[en] Internal G waves excited in a chain of coupled cavities, the drift tube of which is filled with a uniform magnetized plasma, have a high bandwidth coupling impedance of up to 50%. In this connection it is of great interest to study the interaction between electron beams and these systems in order to produce efficient microwave devices based on the beam-plasma interaction. As shown by Mitin et al., in periodic plasma-cavity systems for oscillations of the cavity cells of a single radical type a whole family of internal waves is excited, which can be divided into two classes according to the criterion of emissivity into the external microwave feeders: plasmalike and electromagnetic. The energy fluxes of the former are completely concentrated in the drift tube of the system, and it is therefore physically completely acceptable to assume that they are space-charge fields, while the electromagnetic component of the total field can be regarded as the active wave of the system. We have solved the problem using the macroparticle technique, where the working equations are the equations of plasma-filled backward wave tube