Langmuir Oscillations Research Articles

Quantum effects on propagation of surface Langmuir oscillations in semi-bounded quantum plasmas

The quantum effects on the propagation of surface Langmuir oscillations are investigated in semi-bounded quantum plasmas. The specular reflection method is employed to obtain the dispersion relation of the surface Langmuir oscillations. The results show that the surface Langmuir oscillations can be propagated due to the quantum effects. It is also shown that the quantum effect enhances the propagation velocity. However, in high wave number domains, the group velocity of the propagation of surface Langmuir oscillations decreases with increasing the wave number. In addition, the electrostatic fast surface oscillating mode is found in the semi-bounded cold quantum plasmas.

Numerical simulations of the charging of dust particles by contact with hot plasmas

Abstract. Charging of individual dust particles in contact with hot plasmas is studied by numerical methods. The dust particle is treated as a rigid solid body, composed by either perfectly insulating or conducting material. The collisionless plasma, consisting of electrons and singly charged ions, is simulated by Particle-in-Cell methods in two spatial dimensions. It is demonstrated that the surface conditions, i.e. roughness, of the dust particles are significant for the charging. In a streaming plasma, a dust grain develops an electric dipole moment which varies systematically with the relative plasma flow. The strength and direction of this dipole moment depends critically on the material. We observe also Langmuir oscillations excited in the vicinity of the particles, and analyze the spatial variation of their spectral distribution.

Diffusive radiation in one-dimensional Langmuir turbulence

We calculate spectra of radiation produced by a relativistic particle in the presence of one-dimensional Langmuir turbulence which might be generated by a streaming instability in the plasma, in particular, in the shock front or at the shock-shock interactions. The shape of the radiation spectra is shown to depend sensitively on the angle between the particle velocity and electric field direction. The radiation spectrum in the case of exactly transverse particle motion is degenerate and similar to that of spatially uniform Langmuir oscillations. In the case of oblique propagation, the spectrum is more complex, it consists of a number of power-law regions and may contain a distinct high-frequency spectral peak. The emission process considered is relevant to various laboratory plasma settings and for astrophysical objects as gamma-ray bursts and collimated jets.

Reflection and transmission of plasma waves at the interface of crystallites

A linearized problem of the reflection and transmission of a plasma wave at the boundary of a half-space (namely, the plane separating two crystallites) is formulated and analytically solved. The electron distribution function and the electric field inside the half-space of a degenerate plasma are found. The reflection and transmission coefficients are determined as functions of the input parameters of the problem. The longwave limit (i.e., the resonance case when the oscillation frequency of the self-consistent electric field is close to the natural (Langmuir) oscillation frequency) is analyzed.

On the stability of spatially uniform Langmuir oscillations of electronic plasmas

We investigate the stability of spatially uniform, time-periodic solutions of the one-dimensional Vlasov–Maxwell system describing the longitudinal oscillations of an electronic plasma in an uniform neutralizing ion background. We show that such a stability problem can be trivially solved since the zero wave number mode of the electric field, i.e. its space average, performs pure Langmuir oscillations independently of the other modes. We however point out that such oscillations do affect on time average the evolution of the velocity distribution function in the frame at rest.

Possible Langmuir oscillations in the He β spectral line profile

A 3.4 ps duration, high-repetition rate laser is used to create an aluminium ablation plasma at intensities between 10 15 W/cm 2 and 10 17 W/cm 2 . K-shell emission is observed from the target surface and several 100 μm in to the plume. High resolution, spatial resolved measurements of the He/5 (1s3p - 1s 2 ), Heγ (1s4p - 1s 2 ), Heδ (1s5p - 1s 2 ) and Hee (1s6p - 1s 2 ) transitions are obtained using a highly dispersive toroidal crystal spectrometer coupled to a large area charged-coupled device. This data shows unusual intensity modulations on He/( transitions. These oscillations are observed to 50 μm above the target and are found to be reproducible, and the intensity of the modulations is laser irradiance dependent.

Landau damping in space plasmas with generalized (r,q) distribution function

Space plasmas possessing non-Maxwellian particle distribution functions with an enhanced high-energy tail and shoulder in the profile of distribution function take an important role to the wave particle interaction. In the present paper Landau damping of electron plasma (Langmuir) waves and ion-acoustic waves in a hot, isotropic, unmagnetized plasma is studied with the generalized (r,q) distribution function. The results show that for the Langmuir oscillations Landau damping becomes severe as the spectral index r or q reduces. However, for the ion-acoustic waves Landau damping is more sensitive to the ion temperature than the spectral indices.

Excitation of Langmuir oscillations by a laser pulse in a semi-infinite dense plasma

A study is made of the nonlinear mechanism for the excitation of Langmuir waves in a dense plasma by an intense laser pulse with the frequency ω = ωp/2 (where ωp is the electron plasma frequency).

Nonlinear dynamics of the interaction of a modulated electron beam with a plasma

The excitation of plasma waves during the injection of an unmodulated and a density-modulated electron beam into a semi-infinite cold plasma is investigated. It is shown that the Langmuir oscillation energy accumulated in the plasma increases substantially near the plasma boundary and that the dimension of the region where the Langmuir oscillation energy is localized decreases with time.

Nonlinear Wave Phenomena in Inhomogeneous Plasma Media

Based on the hydrodynamics description, the influence of inhomogeneity and finite pressure of 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 anharmonic and are described by the Duffing equation.

Low frequency electromagnetic waves as a supplemental energy source to sustain microbial growth?

Microbial populations in tetra-distilled water collapsed when cultured in a permalloy chamber shielding the populations from the sun's and earth's electromagnetic field, but thrived when cultured in an ordinary thermostat open to the electromagnetic field. Theoretically, protons in liquid water can be excited at their natural resonance frequencies through Langmuir oscillations and obtain enough kinetic energy to charge the transmembrane potential of a cell. Microbes may be capable of converting this energy into chemical energy to supplement their energy needs.

Method for Studying Local Dynamics of Plasma Fluctuations in the Formation Process of Langmuir Cavities

A collective CO2 laser scattering method for experimental studies of local dynamics of strong Langmuir turbulence driven by a relativistic electron beam is described. The preliminary results of temporal behavior of Langmuir oscillations are presented.

First 100 ms of HF modification at Tromsø, Norway

Experiments were performed with the high‐power, high‐frequency (HF) facility at Tromsø, Norway to test theoretical predictions for the excitation of ion and Langmuir oscillations in the ionosphere. The principal diagnostic of wave‐plasma interactions was the VHF radar at the European Incoherent Scatter (EISCAT) facility. This radar is collocated with the HF facility. High‐resolution radar techniques were used to monitor the temporal development of the ion and Langmuir oscillations. HF pulses 100 ms in duration were periodically transmitted into a smooth background F region plasma. Measurements of the radar backscatter spectra show that all key spectral features predicted by strong Langmuir turbulence theory are simultaneously present in the plasma and that their evolution is in agreement with theoretical expectations. However, several new features have been observed that are not anticipated by current theory. The experimental results reinforce the notion that new theoretical developments are needed to accommodate the large HF electric fields produced at Tromsø and treat the electron acceleration process in a self‐consistent fashion.

Nanolayer parametric instability in near-field optics.

Parametric decay of electromagnetic waves into two Langmuir oscillations near the quarter critical density is suggested as being attributable to an enhanced electric field and to surface-enhanced Raman scattering in near-field optics. A nanolayer of silver aggregates localizes the wave in the evanescent region to a one-wavelength span and results in a wave-number mismatch as well as in a reduced growth rate. The fastest-growing mode has a growth rate that scales with the square root of the nanolayer's thickness.

Dependence of frequency of nonlinear cold plasma cylindrical oscillations on electron density

For cold plasma, the frequency of small amplitude Langmuir oscillations along one Cartesian coordinate is ωpo=4πe2no/me, where np=no is the constant proton density which is equal to the average electron density ne¯. This formula for ωpo is the basis for measurements of ne¯ in passive and active radio experiments located on spacecraft. We find that for cold plasma nonlinear cylindrical oscillations ne¯>np (i.e., a buildup of negative space charge near the axis of the cylinder). The resulting frequency of oscillations ωpe is greater than ωpo. The relation between ωpe and ne¯ is found to be logarithmic: ωpe=ωpo[1+ln(ne¯/no)/12] with 0.5% accuracy for the range 1⩽ne¯/np<6. For quasi-neutral plasma, when ne¯/np≈1, the logarithmic formula reduces to the linear one: ωpe=ωpo[11/12+(ne¯/np)/12]. For ne¯/np≫6, ωpe approaches an upper limit of 2ωpo. These results are expected to be helpful in diagnostics of ne¯ in the solar wind and in magnetospheric plasmas as well as in laboratory plasmas where cylindrical symmetry is present.

Uniform plasma oscillations in ellipsoid of conductive material

The influence of the shape of a sample on the type of uniform dipole collective electrons oscillations is discussed. In samples of a bulk shape uniform bulk dipole oscillation (Langmuir oscillation) cannot exist. It exists in samples of a thin slab shape only. As uniform bulk dipole oscillations cannot penetrate ellipsoidal samples of conductive material they exist in the surface layer of a sample only (Mie oscillations). Frequencies of Mie oscillations are calculated for a sample of the shape of an arbitrary ellipsoid.

Evolution of the electron Langmuir oscillations in an inhomogeneous magnetized plasma

The conditions under which the energy of the electron Langmuir oscillations can escape from the plasma into vacuum are determined in the simplest model of a plane slab of an inhomogeneous cold magnetized plasma in a uniform magnetic field.

Strong Langmuir turbulence with and without collapse: experimental study

Experiments on strong Langmuir turbulence (LT) driven by electron beam are reported. The technique of cold high-current relativistic electron beam (REB) permits to set up experimental conditions that are practically important but difficult for theoretical treatment of LT. These conditions include strong kinetic effects of plasma non-Maxwellian electrons, ion-acoustic oscillations which are weakly damped due to plasma non-isothermality and dispersion of Langmuir waves that are considerably modified by external magnetic field. A relatively dense plasma permits the use of the Thomson scattering method for observation of spectra of plasma fluctuations, electron distribution function, and local dynamics of plasma density. LT is studied in two operating modes that are characterized by moderate and increased current of REB. The experimental results with moderate REB current do not support the widely accepted picture when most of the Langmuir oscillations are trapped in density cavities. The energy flow through turbulence to plasma electrons is explained without major contribution of fully developed collapse, whereas, with increased REB current dynamic density cavities of spatial scale much less than the size of turbulent region are directly observed.

Normal form analysis and chaotic scenario in a Schrödinger–Boussinesq system

The coupled Schrödinger–Boussinesq system is known to describe various physical processes in plasma. On the one hand it describes high-frequency upper-hybrid waves coupled to appropriate low-frequency ones such as magnetosonic modes and on the other hand it also describes the Langmuir oscillations in plasma. The system has been seen to be integrable for very specialised values of the parameters. Here in this communication we have analysed the same set near the resonant region M→1 (where M stands for the Mach number) in a different way. A parameter p= eg 2/ σ has been identified, whose variation exhibits the change in the nature of the fixed point and defines the critical region best suited for normal form analysis. This reduces the four-dimensional system to a two-dimensional one. The nature of this reduced system is analysed graphically. In a certain region of p the system showed chaoticity and it was studied through Lyapunov exponent, Poincaré section and phase space analysis.

Dissipation of strong Langmuir turbulence in nonisothermal non-Maxwellian plasma

The regime of strong Langmuir turbulence characterized by the plasma nonisothermality and by the presence of an appreciable non-Maxwellian hot-electron component was experimentally studied. Turbulence was excited in the preliminary produced plasma by the relativistic electron beam. Thomson scattering of laser IR radiation served as the main diagnostic method. The spatial spectra of the Langmuir turbulence and of the attendant ion-sound turbulence were studied using Thomson collective scattering. Thomson incoherent scattering was used for studying the plasma electron distribution function and searching for the local dips of plasma density. Stark spectroscopy of turbulent microfields and the method of observation of plasma radiation at the double plasma frequency were also used. Based on the experimental data, the mechanism of Langmuir oscillation damping by plasma electrons was analyzed. The Langmuir wave conversion induced by the ion-sound turbulence is the most probable channel for energy transfer from the turbulence to plasma electrons, the low-frequency fluctuations being the direct consequence of the strong Langmuir turbulence.