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Stimulated Brillouin scattering experiments in the ionospheric plasma using a single electromagnetic pump wave have previously been observed to generate an electromagnetic sideband wave, emitted by the plasma, together with an ion- acoustic wave. Here we report results of a controlled, pump and probe beat-wave driven Brillouin scattering experiment, in which an ion-acoustic wave generated by the beating of electromagnetic pump and probe waves, results in electromagnetic sideband waves that are recorded on the ground. The experiment used the EISCAT facility in northern Norway, which has several high power electromagnetic wave transmitters and receivers in the radio frequency range. An electromagnetic pump consisting of large amplitude radio waves with ordinary (O) or extraordinary (X) mode polarization was injected into the overhead ionosphere, along with a less powerful probe wave, and radio sideband emissions observed on the ground clearly show stimulated Brillouin emissions at frequencies agreeing with, and changing with, the pump and probe frequencies. The experiment was simulated using a numerical full-scale model which clearly supports the interpretation of the experimental results. Such controlled beat-wave experiments demonstrate a way of remotely investigating the ionospheric plasma parameters. Nonlinear wave mixing has been explored in space plasma. Here the authors report beat-wave Brillouin scattering experiment at EISCAT, in which two radio waves at different transmitted frequencies are driving ion acoustic waves in the ionosphere, leading to stimulated Brillouin emissions escaping the plasma. [ABSTRACT FROM AUTHOR]

Anisotropic bi-Kappa distributed plasmas, as encountered in the solar wind and planetary magnetospheres, are susceptible to a variety of kinetic instabilities including the cyclotron instabilities driven by an excess of perpendicular temperature T⊥ > T∥ (where ∥, ⊥ denote directions relative to the mean magnetic field). These instabilities have been extensively investigated in the past, mainly limiting to a linear stability analysis. About their quasilinear (weakly nonlinear) development, some insights have been revealed by numerical simulations using PIC and Vlasov solvers. This paper presents a self-consistent analytical approach, which provides for both the electron and proton cyclotron instabilities an extended picture of the quasilinear time evolution of the anisotropic temperatures as well as the wave energy densities. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study of the linear and nonlinear evolution of the electromagnetic electron-cyclotron (EMEC) instability in a bi-Kappa distributed plasma. Distributions with high energy tails described by the Kappa power-laws are often observed in collision-less plasmas (e.g., solar wind and accelerators), where wave-particle interactions control the plasma thermodynamics and keep the particle distributions out of Maxwellian equilibrium. Under certain conditions, the anisotropic bi-Kappa distribution gives rise to plasma instabilities creating low-frequency EMEC waves in the whistler branch. The instability saturates nonlinearly by reducing the temperature anisotropy until marginal stability is reached. Numerical simulations of the Vlasov-Maxwell system of equations show excellent agreement with the growth-rate and real frequency of the unstable modes predicted by linear theory. The wave-amplitude of the EMEC waves at nonlinear saturation is consistent with magnetic trapping of the electrons. [ABSTRACT FROM AUTHOR]

Analytical and numerical studies of the dynamics of relativistic electron and ion holes in a collisionless plasma are presented. Ion and electron holes are localized Bernstein-Greene-Kruskal modes characterized by particle populations trapped in the self-consistent electrostatic potential associated with the holes. Electromagnetic radiation can be trapped in relativistic electron holes due to a combination of the density fluctuations and the relativistic mass increase of the electrons, which changes locally the dielectric properties of the plasma and leads to a localization of the electromagnetic wave envelopes. Relativistic ion holes may be formed in active galactic nuclei, supernova remnant shocks, pulsar winds, and gamma-ray burst jets where relativistic plasma streams are thought to exist. The relativistic ion holes may be responsible for the acceleration of particles to GeV energies. The analytic solutions for relativistic electron and ion holes are employed as initial conditions for numerical simulations in which the dynamics and stability of the phase-space holes are investigated. The results have relevance for intense laser-plasma experiments and for astrophysical plasmas. [ABSTRACT FROM AUTHOR]

We present theoretical and numerical studies of the nonlinear interactions between intense electromagnetic waves in plasmas containing high-and low-energy electron components. Such plasmas are frequently observed in laser-plasma experiments, where the hot electron component is created by the acceleration of electrons by strong electrostatic waves that are created by the laser-induced Raman forward and backward instabilities. The two-component electron plasma is described by the Vlasov equation for the hot electrons and the hydrodynamic equations for the cold electrons, which are coupled nonlinearly to the electromagnetic wave equation and the Poisson equation for the potential. The present nonlinear system is shown to admit electromagnetic solitary waves correlated with a positive potential and trapped electron islands from the hot electron population. [ABSTRACT FROM AUTHOR]

The ever increasing performance of supercomputers is now enabling kinetic simulations of extreme astrophysical and laser produced plasmas. Three-dimensional particle-in-cell (PIC) simulations of relativistic shocks have revealed highly filamented spatial structures and their ability to accelerate particles to ultrarelativistic speeds. However, these PIC simulations have not yet revealed mechanisms that could produce particles with tera-electron volt energies and beyond. In this work, PIC simulations in one dimension (1D) of the foreshock region of an internal shock in a gamma ray burst are performed to address this issue. The large spatiotemporal range accessible to a 1D simulation enables the self-consistent evolution of proton phase space structures that can accelerate particles to giga-electron volt energies in the jet frame of reference, and to tens of tera-electron volt in the Earth’s frame of reference. One potential source of ultrahigh energy cosmic rays may thus be the thermalization of relativistically moving plasma. [ABSTRACT FROM AUTHOR]

Abstract: We present a comprehensive review of recent theoretical and numerical studies of the formation and dynamics of electron and ion holes in a collisionless plasma. The electron hole is characterized by a localized positive potential in which a population of electrons is trapped, and a depletion of the electron number density, while the ion hole is associated with localized negative potential in which a population of ions is trapped and a depletion of both the ion and electron densities occur. We present conditions for the existence of quasi-stationary electron and ion holes in unmagnetized and magnetized electron–ion plasmas, as well as in an unmagnetized pair-ion plasma. An interesting aspect is the dynamic interactions between ion and electron holes and the surrounding plasma. The dynamics is investigated by means of numerical simulations in which analytical solutions of quasi-stationary electron and ion holes are used as initial conditions. Our Vlasov simulations of two colliding ion holes reveal the acceleration of electrons and a modification of the initially Maxwellian electron distribution function by the ion hole potentials, which work as barriers for the electrons. A secondary effect is the excitation of high-frequency plasma waves by the streams of electrons. On the other hand, we find that electron holes show an interesting dynamics in the presence of mobile ions. Since electron holes are associated with a positive electrostatic potential, they repel positively charged ions. Numerical simulations of electron holes in a plasma with mobile ions exhibit that the electron holes are, in general, attracted by ion density maxima and repelled by ion density minima. Therefore, standing electron holes can be accelerated by the self-created ion cavities. In a pair plasma, both the temperatures and masses of the positively and negatively charged particles are assumed equal, and therefore one must treat both species with a kinetic theory on an equal footing. Accordingly, a phase-space hole in one of the species is associated with reflected particles in the opposite species. Here standing solitary large-amplitude holes are not allowed, but they must have a propagation speed close to the thermal speed of the particles. We discuss extensions of the existing non-relativistic theories for the electron and ion holes in two directions. First, we describe a fully nonlinear kinetic theory for relativistic electron holes (REHs) in an unmagnetized plasma, and show that the REHs have amplitudes and widths much larger than their non-relativistic counterparts. Second, we extend the weakly nonlinear theories for the electron and ion holes to include the effects of the external magnetic field and the plasma inhomogeneity. The presence of the external magnetic field gives rise to the electron and ion hole structures which have differential scale sizes along and across the magnetic field direction. Consideration of the density inhomogeneity in a magnetized plasma with non-isothermal electron distribution function provides the possibility of bipolar electrostatic pulses that move with the electron diamagnetic drift across the density inhomogeneity and the magnetic field directions. In a plasma with sheared magnetic field we can have fast reconnection involving phase-space vortices in the lower-hybrid frequency range. We further present theoretical and numerical investigations of the nonlinear interaction between ion and electron holes and large amplitude high-frequency electrostatic and electromagnetic waves in plasmas. Since the ion hole is associated with a depletion of both the electron and ion densities, it can work as a resonance cavity for trapped Langmuir waves whose frequencies are below the electron plasma frequency of the unperturbed plasma. Large-amplitude Langmuir waves can modify the ion hole due to the ponderomotive force which pushes the electrons away from the center of the hole. This process can be modeled by a coupled nonlinear Schrödinger and Poisson system of equations, which exhibit a discrete set of trapped Langmuir eigenmodes in the ion hole in plasmas without and with high- charged impurities. In a kinetic description, however, the trapped Langmuir waves are Landau damped due to the relatively small length scale of the ion hole. Intense electromagnetic waves (IEMWs) can also be trapped by the REHs in an unmagnetized plasma. We study the localization of arbitrary large amplitudes IEMWs by incorporating nonlinearities associated with relativistic electron mass increase, relativistic ponderomotive force of the IEMWs, and non-isothermal electron distributions. We find that the combined effects of these three nonlinearities produce extremely large amplitude REHs which traps localized IEMWs. Such a nonlinear structure can accelerate electrons to very high energies. The relevance of our investigation to numerous localized structures observed in laboratory and space plasmas is discussed. We also propose to conduct new experiments that can confirm our new theoretical and simulation models dealing with kinetic nonlinear structures in electron–ion and electron–positron plasmas. Finally, we present our views of possible extensions of theoretical models and computer simulations that have been reviewed in here. [Copyright &y& Elsevier]

The nonlinear interaction between finite amplitude lower-hybrid (LH) and dispersive Alfvén (DA) waves is considered. For this purpose, a set of equations is derived, which governs the three-dimensional dynamics of nonlinearly coupled LH and DA waves propagating obliquely to an external magnetic field. The interaction between the two wave modes is mediated by the Reynolds stress of the LH waves and the density perturbation associated with the DA wave. Additional terms due to self-interaction nonlinearity of the DA wave are included in order to describe large-amplitude DA waves. Three-wave decay and modulational interactions of the system are analyzed by means of a newly derived nonlinear dispersion relation, which predicts the instability of a finite-amplitude LH pump wave. The fully nonlinear dynamics and the LH wave collapse are studied by solving the governing equations numerically. [ABSTRACT FROM AUTHOR]

Abstract: Dispersion properties of low-frequency (in comparison with the ion gyrofrequency) compressional electromagnetic waves in a nonuniform dusty magnetoplasma are presented. By using the plasma hydrodynamic equations together with the Faraday and Ampère laws, we derive a new dispersion relation. The latter is analyzed to show the relationship between various wave modes in dusty plasmas. The results should be useful in understanding the features of compressional electromagnetic waves in nonuniform astrophysical and laboratory dusty magnetoplasmas. [Copyright &y& Elsevier]

We present a review of recent analytical and numerical studies of the dynamics of electron and ion holes in a collisionless plasma. The new results are based on the class of analytic solutions which were found by Schamel more than three decades ago, and which here work as initial conditions to numerical simulations of the dynamics of ion and electron holes and their interaction with radiation and the background plasma. Our analytic and numerical studies reveal that ion holes in an electron-ion plasma can trap Langmuir waves, due the local electron density depletion associated with the negative ion hole potential. Since the scale-length of the ion holes are on a relatively small Debye scale, the trapped Langmuir waves are Landau damped. We also find that colliding ion holes accelerate electron streams by the negative ion hole potentials, and that these streams of electrons excite Langmuir waves due to a streaming instability. In our Vlasov simulation of two colliding ion holes, the holes survive the collision and after the collision, the electron distribution becomes flat-topped between the two ion holes due to the ion hole potentials which work as potential barriers for low-energy electrons. Our study of the dynamics between electron holes and the ion background reveals that standing electron holes can be accelerated by the selfcreated ion cavity owing to the positive electron hole potential. Vlasov simulations show that electron holes are repelled by ion density minima and attracted by ion density maxima. We also present an extension of Schamel's theory to relativistically hot plasmas, where the relativistic mass increase of the accelerated electrons have a dramatic effect on the electron hole, with an increase in the electron hole potential and in the width of the electron hole. A study of the interaction between electromagnetic waves with relativistic electron holes shows that electromagnetic waves can be both linearly and nonlinearly trapped in the electron hole, which widens further due to the relativistic mass increase and ponderomotive force in the oscillating electromagnetic field. The results of our simulations could be helpful to understand the nonlinear dynamics of electron and ion holes in space and laboratory plasmas. [ABSTRACT FROM AUTHOR]

In quantum electrodynamics, photon–photon scattering gives rise to self-interaction terms in Maxwell''s equations. The effect will be non-zero for electromagnetic waves trapped between regions of conducting material, such as two plasma layers. It is shown numerically that this trapping in conjunction with photon–photon scattering can yield self-compression of electromagnetic waves. We discuss the relevance of our results. [Copyright &y& Elsevier]

Nonlinear interactions between large amplitude upper-hybrid waves and low-frequency electromagnetic waves in a magnetized plasma have been considered. Specifically, the decay of upper-hybrid waves into lower-hybrid and magnetosonic waves, as well as the modulational instabilities leading to the formation of density cavities which trap upper-hybrid wave envelopes, are investigated both theoretically and numerically. It is found that the three-wave process between two upper-hybrid waves and the lower-hybrid wave, which is the fastest growing instability of the system, is important for the generation of waves of small wave numbers, via the self-interaction of the generated decay products from the three-wave interaction. A comparison between the theory of the parametric decay, simulations of a generalized Zakharov system of equations modeling the interaction between upper-hybrid, lower-hybrid and magnetosonic (fast Alfvénic) waves is presented. Comparisons are made with a simulation of the fully electromagnetic Vlasov–Maxwell system for ions and electrons where a sudden onset of cavities and long wavelength magnetosonic wave emission could be seen, similar as in the simulation of the Zakharov-type system. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We present an investigation of the nonlinear propagation of high-frequency coherent electromagnetic waves in a uniform quantum magnetoplasma. Specifically, we consider nonlinear couplings of right-hand circularly polarized electromagnetic-electron-cyclotron (CPEM-EC) waves with dispersive shear Alfvén (DSA) and dispersive compressional Alfvén (DCA) perturbations in plasmas composed of degenerate electron fluids and non-degenerate ion fluids. Such interactions lead to amplitude modulation of the CPEM-EC wave packets, the dynamics of which is governed by a three-dimensional nonlinear Schrödinger equation (NLSE) with the frequency shift arising from the relativistic electron mass increase in the CPEM-EC fields and density perturbations associated with the DSA and DCA perturbations. Accounting for the electromagnetic and quantum forces, we derive the evolution equation for the DSA and DCA waves in the presence of the magnetic field-aligned ponderomotive force of the CPEM-EC waves. The NLSE and the driven DSA and DCA equations are then used to investigate the modulational instability. The relevance of our investigation to laser-plasma interaction experiments and the cores of white dwarf stars is pointed out. [ABSTRACT FROM AUTHOR]

We present a theory for the quantum-electrodynamical (QED) parametric scattering instability of an intense photon pulse in an incoherent radiation background. The pump electromagnetic (EM) wave can decay into a scattered daughter EM wave and an acousticlike wave due to the QED vacuum polarization nonlinearity. By a linear instability analysis we obtain a nonlinear dispersion relation for the growth rate of the scattering instability. The nonlinear QED scattering instability can give rise to the exchange of orbital angular momentum between intense Laguerre-Gaussian mode photon pulses and the two daughter waves, which may be a useful method to detect the highly energetic photon gases existing in the vicinity of rotating dense bodies in the Universe, such as pulsars and magnetars. The observation of the scattered waves may reveal information about the twisted acoustic waves in the incoherent photon gas. [ABSTRACT FROM AUTHOR]

Abstract: It is shown that the ponderomotive force of large-amplitude electromagnetic waves (photons), which includes the electron spin current and exchange potential contributions in a quantum plasma, can generate magnetic fields. The present result can account for the magnetic fields in dense compact astrophysical objects and in the next generation laser–solid density plasma interaction experiments. [Copyright &y& Elsevier]