Common-frequency mode suppressing of overmoded relativistic backward wave oscillator with wide-gap reflector

The mode controlling is a key process for designing an overmoded relativistic backward wave oscillator. Based on the numerical analysis and particle-in-cell simulation, the common-frequency high-order mode competition and output mode controlling of an overmoded RBWO with a wide-gap reflector are studied. It indicates that the high-order mode is mainly originated from the reciprocal mode conversion and excitation in the RF structures, which can be restrained and controlled by optimizing the sensitive parameters, reducing the conversion factor from fundamental mode to high-order one and adjusting the RF phases of different modes that are reflected back to the beam-wave interaction region from the cathode plate. Finally, a beam-wave conversion efficiency of 40% and an output TM01 mode purity of 98% are obtained at frequency of 9.87 GHz from the concerned overmoded RBWO.