Effects of relativistic and ponderomotive nonlinearities on the interaction of high-power laser beam with an inhomogeneous warm plasma

The influence of relativistic-ponderomotive nonlinearities and the plasma inhomogeneity on the nonlinear interaction between a high-power laser beam and a warm underdense plasma are studied. It is clear that the relativistic ponderomotive force and the electron temperature modify the electron density distribution and consequently change the dielectric permittivity of the plasma. Therefore, by presenting the modified electron density and the nonlinear dielectric permittivity of the warm plasma, the electromagnetic wave equation for the propagation of intense laser beam through the plasma is derived. This nonlinear equation is numerically solved and the distributions of electromagnetic fields in the plasma, the variations of electron density, and plasma refractive index are investigated for two different background electron density profiles. The results show that the amplitude of the electric field and electron density oscillations gradually increase and decrease, during propagation in the inhomogeneous warm plasma with linear and exponential density profiles, respectively, and the distribution of electron density becomes extremely sharp in the presence of intense laser beam. It is also indicated that the electron temperature and initial electron density have an impact on the propagation of the laser beam in the plasma and change the plasma refractive index and the oscillations' amplitude and frequency. The obtained results indicate the importance of a proper choice of laser and plasma parameters on the electromagnetic field distributions, density steepening, and plasma refractive index variations in the interaction of an intense laser beam with an inhomogeneous warm plasma.     

Enhancement of electron density in the interaction of high-power electromagnetic waves with inhomogeneous magnetized plasma

Propagation characteristics of a high-power electromagnetic wave through an inhomogeneous magnetized plasma is investigated. Considering the momentum transfer equations for electrons and ions and taking into account the ponderomotive force, the distribution of electron density and dielectric permittivity are obtained. Using non-linear dielectric permittivity and Maxwell's equations in the absence of external current and charge densities, non-linear wave equations are achieved. The results indicate that the external static magnetic field can modify the profiles of both the electric and magnetic fields. It is also shown that the external static magnetic field enhances the amplitude of the electron density and the non-linear dielectric permittivity.     

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.     

Impact of nonlinear absorption on propagation of microwave in a plasma filled rectangular waveguide

In collisional and ponderomotive predominant regimes, the propagation of microwave in rectangular waveguide filled with collisional plasma is investigated numerically. The dominant mode is excited through an evacuated waveguide and then enters a similar and co-axis waveguide filled with plasma. In collisional predominant regime, the amplitude of electric field is oscillated along propagation path; outset of propagation path due to the electron-ion collision, the intensity oscillations are reduced. Afterward, under competition between the collisional nonlinearity and absorption, the intensity is increased, so the electron density peak is created in middle of waveguide. In ponderomotive predominant regime, the intensity is slowly decreased due to collision, so the electron density is ramped. Control parameters, like the frequency, input power, collision frequency, and background electron density are surveyed that can be used to control propagation characteristics of microwave. This method can be used to control heating of fusion plasma and accelerate charged particle.     

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.     

Weakly relativistic and space charge effects in interaction of high-power microwave with plasma

In the present work, numerical studies on the effects of weakly relativistic ponderomotive force and space charge in the nonlinear interaction of a high-power microwave beam with a plasma are carried out. It is shown that, the profiles of the electron density and dielectric permittivity contain high peaks, and modulation of wavelength occurs in electron density distribution by increasing the microwave energy flux. In addition, it is indicated that the profiles of the electric and magnetic fields in relativistic regime are lengthened more than non-relativistic regime by increasing the initial electron density and the relativistic effects cause the increase in oscillation wavelength of electron density, dielectric permittivity and space charge field, in comparison with the non-relativistic regime. Finally, the results of the research show that the steepening in electron density distributions and their oscillation wavelength are enhanced, when the relativistic effects appear.     

Nonlinear Dynamics of Laser Interaction with High Z Plasma

The formation and evolution of a plasma in the interaction of laser radiation with gold targets are studied by computer simulations using MHD code (ESC-CASTOR). The nonlinear features of the interaction including the absorption of laser radiation, heating of the plasma components, and the deformation of the density profile under the action of the ponderomotive force are discussed. The role of these nonlinear effects together and the influence of the radiative and collisional transport in the evolution of the density profile are discussed based on the numerically obtained two-dimensional dynamical structures of the hydrodynamic parameter (electron density n_e, ion density n_i, electron temperature T_e, ion temperature T_i), radiation temperature T_r, ponderomotive force profile, and the space-time dependencies of the absorption efficiency and the ionization rates. The radiation spectrum is analyzed and the regularities in the motion of the critical density surface are clarified.     

高功率微波在等离子体填充波导中的传播特性

 在考虑有质动力情况下对高功率微波在等离子体填充波导中的传播特性进行了理论分析和数值计算,研究了高功率微波在等离子体中的传播特性和微波场强与等离子体密度分布之间的关系。结果表明高功率微波的有质动力将影响微波色散特性,使微波场强分布偏离Bessel分布,并对等离子体有排开作用,当场强足够大时可将波导中心处等离子体排空形成低密度通道。     

低密等离子体通道中的非共振激光直接加速

在低密等离子体通道中, 横向有质动力可以有效调制电子的横向振荡过程. 一方面, 横向有质动力可以向外推动电子, 增大电子横向振荡振幅, 减小失相率, 使电子获得能量增益; 另一方面, 横向有质动力也可以通过对失相率的非线性调制来降低失相率, 在电子横向振荡振幅很小的情况下导致激光直接加速. 横向有质动力调制的大小由等离子体密度、激光强度和束宽共同决定. 三维模型结果也证实可以通过参数放大实现激光直接加速, 弥补了准二维模型的局限性.     

Nonlinear propagation of neutrinos in a strongly magnetized medium

The nonlinear propagation of an intense neutrino flux in an electron-positron plasma with equilibrium density and magnetic field inhomogeneities is considered. It is found that the neutrinos are nonlinearly coupled with electrostatic and electromagnetic disturbances due to weak Fermi interaction and ponderomotive forces. The process is governed by a Klein-Gordon equation for the neutrino flux and a wave equation for the plasma oscillations in the presence of the ponderomotive force of the neutrinos. This pair of equations is then used to derive a nonlinear dispersion relation which exhibits that nonthermal electrostatic and electromagnetic fluctuations are created on account of the energy density of the neutrinos. The relevance of our investigation to the anomalous absorption of neutrinos in a nonuniform magnetized medium is pointed out.     

Nonlinear Evolution of Driven Electron Plasma Oscillations in Inhomogeneous Plasmas

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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     

Propagation Characteristics of a High-Power Microwave in Waveguide Filled with Plasma

Analytical theory of high-power microwave propagation in waveguide filled with plasma is presented in this paper. The ponderomotive force effect of high power microwave is taken into consideration and preliminary numerical calculations are carried out, the propagation characteristics of the high-power microwave and the influence of microwave power on the distribution of plasma density are calculated and discussed.     

Wavenumber oscillations of a linear electron plasma testwave in the presence of a standing large-amplitude wave

A linear electron plasma testwave coexisting with a standing large-amplitude wave shows wavenumber oscillations which may be explained by stationary axial plasma density variations being produced by the pump wave via the ponderomotive force.     

Nonlinear structure of Gaussian laser beam in an axial non-uniform collisional plasma

Nonlinear structure of Gaussian laser beam in axial non-uniform underdense collisional plasma is investigated. Due to the combination effect of nonlinear ohmic heating and non-uniform of plasma, and which it modifies electrons temperature and density distribution. On the one hand, due to the effect of the nonlinear ohmic heating, electron temperature and electron density oscillations become highly peaked. On the other hand, due to add the influence of non-uniform of plasma, lead to the departure from sinusoidal shape of electrons temperature, electron density and electromagnetic fields distributions. With the increase of laser intensity, these nonlinear variations become more and more obvious, and their oscillations wavelength decrease.     

Relativistic ponderomotive forces

The interaction of a relativistic classical electron with an inhomogeneous electromagnetic field is investigated. In second-order perturbation theory the motion is separated into fast and slow motions, and the relativistic Newtonian equation is averaged over the fast oscillations. The rate of change obtained for the slow component of the electron momentum is interpreted as a relativistic ponderomotive force. The result is generalized to the relativistic case of the wellknown expression for the Gaponov-Miller force acting on an electron at rest. The expressions obtained for the relativistic ponderomotive forces are very complicated in the general case. They simplify in the limit of a stationary field (pulses of long duration) and a small gradient. The most typical and simplest special case of an inhomogeneous field—a stationary plane-focused beam—is investigated. The main difference between relativistic ponderomotive forces and their nonrelativistic limit is they have multiple components. In addition to the usual force directed along the gradient of the field, the relativistic case is also characterized by force components that do not have the form of the gradient of a potential and are parallel to the wave vector and the direction of the field polarization. It is shown that when a relativistic electron travels in a direction close to the direction of the wave vector of a focused laser beam, these components can greatly exceed the gradient force. A force directed along the field polarization vector arises even when the gradient of the field in this direction is zero. Zh. éksp. Teor. Fiz. 116, 1198–1209 (October 1999)     

The influence of striction density perturbations on the excitation of plasma oscillations inside thermal inhomogeneities of plasma

In this paper, we continue our studies begun in [Izv. Vyssh. Uchebn. Zaved., Radiofiz.,41, No. 3, 270 (1998)].Calculating the coefficients and nonlinear phase shift in the equation for plasma-wave intensity introduced in the eralier paper, we have solved the problem of the influence of striction perturbations of the plasma density on the excitation of shortwave plasma oscillations by an electromagnetic wave; the above oscillations are captured in a volume of inhomogeneities, which are extended along the magnetic field and have reduced electron density that crosses the level of the upper-hybrid resonance. The dissipative processes of absorption and emission of plasma waves beyond the inhomogeneity are assumed to be weak. The variation of excitation and reflection of plasma waves from the resonance level due to deformation of the plasma- density profile is described. The band of effective generation of eigenmodes of captured oscillations as a function of the total wave-phase increment in an inhomogeneity is determined. The effect of penetration of the field of a high-power plasma wave into the non-transmittance region as a result of the striction expulsion of plasma is calculated. With allowance for the nonlinear phenomena in question, we estimated the heating of artificial inhomogeneities of thermal origin as a result of collisional absorption of the plasma oscillations excited in a volume of inhomogeneities under the action of a high-power radio wave. The materials of this paper were reported at the IIIrd International School on Space Plasma Physics. Institute of Terrestrial Magnetism, Ionosphere, and Radio Wave Propagation, Russian Academy of Sciences, Troitsk, Moscow Region, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 10, pp. 1226–1247, October 1998.     

A hydrodynamic model for profile steepening at resonance absorption

The self-consistent modification of an inhomogeneous plasma density profile near the critical layer due to the ponderomotive force of an obliquely incident p-polarized electromagnetic wave is calculated within a simple hydrodynamic plasma model.     

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提出碰撞吸收型等离子体的等效折射指数,重新计算了折射角,并与利用常规方法得到的折射角进行了比较。分析了等离子体密度和碰撞频率对折射角的影响。考察了斜入射电磁波在吸收型等离子体中的折射特性,并以一维非均匀碰撞吸收型等离子体为例,对斜入射电磁波的反射特性进行了考察。结果表明,等效折射指数的概念涵盖了入射角度的影响,在考察斜入射时更准确、便捷。     

Coupling surface plasmon waves across gaps in a dielectric/metal interface by transformation optics

Propagation of a Gaussian laser beam in a plasma is analyzed by including the nonlinearity associated with the relativistic mass and the ponderomotive force. We set up the nonlinear differential equation for beam width parameter using parabolic equation approach and solve it numerically. Our results show that the ponderomotive self-focusing contributes in the relativistic self-focusing of the laser beam. An impact of plasma electron temperature, relative density parameter, and intensity parameter on the propagation of the laser beam has been explored.