Effect of plasma nonlinearity on radiation spectrum in plasma-filled traveling-wave tubes

It is typical for many microwave sources that as the beam current increases the device exhibit successive transitions, first from self-excitation of constant amplitude oscillations to automodulation, and then to chaotic oscillations. Such transition were found in devices based on the absolute instability of electron beams (backward-wave oscillators, gyrotrons). They were also studied in devices based on the convective instability (traveling wave amplifiers) in which an additional feedback providing a self-excitation can be caused either by reflection of a certain amount of radiated power from the exit (internal feedback) or by the external feedback loop. In all these studies the sources of microwave radiation from electron beams propagating in vacuum were analyzed. The aim of this report is investigation of plasma influence on transit to the chaotic oscillations and spectral characteristics of such oscillations in the microwave sources filled with plasma. The fact that the filling of interaction region of slow wave structures with plasma can significantly enhance efficiency, power and bandwidth was predicted theoretically and observed experimentally in many papers. However, the plasma as a medium with a large number of degrees of freedom can also complicate the radiation processes in these tubes and promotes to development of stochastic processes. Our study described below is devoted only to the effect of the magnetosonic waves, excited in the plasma due to the pondermotive force, on the dynamics of plasma-filled traveling-wave tubes