Hybrid Bulk-Surface Modes Excited in the THz Cherenkov Oscillator with the Double Grating

The operation of the THz Cherenkov vacuum electron devices with nonuniform double gratings supporting the hybrid bulk-surface modes has been considered for an increase of a thickness of a sheet electron beam and its coupling with RF field. It is shown that advantages of a double grating configuration may comprise the increase of up to 3 times of a coupling impedance as well as a widening of the operation frequency range in comparison with the single grating configuration.