Modeling and Analysis of Metamaterial-Based Backward Wave Oscillator Using PIC Simulation

The paper presents the modeling and analysis of backward wave oscillators (BWOs) using the MAGIC particle-in-cell (PIC) solver, a high-resolution 2D/3D finite-difference time-domain (FDTD) tool with perfectly matched layer (PML) boundary conditions. A BWO developed at the University of California, Irvine (UCI) is used as a reference model for structural and operational comparison. According to referred model, UCI PIC simulations, this setup generated an output power of 88 MW at 2.9 GHz when driven by a 490-kV electron beam. However, the experimental setup reported an output power of 22 MW at 3.0 GHz. The researchers noted that “the discrepancy with the PIC simulations can be attributed to features in the experiment that deviated from the idealized calculations in the PIC simulations”. This observation provides the motivation for the present study. In current work, metamaterial-based backward wave oscillator is designed using MAGIC PIC simulation setup, results are validated against those presented in the reference paper. The output power of the BWO is investigated under different emission conditions. The results indicate that the idealized simulations and experimental outcomes is likely due to particle emission from the cathode in azimuthal and transverse directions. In oscillators current density and beam quality changes with change in emission modes, it significantly affects beam– wave interaction and overall power efficiency of the devices. A comparative analysis for two different configurations of metamaterial-based high-power microwave oscillator is presented. case 1 which is idealized condition, with an emitting annular cathode that generates output power of 145.24 MW, and case 2, which is replica of realistic conditions, i.e. with an emit-only geometry that generates 16.466 MW—reveals that emission configuration significantly impacts both output power and oscillation frequency. The finding shows that even within simulation environments, emission geometry and alignment play a vital role in output power. Therefore, idealized models may overlook key non-ideal physical effects, reinforcing the importance of incorporating realistic emission conditions in high-power microwave source simulations.