Nonlinear Evolution of Driven Electron Plasma Oscillations in Inhomogeneous Plasmas

ＮｏｎｌｉｎｅａｒＥｖｏｌｕｔｉｏｎｏｆＤｒｉｖｅｎＥｌｅｃｔｒｏｎＰｌａｓｍａＯｓｃｉｌｌａｔｉｏｎｓｉｎＩｎｈｏｍｏｇｅｎｅｏｕｓＰｌａｓｍａｓ￥ＳＨＥＮＧＺｈｅｎｇｍｉｎｇ；ＸＵＺｈｉｚｈａｎ；ＹＵＷｅｉ；ＭＡＪｉｎｘｉｕ（ＳｈａｎｇｈａｉＩｎ...     

Stimulated Raman scattering of gaussian laser beam in relativistic plasma

This paper presents an investigation of Stimulated Raman Scattering of gaussian laser beam in relativistic Plasma. The pump beam interacts with a pre-excited electron plasma wave and thereby generate a back-scattered wave. Due to intense laser beam, electron oscillatory velocity becomes comparable to the velocity of light, which modifies the background plasma density profile in a direction transverse to pump beam axis. The relativistic non-linearity due to increase in mass of the electrons effects the incident laser beam, electron plasma wave and back-scattered beam. We have set up the non-linear differential equations for the beam width parameters of the main beam, electron plasma wave, back-scattered wave and derived SRS back-reflectivity by taking full non-linear part of the dielectric constant of relativistic plasma with the help of moment theory approach. It is observed from the analysis that self-focusing of the pump beam greatly affects the SRS reflectivity, which plays a significant role in laser induced fusion.     

Interaction of acoustic waves in microinhomogeneous media with hysteretic nonlinearity and relaxation

The propagation of a weak high-frequency pulse in the field of an intense standing low-frequency pump wave excited in an acoustic resonator with quadratic hysteretic nonlinearity and relaxation is theoretically investigated. The nonlinear damping coefficient and the carrier phase delay of the weak high-frequency pulse propagating under the action of an intense low-frequency wave are determined.     

Absorption and emission dynamics in concentrated optical ensembles under laser excitation

A new theoretical model describing the emission and absorption dynamics in an ensemble of molecules under intense coherent pulsed pumping is developed on the basis of the concepts of cooperative light-induced luminescence (CLIL). The CLIL development is described within the framework of formalism of the system density matrix in the space of photon wave functions. It is shown that the fast growth of CLIL relates to the development of coherent states of the quantum field in the area of efficient cooperative interactions of molecules (coherence volume). A system of equations for the calculation of CLIL energy, population of excited states, and optical absorption of the system in dependence on the laser pump energy density is solved. The theoretical results obtained are in good agreement with the experimental data.     

Electron Acceleration by Beating of Two Intense Cross-Focused Hollow Gaussian Laser Beams in Plasma

This paper presents propagation of two cross-focused intense hollow Gaussian laser beams(HGBs) in collisionless plasma and its effect on the generation of electron plasma wave(EPW) and electron acceleration process,when relativistic and ponderomotive nonlinearities are simultaneously operative. Nonlinear differential equations have been set up for beamwidth of laser beams, power of generated EPW, and energy gain by electrons using WKB and paraxial approximations. Numerical simulations have been carried out to investigate the effect of typical laser-plasma parameters on the focusing of laser beams in plasmas and further its effect on power of excited EPW and acceleration of electrons. It is observed that focusing of two laser beams in plasma increases for higher order of hollow Gaussian beams,which significantly enhanced the power of generated EPW and energy gain. The amplitude of EPW and energy gain by electrons is found to enhance with an increase in the intensity of laser beams and plasma density. This study will be useful to plasma beat wave accelerator and in other applications requiring multiple laser beams.     

多尺度等离子体动力学数值模拟中最初的无方程投影积分技术

发展一种针对等离子体多尺度问题的"最初的无方程投影积分(p-EFPI)"方法并成功应用于离子声波的模拟.该方法包括时间推进和时间投影两部分.电子速度通过概率分布函数或累积分布函数投影外推,电子位置坐标则通过投影外推的电子电荷密度重新调出;与电子相比,假设粗糙的离子运动可以很好地描述宏观尺度等离子体的演化行为,通过追踪和投影外推每个离子轨道保持全部离子运动学效应.尝试和检验p-EFPI方法在模拟等离子体物理现象中的应用.以离子声波为范例,数值计算表明:在离子相空间出现离子捕获效应前,p-EFPI模拟能够很好地再现PIC的结果,在离子捕获发生后,p-EFPI模拟仍然可以抓住除了离子捕获特征之外的其它主要物理特征.     

Linear and Nonlinear Wavetransformation and Absorption in the Inhomogeneous Plasma Capacitor

The parametric decay process in inhomogeneous layers existing near the plasma boundaries or in front of antennas and probes in a plasma has been investigated. The linear enhancement of the pump field near ω = ω_p, the threshold fieldstrength, the wavenumber selection rules and the influence of spontaneous low frequency fluctuations are discussed in detail using a one-dimensional model of the inhomogeneous plasma capacitor. According to this model the instabilities appear in the layers with maximum linear transformation and (linear) absorption. In addition, a strong nonlinear part of absorption in the presence of the instability has been observed. The level of the spontaneous low frequency fluctuations influences strongly the spectrum of the parametrically excited ion waves. The experiments show a redistribution of the transferred ion acoustic wave energy over the whole wave continuum up to ω_pi, if a sufficient strong spontaneous fluctuation level exists in the plasma. It is impossible, however, to excite ion acoustic turbulence by the decay of the high frequency pump field under the present conditions. The conditions for the linear field enhancement are disturbed by the action of the ponderomotive forces changing the density profile near the critical point before reaching the strong pump amplitude being necessary for the excitation of a cascade of decay processes.     

Nonlinear Behavior of Electromagnetic Waves in Ultra‐Relativistic Electron‐Positron Plasmas

A set of nonlinear equations which can self‐consistently describe the behavior of high frequency Electromagnetic (EM) waves in un‐magnetized, ultra‐relativistic electron‐positron (e‐p) plasmas is obtained on the basis of Vlasov‐Maxwell equations. Nonlinear wave‐wave, wave‐particle interactions lead to the coupling of high frequency EM waves with low frequency density perturbations which result from EM waves radiation pressure. The same as that in conventional electron‐ion (e‐i) plasmas, strong EM waves in e‐p plasmas will give rise to density depletion in which itself are trapped. But on the contrary to that in e‐i plasmas, there no longer exists electrostatic acoustic–like wave in e‐p plasmas due to the absence of mass difference. For linear polarized EM waves, a stationary EM soliton with a spiky structure will be formed. The possible relation of the localized field to pulsar radio pulse is discussed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

利用离子声波朗道阻尼测量氧化物阴极放电中的离子温度

作为等离子体重要参数之一, 特别是在低温等离子体中离子温度的测量一直较为困难. 在磁化线性等离子体装置氧化物阴极脉冲放电条件下, 利用栅网激发离子声波, 通过测量波幅在朗道阻尼作用下随空间的演化, 利用阻尼长度是离子温度和电子温度的函数, 计算得到离子温度为0.3 eV. 测量值与国外类似装置利用光谱诊断所得结果基本相同.     

Transformation of a nonlinear plasma wave into electromagnetic radiation in a periodic magnetic field

We study transformation of a nonlinear plasma wave into electromagnetic radiation in the periodic static magnetic field of an undulator. Such a wave can be excited by a short laser pulse or a relativistic electron bunch. The features of relativistic upper-hybrid plasma oscillations are analyzed. In the approximation of constant pump, resonance conditions of excitation of an electromagnetic wave and the characteristic transformation length are found. The nonlinear stage of transformation with allowance for pump depletion is considered. The studied phenomenon can be used for development of a high-power terahertz-radiatoin source. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 6, pp. 496–507, June 2007.     

Self-focusing of Gaussian laser beam in collisionless plasma and its effect on stimulated Raman scattering process

This paper presents an investigation of self-focusing of Gaussian laser beam in collisionless plasma and its effect on stimulated Raman scattering process. The pump beam interacts with a pre-excited electron plasma wave thereby generating a back-scattered wave. On account of Gaussian intensity distribution of laser beam, the time independent component of the ponderomotive force along a direction perpendicular to the beam propagation becomes finite, which modifies the background plasma density profile in a direction transverse to pump beam axis. This modification in density affects the incident laser beam, electron plasma wave and back-scattered beam. We have set up the non-linear differential equations for the beam width parameters of the main beam, electron plasma wave, back-scattered wave and SRS-reflectivity by taking full non-linear part of the dielectric constant of collisionless plasma with the help of moment theory approach. It is observed from the analysis that focusing of waves greatly enhances the SRS reflectivity.     

双束“自陷”激光驱动的电子等离子体波的拍频激发

本文提出并详细研究了应用两束“自陷”激光激发电子等离子体波(EPW)来维持等离子体拍频加速器(PBWA)中光束及其激发的EPW的会聚。文中导出了EPW饱和振幅所满足的方程,自洽地研究了泵浦光束的“自陷”条件,并解析地得到了最佳离谐条件及其对应的最佳初始等离子体密度以及EPW的最大振幅。在高斯型自陷泵浦光束情况下,文中应用数值法计算了EPW的横向分布。对于一定的离谐参量,此分布呈现出独特的性质。此外,本文还得到了由泵浦光束的非均匀性所产生的EPW电场的径向分量,并简要地讨论了它对PBWA中粒子加速的影响。 关键词：     

Nonlinear interactions between electromagnetic waves and electron plasma oscillations in quantum plasmas

We consider nonlinear interactions between intense circularly polarized electromagnetic (CPEM) waves and electron plasma oscillations (EPOs) in a dense quantum plasma, taking into account the electron density response in the presence of the relativistic ponderomotive force and mass increase in the CPEM wave fields. The dynamics of the CPEM waves and EPOs is governed by the two coupled nonlinear Schr?dinger equations and Poisson's equation. The nonlinear equations admit the modulational instability of an intense CPEM pump wave against EPOs, leading to the formation and trapping of localized CPEM wave pipes in the electron density hole that is associated with a positive potential distribution in our dense plasma. The relevance of our investigation to the next generation intense laser-solid density plasma interaction experiments is discussed.     

Acoustic field excited by a pulsed laser line source in a cylinder

The excitation and propagation of the acoustic waves in an elastic cylinder are studied by laser ultrasonics both theoretically and experimentally. The theoretical analysis of the two-dimensional acoustic field excited by a pulsed laser line source impacting on the generatrix of an elastic cylinder is presented. The dispersive properties for both cylindrical Rayleigh wave and the higher modes--whispering gallery (WG) modes are analyzed in detail. The numerical transient displacement waveforms for a detecting point located another terminal of the cylinder diameter opposite the source are calculated. The experimental excitation and detection of the acoustic waves in an aluminum cylinder are carried out on a laser ultrasonic system, which mainly consists of a Q-switched Nd:YAG laser and a laser interferometer. The wave components of bulk waves and surface waves (cylindrical Rayleigh waves and WG modes) are analyzed by comparing the numerical and experimental waveforms. The results are in good agreement.     

Experimental Evidence of Parametric Instabilities in an Unmagnetized Plasma Subjected to a Strong H.F. Electric Field

Experimental evidence of parametric excitation, by an intense external H.F. field, of an electron surface mode and an ion wave is presented. The pumping electromagnetic energy density is equal to or slightly larger than the thermal energy density of the electrons. The value of f_pc/f₀ (electron plasma frequency/external field frequency) is that for an electron surface wave. Depending on the pressure and field intensity, this decay instability can lead to three types of low frequency oscillations, with frequencies close to the ion plasma frequency. Two of these are described by Aliev and Silin's intense field theory: one is the volume ion plasma oscillation and the other a surface ion plasma oscillation. The third corresponds to no known ion eigenmode. Several other features of the theory by Aliev and co-workers are also confirmed experimentally, such as the harmonic excitation of the instability (nf₀ ≈ f_pe/√2, where n is an integer), the instability amplitude as a function of f_pe/f₀ (above threshold conditions), the value of the mismatch parameter as a function of field strength and ion mass, and the existence of a fine structure corresponding to the symmetric and antisymmetric electron surface oscillations. Even at high pump field strengths, the decay products are nearly monochromatic i.e. the plasma does not become turbulent.     

Zur simultanen Ausbreitung von Ionenschallwellen und Electron free streaming waves

The paper deals with the propagation of externally excited signals in dc-discharges. The experimentally observed behaviour of signals can be qualitatively correct explained on the basis of the theoretically developed conception of the simultaneous propagation of ion acoustic wave and electron free streaming wave. There exists a satisfactory quantitative agreement between experimental and theoretical values of damping for both types of waves. The assumption of the existence of the electron free streaming wave explains not only the amplitude modulated measuring signal but also leads to an essentially better agreement between the experimental and theoretical values of damping for ion acoustic waves.     

在稀薄等离子体中激光传播的相对论自聚焦

讨论超强、超短脉冲激光在稀薄等离子体中传播过程的某些性质;用二维快速傅立叶变换求解波动方程.相对论自聚焦的基本方程包括非线性源项和衍射的影响.由于有质动力和相对论的影响,使等离子体的频率降低,从而使折射指数发生改变,影响激光在等离子体中的传播.在入射激光功率(p)超过临界功率(p_c)时,激光在传播过程中产生自聚焦;反之,激光在传播过程中逐渐衰减,不产生自聚焦.