On the ponderomotive force and the effect of loss reaction on parametric instability

In this paper, the growth rate, ponderomotive force and the exciting condition for parametric instability are derived by considering the loss reaction using a new method. On the basis of the hydrodynamic equations, we take the production and loss reactions in plasma into account to derive the coupling equations for the electron plasma oscillation and ion acoustic oscillation, and obtain the growth rate for the parametric instability, the ponderomotive force and the exciting condition. The result shows that (a) the production reaction has no effect on the parametric instability, and the effect of loss reaction on the parametric instability is a damping one, (b) the more intensive the external field or pump is, the larger the growth rate is, (c) there exist two modes of the ponderomotive force, i.e.\ the high frequency mode and the low frequency mode, and (d) when ponderomotive force counteracts the damping force, the oscillations become non-damping and non-driving. The ratio of the electron plasma oscillation to ion acoustic oscillation is independent of the loss reaction and the external field.     

Equilibrium profiles for RF-plasma sources with ponderomotiveforces

An analysis is given of the influence of the electron ponderomotive force on the equilibrium plasma profiles of partially ionized, radio frequency discharge sources, The ponderomotive force can be written as a gradient of a potential varying with the square of the RF field in the plasma and is largest for electrons, The impact of this electron ponderomotive force on density and electrostatic potential profiles is demonstrated using a one-dimensional analytic model with supporting numerical solutions and a two dimensional fluid simulation. For nearly collisionless plasmas the ponderomotive force is valid when ω_ce^h/ω<1 where ω_ce ^h is the electron cyclotron frequency due to the RF magnetic field and ω is the RF driving frequency, In processing plasmas with parameters that satisfy this validity criteria, the equilibrium density profiles are weakly modified, For nearly collisionless processing plasmas with parameters such that ω_ce^h /ω>1, the ponderomotive force, is modified by other nonlinear force terms that need to be evaluated     

等离子体中大幅波与低频振荡粒子非线性相互作用效应

本文从Vlasov-Maxwell方程组出发,保留高频场到四级项,导得了纵、横波大幅高频场与低频振荡粒子拍频作用的动力学方程组。结果表明,在空间一维情况下,对亚声波,高阶大幅高频场的存在使形成Soliton的有质动力凝聚作用削弱,而对超声波则更不存在Soliton解;在三维情况下,似乎使Caviton形成变慢。 关键词：     

Terahertz radiation generation by beating of two chirped laser pulses in a warm collisional magnetized plasma

Analytical equations of terahertz(THz) radiation generation based on beating of two laser beams in a warm collisional magnetized plasma with a ripple density profile are developed. In this regard, the effects of frequency chirp on the field amplitude of the terahertz radiation as well as the temperature and collision parameters are investigated. The ponderomotive force is generated in the frequency chirp of beams. Resonant excitation depends on tuning of the plasma beat frequency,magnetic field frequency, thermal velocity, collisional frequency, and effect of the frequency chirp with the plasma density.For optimum parameters of frequency and temperature the maximum THz amplitude is obtained.     

The Effect of High Spatial Harmonics in RF Linac

The effect of high spatial harmonics on beam dynamics in a axisymmetric radio frequency linear accelerator (RF linac) is examined. The high spatial harmonics forms the second order ponderomotive focusing for the relativistical particle beam when the transverse motion is averaged over the period of RF structure, the beam transverse envelop equation is obtained including the ponderomotive focusing force which is useful for the design of RF gun and linac. Under a certain of high spatial harmonics coefficients, the high spatial harmonics increase the energy spread due to the stochasitical beam energy diffusion.     

The time-dependent ponderomotive force

In this paper, we review stress tensor, fluid theory, kinetic and Lie transform approaches for determining the ponderomotive force induced by high-frequency wavepackets in plasmas. After outlining the historical development of the ponderomotive force, stress tensor approaches will be presented. Here important concepts such as split-ups and symmetry of the stress tensors will be discussed. In the next section we compare several fluid theory derivations. Here the plasma dynamics is described in the oscillation-centre picture and necessitates the introduction of a velocity renormalization in the momentum equation. Next kinetic approaches of ponderomotive forces in Vlasov plasmas will be presented. Single-particle and Lie transform methods are then presented. Here we derive the ponderomotive forces and the wave-induced magnetization current from the ponderomotive Hamiltonian. Finally we discuss the present status of the ponderomotive force and suggest topics for further research.     

结合力来自波-粒子互作用(英文)

基于ＢＢＧＫＹ方程，采用二阶扰动理论探索了可观物理量与扰动波矢的相互关系。结果发现，两个扰动带电粒子之间存在一个关联它们的非线性力。这个被称之为结合力的空间尺度是由扰动波矢的虚部决定的。这个结合力的一般表示包含一个吸引项和一个排斥项，它们随粒子的温度和它们的扰动频率而变化。包含在这个结合力中的最重要的信息是同物质的基本构成和它们之间相互作用的性质相联系的。     

双频激光在等离子体中的共振自聚焦

本文从理论上详细地研究了双频激光在等离子体中的共振自聚焦。本章从流体方程出发,导出了双频激光驱动下等离子体的非线性介电常数,从而清楚地展示了等离子体波有质动力的影响。接着,具体地处理了等离子体纵向静电场,进而反映出共振自聚焦的具体特征。最后还讨论了共振自聚焦对拍频波加速器中粒子加速过程的影响。     

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由色散方程和流体方程推导得到了横等离激元和对等离子体相互作用的非线性控制方程,利用场论的方法构建非线性控制方程的拉格朗日密度函数并求得相互作用过程中守恒的等离激元数和总能量。通过标度变换发现横等离激元由于调制不稳定性将坍塌形成小尺度的局域结构。在坍塌过程中横等离激元产生的有质动力随场强的增强而增强。由于有质动力对粒子的排斥,对等离子体中将产生小尺度的密度空穴。     

Dynamical behaviour of transverse plasmons in pair plasmas

This paper analytically investigates the nonlinear behaviour of transverse plasmons in pair plasmas on the basis of the nonlinear governing equations obtained from Vlasov--Maxwell equations. It shows that high frequency transverse plasmons are modulationally unstable with respect to the uniform state of the pair plasma. Such an instability would cause wave field collapse into a localized region. During the collapse process, ponderomotive expulsion is greatly enhanced for the increase of wave field strength, leading to the formation of localized density cavitons which are significant for the future experimental research in the interaction between high frequency electromagnetic waves and pair plasmas.     

Elasticity of a magnetic fluid in a strong magnetic field

Complex measurements of the following elastic-magnetic parameters of a magnetic fluid suspended by magnetic levitation within a horizontal tube in a strong magnetic field were performed: the oscillation frequency and decay coefficient; the static, ponderomotive, and dynamic elasticity coefficients; the fluid displacement under hydrostatic pressure; magnetization curve; and the magnetic field strength and gradient. Calculations based on a model of ponderomotive elasticity with correction for the resistance of a viscous fluid in motion and on the fluid column displacement for two magnetic fluid samples agree well with the experimental magnetization curve. The discussed technique holds promise for research into magnetophoresis and nanoparticle aggregation in magnetic colloids.     

Effects of the evolution of two cross‐focused Gaussian laser beams on the terahertz generation in thermal collisional plasma

Generation of the terahertz (THz) radiation based on the beating of two cross‐focused high intensity Gaussian laser beams in a warm rippled density plasma is numerically investigated, taking into account the ponderomotive force, Ohmic heating, and collisional nonlinearities. The beat ponderomotive force as a result of cross‐focusing of beams induces a vertical velocity component that by coupling with the rippled density gives rise to a nonlinear current deriving THz radiation. The effect of laser beams spot size evolution and plasma parameters on the THz generation is studied. It was found that there exist special electron temperature and laser intensity ranges with “turning points” where the generation of THz radiation reaches its maximum value and outside of these ranges, it disappears. The results also indicated that increasing the background electron density as well as taking into account the collision frequency help THz generation. Moreover, the maximum yield of THz radiation occurs when the beat wave frequency approaches the plasma frequency.     

Relativistic Derivation of the Ponderomotive Force Produced by Two Intense Laser Fields

The ponderomotive force plays a fundamental role in the absorption of laser light on self-consistent plasma density profiles, in multiple-photon ionization, and in intense field electrodynamics. The relativistic corrections to the ponderomotive force of a transversely polarized electromagnetic wave lead to an approximately 20-percent reduction in the single particle ponderomotive force produced by a 10-?m 1016-W/cm2 laser field. Recent experimental investigations are based on using two intense laser fields to produce desired laser-matter interactions. This paper presents the first derivation of the nonlinear relativistic ponderomotive force produced by two intense laser fields. The results demonstrate that relativistic ponderomotive forces are not additive.     

Ion larmour radius effect on rf ponderomotive forces and induced poloidal flow in tokamak plasmas

Analytical approximations are used to clarify the effect of Larmour radius on rf ponderomotive forces and on poloidal flows induced by them in tokamak plasmas. The electromagnetic force is expressed as a sum of a gradient part and of a wave momentum transfer force, which is proportional to wave dissipation. The first part, called the gradient electromagnetic stress force, is combined with fluid dynamic (Reynolds) stress force, and gyroviscosity is included into viscosity force to model finite ion Larmour radius effects in the momentum response to the rf fields in plasmas. The expressions for the relative magnitude of different forces for kinetic Alfven waves and fast waves are derived.     

NONLINEAR LOCALIZED STRUCTURE IN DUSTY PLASMA

The nonlinear effect of ponderomotive force of high-frequency ion motion on the low-frequency motion of ions coupling with the dust density fluctuation is investigated. The nonlinear localized structure described by Zakharov equations and nonlinear Schr?dinger equation in dusty plasma are obtained. Envelope solitons for high-frequency ion motion and the dust density cavitons are also obtained and discussed.     

Cross-focusing of two laser beams in a plasma

Cross-focusing of two copropagating laser beams in a plasma is investigated using paraxial ray theory. If the lasers have a frequency difference equal to the electron plasma frequency, they can drive a large amplitude plasma wave. The ponderomotive force due to the plasma wave forces the plasma electrons outwards thereby generating a parabolic density profile giving rise to cross-focusing. The results show a decrease in threshold for focusing by two orders of magnitude as compared to focusing due to the ponderomotive force of the laser beams.     

Quantum effects on magnetization due to ponderomotive force in cold quantum plasmas

The quantum effects on the magnetization due to the ponderomotive force are investigated in cold quantum plasmas. It is shown that the ponderomotive force of the electromagnetic wave induces the magnetization and cyclotron motion in quantum plasmas. We also show that the magnetic field would not be induced without the quantum effects in plasmas. It is also found that the quantum effect enhances the cyclotron frequency due to the ponderomotive force related to the time variation of the field intensity. In addition, it is shown that the magnetization diminishes with an increase of the frequency of the electromagnetic field.     

Electron acceleration considering pondermotive force effect in a plasma-filled rectangular waveguide by microwave radiation

The electron acceleration inside the plasma-filled rectangular waveguide is numerically investigated for the externally injected single-electron model considering the effects of density modification under a balance between the ponderomotive force and the pressure gradient force. Using Maxwell’s equations, we evaluate the field components of the fundamental mode in the plasma-filled rectangular waveguide, where the obtained equations are solved numerically using the fourth-order Runge–Kutta method for the electric field amplitude of the microwave. Besides, by solving the relativistic momentum and energy equations using the fourth-order Runge–Kutta method, the deflection angle and the total energy of the electron in the waveguide are obtained. Furthermore, it is shown that the electron energy gain can be controlled using superposing microwave fundamental modes. Effects of various parameters on the results are graphically presented.     

Plasma ions dynamics in the wake of a short laser pulse

A new physical effect of a plasma channel formation by the ponderomotive force of a wakefield generated by a laser pulse with a length of the order of the electron plasma wavelength is discussed. For a narrow pulse, wherein the width is less than c/omega(pe) ( omega(pe) and c are the plasma frequency and light velocity, respectively), the channel has an annular form with on-axis density maximum. The depth of the channel increases with the distance from the pulse until the phase mixing arises and the wake starts to break. The linear fluid theory is used to obtain the scaling for wave-breaking conditions. The results of numerical simulations for high intensity laser pulses are in good agreement with theoretical predictions.     

有质动力和静电分离场对激光等离子体流体力学状态的影响

利用建立在欧拉坐标系上的一维电子_离子双流双温流体力学程序, 模拟了超短脉冲强激光 (1×1015W/cm2, 150fs)与线性密度梯度等离子体相互作用的流体力学过程. 模拟结果显示，入射激光与临界密度面的反射光叠加，在临界密度以下区域形成局域驻波， 产生的强有质动力在低密区驱动电子形成周期性密度结构——Bragg光栅，激光的反射被增 强. 临界密度处有质动力将等离子体分成向内和向外运动的两部分. 由于离子所受的有质动 力和热压强的梯度力远小于电子，体系产生了强静电分离场，离子的运动主要由该静电分离 场决定. 对双流双温模型和单流双温模型的模拟结果进行了比较. 当有质动力和热压强梯度 力较大时，两种模型对等离子体流体力学状态的描述有明显差异，单流双温模型无法描述此 时的流体力学状态. 关键词： 有质动力 密度调制 双流双温流体力学模型 单流模型