Design and modeling of multistage depressed collectors using 3D conformal finite-difference time-domain particle-in-cell simulations

Summary form only given. The feasibility of designing and modeling a multistage depressed collector (MDC) using 3D conformal finite-difference time-domain (CFDTD) particle-in-cell (PIC) simulations as implemented in VORPAL has been studied. A simple circuit model employing feedback mechanisms has been implemented to provide stable time-dependent voltages for each stage of the depressed collector and an arbitrary space-time dependent spent beam distribution can be given in our time-domain simulations. We demonstrate the design of a five-stage depressed collector recovering a triangular-like spent beam distribution imported from a large signal simulation achieving an energy recovery efficiency of 75%. Most importantly, the MDC after optimization can be integrated in an S-band traveling wave tube and fitted into the limited space in the compact microwave power modules (MPMs).