考虑空间电荷效应的色散慢波结构行波管的异常简并
Exceptional Degeneracies in Traveling Wave Tubes with Dispersive Slow-Wave Structure Including Space-Charge Effect
摘要：
在这种交互系统支持的简并例外点（EPD）竞赛中，研究了直线电子注与导波电磁波的相互作用。研究的重点是一个线性束行波管（TWT）的情况下，一个现实的螺旋波导慢波结构（SWS）。的相互作用是由一个分析模型，这是一个概括的皮尔斯模型，假设一个一维的电子流沿色散单模引导SWS，并考虑到系统中的空间电荷效应。通过计算增益与频率的关系并与更复杂的电子束模拟器进行比较，验证了使用全波模拟获得的相速度和特性阻抗的增强模型。这种比较也显示了我们的新模型与非色散皮尔斯模型相比的准确性。EPDs，然后调查使用增广模型，观察合并的复值波数和系统的特征向量。复杂弥散图中TWT系统开始/停止表现出对流不稳定性的点，即，模式开始/停止沿TWT指数增长，即EPD。我们还证明了EPD的存在性表明，Puiphix分数幂级数展开以及近似的色散图在EPD的分歧。后一个概念也解释了当在EPD附近操作时，行波管系统对束流电子速度变化的“异常”敏感性。
英文摘要：
The interaction between a linear electron beam and a guided electromagnetic wave is studied in the contest of exceptional points of degeneracy (EPD) supported by such an interactive system. The study focuses on the case of a linear beam traveling wave tube (TWT) with a realistic helix waveguide slow-wave structure (SWS). The interaction is formulated by an analytical model that is a generalization of the Pierce model, assuming a one-dimensional electron flow along a dispersive single-mode guiding SWS and taking into account space-charge effects in the system. The augmented model using phase velocity and characteristic impedance obtained via full-wave simulations is validated by calculating gain versus frequency and comparing it with that from more complex electron beam simulators. This comparison also shows the accuracy of our new model compared with respect to the non-dispersive Pierce model. EPDs are then investigated using the augmented model, observing the coalescence of complex-valued wavenumbers and the system's eigenvectors. The point in the complex dispersion diagram at which the TWT-system starts/ceases to exhibit a convection instability, i.e., a mode starts/ceases to grow exponentially along the TWT, is the EPD. We also demonstrate the EPD existence by showing that the Puiseux fractional power series expansion well approximates the bifurcation of the dispersion diagram at the EPD. This latter concept also explains the "exceptional" sensitivity of the TWT-system to changes in the beam's electron velocity when operating near an EPD.
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