Nonisothermal Plasma Research Articles

Effect of magnetic field on deceleration of ion beam in plasma with ion-acoustic turbulence

The deceleration of a monoenergetic rarefied ion beam in nonisothermal plasma in a constant magnetic field has been studied. It is shown how ion-acoustic turbulence generated by a current along the magnetic field leads to an effective decrease in the velocity of ions moving with a speed higher than the speed of ion sound. When an ion beam is injected into plasma across the magnetic field, the trajectory of the ions has the form of a contracting spiral elongated along the magnetic field. The deceleration occurs due to the Cherenkov interaction of ions with ion-acoustic waves and stops when the ion velocity decreases to the speed of ion sound. The braking lengths and the beam velocity components, which are set at the moment of stopping braking, are found. After the end of deceleration, the ions move with constant velocity in a spiral along the magnetic field.

Neoclassical transport computations in non-isothermal tokamak plasmas

Neoclassical transport in a non-isothermal plasma in which each plasma species has different equilibrium temperature is investigated by solving the drift kinetic equation with a Fokker–Planck (FP) collision operator in a circular tokamak model. Since it is known that a linearized FP operator does not have a self-adjoint property in a non-isothermal plasma, approximate models are developed for comparison to intend to have the self-adjoint property in the non-isothermal case. To achieve this, we set a common temperature that the system should reach after a long time, and the individual temperature of each particle species is expressed by a parameter to measure a shift of the individual temperature from the common one. Then, both the Vlasov part and the collision term of the kinetic equation are expanded around the common temperature, taking the temperature shift parameter up to the first order. It is found that the lowest order collision term of expansion preserves the self-adjointness while the first-order, nonlinear FP term does not. A large difference of the ion heat neoclassical transport is found in comparison between the developed models with and without the self-adjointness and the original FP collision term in the non-isothermal plasma, especially in a strong temperature equilibration regime, showing that a contribution of the collision term without the self-adjointness seems to be significant. Furthermore, when an impurity species is included, the result is complicated where the usual enhancement in the main ion particle transport coefficient, due to the impurity effect, is rather suppressed with the increase in the ion heat transport coefficients by the non-isothermal effects.

Isofield plasma expansion in kJ petawatt laser-driven ion acceleration with a tailored fast electron temperature

Kilojoule-class relativistic intensity lasers, having multi-picosecond (ps) pulse durations, enable efficient ion acceleration in the interaction with thin foil targets. The foil plasma expands under the laser energy input over picoseconds where fast electrons keep increasing their effective temperature, while they convert a part of the energy into fast ions through generation of a sheath electric field. The temporal evolution of the sheath electric field is the key to understanding the efficient ion acceleration seen in kJ-class laser experiments. Here, we extend the non-isothermal plasma expansion model by introducing a temporal function of the effective temperature of fast electrons to obtain the sheath electric field in the expanding plasma. We theoretically derived that when the effective temperature of fast electrons increases in proportional to the square of the time, the strength of the sheath electric field is kept constant without depletion during the expansion. This ‘isofield’ expansion is confirmed by a quasi-one-dimensional particle-in-cell simulation. The isofield expansion results in a high energy ion acceleration with a small expansion length, which is favorable for realizing an efficient ion acceleration with less lateral energy loss in multi-dimensional situations.

INFLUENCE OF ION VISCOSITY ON THE DISTRIBUTION OF PARAMETERS IN THE SHEATH AT THE BOUNDARY OF A STATIONARY WEAKLY IONIZED STRONGLY NONISOTHERMAL PLASMA

A stationary weakly ionized highly nonisothermal plasma is considered in the hydrodynamic approximation. Taking into account the effects of ionization, recharging, and a self-consistent field, the effect of ion viscosity on the distribution of plasma discharge parameters in the sheath was investigated. Distributions of hydrodynamicion velocity and ion density, electron density, and self-consistent field potential in the sheath were obtained.

Studies on solitary waves in non-isothermal plasma

In single and two-temperature non-isothermal electron plasma along with warm positive ion, warm negative ion and warm positron, propagation of non-linear ion-acoustic solitary waves are investigated under the variation of different plasma parameters. In this paper, we have studied the first, second and third order compressive non-linear solitary wave solutions along with their respective amplitudes by a very familiar approach known as ‘tanh – method’ with existence condition for solitary wave solutions. Again we are trying to compare the amplitudes between isothermal and non-isothermal two-temperature electron plasma. In addition to this, for two-temperature non-isothermal electron plasma - variation of energy connected with those amplitudes, fast and slow ion-accoustic phase velocity and profiles of Sagdeev potential for temperature variation of positive and negative ions are critically discussed. All the results obtained are represented graphically.

Higher Order Solitons and Double Layers in Non-isothermal Plasma

Higher Order Solitons and Double Layers in Non-isothermal Plasma

On the Mechanisms of Formation of Density Cavities under Instability of Intense Langmuir Oscillations in a Plasma

The paper considers the instability of intense Langmuir oscillations in nonisothermal (Zakharov's model) and cold (Silin's model) 1D plasma. The main attention is paid to the formation of plasma density caverns in the hydrodynamic and hybrid (electrons are described hydrodynamically, ions are described by model particles) representations. In the hydrodynamic representation, with a small number of spectrum modes, large-scale plasma density caverns are observed, which rapidly deepen. This process is supported by the appearance of small-scale perturbations, and phase synchronization of the Langmuir waves of the instability spectrum is observed. This phase synchronization of the spectrum modes is quite capable of fulfilling the role that was previously proposed to be given exclusively to the effect of extrusion of particles from the cavity by the field. In hybrid models, in the region of consideration, ions are described by model particles, the number of which in the one-dimensional case 104-5*105 (which in the three-dimensional case corresponds to the number of particles 1012-1014). The initial spectrum of perturbations is very wide and rather intense, which leads to an explosive growth of perturbations in the Zakharov model and a rapid development of instability in the Silin model. In this case, in the developed instability regime, the formation of many small-scale plasma density caverns is observed. It is the presence of this small-scale modulation due to the Fermi effect that quickly forms the normal distribution of ions over velocities. In this case, the effect of particle heating due to Landau damping loses its primacy. It is shown that the caverns practically do not change their position; phase changes for the spectral components of the plasma density were not observed. Only individual small-scale caverns demonstrate dynamics similar to the development of caverns in the hydrodynamic representation.

Compressive Solitons and Double Layers in Non-Isothermal Plasma

Compressive Solitons and Double Layers in Non-Isothermal Plasma

Conversion of CO2 in stabilized low-current arc discharge at atmospheric pressure

One of the direct ways to achieve CO2 conversion is through the use of a non-isothermal plasma environment. In this work, we present an experimental study of the dissociation of CO2 in a magnetically-stabilized arc discharge in a cross-flow configuration, where the CO2 gas flow is perpendicular to both the arc and the external magnetic field. The system works at atmospheric pressure. The study examines the effect of the gas flow and discharge current on the quantities of most interest, namely, the CO2 conversion percentage and the energy efficiency of the process. The experimental results show that the conversion tends to increase with the current, while it drops as the gas flow rate is increased. The efficiency seems to decrease with the conversion percentage, as it increases with the flow rate.

Numerical Study of Grain Charging Kinetics on the Basis of BGK Kinetic Equation

An investigation of charging a spherical particle in partially ionized nonisothermal plasma is carried out on the basis of the numerical solution of the BGK (Bhatnagar–Gross–Krook) model kinetic equation. Stationary values of the particle charge and the electron and ion currents are calculated for various collisional regimes. It is verified that, for the strongly collisional regime, the effective potential has a Coulomb form at large distance from the particle surface. A new BGK-type model for binary gas mixtures is proposed. It is shown that this model satisfies all the basic properties of Boltzmann collision integrals including the correct exchange coefficients. A high-order implicit numerical method for solving the kinetic equations is developed. The method is conservative with respect to the collision integrals for arbitrary values of the Knudsen number.

Осаждение планарных волноведущих структур со фторсиликатной оболочкой на кремниевые и кварцевые подложки в локальном СВЧ-разряде пониженного давления.

An efficient method of gas-phase multilayer heterogeneous deposition of quartz and fluorosilicate glass in a non-isothermal plasma of a resonant local low pressure microwave discharge on quartz glass substrates and silicon wafers for the optical structures formation of waveguides and other waveguide elements based on them, is presented. It is shown that the nonisothermal plasma of a resonant local low pressure microwave discharge is an effective tool for the films formation on silicon and quartz substrates, both pure silicon dioxide and doped with fluorine. The cracks presence in films doped with fluorine is not observed even at their considerable thicknesses (20…60 µm). Deposition high rates and efficiency of silica glass doped with fluorine have been achieved (up to 7 wt.% of glass doping with fluorine at a film deposition rate of more than 3 μm/min). Planar and strip multimode and single-mode optical waveguides have been created. They are the basic structures of various fiber-optic components of local information transmission systems.

Microstructure evolution and densification during spark plasma sintering of nanocrystalline W-5wt.%Ta alloy

ABSTRACT The present work reports the effect of Ta on densification and microstructure evolution during non-isothermal and spark plasma sintering of nanocrystalline W. Nanocrystalline W-5wt.%Ta alloy powder was synthesised using mechanical alloying. The nanocrystalline powder was characterised thoroughly using X-ray diffraction line profile analysis. Furthermore, the shrinkage behaviour of nanocrystalline powder was investigated during non-isothermal sintering using dilatometry. Subsequently, the alloy powder was consolidated using spark plasma sintering up to 1600°C. The role of Ta on stabilising the microstructure during spark plasma sintering of nanocrystalline W was investigated in detail using electron backscatter diffraction. The average grain size of spark plasma sintered W-5wt.%Ta alloy was observed as µm.

Temperature anisotropy relaxation processes in dense plasma

In this work the relaxation processes of dense plasmas were studied. The relaxation rate of a Maxwellian velocity distribution function that has an initially anisotropic temperature (T∥ ≠ T^) is an important physical process inertial confinement fusion plasmas. Relaxation characteristics in dense plasmas were studied on the basis of the effective potentials using the Coulomb logarithm. The effective potential is derived using the long wavelength expansion of the polarization function and quantum potential which takes into account the finite value of the interaction potential at close distance. In presented work temperature anisotropy relaxation processes in dense, non-isothermal plasma are considered. These interaction potential between particles take into account such collective effects as the ionization energy depression (reduction) and exchange-correlation effects. Therefore, this allowed us to examine the sensitivity of the computed relaxation time and the corresponding equilibrium plasma temperature on the quality of the description of the screening effect in dense plasmas.

Equation of state for dense non-isothermal plasma

In this work the effective potentials taking into account screening effects at large distances and quantum-mechanical effects of diffraction at small distances were used as models of interaction between particles. Thermodynamic properties of dense non-ideal non-isothermal plasma were calculated using these potentials and obtained on their basis radial distribution functions (RDFs). The influence created by difference between temperatures of electrons and ions was also considered and found to be able to significantly influence the effects in such plasmas.

Electron density fluctuations in collisional dusty plasma with variable grain charge

The kinetic theory of electric fluctuations in a collisional weakly ionized dusty plasma is formulated with due regard to the grain charging dynamics. The correlation functions of electron and ion density are obtained by considering their collisions with neutrals described within the Bhatnagar-Gross-Krook model. The electron density correlation spectra in isothermal and nonisothermal plasma are calculated for various values of grain density, grain size, and ion collisionality.

The effect of static external magnetic field on the nonlinear absorption of the S-polarised short laser pulse in collisional underdense plasma

Inverse Bremsstrahlung absorption is a mechanism for generating heat in the inertial confinement fusion (ICF) process. To maximise the heat produced, it is desirable to investigate the possibilities for increasing the absorption rate through the inverse Bremsstrahlung process. It should be noted that some absorption mechanisms found for nanosecond long laser pulses also appear for ultrashort laser pulses. In this paper, the physics of absorption for S-polarised laser pulse and magnetised underdense plasma interaction in the presence of electrons ohmic heating and ponderomotive nonlinearities is analysed for both collisional isothermal and collisional non-isothermal magnetised plasmas. Here, we show that, in the presence of a static magnetic field, the absorption rate of the S-polarised laser pulse through interaction with underdense plasma can be increased intensively. In other words, by applying an external magnetic field, the laser pulse radiation will penetrate a region of greater plasma density compared to the case of non-magnetised plasma for the S-polarised absorption. It is remarkable that due to the heat of the plasma at the expanse of the wave energy in the case of the non-thermal, magnetised and collisional plasma, the absorption coefficient is increased intensively in comparison with the collisional plasma.

A kinetic description of ion-acoustic waves in collisional dusty plasma: Effects of grain charge fluctuations

The dispersion relation for ion-acoustic waves in collisional weakly ionized dusty (complex) plasma is formulated with due regard to the grain charge fluctuations. Calculations of the dielectric response function are performed using the Bhatnagar-Gross-Krook kinetic equation. The grain charging currents are described by the Khrapak-Morfill interpolation formula [S. A. Khrapak and G. E. Morfill, Phys. Plasmas 15, 114503 (2008)]. The dependencies of the charging frequencies and effective collision frequencies on dusty plasma parameters are studied in detail. The analysis of the ion-acoustic wave spectrum is presented for the wide range of the ion collisionality for both nonisothermal and isothermal plasmas.

Synthesis of bactericidal polymer coatings by sequential plasma-induced polymerization of 4-vinyl pyridine and gas-phase quaternization of poly-4-vinyl pyridine

Plasma-based technology is an alternative to produce universal polymer coatings with the appropriate requirements of robustness and stability for antibacterial applications. Here, we proposed a sequential two-step alternative to synthesize antibacterial polymer coatings. A non-isothermal plasma reactor, operated at atmospheric pressure (Patm) and room temperature (Troom), was used to induce free radical polymerization of 4-vinyl pyridine (4VP) on high-density polyethylene (PE). In a subsequent step, the poly-4VP (P4VP) films were treated with a bromoethane/He gas stream to produce quaternized P4VP (P4VPQ) films. Chemical structure of polymer films was validated by infrared and UV–visible spectroscopy, and morphology was evaluated by optical and atomic force microscopy; scanning electron microscopy was used to determine films thickness, which was then used to estimate the surface charge density. The bactericidal capacity was determined with a standard test by using Escherichia coli. Both types of films had an estimated charge density in the order of 1016 positive charges per cm2; P4VP films removed about 95–99% of bacteria, whereas 4PVPQ films eliminated 100%. The methodology proposed for the synthesis of antibacterial polymer coatings is simpler, faster, and more environmentally friendly than other plasma-based methods; operation at Troom and Patm may also have a significant effect on the economics and the ease of implementation of the process at commercial scale. The suggested approach may facilitate the development of new universal coatings, and operating plasma conditions could be extrapolated for engineering antibacterial coatings in industrial areas where bacterial attachment is of concern.

Heat blanketing envelopes vs cooling of neutron stars

We discuss the effect of the chemical composition of heat blanketing envelopes of neutron stars (NSs) on the interpretation of the observations of these stars. First we analyze the diffusive fluxes of ions in non-isothermal and non-ideal Coulomb plasmas. Then we outline models of diffusively-equilibrated heat blanketing envelopes composed of binary ionic mixtures and finally we study their effect on the cooling of isolated NSs.

Analysis of macroparticle charge screening in a nonequilibrium plasma based on the kinetic collisional point sink model

The screening of macroparticles in a nonequilibrium plasma is considered on the basis of the Vlasov kinetic equations supplemented with the collisional term in the Bhatnagar–Gross–Krook approximation and the point sink method. In this method, the absorption of electrons and ions by a macroparticle is described by introducing effective point sinks into the kinetic equations for plasma electrons and ions. Explicit expressions are derived for the potential distribution around a macroparticle and effective charges that determine the behavior of the potential at large distances taking into account collisions of electrons and ions with neutral buffer gas atoms. We consider the cases of a constant collision frequency and constant mean free paths of electrons and ions in the buffer gas. Numerical calculations are performed for dusty isothermal and nonisothermal plasmas in helium, neon, argon, krypton, and xenon at pressures of 10–1 to 104 Pa, which are typical of experiments with dusty plasmas.