【作者】 巩华荣；

【导师】 宫玉彬；

【作者基本信息】 电子科技大学 ， 物理电子学， 2006， 博士

【摘要】 由于微波管中总会存在残余气体，它与电子束发生碰撞并发生电离是不可避免的。在长脉冲或者连续波的工作状态下，电离出的正离子与管子中的静电势阱相互作用会引起离子噪声，通常表现为输出信号相位与幅度的缓慢波动。这种低频的离子噪声特别是相位噪声，会严重影响雷达系统的分辨能力和通讯系统的编码位错率。本文采用理论分析与计算机模拟的方法，深入研究了离子噪声的产生机理、特性及抑制方法，论文的主要内容与创新点如下： 1．研究了微波管内离子的产生、运动、积累与平衡及其对电子束的影响，这对解释离子噪声的形成机理有重要意义。 2．采用一维混合模型，将电子束用包络方程描述，正离子用离散的一维宏粒子代替，采用粒子模拟方法研究了行波管与速调管的离子噪声问题，得到了离子噪声的图像，研究了电子束电流、电压、聚焦磁场以及残余背景气体对离子噪声的影响。 3．研究了离子张驰振荡序列的特性，通过分析其重构相图、功率谱与最大lyapunov指数，得出离子噪声具有混沌性质这一重要结论。并将其原因归结为离子噪声产生系统的开放性。 4．通过小信号近似，采用波动理论与运动学理论，严格地给出了行波管低频离子噪声被调制到载波上的机理。并对离子噪声形成的相位噪声特性进行分析，得到了相位噪声表达式，揭示出影响相位噪声的因素。 5．采用二维粒子模拟软件进一步研究离子噪声，通过对实际微波管的合理简化，建立了一个可计算模型，对离子噪声做了二维分析，得到了离子噪声与真空度、管子长度、聚焦磁场间的关系，并指出了抑制与消除离子噪声的关键所在。 6．通过对管内离子运动状态的深入分析，揭示出离子径向逸出的原理，指出菲尔德离子积累理论的局限性，这对深入理解离子噪声的产生原理有重要意义。 7．采用粒子模拟的方法，并考虑电子束与电磁波的互作用，首次直接得到了速调管输出信号中的离子噪声图像，阐述了束电子、二次电子、离子、更多还原

【Abstract】 Since there is always some background gas in microwave tubes, the collision between electron beam and ambient gas is inevitable, and ions are created in the system. For long pulse times and especially for CW mode, the coupling between ions and electrostatic potential wells in the devices will lead to ion noise, which generally manifests itself as a slow phase fluctuation on the output signal. The low frequency ion noise has negative influence on delectability in radar application and data rates in communication system. In this dissertation, we have made detailed theoretical study and computer simulation on this issue. The major achievements are listed as the following:1. The producing, motion, accumulation and balance of the ion are studied in the microwave tube, this is the fundament to study the ion noise phenomenon2. Characteristics of ion noise in the PPM TWT and the Klystron have been discussed by means of a hybrid model. One-dimensioned Particle-in-Cell method (PIC) simulation code is developed and the relation between ion noise and phase distortion was obtain. The numerical simulation result shows that increasing beam current; the ion noise amplitude will decrease and become stable. There exist optimal value of magnetic focusing field and beam voltage. That can minimize the ion noise amplitude.3. The time series of ion relaxation oscillation are obtained by the presented method. The ion relaxation oscillation is treated as the response of a complex nonlinear dynamical system, and the time series is analyzed by power spectrum; restructure phase diagram and Lyapunov exponent. From the analysis results we find that the ion relaxation oscillation has chaotic character at the first time.4. The ion noise of TWTs is analyzed using small signal by motion theory. The relation between noise to signal ration and signal frequency, voltage motipn amplitude is obtained. From the analysis results we find when the amplitude of voltage motion and signal frequency increase, the noise to signal ration would increase.5. The ion noise in microwave tube is studied using two-dimensional particle-in-cell method. The fluctuation of the ion amount, which is the source of ion noise of the tube, is observed in the simulation process. It is found that the sufficient ions amount in drift tube and beam envelope scalloping appear to be responsible for ion noise after changing the gas pressure, magnetic focusing field, and drift tube length. A great number ions escape radically and their amount is about half of the beam更多还原