PIC-FDTD code for beam-wave interaction analysis in rippled wall slow wave structure

Abstract

Summary form only given. A plasma-assisted high power microwave (HPM) source `PASOTRON' is being developed at CSIR-CEERI, where a rippled wall waveguide is used as slow wave structure (SWS) 1 . In this device, very strong non-linear interaction between electron beam and electromagnetic wave can occur, making analytical design very cumbersome. So, a particle simulation code is highly required to make its design simpler. In this work an effort has been made and a particle-in-cell finite-difference-time-domain (PIC-FDTD) code is developed. In designing the field solver for this code, the FDTD algorithm2 is taken up as the method of choice as it allows having frequency domain analysis by applying a fast Fourier transform. The time component in the FDTD code allows the particle wave interaction to be solved self-consistently wherein the Yee's grid2 scheme for the field arrangement ensures that the divergence free nature of the electromagnetic waves is maintained even after the curl equations are discretized. The charge densities due to the particles are interpolated to the grids using the PIC method3. The particle push is implemented using the Boris push method which takes care of the translational motion due to the electric field as well as the rotational motion due to the magnetic field. The current due to particle movement is calculated on the grid using a charge conservation scheme. The phase space patterns produced by the code are then compared with the published results and with the MAGIC simulation software. The axial phase space plots are found to be similar to those which are published elsewhere4 and also to those which are obtained using MAGIC software tool. The results of these efforts will be presented.