等离子体对电磁波衰减的优化模拟研究

发布时间：2018-04-21 13:51

本文选题：等离子体 + 电磁波　；参考：《大连理工大学》2015年硕士论文

【摘要】：电磁波和等离子体的相互作用是等离子体物理学中一个非常重要的分支,一直是十分活跃的研究领域。近些年,它在许多领域,如等离子体隐身、空间通信、等离子体天线等方面的应用十分广泛。本文以等离子体隐身为切入点,数值模拟了高频电磁波在均匀、非均匀高密度等离子体层中的传播特性,以及磁化等离子体的电磁特性。研究采用FDTD方法,讨论了电子密度、碰撞频率、厚度、边缘密度梯度、不同类型剖面、和外磁场的加入对电磁波传播特征的影响。考虑到隐身应用中对电子密度的要求很高,同时讨论了影响等离子体吸收电磁波最佳电子密度的各个因素,给出降低电子密度的方法。第一章,简要介绍了等离子体及其相关知识,电磁波基本概念及它和等离子体作用领域的实际应用及研究进展。第二章,数值模拟方法简绍,给出了时域有限差分(FDTD)方法及其数值稳定性、相关吸收边界条件。第三章,数值研究了电磁波在均匀等离子体中的传播,模拟得出：等离子体具有高通滤波性,适当增加电子-中性粒子碰撞频率,可以使这个性质得到弱化；等离子体吸收电磁波时,存在一个最佳电子密度,一定范围内增加电子-中性粒子碰撞频率以及厚度,可以拓宽吸收带宽,增大吸收峰值,另外,该最佳吸收电子密度移向低密度区。这降低了隐身应用中对高密度等离子体制备的要求,使得较低密度的等离子体也能实现高效吸收。第四章,数值模拟了电磁波在非均匀等离子体中的传播,模拟得出：呈Epstein分布的非均匀等离子体对电磁波的衰减,共振吸收占主导；边缘电子密度大小和密度梯度影响电磁波的吸收,当边缘电子密度梯度平缓时,电磁波吸收能力强；当等离子体呈现抛物线分布的时候,其吸收电磁波的能力优于Epstein分布和均匀等离子体,具有最佳吸收效果。第五章,对磁化等离子体的电磁特性做了研究,模拟发现：外加磁场方向和波方向平行的磁化等离子体,和电磁波作用时会产生电子回旋共振,当电子密度大的时候,共振效果会变强；与此同时,磁场加入使电子绕磁力线旋转,相当于增加传播路径和碰撞频率,因而磁场越强,等离子体对电磁波的衰减越多。
[Abstract]:The interaction between electromagnetic waves and plasma is a very important branch of plasma physics and has been a very active research field. In recent years, it has been widely used in many fields, such as plasma stealth, space communication, plasma antenna and so on. In this paper, the propagation characteristics of high frequency electromagnetic waves in homogeneous and non-uniform high density plasma layers and the electromagnetic characteristics of magnetized plasma are numerically simulated by using plasma stealth as the starting point. The effects of electron density, collision frequency, thickness, edge density gradient, different types of profiles and the addition of external magnetic field on the propagation characteristics of electromagnetic wave are discussed by using FDTD method. Considering the high requirement of electron density in stealth application, the factors affecting the optimum electron density of electromagnetic wave absorbed by plasma are discussed, and the method of reducing electron density is given. In the first chapter, we briefly introduce the plasma and its related knowledge, the basic concept of electromagnetic wave, its practical application and research progress in the field of plasma interaction. In the second chapter, the numerical simulation method is briefly introduced. The FDTD method and its numerical stability and absorbing boundary conditions are given. In chapter 3, the propagation of electromagnetic wave in homogeneous plasma is numerically studied. The simulation results show that the plasma has high pass filtering property and the electron neutral particle collision frequency can be weakened by increasing the electron neutral particle collision frequency properly. When the plasma absorbs electromagnetic wave, there exists an optimum electron density. Increasing the collision frequency and thickness of the electron-neutral particle in a certain range can widen the absorption bandwidth and increase the absorption peak. The optimum absorption electron density shifts to the low density region. This reduces the requirement for the preparation of high density plasma in stealth applications, and enables the low density plasma to achieve high efficiency absorption. In chapter 4, the propagation of electromagnetic wave in inhomogeneous plasma is numerically simulated. It is concluded that the attenuation of electromagnetic wave is dominated by resonance absorption in the inhomogeneous plasma with Epstein distribution. The density and density gradient of edge electrons influence the absorption of electromagnetic wave. When the gradient of edge electron density is smooth, the absorption ability of electromagnetic wave is strong, and when the plasma presents parabola distribution, the absorption ability of electromagnetic wave is strong when the edge electron density gradient is smooth. Its ability to absorb electromagnetic wave is better than that of Epstein distribution and uniform plasma, and it has the best absorption effect. In the fifth chapter, the electromagnetic characteristics of magnetized plasma are studied. The simulation results show that the magnetized plasma with parallel direction of external magnetic field and wave will produce electron cyclotron resonance when interacting with electromagnetic wave, when the electron density is high, At the same time, the addition of magnetic field makes the electron rotate around the magnetic force line, which is equivalent to increase the propagation path and collision frequency, so the stronger the magnetic field is, the more the plasma attenuates the electromagnetic wave.
【学位授予单位】：大连理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O53;O441.4

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