Langmuir Oscillations Research Articles

Influence of Inhomogeneity and Finite Pressure of a Plasma on Nonlinear Electron Oscillations

Based on the hydrodynamic description, the influence of inhomogeneity and finite pressure of a plasma on the characteristics of nonlinear Langmuir oscillations is considered. It is demonstrated that in the case of weak nonuniformity the nonlinear Langmuir oscillations become nonharmonic and are described by the Duffing equation.

Generation of plasma oscillations in a low-pressure microwave discharge

The resonant excitation of plasma (Langmuir) oscillations during the microwave breakdown of a low-pressure gas is studied both analytically and numerically using the simplest uniform model. It is shown that, because of a significant delay in electron heating and cooling, this effect ensures that the plasma density increases at a high (resonant) rate, even after exceeding a critical value, and can reach a very high (overcritical) level.

Nonlinear Langmuir oscillations under nonequilibrium conditions

The influence of external ionization sources on the characteristics of Langmuir oscillations in a partially ionized plasma is considered. It is demonstrated that in the case of continuous sources of ionization the nonlinear Langmuir oscillations are nonharmonic and are determined by the Airy equation.

Transition from Langmuir-Jeans to Alfvén-Jeans Modes in Dusty Plasmas

Dusty plasmas are a mixture of standard plasma components together with charged and heavy dust grains, for which self-gravitational effects might become important. For parallel electrostatic modes Langmuir oscillations combine with the Jeans instability, known from neutral self-gravitating systems, whereas at strictly perpendicular propagation the magnetosonic part of the extraordinary mode couples to the Jeans mode. Spurred by these limiting cases, we investigate oblique waves to show how self-gravitation goes over from parallel electrostatic to perpendicular magnetosonic modes, and give elements of the general dispersion law. The startling conclusion is that the critical Jeans lengths are exactly as derived from parallel electrostatic modes, except very close to perpendicular propagation, where an abrupt transition occurs to the critical lengths determined from the magnetosonic-Jeans modes. Furthermore, the inclusion of neutral dust or gas can drastically shorten the critical Jeans-like length scales.

Langmuir oscillations under nonequilibrium conditions

The influence of external ionization sources on the characteristics of Langmuir oscillations in a partially ionized plasma is considered. It is demonstrated that in the case of continuous sources of ionization the nonlinear Langmuir oscillations are nonharmonic and are determined by the Airy equation.

Well-posedness of the cauchy problem for the coupled system of the Schrödinger-KdV equations

This paper is devoted to the study of the Cauchy problem for the coupled system of the Schrodinger-KdV equations which describes the nonlinear dynamics of the one-dimensional Langmuir and ion-acoustic waves. Global well-posedness of the problem is established in the spaceH κ ×H κ (κ eZ +), the first and second components of which correspond to the electric field of the Langmuir oscillations and the low-frequency density perturbation respectively.

Diagnostics of Langmuir oscillations in a superdense plasma

The level and the angular distribution of Langmuir oscillations in a dense plasma produced on the Phoenix plasma radiation source (PRS) were measured. Line profiles of several lines in the Lyman series of Al XIII were measured using crystal spectrometers. A spectral line shape model was used, which attempted to take into account all significant broadening mechanisms. The parameters of the plasma and the Langmuir oscillations were found by generating profiles using the model and comparing these profiles to the experimental spectra. The strength of the Langmuir oscillations was found to be E/sub 0//spl ap/1-9 GV/cm, indicative of a strong Langmuir turbulence. The polarization analysis of the profiles of the Al XIII Lyman /spl gamma/ line has shown that the Langmuir oscillations develop anisotropically, primarily in the direction of the plasma current.

Stark-profile calculations for spectral lines of hydrogenic ions in plasmas submitted to a strong oscillating electric field

Spectral line shapes of ions in hot plasmas submitted to a strong oscillating electric field have been theoretically studied by applying standard hypotheses of plasma line broadening along with a nonperturbative (Floquet) treatment of the (external) oscillating field. The formulation has been applied to the two first resonance lines of various hydrogenic ions in hot plasmas subjected to a strong Langmuir oscillation or submitted to an intense laser field. It is shown that the simultaneous action of a strong oscillating field and the plasma particle fields can lead to large modifications of the spectral line shapes.

Turbulization of nonlinear Langmuir oscillations in a cold plasma

It is shown that the electric field of Langmuir oscillations in a cold plasma contains a component, independent of time, setting ions in motion. Using Lagrange variables, one-dimensional dynamics of plasma in respect to the interaction between electron oscillations and ion movement is investigated. As a consequence of this interaction, the crossing of electron trajectories occurs even at small amplitudes at time tc, i.e., one-dimensional turbulence appears in the system. The expression for tc is derived. In time tc ion displacements as well as ion energy are found to depend only on the electron–ion mass relationship.

Limiting nonideal metastable supercooled plasma

Direct modeling of the dynamics of a system of many Coulomb particles is applied to analyze the formation stage of a metastable plasma state from an initial, highly nonideal state, and also to consider some properties of this metastable supercooled state. It is shown that relaxation of the average particle kinetic energy may be characterized by a universal dimensionless function and in particular, there is a limiting degree of plasma nonideality which may be achieved in the metastable state, in the absence of any external influence. The calculated pair correlation functions agree with the results of the Debye model, even outside its limits of validity. The time dependence of the total dipole moment of the particle system is investigated. It is shown that oscillations of the total dipole moment are observed. These collective oscillations take place at a frequency slightly below the Langmuir frequency and the oscillations of free and bound electrons are in antiphase. The hypothesis is put forward that recombination relaxation is frozen as a result of interaction between quasibound electrons and Langmuir oscillations of free electrons.

On the amplitude of intense Langmuir waves in the terrestrial electron foreshock

Waveforms of large‐amplitude Langmuir oscillations were recorded by the Wind spacecraft in the Earth's upstream electron foreshock region. We present some statistics of the waveforms and discuss them in the context of various saturation mechanisms. In particular, it is found that the value of Epeak/Erms is not large, as previously suggested, and that the largest‐amplitude Langmuir waveforms are generally somewhat sinusoidal and lack structure on small spatial scales. The measured probability distribution of electric field amplitude and dimensionless energy suggest that some stochastic process may play a role in wave generation. The values of dimensionless energy needed to arrest Langmuir wave collapse occur with very small probability and the value of Epeak/Erms for large fields suggests that, statistically, Langmuir wave collapse is not an important process in the terrestrial foreshock.

The magnetic field of Langmuir oscillations

The small-scale quasistationary magnetic field appearing in a plasma exhibiting plasma oscillations is considered. It is shown that this magnetic field is capable of leading to dissipation of the electromagnetic waves propagating in the plasma.

Some properties of an ultimately nonideal metastable supercooled plasma

The formation of a metastable plasma state from an initial strongly nonideal state and certain properties of this metastable supercooled state are considered by directly modeling the dynamics of a system of many Coulomb particles. It is shown that the relaxation of the average kinetic energy of the particles can be characterized by a universal dimensionless function and, in particular, that an ultimate value degree of plasma nonidealness occurs which can be reached in the metastable state when no external action is present. The calculated binary correlation functions are in good agreement with the results of the Debye model, even outside its range of applicability. The time dependence of the total dipole moment of the system of particles is investigated. It is shown that there are oscillations of the total dipole moment. These collective oscillations take place at a frequency which is somewhat below the Langmuir frequency, the oscillations of the free and bound electrons occurring in antiphase. A hypothesis is advanced to the effect that recombination relaxation is frozen on account of the interaction of quasibound electrons with the Langmuir oscillations of the free electrons.

Collective oscillations of electrons for modeling from first principles and the nature of anomalous drift along the energy axis

A hypothesis is advanced that a metastable supercolled state of a system of classical Coulomb particles can be provided by the quasiresonant interaction of coupled electrons with collective oscillations of plasma electrons. This interaction is particularly strong when the Kepler frequency is of the order of the Langmuir oscillation frequency (which occures when the radius of an electron orbit is of the order of the average distance between the charges). Modeling from first principles has shown that the characteristic oscillation time of the dipole moment of a system of Coulomb particles is of the order of the Langmuir oscilation frequency.

Langmuir oscillations in a cold inhomogeneous plasma.

One-dimensional nonlinear Langmuir oscillations in a cold inhomogeneous plasma are considered. The spatial distribution of the amplitude of oscillations is set by the initial disturbance and can be arbitrary, i.e., it is not in any way connected with the inhomogeneity of the plasma. Taking place at small spatial gradients of the initial disturbance because of a growing with time phase shift of oscillations of different electrons, the effect of formation of narrow density peaks is illustrated. The density peaks always move in the direction of a decrease of ion concentration. In this movement their amplitude can grow or decrease depending on the direction of the initial disturbance gradient. A number of electrons, forming density peaks, reduce with a diminution of plasma inhomogeneity but the peak amplitudes always increase unlimitedly with time up to the self-intersection of electron trajectories. An equation, making it possible to determine the instant of trajectory intersection in case of small plasma inhomogeneity of arbitrary kind and arbitrary gradients of the initial disturbance, is obtained. It is shown by a numerical calculation that the analytical relations obtained are not essentially changed if one takes into account the nonlinearity of corresponding differential equations.

Communication with reentry space vehicles via short pulses

The resonant absorption of a short pulse of electromagnetic radiation in a plasma slab is considered in order to examine the effectiveness of using short pulses for information transfer through the plasma sheaths surrounding reentry vehicles. The amplitudes of the Raman scattering (RS) on the Langmuir oscillations associated with resonant absorption and the amplitude of the Brillouin scattering (BS) on the nonlinear modifications of the plasma profile are calculated. On‐board detection of the RS and BS signals are proposed as parallel and independent channels for reading the message encoded on the electromagnetic pulse sequence. The information transfer capacity of two other nonlinear effects, the generation of the fast electrons in the wave breaking process, and the excitation of the ion‐sound waves by the radiative pressure of the Langmuir oscillations are also considered.

On a nonlocal Zakharov equation

This article deals with the Cauchy problem for a nonlocal Zakharov equation. We will first recall the physical motivation (due to V.E. Zakharov) of this system. Then we will study the local Cauchy problem for certain initial data, and will identify the limit of the solutions when the ion velocity tends to infinity. 1 Origin of the nonlocal Zakharov system The Physical theory which follows has been developed by V.E. Zakharov5,6 to describe the Langmuir Oscillations in Plasma Physics. We assume that: 1. the plasma is sufficiently uniform, 2. the magnetic field is sufficiently weak, 3. the nonlinearity level is not too high, 4. there are no transverse high frequency electromagnetic waves. We consider the following equations that model the phenomena: Linearized hydrodynamical equations ∂ ∂t δne +div(n0 +δn)~ Ve = 0, ∂ ∂t δ~ Ve + 3V 2 Te n ~∇δn = e me ~ E .

Multistability and hysteresis of non-linear electron oscillations induced in a rippled plasma

In the framework of the hydrodynamic approximation, we study the Langmuir oscillations of an ion density ripple background plasma under the influence of a single external harmonic r.f. field. An analytic frequency response curve is derived for the late-time behaviour exhibiting multistability and hysteresis.

Interaction of an ultrashort, relativistically strong laser pulse with an overdense plasma

The results of an analytical description and of a particle-in-cell simulation of the interaction of an ultrashort, relativistically intense laser pulse, obliquely incident on a nonuniform overdense plasma, are presented and several novel features are identified. The absorption and reflection of the ultraintense electromagnetic laser radiation from a sharp-boundary plasma, high harmonic generation, and the transformation into low-frequency radiation are discussed. In the case of weak plasma nonuniformity the excitation of nonlinear Langmuir oscillations in the plasma resonance region and the resulting electron acceleration are investigated. The vacuum heating of the electrons and the self-intersection of the electron trajectories are also studied. In the case of a sharp-boundary plasma, part of the energy of the laser pulse is found to be converted into a localized, relativistically strong, nonlinear electromagnetic pulse propagating into the plasma. The expansion of the hot electron cloud into the vacuum region and the action of the ponderomotive force of the laser pulse in the localized longitudinal electric field of the Langmuir oscillations lead to ion acceleration. The energy increase of a minority population of multicharged ions is found to be much greater than that of the ambient ions.

Langmuir oscillations in two-dimensional plasma

Langmuir oscillations in two-dimensional plasma