Nonlocal theory of the spectra of modified ion cyclotron oscillations in a charged plasma produced by gas ionization

The problem of the stability of a charged plasma cylinder in crossed longitudinal magnetic and radial electric fields is considered under the assumption that the plasma electrons are magnetized and distributed uniformly in space and that the plasma ions have a low density and move without collisions. By using the Vlasov and Poisson equations for the electric and magnetic fields of arbitrary strengths and by expanding the radial eigenfunctions in Bessel functions, a dispersion relation is obtained for the modified ion cyclotron frequencies. The dispersion relation obtained is solved for the case of hot plasma electrons. At low ion densities, the oscillation spectra are stable and are described by the families of dispersion curves lying closely around the harmonics of the modified cyclotron frequency (including the zeroth harmonic). At higher ion densities, the dispersion curves for the frequencies of the lowest radial oscillation modes in neighboring families can intersect, leading to instability. The maximum instability growth rate can be several tenths of the modified ion cyclotron frequency.     

Relativistic Ion-Acoustic Solitary Waves in a Magnetized Pair Ion Dense Plasma with Nuclei of Heavy Elements

The propagation of ion-acoustic solitary waves (IASWs) in a magnetized collisionless degenerate plasma system for describing collective plasma oscillations in dense quantum plasmas with relativistically degenerate electrons, oppositely charged inertial ions, and positively charged immobile heavy elements is investigated theoretically. The perturbations of the magnetized quantum plasma are studied employing the reductive perturbation technique to derive the Korteweg–de Vries (KdV) and the modified KdV (mKdV) equations that admit solitary wave solutions. Chandrasekhar limits are used to investigate the degeneracy effects of interstellar compact objects through the equation of state for degenerate electrons in nonrelativistic and ultrarelativistic cases. The basic properties of small but finite-amplitude IASWs are modified significantly by the combined effects of the degenerate electron number density, pair ion number density, static heavy element number density, and magnetic field. It is found that the obliqueness affects both the amplitude and width of the solitary waves, whereas the other parameters mainly influence the width of the solitons. The results presented in this paper can be useful for future investigations of astrophysical multi-ion plasmas.     

Calculation of transport coefficients with allowance for the chemical composition of a low-temperature high-density metal plasma

The model proposed by Ichimaru for calculating transport coefficients is generalized to describe a plasma containing neutral atoms and ions with different charges. Ichimaru's model was developed for a fully ionized two-component (electrons and a single ion species) plasma with a temperature above 10⁵ K. Taking into account several species of positive ions and neutral atoms makes it possible to extend Ichimaru's model to a partially ionized plasma. Transport coefficients calculated from different models are compared with the experimental data.     

Ion-acoustic Gardner solitons in a four-component nonextensive multi-ion plasma

The nonlinear propagation of ion-acoustic (IA) solitary waves (SWs) in a four-component non-extensive multi-ion plasma system containing inertial positively charged light ions, negatively charged heavy ions, as well as noninertial nonextensive electrons and positrons has been theoretically investigated. The reductive perturbation method has been employed to derive the nonlinear equations, namely, Korteweg?deVries (KdV), modified KdV (mKdV), and Gardner equations. The basic features (viz. polarity, amplitude, width, etc.) of Gardner solitons are found to exist beyond the KdV limit and these IA Gardner solitons are qualitatively different from the KdV and mKdV solitons. It is observed that the basic features of IA SWs are modified by various plasma parameters (viz. electron and positron nonextensivity, electron number density to ion number density, and electron temperature to positron temperature, etc.) of the considered plasma system. The results obtained from this theoretical investigation may be useful in understanding the basic features of IA SWs propagating in both space and laboratory plasmas.     

Plasma Decay in the Afterglow of High-Voltage Nanosecond Discharges in Unsaturated and Oxygenated Hydrocarbons

Results of experimental and theoretical study of plasma decay in the afterglow of high-voltage nanosecond discharges in gaseous ethylene and dimethyl ether at room temperature and pressures from 2 to 20 Torr are presented. Using a microwave interferometer, the time behavior of the electron density in the range from 2 × 10¹⁰ to 3 × 10¹² cm^–3 during plasma decay is investigated. By processing the experimental data, the effective coefficients of electron–ion recombination as functions of the gas pressure are obtained. It is found that these coefficients substantially exceed the recombination coefficients of simple hydrocarbon ions. This distinction, as well as the increase in the effective recombination coefficient with pressure, is explained by the formation of cluster ions in three-body collisions, which recombine with electrons more efficiently than simple molecular ions. The coefficients of three-body conversion of simple molecular ions into cluster ions in the plasmas of ethylene and dimethyl ether, as well as the coefficients of recombination of electrons with cluster ions in these gases, are determined by analyzing the experimental data.     

Investigation of ion acceleration in an expanding laser plasma by using a hybrid Boltzmann-Vlasov-Poisson model

The acceleration of ions of different species from a plasma slab under the action of a charge-separation electric field driven by hot and cold electrons is studied by using a hybrid Boltzmann-Vlasov-Poisson model. The obtained spatial and energy distributions of light and heavy ions in different charge states demonstrate that the model can be efficiently used to study the ion composition in a multispecies expanding laser plasma. The regular features of the acceleration of ions of different species are investigated. The formation of compression and rarefaction waves in the halo of light ion impurity, as well as their effect on the energy spectrum of the accelerated ions, is analyzed. An approach is proposed that makes it possible to describe the production of fast ions by laser pulses of a given shape. It is shown that the energy of fast ions can be increased markedly by appropriately shaping the pulse. The effect of heating of the bulk of the cold target electrons on the ion acceleration is discussed.     

Skin Effects in a Dusty Plasma

A multifluid MHD model is applied to study the magnetic field dynamics in a dusty plasma. The motion of plasma electrons and ions is treated against the background of arbitrarily charged, immobile dust grains. When the dust density gradient is nonzero and when the inertia of the ions and electrons and the dissipation from their collisions with dust grains are neglected, we are dealing with a nonlinear convective penetration of the magnetic field into the plasma. When the dust density is uniform, the magnetic field dynamics is described by the nonlinear diffusion equations. The limiting cases of diffusion equations are analyzed for different parameter values of the problem (i.e., different rates of the collisions of ions and electrons with the dust grains and different ratios between the concentrations of the plasma components), and some of their solutions (including self-similar ones) are found. The results obtained can also be useful for research in solid-state physics, in which case the electrons and holes in a semiconductor may be analogues of plasma electrons and ions and the role of dust grains may be played by the crystal lattice and impurity atoms.     

Two-dimensional modeling of a transverse collisionless shock wave

Transverse collisionless shock waves in a plasma in which the initial β value is equal to zero for electrons and is small but nonzero for ions are studied in the two-dimensional approximation with allowance for anomalous resistivity. A hybrid model is applied such that the ions are treated in the kinetic approximation and the electrons are described in the hydrodynamic approximation. A collisionless shock wave is generated using a piston with a small two-dimensional perturbation. The ion distribution downstream of the shock front and the effect of electron and ion heating are analyzed. It is shown that, for Alfvén-Mach numbers M _A>2, ion heating is attributed primarily to the ions that have experienced a reflection from the shock front and whose velocities downstream of the front are very high. This conclusion agrees with the results of one-dimensional calculations. Solving the problem as formulated shows that two-dimensional effects are insignificant in the range of low Alfvén-Mach numbers (M _A≤5): the direction of the magnetic field is always close to its initial direction, the ions acquire low velocities along the magnetic field, and the quantitative parameters of the plasma downstream of the shock front are close to those obtained from the one-dimensional model. In the range of higher Alfvén-Mach numbers, two-dimensional effects are more pronounced and the ion distribution function is less anisotropic.     

Theory of the ICR heating of a plasma column: Methodological note

A set of wave equations is derived that describes electromagnetic waves at frequencies on the order of the ion gyrofrequency in a plasma column with an arbitrary electron temperature. This set takes into account, in particular, the resonant interaction of electrons with waves in the transit-time magnetic pumping regime. The effect of the amplification of the electromagnetic fields of current-carrying antennas by the plasma is analyzed. The evolution of the fields with an increase of plasma density from a zero value (vacuum) is considered. The main parameters are determined for minority ion cyclotron resonance heating in the planned EPSILON system.     

Nonuniformity of the chemical composition of a capillary discharge plasma

A steady-state distribution of the concentration of two ion species in a capillary discharge plasma is studied using MHD equations for a plasma with a spatially nonuniform, time-dependent chemical composition. In our case, the set of equations is significantly simplified because of the steady-state character and symmetry of the problem. Even with such simplification, however, some results could be obtained only by numerical integration. The factors affecting the distribution of heavy ions are studied. It is shown that the distribution of the heavy impurity over the discharge cross section can be much more nonuniform than the distribution of the main component (hydrogen). A simple criterion for such a nonuniformity is obtained.     

Experimental and theoretical study of the near IR emission of xenon excited by a fast electron beam

Emission of xenon excited by a 120-keV electron beam at gas pressures of 100, 200, 500, and 760 Torr nm was studied experimentally and theoretically. More than 30 spectral lines were identified in the wavelength range of 750–1000 nm. A self-consistent kinetic model is developed to calculate the emission intensity of xenon atoms in the near IR range. The model includes balance equations for the number densities of electrons, ions and excimer molecules; equations for the populations of electron levels; and the Boltzmann equation for the low-energy part of the electron energy distribution function with a source of slow electrons. Excitation and ionization rates of xenon by the beam electrons and the energy spectrum of slow electrons are calculated by the Monte Carlo method. It is shown that, under these conditions, the main mechanism of xenon atom excitation is dissociative recombination of Xe₃ ⁺ ions.     

Nonstationary kinetic theory of ion transport in plasma with small perturbations

A theory of charged particle transport for small potential perturbations in a fully ionized plasma is developed on the basis of solving a linearized kinetic equation with the Landau collision integral. This theory is free of any constraints on the characteristic time and spatial scales of perturbations. Ion fluxes appropriate for an arbitrary ion-ion collision frequency that can ensure nonlocal space-time transport in the plasma are calculated. The obtained ion transport coefficients are used to calculate the partial contribution of ions to the longitudinal permittivity of collisional plasma. The resulting expression for the plasma permittivity is applicable in the entire range of frequencies and wavenumbers.     

Oscillation spectrum of an electron gas with a small density fraction of ions

The problem is solved of the stability of a nonneutral plasma that completely fills a waveguide and consists of magnetized cold electrons and a small density fraction of ions produced by ionization of the atoms of the background gas. The ions are described by an anisotropic distribution function that takes into account the characteristic features of their production in crossed electric and magnetic fields. By solving a set of Vlasov-Poisson equations analytically, a dispersion equation is obtained that is valid over the entire range of allowable electric and magnetic field strengths. The solutions to the dispersion equation for the m = +1 main azimuthal mode are found numerically. The plasma oscillation spectrum consists of the families of Trivelpiece-Gould modes at frequencies equal to the frequencies of oblique Langmuir oscillations Doppler shifted by the electron rotation and also of the families of “modified” ion cyclotron (MIC) modes at frequencies close to the harmonics of the MIC frequency (the frequencies of radial ion oscillations in crossed fields). It is shown that, over a wide range of electric and magnetic field strengths, Trivelpiece-Gould modes have low frequencies and interact with MIC modes. Trivelpiece-Gould modes at frequencies close to the harmonics of the MIC frequency with nonnegative numbers are unstable. The lowest radial Trivelpiece-Gould mode at a frequency close to the zeroth harmonic of the MIC frequency has the fastest growth rate. MIC modes are unstable over a wide range of electric and magnetic field strengths and grow at far slower rates. For a low ion density, a simplified dispersion equation is derived perturbatively that accounts for the nonlocal ion contribution, but, at the same time, has the form of a local dispersion equation for a plasma with a transverse current and anisotropic ions. The solutions to the simplified dispersion equation are obtained analytically. The growth rates of the Trivelpiece-Gould modes and the behavior of the MIC modes agree with those obtained by numerical simulation.     

Possibility of X-ray spectral diagnostics of a plasma in the tracks of fast multicharged ions

A plasma model of the relaxation of a medium within the tracks of heavy ions in condensed matter is proposed that is based on solving time-dependent radiative collisional kinetic equations with the initial condition corresponding to a medium’s state described by the classical model of multiple ionization of the target atoms by the field of fast multicharged ions. It is shown that the plasma model allows one to describe X-ray spectra recorded in the interaction of ion beams with condensed targets. An X-ray spectral method for plasma diagnostics is proposed that is based on the plasma model. The results obtained can also be used to study the initial stage of the formation of defects in solid bodies under the action of individual fast heavy ions.     

Transport processes in plasma with an admixture of several heavy impurities

A two-temperature magnetohydrodynamic model of an ideal, fully ionized magnetized plasma consisting of electrons and several types of ions is developed for the case in which the mass of ions of the first type is much lower than that of jth-type ions, where j = 2,3,…, m ₁ ? m _j, while the densities of heavy ions are so low that collisions between them can be neglected. The ion component is assigned a common velocity, common temperature, and common density, while its composition can vary in time and space.     

Modeling of particle dynamics in a thruster

Numerical solutions to the equations describing the process of ion acceleration in a Hall current plasma accelerator (thruster) are studied. The system itself represents a three-component plasma: neutral atoms, free electrons, and singly-ionized atoms. The ions in the acceleration tract move without collisions, i.e., the length of the free path of ions is larger than that of the acceleration tract, while electrons move in a diffusion mode across the magnetic field. It is shown that in case the Poisson equation for an electric field is used the set of dynamic equations does not have an acoustic peculiarity that appears when solving a quasineutral set when the velocity of the ion flow and the ion-acoustic velocity coincide.     

An ecofriendly approach for bioremediation of contaminated water environment: Potential contribution of a coastal seaweed community to environmental improvement

High levels of heavy metals like copper ions in many industrial based effluents lead to serious environmental and health problems. Biosorption is a potential environmental biotechnology approach for biotreatment of aquatic sites polluted with heavy metal ions. Seaweeds have received great attention for their high bioremediation potential in recent years. However, the co-application of marine macroalgae for removal of heavy metals from wastewater is very limited. Thus, for the first time in literature, a coastal seaweed community composed of Chaetomorpha sp., Polysiphonia sp., Ulva sp. and Cystoseira sp. species was applied to remove copper ions from synthetic aqueous medium in this study. The biosorption experiments in batch mode were conducted to examine the effects of operating variables including pH, biosorbent amount, metal ion concentration and contact time on the biosorption process. The biosorption behavior of biosorbent was described by various equilibrium, kinetic and thermodynamic models. The biosorption of copper ions was strongly influenced by the operating parameters. The results indicated that the equilibrium data of biosorption were best modeled by Sips isotherm model. The values of mean free energy of biosorption computed from Dubinin-Radushkevich isotherm model and the standard Gibbs free energy change indicated a feasible, spontaneous and physical biotreatment system. The pseudo-second-order rate equation successfully defined the kinetic behavior of copper biosorption. The pore diffusion also played role in the control of biosorption process. The maximum copper uptake capacity of biosorbent was found to be greater than those of many other biosorbents. The obtained results revealed that this novel biosorbent could be a promising material for copper ion bioremediation implementations.     

Study of kinetic effects arising in simulations of Farley-Buneman instability

The Farley-Buneman instability, which has been observed in the E region of the Earth’s ionosphere, is studied using fluid equations for electrons, a four-dimensional (in coordinate-velocity space) kinetic equation for ions, and Poisson’s equation. Numerical simulations with allowance for Landau damping show that the Farley-Buneman instability results in anisotropy of the ion velocity distribution function.     

Simulations of the nonlinear stage of Farley-Buneman instability with allowance for electron thermal effects

The Farley-Buneman instability is a two-stream instability observed in the weakly ionized plasma of the E region of the Earth’s ionosphere. In the present paper, the effect of nonisothermal behavior of electrons on the development of this instability is investigated by numerical simulations. The instability is described using fluid equations for the electron density and temperature, a kinetic equation for ions, and Poisson’s equation. In contrast to most previous studies, the simulations are performed by numerically solving partial differential equations, rather than by the particle method. With allowance for thermal effects, the simulation results become more realistic, because the amplitudes of the perturbed electric field and plasma oscillations decrease and the instability develops over a longer time. It is shown that the influence of electron thermal effects is more pronounced at low values of the external electric field.     

Plasma decay in high-voltage nanosecond discharges in oxygen-containing mixtures

Plasma decay in high-voltage nanosecond discharges in CO₂: O₂ and Ar: O₂ mixtures at room gas temperature and a pressure of 10 Torr is studied experimentally and theoretically. The time dependence of the electron density during plasma decay is measured using microwave interferometry. The time evolution of the charged particle density, ion composition, and electron temperature is simulated numerically. It is shown that, under the given conditions, the discharge plasma is dominated for the most time by O ₂ ⁺ ions and plasma decay is determined by dissociative and three-body electron?ion recombination. As in the previous studies performed for air and oxygen plasmas, agreement between measurements and calculations is achieved only under the assumption that the rate of three-body recombination of molecular ions is much greater than that for atomic ions. The values of the rate constant of three-body recombination of electrons with О₂ ⁺ ions in a wide range of electron temperatures (500–5500 K), as well as for thermal (300 K) electrons, are obtained by processing the experimental results.