Design and Performance Analyses of High-Efficiency $X$ -Band Relativistic Backward-Wave Oscillator Using an Improved Resonant Reflector Under Low Guiding Magnetic Field

Design and particle-in-cell (PIC) simulation studies of an overmoded and the highly efficient X-band relativistic backward-wave oscillator (RBWO) at the lower external guiding magnetic field are presented. The required magnetic field is reduced by using an overmoded cavity resonant reflector (RR) and slow-wave structure (SWS), while the efficiency of the device is increased by using nonuniform SWS. The eigenmode simulation of improved cavity RR and SWS is done in MAGIC-3D to analyze the field variation around their surface axially. In this paper, both uniform and nonuniform RBWOs using an overmoded rectangular and trapezoidal cavity RR are analyzed for their performance. All four RBWO configurations are driven by the dc cathode voltage of 550 kV and the developed electron beam current of ~6 kA. The performance analyses predict that an RBWO using a trapezoidal cavity RR with nonuniform SWS is capable of generating an RF power of ~1.35 GW centered at ~9.35 GHz under the low guiding magnetic field of 0.57T. The power conversion efficiency is calculated as ~41%.