EXCITATION OF ELECTROMAGNETIC-WAVES BY RELATIVISTIC ELECTRON-BEAM IN A PLASMA-FILLED RIPPLED WALL WAVE-GUIDE

An analytical and numerical study is presented herewith to get an insight into the excitation of forward and backward waves caused by an intense relativistic electron beam in a rippled wall plasma filled waveguide with weak modulation. The numerical results of growth rate are derived in the case of weak modulation at k2 = pi/z0 (the pi point). Numerical results also show that no excitation of waves takes place if relativistic factor of the beam gamma < (1 + mu0s2/R0(2)k0(2))1/2. For gamma > (1 - mu0s2/R0(2)k0(2))-1/2, the beam excites both forward and backward waves, and only forward waves if (1 + mu0s2/R0(2)k0(2))1/2 < gamma < (1- mu0s2/R0(2)k0(2))-1/2. The dependence of the frequency of the generated forward waves on beam energy is also studied numerically and the results are compared with those of the experiment [IEEE Trans. Plasma Sci. PS-18, 490 (1990)]. The effect of corrugation depth of rippled wall plasma filled backward wave oscillator (BWO) on minimum frequency generated is also studied.