MICROWAVE GENERATION BY EXCITATION OF A PLASMA-FILLED SLOW-WAVE STRUCTURE

An axial relativistic electron beam passing through a slow wave struct ure is unstable to an electromagnetic perturbation whose phase velocit y equals the velocity of the beam. This phenomenon of Cherenkov emissi on is the basis of all traveling wave tubes. In this paper, through th e use of self-consistent linear field theory, the electron three-dimen sional perturbation affected by the perturbed electromagnetic fields i s discussed. Cherenkov radiations excited by a thin annular relativist ic electron beam and a solid relativistic electron beam in a plasma-fi lled slow-wave structure are analysed in detail. The dispersion equati ons 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 electr on beam. Finally, the growth rates of the wave are obtained, and the e ffects of the background plasma density and the electron beam radius o n the growth rate of the wave are calculated and discussed.