PARAMETRIC-EXCITATION OF ELECTROMAGNETIC-RADIATION BY AN ELECTRON-BEAM IN A STRATIFIED PLASMA WAVE-GUIDE

The excitation of electromagnetic radiation by an electron beam in pla sma waveguides in which the plasma density varies periodically along t he device is examined. In the scheme in question, a plasma wave synchr onized with a beam is parametrically coupled with a fast electromagnet ic wave due to periodic variations in the plasma density. This fast wa ve propagates in a vacuum gap between the plasma boundary and the cond ucting shell. It is shown that, in such a system, parametric conversio n of the plasma wave into electromagnetic radiation increases the tota l efficiency of the beam-power conversion. An important point is that the mechanism for transformation of slow plasma waves makes it possibl e to not only solve the problem of extracting microwave power from the plasma but also substantially increase the total efficiency of the be am-power conversion.