Microwave generation by excitation of a plasma-filled slow wave structure

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Abstract
An axial relativistic electron beam passing through a slow wave structure is unstable to an electromagnetic perturbation whose phase velocity equals the velocity of the beam. This phenomenon of Cherenkov emission is the basis of all traveling wave tubes. In this paper, through the use of self-consistent linear field theory, the electron three-dimensional perturbation affected by the perturbed electromagnetic fields is discussed. Cherenkov radiations excited by a thin annular relativistic electron beam and a solid relativistic electron beam in a plasma-filled slow-wave structure are analysed in detail. The dispersion equations of the beam-wave interaction are derived. It is clearly shown that the beam-wave interaction results from the coupling of the TM mode in the plasma-filled slow-wave structure to the beam mode via the electron beam. Finally, the growth rates of the wave are obtained, and the effects of the background plasma density and the electron beam radius on the growth rate of the wave are calculated and discussed.