We investigate the interaction of electromagnetic waves and electron beams in a 4 m long traveling wave tube (TWT). The device is specifically designed to simulate beam-plasma experiments without appreciable noise. This TWT presents an upgraded slow wave structure (SWS) that results in more precise measurements and makes new experiments possible. We introduce a theoretical model describing wave propagation through the SWS and validated by the experimental dispersion relation, impedance, and phase and group velocities. We analyze nonlinear effects arising from the beam–wave interaction, such as the modulation of the electron beam and the wave growth and saturation process. When the beam current is low, the wave growth coefficient and saturation amplitude follow the linear theory predictions. However, for high values of current, nonlinear space charge effects become important and these parameters deviate from the linear predictions, tending to a constant value. After saturation, we also observe trapping of the beam electrons, which alters the wave amplitude along the TWT.

中文翻译：

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具有升级螺旋的长行波管中的波粒相互作用

我们研究了 4 m 长行波管 (TWT) 中电磁波和电子束的相互作用。该设备专为模拟光束等离子体实验而设计，没有明显的噪音。该 TWT 提出了升级的慢波结构 (SWS)，可实现更精确的测量并使新的实验成为可能。我们引入了一个理论模型，描述了通过 SWS 的波传播，并通过实验色散关系、阻抗以及相位和群速度进行了验证。我们分析了由束波相互作用引起的非线性效应，例如电子束的调制以及波的增长和饱和过程。当束流较低时，波增长系数和饱和幅度遵循线性理论预测。然而，对于高电流值，非线性空间电荷效应变得重要，这些参数偏离线性预测，趋于恒定值。饱和后，我们还观察到束电子的俘获，这改变了沿 TWT 的波幅。