【作者】 鄢然；

【导师】 罗勇；

【作者基本信息】 电子科技大学 ， 物理电子学， 2010， 博士

【摘要】 回旋管是一种重要的新型毫米波器件,具有高平均功率、高脉冲功率等特点,它在毫米波雷达、通信及电子对抗、受控核聚变、等离子体加热、工业加工等方面有着十分重大的应用前景。回旋管两大主要组成部分为电子枪和高频互作用结构。在本文中,对这两大主要部分进行了深入的理论研究、数值计算与实验工作。对电子枪的研究着眼于磁控注入电子枪,其提供的回旋电子注质量是回旋管获得高性能的关键。因此具有重要的研究价值,在国际上受到高度重视和深入研究。衡量电子注质量的一个重要指标在于其速度离散量的大小,速度离散量愈大,注-波互作用效率越低。所以有效降低电子注的速度离散,是回旋管磁控注入电子枪设计的一个核心问题。导致电子枪速度离散的原因很多,在这方面各个研制回旋管的团队做了大量的理论研究,数值模拟与实验工作。近来年在电子枪区一个新的不稳定性机理在实验中被发现,这是导致回旋管电子注质量降低的一个主要因素：电子枪区的低频振荡现象(low frequency oscillation)。在美国能源部(DOE)的资助下,本人在美国Maryland大学对回旋管磁控注入电子枪中的低频振荡机理进行了深入细致的理论分析与实验模拟工作,为低频振荡的抑制提供了一套行之有效的方法,并在实验中得到了验证。主要研究工作如下：1.建立了磁控注入电子枪中电子在外加静态场中的运动模型。引入势阱概念,导入电子枪区电子的初始速度离散,在静态场中对不同初始速度的电子运动进行了分类分析,把阴极发射出来的电子分为两类：一类为传输电子,一类为束缚电子。传输电子不发生返转,直接进入高频结构；束缚电子由于绝热压缩区磁镜作用发生返转,被束缚在电子枪区,这类电子的出现导致了低频振荡的产生。2.在静态分析的基础之上,利用空间电荷波概念,在欧拉坐标系中建立了小信号自洽理论。导出了低频振荡小信号色散方程,结合边界条件,给出了低频振荡的复振荡频率的确定方法。对低频振荡传输不稳定性(convective instability)与绝对不稳定性(absolute instability)进行了研究。3.在小信号分析基础上建立了一维自洽的PIC模拟程序,此程序能对磁控注入电子枪中的低频振荡现象进行快速准确的模拟,所得结论与MIT的实验结论相吻合。借助此程序对低频振荡的物理机理进行深入的研究与分析。对如何抑制低频振荡的产生提供正确的思路和有效的方法,并得到了俄罗斯应用物理研究所,所做低频振荡实验的印证。对于高频系统的研究,本文着眼于现在具有很好发展潜力的回旋行波放大器,并结合本课题组在“十·五”开展的宽频带高功率Ka波段回旋行波管研制工作。将小信号理论分析,非线性数值计算与计算机模拟相结合,研究了Ka波段基波回旋行波放大高频系统各项关键技术,给出了详细的理论分析和主要的数值模拟结果。为高频系统的设计提供技术支撑,并与高频系统结合,研究了输出输入系统,最后给出了的实验结论。对回旋行波管的主要研究工作如下：1.推导了自洽小信号理论,分析了回旋行波管自激振荡问题,综合分析小信号理论得出的相应结论,结合制管实际给出了Ka波段介质加载行波管的优化参数选取范围。2.编制了自洽非线性程序,对回旋行波管的饱和机理进行研究,与小信号结论结合给出了在考虑速度离散,介质加载条件下,回旋行波管稳定工作情况下的优化设计参数。3.通过场匹配方法,优化设计了输入耦合器,利用模拟软件分析了耦合器中的模式纯度。比较了耦合器各个结构参数对模式纯度的影响,最终设计出了高模式纯度宽频带输入耦合器。4.对回旋行波管输出渐变段与输出窗进行了理论分析,设计出了与高频结构和收集极匹配很好的输出渐变段。设计出了反射系数只有1%,且吸收功率很低的输出窗。5.以上理论分析与数值模拟为本各题组回旋行波管研究工作提供了理论支撑和优化设计的工具,使本课题组成功研制出了输出峰值功率为160kW、增益为38dB和3dB带宽1.5GHz的Ka波段回旋行波管。更多还原

【Abstract】 Gyrotron are important sources for millimeter and sub-millimeter wave with the characteristics of high peak and average power, high efficiency and suitability bandwidth and so on. It can be used as the next generation source for the millimeter wave radar system and weapons system, millimeter wave communication, Plasma heating. There are two main parts in the Gyrotron:the Electronic gun and the High frequency structure. This thesis focuses on these two parts.As for electronic gun, this thesis focuses on the MIG (Magnetic injection gun); the quality of gyro-beam it produced has great influence on the performance of Gyrotron. The velocity spread is one of the most important factors of the beam quality. Many groups have focus on this aspect, recently a new mechanism, which cause velocity spread has been observe in experiments:The Low Frequency Oscillation.Supported by the Office of Fusion Energy of the US Department of Energy, this thesis has analyzed the low frequency oscillation deeply and proposed the methods to suppress the low frequency oscillation, which are confirmed by the experiments. The main works as follows:1. A static model is built to describe the electron moving in the external electromagnetic fields. In the static model, a potential well is introduced and the electrons emission from cathode is catalog into two groups, one group is transited electron another one is trapped electron.2. An analytical model is considered which allows one to apply the space-charge wave theory to the analysis of such oscillations. In the framework of the small signal theory, the regions of low frequency oscillations, the oscillation frequency and the temporal and spatial growth rates of low frequency oscillations are determined in the parameter space. These results are consistent with some experimental dates. They also allow recommending some means for suppressing low frequency oscillations.3. A version of a one-dimensional numerical simulation method is developed to analyze the self-consistent accumulation and bunching caused by the space charge of these trapped electrons. The velocity spread and the sink mechanism for the trap electrons are taken into account. The threshold conditions for excitation of LFOs, the spatial character, the origin and evolution of the LFOs are analyzed and interpreted. Numerical simulation results agree with the experimental data.As for the High frequency structure, in this thesis the Ka bands Gyro-twt has been studied in theory and experiment.Main efforts are as follows:1. An approximate physical model which using theoretical analysis of the input coupler is described in detail, combining this analytical model and the software of HFSS, the high transform efficiency input cavity with pure mode are obtained.2. Using the small signal linear theory to analyze the amplification of the working and competition mode. After the analyze, the optimum design parameter is given by this small signal linear theory.3. Nonlinear theory is used to simulate the beam-wave interaction of Gyro-twt. The influence of the velocity spread and the dielectric load is taken into consideration in this model, which can provide a high efficient method to design the gyro-twt.4. The output section between the beam-wave interaction section and the output window is studied to obtain the low reflector coefficiency of the working and competition mode. The characteristic of the output window, Such as the reflector and absorber of high average power are analyzed. An output window for Ka band, TEoi high power gyro-twt amplifiers is designed with the reflectivity less than 1%, and absorbing power is about 2W while the output power is lOkW.5. A gyro-twt has been designed and fabricated which achieved 160kW peak plused output power, and 38dB saturated gain with 1.5 GHz bandwidth centered at 34GHz for a 70 kV,10A electron beam.更多还原