Determination of current limits in bunched annular electron beams using Green's function techniques

Abstract

Summary form only given, as follows. Three-dimensional Green's functions, which solve Maxwell's equations, can be utilized for modeling space charge effects of bunched annular electron beams in high-power microwave (HPM) sources, such as relativistic klystron amplifiers (RKA), relativistic klystron oscillators (RKO), and backward wave oscillators (BWO). We model bunched annular beams as periodic annuli of charge with negligibly small longitudinal thickness in a perfectly conducting drift tube, and use Green's functions to solve for the space-charge interactions of the beams with appropriate boundary conditions. We present both theoretical and computational analysis of the beam equilibrium based on the three-dimensional Green's function technique. In particular, we show the existence of an annular beam confinement limit, and demonstrate that the limit agrees with the observed current limit for pulse shortening in the 1.3 GHz; RKA experiment at the Los Alamos National Laboratory. We also present beam simulation results of the LANL RKA experiment using PFB3D, a newly developed Green's function code.