Mode control in an oversized backward wave oscillator

Internal field emission breakdown in the electrodynamic structures of high-power microwave devices can seriously limit the devices’ output power and pulse duration. Increasing the diameter of the electrodynamic structure beyond the cutoff radius can reduce these internal fields to levels, which are below critical breakdown levels, but may introduce mode competition as unwanted side effects. An oversized 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.