Cold test of homogeneous and inhomogeneous slow wave structures for high power backward wave oscillators

We present the fabrication, testing and validation of novel slow wave concepts for slow wave structures used in designing high power backward wave oscillators(BWO). A key aspect of the design is the reversal of the mode dominance to ensure mode purity. Cold test results of the designed homogeneous slow wave structure showed excellent agreement with simulated dispersion curves and validated mode dominance reversal. Hot test simulations using a commercial Particle-in-Cell code also demonstrate an output power of 8.25 MW at 2.62 GHz corresponding to a beam-to-mode conversion efficiency of 70% when using a 3-section inhomogeneous SWS. By contrast, nominal efficiencies of homogeneous conventional SWSs are 20-30%.