Detailed measurements showing the influence of the forward propagating wave and end reflections on the performance of relativistic backward wave oscillators

Summary form only given, as follows. The primary energy exchange in a relativistic backward wave oscillator (BWO) occurs between the electron beam and the backward travelling wave within the slow wave structure (SWS). In most high power BWOs the backward travelling wave is reflected by a cutoff neck at the entrance of the SWS and radiation is extracted in the direction of the electron beam. Recently, researchers have investigated the effect of the forward travelling wave on the energy exchange between the electron bunches and the backward wave and the effect of multiple end reflections and cavity effects on the efficiency of microwave generation. This poster paper presents detailed measurements of the interaction of the electron beam with the forward travelling wave, and the effect of end reflections on the radiation frequency and efficiency. Numerical simulation results are found to be in agreement with the experimental measurements. A Sinus 6 relativistic electron beam accelerator is used for a detailed mapping of BWO performance as a function of input parameters. For uniform amplitude SWSs of various lengths the BWO output power, rf frequency and conversion efficiency were measured as a function of beam current and cathode voltage In addition, BWO performance was characterized as a function of phase of reflections at both ends of the SWS.