Three dimensional modelling of multistage depressed collectors

Summary form only given. The computer modeling of instantaneous currents within three dimensional multistage depressed collectors (MDC) will be discussed. MAFIA, a three dimensional particle-in-cell (PIC) code available from AET associates, is used for these computations. For several years, the method of modeling MDCs at NASA Lewis Research Center employed two dimensional computer codes. The Detweiler code was used for the large signal analysis of the slow wave circuit that produces the spent beam model and the Hermannsfeldt code was used for the actual collector analysis. While this computational procedure has been successfully applied to the analysis of circularly symmetric collectors, it can only be applied to asymmetric collectors as an approximation. In addition, the Hermannsfeldt code is a steady state solver and cannot utilize any phase space information associated with the spent beam model. The MAFIA code can analyze the time dependency of collector currents, and compute the energy dissipated by the incident beam on the collector electrodes. The computational procedure to be reported will again use the Detweiler code to produce a spent beam model that will be converted to a PIC model for use by MAFIA.