Wave theory of a traveling-wave tube operated near the cutoff

We outline the main principles of the wave theory of interaction between an electron beam and waves in a slow-wave structure near the edge of the transmission band. Formulation of the basic equations and the boundary conditions is considered taking consistently into account that the interaction parameter is small. A comparison of the results with a discrete version of the theory is discussed. We also consider the starting conditions for the oscillation regime, the linear amplification regimes, and some effects found within the framework of the nonstationary nonlinear theory, e. g., parasitic self-excitation in the amplification regime and hard excitation of the oscillation regime. © 2004 Springer Science+Business Media, Inc.