Efficiency of moderately relativistic resonant S-band BWO

The scheme of a resonant relativistic backward wave oscillator (BWO) was proposed by the group of researchers from IHCE SB RASfor efficient generation of high-power microwave radiation in the S-band while maintaining relatively small structure length about 2.5 λ. As far as can being found from publications, the scheme proposed uses high-current relativistic electron beams with energies of 0.7–1.5 MeV and a strong guiding magnetic field (at least 1.5 T, typically 2–3 T). In this paper, we propose a variant of a resonant relativistic backward wave oscillator that operates at moderately relativistic beam energies (450–550 keV) and at guiding magnetic field values starting from 1.3 T. Compared to the original resonant BWO geometry, in the current investigated scheme, the length of the periodic structure is increased by 1 period. For optimization using particle-in-cell code XOOPIC, the length of the insert between the cutoff-neck and the periodic structure, as well as the profiles of two terminal corrugations (defining the reflections from boundaries of periodic structure) are varied. It is shown in the numerical simulation that for a beam energy of 500–550 keV the average radiation power in proposed RBWO reaches level of 1 GW and efficiency is up to 27–28%.