Collective Variable Model for the Analysis of Traveling-Wave Tube

Traveling-wave tube (TWT) is an important kind of high-power microwave/terahertz source. The phys-ical mechanism of the inherent nonlinear beam-wave interaction process in TWT should be accurately investi-gated for fast and accurate design. Conventional treatment involves a large amount of computation and is thus time-consuming. In this article, we propose a novel method to expound the nonlinear beam-wave interaction process in TWT, i.e., a 1-D collective variable for TWT (CV-TWT) model. It utilizes two macroscopic variables, i.e., the bunching factor Iand the collective velocity p. Then, a set of CV equa-tions are derived to describe the motion of macroparticles denoting the electron beam and its statistics. The equation number is eventually reduced from 2N + 1 to 3, which is beneficial for manipulation, and computation time is greatly saved. A 1-D code based on the Runge-Kutta algorithm is developed to solve the equations. For demonstration, the proposed CV-TWT model is applied in a Ka-band helix TWT example. The results predicted by the CV-TWT model are consistent with those obtained from the traditional model. However, the time cost of the CV-TWT model is only one-fiftieth of that taken by the traditional model. Such an important feature plays an important role in facilitating the design process of TWT.