中文摘要：

螺旋线行波管中返波振荡是影响行波管设计的重要问题，行波管中当高频信号滞后于高压信号或者高频信号脉宽小于高压信号时，也就是在高电压信号的上升和下降沿，这时没有高频信号但返波振荡也有可能被激起，这在以往是被忽略的，本文从瓦因斯坦的波导激励理论出发，导出了在布里渊条件下此种特殊情况的非线性返波振荡工作方程；分析了周期永磁场的磁场周期和磁场强度抑制返波振荡的效果，同时考虑了损耗因子、空间电荷场、不同磁场位形对抑制返波振荡效果的影响，从理论上说明了该方法的有效性，为行波管的设计和优化提供了依据。

英文摘要：

The backward-wave oscillation in helix traveling wave tube （HTWT）under permanent periodic magnetic （PPM） focusing was theoretically studied to suppress its spontaneous oscillation. A novel nonlinear equation, describing the backward-wave oscillation under the special condition of Brillion electron flow,was derived on the basis of the waveguide excitation theory. The impacts of various factors, including the field strength and period of the permanent periodic magnetic field, loss factor, space-charge induced electric field, and magnetic field distribution on the suppression of the backwarwave oscillation were evaluated. We suggest that an optimization of the PPM focusing may significantly suppress backwardwave oscillation and improve the efficiency and gain of an HTWT even with no change in its stmeture.