人工等离子体云的时间演化

分析了高空中人工等离子体云的时间演化。发现人工等离子体云中电子密度的空间分布存在着指数衰减区和平缓衰减区。等离子体发生器的粒子流密度仅影响指数衰减区,对平缓衰减区没有什么影响。平缓衰减区中的平均电子密度约为中性分子密度的十万分之一。并且可以覆盖较大范围。这些结果对于电磁波与人工等离子体相互作用的研究、导弹和空间飞行器的等离子体隐身研究及人工等离子体发生器的设计有一定的参考价值。     

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     

飞秒激光与等离子体相互作用中自生磁场的测量

自J．A．Stamper首先对自生磁场进行实验研究以来，人们的探索表明超强激光与固体靶相互作用中，在过密和次密等离子体区产生可能高达10^4T的自生磁场。     

真空环境中等离子体喷流对反射电磁波衰减的实验研究

在真空环境中，利用传输线测量装置，开展微波等离子体喷流对反射电磁波衰减的实验研究.实验结果表明，采用传输线测量方法能够有效地获得等离子体对反射电磁波的衰减；在5GHz附近，以氩气为工质，流量为52.5mg/s时，52W微波功率在真空环境中产生的等离子体喷流能对反射电磁波产生最大的衰减；增加微波功率、降低真空环境压强可以提高等离子体对反射电磁波的衰减；要使等离子体能够对反射电磁波产生最大的衰减，必须选取合适的发生器参数. 关键词： 电磁波在等离子体中的传输 等离子体基本过程 电磁波     

电磁波在大气层人造等离子体中的衰减特性

利用洛沦兹模型来研究大气层人造非均匀等离子体的电磁响应特性,讨论了电磁波频率、等离子体密度及电子碰撞频率对电磁波衰减特性的影响.结果表明,电磁波在长波长区域及等离子体密度大时,其能量衰减越快.当等离子体密度高时,电子温度越低,大气层高度越高,电磁波的能量衰减越快. 关键词： 电磁波 大气等离子体 能量衰减     

等离子体中电磁波传输特性理论与实验研究

本文对35 GHz和96 GHz电磁波在等离子体中的传输特性进行了理论与实验研究, 得到了电磁波衰减随等离子体密度、碰撞频率和电磁波频率的变化规律. 等离子体密度增加一个数量级时, 电磁波衰减增加一个数量级; 随着等离子体碰撞频率的增加, 电磁波衰减先增加后减小; 随着电磁波频率的增加, 衰减下降. 以激波管为实验平台进行了电磁波在等离子体中传输特性的实验研究, 实验结果和理论结果吻合较好. 理论和实验结果均表明, 提高电磁波频率是解决黑障问题的有效途径.     

电磁波在磁化等离子体表面的功率反射系数计算研究

采用等效输入阻抗方法计算金属平板前非均匀磁化等离子体层对垂直入射电磁波的功率反射系数，结果表明，电子数密度大小、等离子体层厚度、入射波频率和外磁场是功率反射系数的主要影响因素.电子数密度取值必须合适，外加磁场才能明显降低等离子体对入射电磁波的功率反射系数.入射电磁波频率增加时，必须加大外磁场强度，才能明显降低功率反射系数. 关键词： 等离子体中电磁波的传输 等离子体特性 电磁波     

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。     

磁化等离子体对平面电磁波吸收特性的数值研究与全波仿真

研究了平面电磁波在磁化、稳定、二维、非均匀等离子体中的传播特性;采用等效输入阻抗方法计算非均匀磁化等离子体层对不同模式入射电磁波的功率吸收情况。结果表明,电子数密度、碰撞频率和外磁场大小是等离子体对电磁波功率吸收的主要影响因素。采用等效介电常数的方法模拟等离子体特性,代入有限元软件进行平面电磁波入射等离子体仿真,得到了非寻常波与右旋极化波的吸收特性。根据数值计算和全波仿真结果可知,当等离子体密度为1017 m-3、碰撞频率2.5 GHz、外加磁场的磁感应强度为0.15 T时,磁化等离子体对电磁波有强烈的吸收特性。     

等离子体微带开关特性

提出一种基于微放电等离子体的微带开关。它是以“时变等离子体”取代微带线射频微机电开关的“金属悬臂”,利用等离子体的导体或介质特性使电磁波沿其表面进行传输或截止,从而实现微带线上电磁波传输的动态控制。等离子体微带开关的基本结构包括用以隔断电磁波的微带间隙和产生片状等离子体的放电装置。放电产生时,电磁波因等离子体导体性通过开关,形成“开”状态;放电停止后,电磁波被微带间隙反射,形成“关”状态。利用CST软件仿真研究了等离子体开关特性,结果表明:这种开关的带宽由等离子体密度决定,隔离度由间隙决定,而工作插损与等离子体密度和电子碰撞频率有关。等离子体位形（宽度、厚度等）对于开关性能也非常重要。     

Total absorption of an electromagnetic wave by an overdense plasma

We show both theoretically and experimentally that an electromagnetic wave can be totally absorbed by an overdense plasma when a subwavelength diffraction grating is placed in front of the plasma surface. The absorption is due to dissipation of surface plasma waves (plasmons polaritons) that have been resonantly excited by the evanescent component of the diffracted electromagnetic wave. The developed theoretical model allows one to determine the conditions for the total absorption.     

Study of propagation of ultraintense electromagnetic wave throughplasma using semi-Lagrangian Vlasov codes

Interaction of relativistically strong laser pulses with underdense and overdense plasmas is investigated by a semi-Lagrangian Vlasov code. These Vlasov simulations revealed a rich variety of phenomena associated with the fast particle dynamics induced by the electromagnetic wave as electron trapping, particle acceleration, and electron plasma wavebreaking. To describe the distribution of accelerated particle momenta and energy will require a very detailed analysis of the kinetic and time history of the plasma wave evolution. The semi-Lagrangian Vlasov code allows us to handle the interaction of ultrashort electromagnetic pulse with plasma at strongly relativistic intensities with a great deal of resolution in phase space     

Excitation of surface plasmons at the boundary of overdense plasma

The excitation of surface plasmons （SPs） with a strip grating at the boundary of an unmagnetized overdense plasma has been investigated theoretically and experimentally. An incident electromagnetic radiation was p-polarized at the frequency of 5 GHz. Experiments showed that when the plasma density was four times higher than the critical density with the grating present, and the SPs could be excited at the boundary of the overdense plasma. Contribution of the glass layer in the formation of the SP dispersion relation was examined. When the incident electromagnetic radiation was coupled into SPs the coupling order with the effective permittivity was simulated qualitatively. We find that the existence of SPs at the boundary of overdense plasma indicates that the reflection coefficient of the incident electromagnetic radiation reaches its minimum and even becomes total absorption. In this work the plasma density was diagnosed by a Langmuir double probe.     

Resonant interaction of an electromagnetic wave with an inhomogeneous plasma slab

Resonant interaction at oblique incidence of an electromagnetic wave on an inhomogeneous plasma slab is studied. The time evolution of this interaction is solved numerically from two-fluid equations, adiabatic equation for electron pressure and from Maxwell equations. It is shown that the electromagnetic energy of an incident wave is transformed both into the heat energy and into the energy of plasma oscillations in the direction of density gradient. The distribution of the transformed energy between the heat energy and the energy of plasma oscillations is strongly dependent on the plasma temperature. The ratio of heat energy to the energy of plasma oscillations is growing with growing temperature. The plasma oscillations are generated by magnetic induction of the penetrating wave. In a cold plasma they are generated especially in the overdense region and their frequency is equal to local plasma frequency. The electric field in the direction of plasma gradient has a form of a wave packet whose envelope reaches a maximum at resonance. The characteristic wavelength in the wave packet decreases and the amplitude of the packet increases with the time.     

Interaction of relativistically strong electromagnetic waves with a layer of overdense plasma

Plasma-field structures that arise under the interaction between a relativistically strong electromagnetic wave and a layer of overdense plasma are considered within a quasistationary approximation. It is shown that, together with known solutions, which are nonlinear generalizations of skin-layer solutions, multilayer structures containing cavitation regions with completely removed electrons (ion layers) can be excited when the amplitude of the incident field exceeds a certain threshold value. Under symmetric irradiation, these cavitation regions, which play the role of self-consistent resonators, may amplify the field and accumulate electromagnetic energy.     

Nonlinear propagation of relativistically intense electromagnetic waves in a collisionless plasma

We discuss the nonlinear propagation of relativistically intense electromagnetic waves into collisionless plasmas with special emphasis on one dimensional plane wave solutions of the propagating, standing and modulated types. These solutions exhibit a rich variety of phenomena associated with relativistic electron mass variation and coupling between transverse electromagnetic and longitudinal fields. They have important applications to problems of laser propagation, self-focusing in overdense plasmas, particle and photon acceleration and to electromagnetic radiation around pulsars.     

The anomalous penetration of intense circularly polarized electromagnetic beam through overdense magnetized plasma

The steady state nonlinear propagation of an intense, circularly polarized electromagnetic beam in an inhomogeneous magnetized plasma has been investigated in paraxial approximation. The laser induces a large oscillatory velocity on electrons, raising their mass and lowering the plasma frequency. Further, rising due to cyclotron resonance effect. The propagation of the electromagnetic waves in magnetized plasma in both the extraordinary and ordinary mode is analyzed. The nonlinearity in dielectric function is considered in presence of external magnetic field due to saturation effects for arbitrary large intensity, which leads to focusing/defocusing of the beam. The focusing effect along with magnetic field helps in the process of anomalous penetration of the beam by enhancing the depletion of the plasma from the axial region. The penetration increases with the incident beam power up to some critical value beyond which it rises abruptly when all electrons have been driven out of the axis. The cyclotron resonance effect awfully supports the laser beam to propagate inside the overdense plasma region. Numerical computations are performed for typical parameters of relativistic laser–plasma interaction applicable for underdense and overdense plasma.     

Laser-hole boring into overdense plasmas measured with soft X-Ray laser probing

A laser self-focused channel formation into overdense plasmas was observed using a soft x-ray laser probe system with a grid image refractometry (GIR) technique. 1.053 &mgr;m laser light with a 100 ps pulse duration was focused onto a preformed plasma at an intensity of 2x10(17) W/cm (2). Cross sections of the channel were obtained which show a 30 &mgr;m diameter in overdense plasmas. The channel width in the overdense region was kept narrow as a result of self-focusing. Conically diverging density ridges were also observed along the channel, indicating a Mach cone created by a shock wave due to the supersonic propagation of the channel front.     

Influence of surface waves on plasma high-order harmonic generation

The influence of surface plasma waves on high-order harmonic generation from the interaction of intense lasers with overdense plasma is analyzed. It is shown that the surface waves lead to the emission of harmonics away from the optical axis, whereas the high-order on-axis harmonics are lowered in intensity. Our simulation results indicate that surface plasma wave generation plays a crucial role in surface high-order harmonic generation experiments. Furthermore, a novel surface plasma wave generation process different from the well-known two-surface wave decay is observed in the highly relativistic regime.     

Influence of Quantum Effects on the Magnetic Field Behavior in Overdense Plasma

We study the conditions for the anomalous transmission of electromagnetic waves through quantum overdense plasma. We show that this anomalous transmission is triggered due to the excitation of surface waves, as was observed in the classical overdense plasma. The conditions for the excitation of surface waves are obtained by studying the dispersion relation within the framework of quantum hydrodynamics. The corresponding consequences at the classical limits are consistent with the previous studies. In comparison with the classical regimes, the quantum dispersion curve exhibits an asymptotic behavior which indicates significant effects, in particular, at large wavelengths. Herein, to create the required evanescent waves, we consider the quantum plasma to be placed between two ordinary prisms and dielectrics. The effects of the main parameters, such as the permittivity of the prisms and dielectrics and the Fermi velocity, on the rate of the transmission and the magnetic field propagation are also evaluated.