Study on Mode Control in an Over-sized Backward Wave Oscillator

Internal field emission breakdown in the electro-dynamic structures of high-power microwave devices can seriously limit the devices' output power and pulse duration. Increasing the diameter of the electro-dynamic structure beyond the cut-off radius can reduce these internal fields to below critical breakdown levels, but may introduce mode competition as unwanted side effects. An over-sized backward wave oscillator with rectangular profile corrugations is designed to produce TM01 high power microwave radiation without mode-competition. The slow wave structure and the reflector are matched to achieve mode selection and enhance interaction efficiency. The physical mechanism for mode selection is explored both in theoretical investigation and particle in cell simulation.