Control of the Reflections at the Terminations of a Slow Wave Structure in the Nonstationary Discrete Theory of Excitation of a Periodic Waveguide

The nonstationary simulation of traveling-wave tubes (TWTs) is an important issue in vacuum electronics as it enables the study of a wide range of spurious phenomena. Software based on general time-domain models generally needs huge computational resources and is often useless for design activities. Various nonstationary reduced models of interaction in a TWT have been developed as an alternative to general ones. Among them, the discrete model of excitation of a periodic waveguide appears to be convenient. However, one of the main obstacles to an accurate representation of the slow-wave structure in this model is that reflections at its terminations are hard to control. In this paper, we present a simple method that overcomes this problem, and we apply it to a coupler of a helix TWT.