Nonstationary Nonlinear Discrete Model of a Coupled-Cavity Traveling-Wave-Tube Amplifier

A nonstationary nonlinear model for numerical simulation of a coupled-cavity traveling-wave tube is described. The model is based on the nonstationary discrete theory of excitation of a periodic waveguide structure, when it is supposed that the beam-wave interaction takes place only inside the cavity gaps separated by drift spaces. Such an approach allows one to consider properly the dispersion of the slow-wave structure (SWS) and to simulate processes at any point inside the SWS passband, including interaction near cutoff and even beyond the passband. Results of numerical simulations of amplification in small-signal and large-signal regimes are presented. Self-excitation processes near cutoff frequency are studied. In particular, drive-induced self-excitation that takes place only in the presence of a sufficiently strong driving signal is discussed.