Subgigawatt Relativistic Resonant S-Band Backward Wave Oscillator

Abstract

The resonant relativistic backward wave oscillator (RBWO) was initially developed for efficient generation of high-power microwaves in the S-band (frequency of 3.6 GHz) while maintaining a relatively short structure length (about 2.5λ). The high-current electron beam with the energy of 0.7–1.5 MeV and the strong guiding magnetic field (2–3 T as a rule) were crucial parameters for such BWO. In the present paper, we propose a new layout of RBWO operating at moderately relativistic beam energy (450–550 keV) and at guiding magnetic field values starting from 1.3 T. Compared to the previously published RBWO design, the length of the periodic structure in the proposed configuration is increased by one period. To obtain high efficiency, the length of the insert between the cutoff neck and the periodic structure and the profiles of two terminal corrugations (defining reflections from the boundaries of the periodic structure) were optimized using particle-in-cell code XOOPIC. For the RBWO proposed, the numerical simulations show the average output power of 1 GW and 27–28% efficiency for the beam energies of 500–550 keV.