Backward-Wave Oscillator Operating in Low Magnetic Fields Using a Hybrid-TE11 Mode

We present the design of a backward-wave oscillator based on a novel slow-wave structure (SWS) operating under low magnetic field conditions (<;0.2 T). The design features a high-power electron beam interacting in dual synchronism with TM01 and hybrid TE11 modes. By exploiting mode control techniques, low magnetic fields with asymmetrical beam trajectories, a dominant interaction with the higher frequency hybrid TE11 mode is established. We present a design of the full interaction circuit, which also features a compact mode converter and an output coupler to produce a TE01 mode at the dual rectangular waveguide output. Simulations with a high-frequency structural simulator demonstrate dual-mode backward wave synchronism. A quantitative analysis of the electric field profiles is also presented. We also use a particle-in-cell (PIC) solver to predict the SWS performance under hot-test facility specific conditions. Using a 490-kV, 84-A electron beam under a guiding magnetic field of 0.15 T, PIC simulations predict an output power of 18 MW at 5 GHz with a peak power efficiency of 44%.