电磁波与非磁化等离子体的相互作用

研究了频率为0．5-10HGz的电磁波在非磁化等离子体中的传播。在厚度为10cm的、密度n=10^10或10^11cm^-3的均匀和密度分布n=n0exp[2(z/d-1)]非均匀的等离子体中，计算了等离子体中的电子与中性气体的碰撞频率为0．1-10GHz间的电磁波的反射功率，吸收功率 透射功率的变化。结果表明当等离子体密度比较大（n=10^11cm^-3)、电子与中性气体的碰撞频率比较大时，无论是均匀还是非均匀等离子体对电磁波能量的吸收都比较大，最大可达90％。     

磁化碰撞等离子体对雷达波的共振吸收

使用平板几何对雷达工作频段的电磁波在磁化碰撞等离子体中的传播作了数值计算,计算结果表明,在均匀等离子体中,当等离子体碰撞频率f∞=0.1,0.5,1GHz及电磁波频率接近高混杂频率时,电磁波衰减和被吸收功率出现最大峰值,即出现共振吸收;当fen=1,10GHz时,电磁波衰减、被吸收功率和透射功率曲线变得很平坦;衰减和吸收功率随等离子体密度的增大而增大,在n=10^11cm^-3时,衰减可达100dB,吸收比可达80％。在非均匀等离子体中,电磁波的反射功率峰值比在均匀等离子体中大。因此,磁化均匀等郭了体更有利于等离子体隐身。     

放电功率变化对电磁波在电感耦合闭式等离子体中的衰减特性

射频电感耦合等离子体(ICP)放电方式能够在较宽的压强范围内产生大面积、密度高的等离子体,在对电磁波衰减应用中具有较大优势。通过研究ICP等离子体与电磁波相互作用的过程,改进闭式等离子体模型,建立电磁波在非均匀等离子体中传播的分层计算模型,对实测诊断分布情形下等离子体与电磁波的相互作用进行研究,得到不同功率条件下电磁波衰减的变化情况;提出射频电感耦合闭式等离子体用于电磁波衰减的方法并实验验证,基于等离子体覆盖金属平板的测量模型,在实验室内搭建了以金属板为衬底的弓形微波反射测试系统,研究了闭式等离子体对4～8 GHz频段范围内微波反射的作用特性,以及不同射频功率对微波反射的影响规律,并将实验测量与计算结果进行对比分析。实验表明,通过功率调节,电感耦合闭式等离子体对5.92～6.8 GHz频带电磁波具有明显的衰减作用。     

等离子体对高功率微波的防护

提出了用等离子体防护高功率微波破坏电子设备的方法。建立了“介质层-等离子体层-介质层-等离子体层”的反射/吸收模型,其中两层均匀非磁化等离子体厚度各为50mm,等离子体频率为30GHz,等离子碰撞频率为70GHz。计算了微波的透射功率、防护结构的最小防护距离。计算结果表明：对功率10GW、脉冲宽度100ns、天线100m² (效率50%)的微波源产生的微波,频率小于30GHz时,将被防护装置反射;频率为31～80GHz时,防护结构的最小防护距离约为5km。     

等离子体的三频点微波透射衰减诊断方法

 依据微波在等离子体中的传播特性，并利用微波透射非磁化等离子体时在三个相邻频率点的透射能量衰减值，可同时诊断等离子体中的电子密度和电子碰撞频率。使用该方法对100～700 Pa范围内氦气辉光放电等离子体进行了诊断，选择6.2，6.8和7.4 GHz三个频率点，并与使用双探针诊断的诊断结果进行比较。结果表明：两种诊断方法所得碰撞频率基本一致；微波透射衰减法诊断出的电子密度值与探针法的诊断结果在同一数量级(1016 m^-3)，但前者约是后者的1.67倍。最后对造成这一差异的原因进行了分析。三频点微波透射衰减诊断方法可用于较高气压及其它静电探针使用受限的环境下，并且可以采用能量较小的微波，不会对等离子体本身造成显著影响，适用于等离子体的初步诊断。     

等离子体双频点微波透射衰减诊断法

介绍了利用非磁化等离子体中微波在两个相邻波长处的透射衰减值来反推该等离子体频率(从而得到电子密度)和电子碰撞频率的方法───双频点微波透射衰减诊断方法。陈述了利用扫频信号源、标量网络分析仪和宽带喇叭天线等构成的系统对微波衰减测量的过程,对该方法的诊断误差进行了讨论。双频点微波透射衰减诊断法适用于大气压等离子体的初步诊断。     

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在HL-2A装置上研制了用于测量等离子体密度分布的两套幅度调制微波反射仪。微波反射仪采用时间延迟法。这两套微波反射仪有不同的频率范围(26.5～40GHz和40～60GHz),它们所对应的密度测量范围是(0.84～1.98)×1019m-3和(1.98～4.47)×1019m-3。时间分辨率可达1ms,空间分辨率约为5mm。     

对"关于‘电磁波在非均匀等离子体中的吸收''的评论"的回复

在张海峰等的评文 (以下简称评文 )中提到 ,总出射波振幅应等于每层等离子体反射与透射振幅的矢量和 ,而在我们文章中认为总出射功率等于每层等离子体反射与透射功率之和。我们认为在对空间取平均后 ,这两种观点是一致的。与我们原来文章的假定一样 ,我们设非均匀等离子体层的厚度为ｄ。电磁波由等离子体的一侧入射 ,另一面为金属反射面。电磁波电场的极化方向如图 1所示。取ｚ轴垂直于等离子体层 ,平衡等离子体密度在ｚ方向具有非均匀性。Ｅ′ｉ 为电磁波在第ｉ层与第ｉ + 1层界面反射后 ,最后射出等离子体层的出射电场矢量为 :Ｅ′ｉ =-Ｅ…     

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利用搭建的实验测量系统,从放电单元数量、放电单元分布及放电电压三个方面进行实验,测量了柱状放电等离子体阵列对2~18GHz TM电磁波的透射衰减影响.结果表明,放电单元数量的减少可以改善等离子体对10~18GHz入射波的衰减效果;在整个2~18GHz范围内,等离子体放电单元之间取适当的间距可以提高等离子体对入射电磁波的衰减性能;放电电压的增大有利于增大衰减程度和扩大衰减频带范围.     

柱状放电等离子体阵列对2～18GHz TM波透射衰减影响的实验研究

利用搭建的实验测量系统,从放电单元数量、放电单元分布及放电电压三个方面进行实验,测量了柱状放电等离子体阵列对2~18GHz TM电磁波的透射衰减影响。结果表明,放电单元数量的减少可以改善等离子体对10~18GHz入射波的衰减效果;在整个2~18GHz范围内,等离子体放电单元之间取适当的间距可以提高等离子体对入射电磁波的衰减性能;放电电压的增大有利于增大衰减程度和扩大衰减频带范围。     

大气压微波等离子体射流装置放电特性研究

基于同轴传输线结构设计了两种不同喷嘴结构的大气压微波等离子体射流(MW-APPJ)装置,其工作频率2.45 GHz,工作气体为氩气,分别研究了两种不同喷嘴结构对等离子体放电特性产生的影响。仿真结果表明,MW-APPJ在气体喷嘴处会产生高强度的电场,经过优化结构,实现在频率2.45 GHz下,喷嘴处的场强满足氩气电离的击穿场强阈值要求。同时,利用多物理场耦合仿真软件对装置的气流分布进行了稳态模拟,并通过实验对比分析了两种喷嘴结构下大气压氩等离子体射流的基本特性。实验结果表明,不同的喷嘴结构会影响等离子体装置的反射系数随输入功率的变化规律,但并不影响等离子体射流长度随输入功率的变化规律和反射功率随进气流量的变化规律;同时,在大气压下,稳态微波等离子体射流呈现出类金属性,等离子体中的电子只能在很薄的区域中吸收微波能量,因而造成微波的反射功率较大。     

Experimental study of a plasma-filled backward wave oscillator

Experimental studies of a plasma-filled X-band backward-wave oscillator (BWO) are presented. Depending on the background gas pressure, microwave frequency upshifts of up to 1 GHz appeared along with an enhancement by a factor of 7 in the total microwave power emission. The bandwidth of the microwave emission increased from ⩽0.5 GHz to 2 GHz when the BWO was working at the RF power enhancement pressure region. The RF power enhancement appeared over a much wider pressure range in a high beam current case (10-100 mT for 3 kA) than in a lower beam case (80-115 mT for 1.6 kA). The plasma-filled BWO has higher power output than the vacuum BWO over a broader region of magnetic guide field strength. Trivelpiece-Gould modes (T-G modes) are observed with frequencies up to the background plasma frequency in a plasma-filled BWO. Mode competition between the T-G modes and the X-band Tm₀₁ mode prevailed when the background plasma density was below 6×10¹¹ cm^-3 . At a critical background plasma density of ≃8×10¹¹ cm^-3 power enhancement appeared in both X-band and the T-G modes. Power enhancement of the S-band in this mode collaboration region reached up to 8 dB. Electric fields measured by the Stark-effect method were as high as 34 kV/cm while the BWO power level was 80 MW. These electric fields lasted throughout the high-power microwave pulse     

FDTD Simulation of Electromagnetic Reflection of Conductive Plane Covered with Imhomogeneous Time-Varying Plasma

A finite-difference time-domain (FDTD) algorithm is applied to study the electromagnetic reflection of conduction plane covered with inhomogeneous, collision, warm, time-varying plasma. The collision frequency of plasma is a function of electron density and plasma temperature. Under the one-dimensional case, transient electromagnetic propagation through various plasmas have been obtained, and the reflection coefficient of EM wave through inhomogeneous time-varying plasma (ITVP), homogeneous time-varying plasma (HTVP) and inhomogeneous plasma (IP) are calculated under different conditions. The results illustrate that a plasma cloaking system can successfully absorb the incident EM wave.     

Numerical Analysis of Symmetrical Waves Dispersion in a Nonisothermal Plasma Waveguide in a Magnetic Field

Dispersion equations of a nonisothermal plasma waveguide in a constant external magnetic field are derived, when the magnetic field intensity tends to infinity. The plasma electrons' thermal velocity are taken in mind. A numerical analysis of dispersion equations for the E- (TH-) and H- (TE-) waves is made. In the high-frequency range it shows the possibility of the slow E-waves exciting with a higher frequency than the electron Langmuir frequency. In the range near to the ion Langmuir frequency it shows the existence of waves with an anomalous dispersion. These waves are named low-frequency backward E-waves and it is shown, that in some frequency ranges they change the group velocity sign. The dispersion is investigated also in respect to the waveguide plasma filling.     

电磁波在非均匀等离子体中的吸收

研究了电磁波在非均匀碰撞等离子体中的传播和吸收,提出了一种计算电磁波在非均匀等离子体层中反射和透射功率的模型。对几种典型的非均匀密度剖面,计算了在不同的碰撞频率和层边缘密度下电磁波衰减率与电磁波频率的关系,结果表明,对于给定的密度剖面和有效吸收频宽,存在一个最佳的磁撞频率。     

真空中不同极化电磁波在微波等离子体喷流中的衰减特性实验研究

在真空环境中，利用空间反射电磁波测量装置，开展微波等离子体喷流对垂直和水平极化电磁波衰减的实验研究，分析不同极化电磁波在等离子体中衰减的影响因素.实验结果表明：以氩气为工质，真空室中微波等离子体喷流对垂直和水平极化电磁波具有显著的吸收效应.发生器流量、功率以及实验真空度对垂直极化电磁波在等离子体中的衰减影响明显.真空度和发生器功率对水平极化电磁波没有显著影响. 关键词： 等离子体中的电磁波 等离子体基本性质 电磁波     

Moving perturbations of the ionization in a field of strong electromagnetic waves

The perturbation of the ionization and of the electron temperature is considered in a plasma in a field of strong electromagnetic waves. It is shown that the intensified absorption of the waves in the region of their reflection leads to the appearance of the moving perturbations of the plasma ionization. The conditions governing the development of moving perturbations are determined along with their velocity and spatial structure. It is demonstrated that in a weakly inhomogeneous plasma such perturbations appear in the neighborhood of the reflection point of the waves and move toward the wave so as to cause perturbation. This leads to the generation of nondecaying nonlinear oscillations in the plasma. The frequency of the oscillations is determined, and it decreases with increasing absorbed power of the waves.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 1, pp. 11–18, January, 1972.The author is indebted to V. L. Ginzburg for his useful discussions.     

Anomalous microwave reflection from a metal surface induced by spoof surface plasmon

The reflection of X-band microwaves (8-12 GHz) from a metallic aluminum (Al) surface with groove grating corrugations was investigated experimentally. It was shown that the reflection of p-polarization is much less than the microwave reflected from the corresponding area of an unruled Al surface, with selective wavelength. The experimental results demonstrated that the anomalous microwave reflection is strongly associated with the excitation of spoof surface plasmons at the Al-air interface by the surface grating coupler. This near-total absence of reflected microwaves is similar to the famous Wood's anomaly in the optical regime and is of fundamental importance to the applications of spoof surface plasmons in the microwave regime.