Langmuir Waves In Plasma Research Articles

TRANSPORT EQUATION FOR MHD TURBULENCE: APPLICATION TO PARTICLE ACCELERATION AT INTERPLANETARY SHOCKS

The aim of the present paper is to unify the various transport equations for turbulent waves that are used in different areas of space physics. Here, we mostly focus on the magnetohydrodynamic turbulence, in particular the Alfvturbulence. The applied methods, however, are general and can be extended to other forms of turbulence, for example the acoustic turbulence, or Langmuir plasma waves. With minor modifications, the derivations followed here can be extended for relativistic motions, thus making it possible to apply them to the wave transport in astrophysical objects with high plasma speeds (radiojets), or strong gravity (black hole surroundings).

Quasi-stationary solitons for Langmuir waves in plasmas

The multiple-scale perturbation analysis is used to study the perturbed nonlinear Schrödinger’s equation, that describes the Langmuir waves in plasmas. The perturbation terms include the non-local term due to nonlinear Landau damping. The WKB type ansatz is used to define the phase of the soliton that captures the corrections to the pulse where the standard soliton perturbation theory fails.

Intense laser pulse amplification using Raman backscatter in plasma channels

It has been proposed that the Raman backscatter interaction in a plasma can be used to amplify ultra-intense laser pulses. To accomplish this, energy is transferred from a long drive pulse at frequency ω pump to an intense seed pulse at frequency ω seed, with a Langmuir plasma wave at frequency w p mediating the transfer; the frequencies are chosen to satisfy the resonant condition ω p= ω pump− ω seed. Diffraction of the pulses limits the interaction length in a uniform plasma, and hence the energy transfer between the pulses. However in a parabolic plasma density channel it is shown, through two-dimensional particle-in-cell simulations, that such a plasma channel can be used to guide both the amplified and drive pulses over an interaction distance much greater than a diffraction length. The seed pulse is amplified by a factor of more than 200 in energy for pulses whose widths are matched to the channel size, and achieve a peak intensity of more than 6×10 17 W/cm 2. Unmatched pump pulses are seen to generate much smaller gain.

Dynamics of Magnetically Trapped Boson-Fermion Mixtures

We investigate the dynamics of magnetically trapped boson-fermion mixtures at very low temperature. Using the mean field approach, we derive the Gross-Pitaevskii equation for the Bose-Einstein condensate wavefunction. We apply the Thomas-Fermi approximation and the hydrodynamic approach to the degenerate Fermi gas and obtain an equation of motion for its number density perturbation. It is remarkable that coupled time-evolution equations for the mixture can be regarded as an extension of the Zakharov equations, a model for the Langmuir waves in plasma.

Evolution of Langmuir waves in a plasma contaminated by variable-charge impurities

The propagation of Langmuir waves in nonisothermal plasmas contaminated by fine dust particles with variable charge is investigated for a self-consistent closed system. Dust charge relaxation, ionization, recombination, and collisional dissipation are taken into account. It is shown that the otherwise unstable coupling of the Langmuir and dust-charge relaxation modes becomes stable and the Langmuir waves are frequency down-shifted.

Stochastic heating in a plasma-beam system

The excitation of a Langmuir plasma wave by a monoenergetic electron beam for which resonant interaction conditions hold is investigated within a hydrodynamic description of the plasma. It is shown that parametric and modulation effects lead to the formation of nonlinear stationary waves with a low-frequency soliton-like envelope in the plasma. The behavior of electrons in the field of the wave packet formed by Langmuir waves with different phase velocities is investigated. The level of stochasticity in the system and the relative level of plasma fluctuations are determined.

Inertial fractal sets for dissipative Zakharov system

[1] has proved that the dissipative Zakharov system has ane2-weak compact attractor. In this paper, we further show that the dissipative Langmuir waves in plasmas admit an inertial fractal set of (e2,e1)-type. We also make the estimates on its fractal dimension and exponential attraction.

Finite Difference Method for Generalized Zakharov Equations

Abstract. A conservative difference scheme is presented for the initial-boundary value problem for generalized Zakharov equations. The scheme canbe implicit or semiexplicit depending on the choice of a parameter. On thebasis of a priori estimates and an inequality about norms, convergence of thedifference solution is proved in order 0(h2 + t2) , which is better than previous results. IntroductionThe Zakharov equations [20](1.1) iEt + Exx-NE = 0,(1.2) ^Ntt-{N+\E\2)xx = 0describe the propagation of Langmuir waves in plasmas. Here the complexunknown function E is the slowly varying envelope of the highly oscillatoryelectric field, and the unknown real function N denotes the fluctuation of the ion density about its equilibrium value.The global existence of a weak solution for the Zakharov equations in one dimension is proved in [19], and existence and uniqueness of a smooth solutionfor the equations are obtained provided smooth initial data are prescribed.Numerical methods for the Zakharov equations are studied only in [5, 9, 10,

Instability of Langmuir waves in plasma irradiated by directed gamma rays.

In this Letter we investigate the possibility of Langmuir turbulence generation by directed gamma rays penetrating a background plasma. Turbulence is generated because Compton scattering creates superthermal electrons whose distribution can be unstable to the Cherenkov radiation of Langmuir waves. Using the Klein-Nishina cross section for relativistic Compton scattering, we calculate the momentum distribution of recoil electrons and derive the increment of instability for nonmagnetized plasma. The instability appears when there is a sufficiently narrow bump, for example, annihilation line $h\ensuremath{\nu}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}m}_{e}{c}^{2}$ with a width less than $0.3{m}_{e}{c}^{2}$, in the gamma spectrum.

Stability of isotropic self-similar dynamics for scalar-wave collapse.

The scalar model for collapse of Langmuir waves in plasmas is studied numerically in two and three dimensions, for both radially symmetric and anisotropic initial conditions. Using a dynamic rescaling method, singular solutions are shown to become isotropic and self-similar near collapse. In two dimensions, the self-similar profile is not universal. In the limit where the mass of the wave tends to its minimal value for collapse, the solution approaches a subsonic regime different from the generic singularity of the nonlinear Schr\"odinger equation.

Waves with nonlinear polarization due to a self-generated magnetic field in a plasma

We investigate a new mechanism of nonlinear wave interaction in a plasma with an electromagnetic wave, a Langmuir plasma wave and a self-generated quasi-stationary magnetic field involved in the three-wave process. It is demonstrated that magnetic field generation supports a new wave of hybrid polarization, which can be changed during the nonlinear evolution. Periodic regimes, as well as regimes of soliton (instanton) formation and kink-shaped transitions, can be realized.

Stability of plane wave solutions of nonlinear systems

The linear stability of plane wave solutions of various systems of nonlinear partial differential equations is treated. They include an equation for the envelope of a surface wave train on deep water, Zakharov's system for Langmuir waves in plasmas, coupled Schrödinger and Klein-Gordon equations for nucleon and meson fields, and a pair coupled Schrödinger equations. The method of analysis, which was presented previously by the authors, is explained and its scope is broadened.

Ionospheric plasma modification in the vicinity of a spacecraft by powerful radio pulses in topside sounding

A mechanism of strong turbulence is proposed for interpretation of the resonances observed by a wide-band receiver during topside sounding. The turbulence is created in the vicinity of the spacecraft due to the striction modulation instability. Experimental results obtained with the aid of a wide-band receiver on board the Intercosmos-19 satellite are discussed in terms of strong wave-wave and/or wave-particle interaction, namely electron acceleration in Langmuir cavitons and non-linear generation of the electron Langmuir plasma waves and Tonks-Dattner resonances.

Observation of high‐frequency turbulence induced by an artificial ion beam in the ionosphere

High‐frequency electrostatic waves have been studied during the injection into the ionosphere of an artificial xenon ion beam in a direction quasi‐perpendicular to the magnetic field. The xenon ion plasma source was situated on a small ejectable payload, and the main characteristics of the beam were recorded on the central payload when the separation distance was increasing. Both active and passive methods of observation have been used. The electron density and temperature inside the beam have been derived from the active method of measurement, based on the propagation of artificial waves. The high‐frequency turbulence, detected with the passive method, appeared to be mainly electrostatic and was localized in two main different regions. At small distances from the source the strongest signals were recorded in the region of large‐density gradients situated in the leading edge of the beam. Then the spiky structure of the high‐frequency turbulence can be interpreted as resulting from the coupling between the lower hybrid drift instability and the Langmuir plasma waves. At larger distances from the source, another type of high‐frequency turbulence was set up in regions of low density situated in front of the beam. This last turbulence resulted from the destabilization of electron cyclotron harmonic waves and was localized inside a well‐defined density dip situated in front of the beam.

Microwave signature of thick-target electron beams in solar flares

The steady-state behavior of a flux of nonthermal electrons injected into a fully ionized thick target is examined. Owing to the (inverse square) energy dependence of the Coulomb collisional cross section, it is found that injected electron distributions that are monotonically decreasing functions of electron energy develop at finite depths into distributions that have 'humps' in velocity space; the electron energy corresponding to the hump correlates with the overlying particle column density to the target. This results in a two-stream unstable situation. The distribution is constantly being relaxed by quasi-linear relaxation and re-created by collisions; in this way a steady nonthermal level of Langmuir plasma waves is created, and these waves in turn produce microwave plasma radiation with a typical flux of 3 x 10 to the -16th erg/sq cm-sec. This flux can be enhanced by a factor of up to 100 by a high level of low-frequency (such as ion-acoustic) turbulence, which prevents quasi-linear relaxation for a sufficient fraction of the path length.

Theory of plasma turbulence in presence of intense high-frequency electromagnetic radiation

On the base of the kinetic Vlasov equation, and equation describing the nonlinear interaction of turbulent plasma waves in an intense high-frequency field is obtained. This equation is considered for a process of induced scattering of plasma Langmuir waves and stationary spectrum of turbulent plasma noise in a strong external high-frequency field is analyzed.