented. The particles are inserted with an initial Gaussian distribution in the transverse space and in the momentum coordinates or with a uniform initial current distribution. The particle trajectory equation is derived for parameters of any stationary applied fields configuration with cylindrical symmetry, permitting the non-vanishing initial canonical angular momentum. In the absence of an initial momentum spread particles launched above a critical radial distance from the axis exhibit a `phase-space tearing' effect in the electron distribution. The inclusion of initial angular momentum spread in the model allows for skewed trajectories with strong centrifugal force which prevents the appearance and overshadows the effect of strong space charge forces near the axis which are responsible for the phase space tearing effect.!7