圆柱体的外系统电磁脉冲模拟

为深入研究具有复杂角分布和能谱分布的系统电磁脉冲(SGEMP)的规律和特性,利用三维全电磁粒子模拟(PIC)程序,并添加相应功能模块——用蒙特卡洛方法实现电子发射的余弦角分布和指数能谱分布。模拟计算光电子由圆柱端面向外发射引起的SGEMP模型,选取2组X射线数据进行计算,并与文献估算结果进行对比。2次计算所得结果量级都与文献结果一致,说明本程序可用于深入研究各种SGEMP问题,为抗核加固和SGEMP效应研究提供基础数据。     

多层各向异性等离子体球电磁散射的解析解

给出s层各向异性等离子体球电磁场球矢量波函数解析表达式,应用电磁场在(s-1)层球壳边界上切向电磁场连续以及辐射条件,导出了平面波入射情况下,s层等离子体球电磁场的展开系数。将数值计算结果分别与矩量法-共扼梯度-傅里叶变换(MOM-CG-FFT)计算结果和均匀等离子体球的结果进行了比较,符合得较好。该文研究结果预期可应用于新型天线的研制和卫星通信等领域。     

强流电子枪电流密度和空间电荷密度计算的曲光轴传递理论与数值分析

强流电子束系统里，一般不能直接进行解析或数值分析计算其电磁场、电子轨迹和电子束的性能，而采用迭代法计算其自治的空间电荷场，在考虑电子发射的热初速时，有关的数值计算方法也非常复杂。本文利用旋转对称电子光学系统里的子午面投射轨迹理论，导出了围绕环形电子束元曲光轴的傍轴的傍轴轨迹方程，利用这一理论研究了在空间电荷和电子热初速效应同时作用下环形电子束元电子电流密度分布的演化发展，并由此建立了一套简便的计算圆形强流电子枪电流密度和空间电荷密度的数值方法。作为例子，分析计算了理想的Pierce枪的电流密度的传输规律，并证实了本方法是一种实用而有效的方法。     

两同心各向异性等离子体球电磁散射的解析解

利用各向异性等离子体介质的电磁场满足各向异性等离子体球矢量波函数的条件，根据球Bessel函数的特点，分别给出两同心各向异性等离子体介质的球矢量波函数的解析表达式。在此基础上，应用电磁场在球边界上切向电场和磁场连续和远区辐射条件，导出在平面波入射情况下，两同心各向异性等离子体介质本征函数解的展开系数。理论分析和数值计算的结果表明：当两同心等离子体球媒质参数相同时，本文所得的结果可退化为单层各向异性等离子体解析解。同时数值计算还给出了本方法与矩量法-共扼梯度-傅立叶变换(MOM-CG-FFT)的比较结果，两者符合较好。     

铁电阴极低真空电子发射性能的分析

采用锆钛酸铅(PZT)铁电阴极,在高真空4×10-3 Pa和低真空1.4 Pa条件下分别进行了电子发射实验.对收集电流波形进行积分,计算出收集电荷,低真空与高真空的电荷比值为0.193 3,说明低真空条件下发射出的电子损失较大.运用分子运动理论和等离子体放电理论对发射电子损失的原因进行了分析.通过分子运动理论计算了分子碰撞对到达收集极的电子数目的影响,得到的低真空与高真空的电子到达几率分别为89.58%和99.97%,二者的比值为0.896 1.该数值与通过实验收集电流波形计算出的到达电子比值相差很大.考虑低真空下等离子体的作用,发射电子除了与气体分子碰撞有部分损失外,还有通过等离子体和栅电极形成的对地放电损失.由等离子体放电理论计算出等离子体覆盖栅电极时间为23.8 ns,与低真空的收集电流振荡周期20 ns非常接近,是低真空下等离子体放电损失的有力证明.     

无引导磁场电子注的空间电荷波

本文导出了无外磁场电子注在等离子体约束下其上传播的空间电荷波波动方程,详细讨论了该条件下的波特性,并对等离子体频率降低因子进行了分析．研究表明,等离子体填充状况对空间电荷波性质影响甚大,选择等离子体填充因子可对空间电荷波性质进行适当的控制．     

等离子体圆柱波导慢电磁波的激励

本文在考虑等离子体厚度效应的情况上,详尽地推导了充填圆环状等离子体的圓柱波导中TM模慢电磁波的色散方程;利用相对论空间电荷波理论,导出了相对论电子注在轴向磁场引导下沿等离子体内表面传输时的空间电荷波方程;求得了电子注和慢空间电荷波相互作用的线性增益和频率漂移;讨论了等离子体厚度、密度对色散特性和互作用增益的影响。     

带状电子注空间电荷场的格林函数法求解

带状电子注具有非轴对称性和大宽高比的特性,为了研究其空间电荷效应,本文建立了相应的二维宏粒子物理模型,并通过格林函数法求解带状电子注内的空间电荷力。在该模型中,带状电子注用一系列窄带代替,每个窄带受到的空间电荷力通过叠加其它窄带作用于该窄带的电场力得到。本文对该窄带模型进行了详细的分析,计算了电子注内的空间电荷力,编写了基于该模型的数值模拟程序,模拟了带状电子注在不同静电磁约束下的运动及传输情况,计算结果与三维PIC 软件有很好的一致性,验证了基于该二维宏粒子模型的格林函数法求解带状电子注空间电荷场的合理性和准确性。     

基于COMSOL的感应耦合等离子体刻蚀机流体模型

流体动力学模型被广泛地用于感应耦合等离子体（ICP）的仿真,即使连续性方程在这样低的压力下通常会被认为是不适用的。本课题模拟了一个真实的充满氩等离子体的ICP刻蚀机。本模拟基于一个多物理场仿真软件——COMSOL,一种偏微分方程求解器。正如其他的等离子体流体模型所示,在本模型中用漂移扩散近似描述离子,对电子运动用准中性假设,用简化的Maxwell方程计算电磁场,用电子能量方程求解电子温度,用Navier-Stokes方程来描述中性背景气体。本文展示了在功率200W和气压1.33Pa（10 mTorr）条件下的2维等离子体参数分布情况。进而对比了电子数密度和电子温度随功率的变化。我们确信在预测值与真实值之间存在不一致情况,造成这种差异的原因主要是电子能量分布函数（eedf）的麦克斯韦假设以及对碰撞截面和反应速率的缺失。     

无引导磁场电子流的空间电荷波

本文导出了无外磁场电子注在等离子体约束下其上传播的空间电荷波波动方程，详细讨论了该条件下的波特性，并对等离子 频率降低因子进行了分析。研究了离子体填充状况空间电荷波性质影响甚大，选择等离子体填充因子对空间电荷波性质进行适当的控制。     

Radiation from a uniformly moving distribution of electric charge in an anisotropic, compressible plasma

The radiation characteristics of a linear distribution of electric charge moving with a uniform velocity in a homogeneous electron plasma of infinite extent are investigated for the case in which a uniform static magnetic field is impressed externally throughout the medium. The linear distribution of charge and its direction of motion are assumed to be parallel and perpendicular, respectively, to the direction of the external magnetic field. Of the two possible modes of waves of small amplitude, namely, the modified electromagnetic mode and the modified electron plasma mode, the uniformly moving charge distribution excites the modified electron plasma mode. The emitted radiation has no frequencies less than the plasma frequency. For a particular value of the ratio of the gyrotropic to the plasma frequency of the electrons, the frequency and the angular spectrum of the emitted radiation are determined for two values of the velocity of the charge.     

空间电荷波传播特性的PIC粒子模拟

采用周期性边界条件的二维准静电PIC粒子模拟程序对空间电荷波的产生及传播过程进行了数值模拟,给出了静止和一维定向漂移空间电荷波的产生及传播特性随等离子体参数变化的关系,通过单电子跟踪的方法,得到了波动过程带电粒子的空间状态的变化规律。其结果,将作为进一步实现空间电荷波与电磁波产生波一波相互作用过程模拟的基础。     

等离子体中电磁波色散关系的PIC粒子模拟

等离子体参数的变化对在其中传播的电磁波有重要影响,文章采用周期性边界条件的二维PIC粒子模拟程序对电磁波在等离子中的传播过程进行了数值模拟,给出了电磁波在不同密度等离子体中传播的色散关系,得到了电磁波在等离子体中的传播特性。其结果,将作为进一步实现电磁波与等离子体中空间电荷波产生波-波相互作用过程模拟的基础。     

Radiation from electromagnetic sources in a plasma

The radiation from electromagnetic sources in an unbounded, isotropic plasma is treated. Using a two-fluid magnetohydrodynamic approach, the problem is formulated in terms of three orthogonal modes, namely, i) the electromagnetic mode, ii) the electron plasma mode and iii) the ion plasma mode. When formulated in this manner, the radiation from simple electromagnetic sources are obtained easily. Three specific sources are treated, namely, i) a point source of electric current, ii) a uniformly moving charge and iii) a short filament with prescribed current distribution. For the case of the electric dipole and the current filament, the total power radiated in each of the three modes are obtained. A point charge moving uniformly with the velocity of sound, for example, is found to excite only the ion plasma mode. The frequency and the angular spectrum of the emitted radiation are obtained. It is found that at frequencies less than a critical frequency which is approximately equal tosqrt{2}times the ion plasma frequency, the radiation has the character of a simple sound wave.     

The effect of material stresses on electromagnetic boundary conditions

The appearance of a layer of charge or current on the boundary of a material usually implies that a discontinuity in an electromagnetic field occurs at that boundary. The converse is not necessarily true. The reaction of the electromagnetic field to the charge or current layer is a stress communicated across the boundary. Determination of the charge or current on a boundary must take all the stresses and electromechanical interactions at the boundary into account. Calculating surface currents or charges derived from electromagnetic field quantities alone, ignoring mechanical stresses, may lead to wrong answers at material boundaries. In short, the occurrence of charge or current on material in the presence of an electromagnetic field is intimately related to momentum conservation. A postulate equivalent to identifying the Poynting vector with energy flow is introduced, linking surface currents and charges to momentum balance at the surface. A formally correct method for calculating surface currents and charges based on momentum balance is described.     

Radiation from an electromagnetic source in a half-space of compressible plasma-surface waves

The radiation characteristics of a line source of magnetic current are studied for the case in which the source is situated in a half-space of isotropic, compressible plasma which is bounded on one side by a perfectly conducting, rigid plane screen. In addition to the electromagnetic and plasma space waves, the line source excites a boundary wave. This boundary wave is a coupled wave. It has associated with it both a magnetic field component and the pressure term. This is in contrast to the space waves which can be decomposed into an electromagnetic (EM) mode with no pressure term and a plasma (P) mode with no magnetic field associated with it. The characteristics of this boundary wave are evaluated. The boundary wave propagates for all frequencies and the power carried by the boundary wave becomes smaller as the frequency is increased.     

电荷守恒和电流守恒

守恒定律是构成电磁理论大厦的重要支柱之一.在文中引入了扩展全空间概念,由此得到电荷守恒和电流守恒的一般形式.电荷守恒对应于时间对称性,而电流守恒则对应于空间的对称性.在不同的惯性系中,电流和电荷联合起来,构成四维矢量,它们具有Lorentz时间-空间对称性.文中最后还给出了应用实例.     

Transport effects in cesium thermionic converters

One of the primary reasons for the failure of thermionic converters to attain their ultimate theoretical performance is electron transport effects occurring in the interelectrode spacing. Two major types of transport effects, electron scattering and electron space charge, are discussed and theoretical results compared with experimental data. The uniform plasma theory is reviewed and experimental data show that for a monocrystal emitter this theory is consistent with the energy equation. Space charge neutralization is discussed. Both surface ionization and volume ionization are considered. Experimental results indicate that surface ionization is not as effective as would be expected by theory. This fact is responsible for the discrepancy between theoretically expected and experimentally obtained performance of converters. Under the conditions where surface ionization is inadequate for space charge neutralization, volume ionization can provide the necessary ions. Volume ionization, however, is achieved at the expense of the output power of the converter.     

调制电子束在空间等离子体中激发的电磁波辐射

当调制电子束入射进空间等离子体时,由于电子束本征电磁场在非均匀等离子体中的散射(渡越辐射transition radiation)或者电子束的纵向约束性可以产生电磁波辐射.基于这两种辐射机制,研究了半无界调制电子束从航天器入射进平面分层各向同性非均匀空间等离子体产生的电磁波辐射.结果表明,由背景等离子体非均匀性产生的电磁波辐射强度高于由束的纵向约束性引起的辐射强度通过对电子束的适当调制,可以满足辐射电磁波在局部等离子体谐振区域的共振条件,从而增大辐射强度.研究结果可用于对主动空间等离子体试验数据的分析.