Nonuniform Plasma Research Articles

Generation of tunable terahertz pulse carrying orbital angular momentum in non-uniform vortex plasma channel

An amplitude modulated Laguerre-Gaussian (LG) laser beam carrying orbital angular momentum (OAM) is considered for terahertz radiation using non-uniform plasma vortex channel under relativistic conditions. The suggested approach involves the exchange of angular momentum between a non-uniform vortex plasma and a laser beam. During the interaction of non-uniform vortex plasma with photons, the laser angular momentum changes and twisted terahertz radiation is generated. The resultant THz radiation is shown to be substantially dependent on the beam width parameter and non-uniformity in the plasma channel. The amplitude of THz increases with beam focusing and the orbital angular momentum parameter. Due to higher amplitude of THz this study is useful in THz applications like, detection of counterfeit drugs, explosive material, analyze and identify defects in materials, medical imaging and communication.

Generatsiya elektricheskogo polya v pylevoy plazme

A nonuniform dusty plasma, micrometer-size particles or microdroplets of which are located in a dense gas or in atmospheric air, is excited by an energy pulse leading to the weak ionization of the gas. As a result, the particles charge through the attachment of gaseous ions to them. The stability of dusty plasma is determined by the low mobility of charged microparticles. The conditions under which the separation of negative and positive charges occurs in a dusty plasma with the creation the electric field are considered. The criteria are presented for the generation of atmospheric electricity in a dense cloud as a result of the gravitational falling of charged water microdroplets in the atmosphere, the weak ionization of which occurs under the action of cosmic rays. It is shown that this is possible only under a nonuniform space distribution of water microdroplets in the cloud. The peculiarities of a dusty plasma are considered. This plasma exists in Saturn’s rings and in the flow of coal combustion products, as well as in the dusty atmosphere of a coal mine.

Particle dynamics and weak gravitational lensing around nonlinear electrodynamics black hole

The manuscript focuses on the characteristics of a nonlinear electrodynamics black hole in a weak gravitational field, including particle dynamics and plasma effect on weak lensing. In order to complete this study, we analyze the nonlinear electrodynamics black hole geometry. We investigate particle dynamics by computing the ISCO radius for massive particles. We examine the impact of plasma on lensing properties by calculating the deflection angle for uniform and non-uniform plasma. Furthermore, we investigate the impact of plasma on the source brightness image magnification.

Numerical Study of Plasma Behavior and Power Generation Characteristics in a Disk MHD Generator With Xenon-Seeded Neon Gas

Plasma behavior and power generation characteristics in a disk-shaped magnetohydrodynamic (MHD) power generator with xenon (Xe)-seeded neon (Ne) working gas have been examined by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$r$</tex-math> </inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\theta $</tex-math> </inline-formula> 2-D numerical simulation under the assumptions of isentropic gas flow and a non-MHD interaction. The seed fraction (mole% of Xe in the mixture) is varied from 0.0% (pure Ne) to 100.0% (pure Xe) to assess the effect that Xe seeding has on plasma behavior and power generation characteristics. Adding a small amount of Xe to Ne improves the power performance due to the resulting enhancement of electrical conductivity, whereas adding an excessive amount (over 5.0%) deteriorates the performance. At an appropriate load resistance, uniform plasma structure occurs for low seed fractions. However, the plasma structure becomes nonuniform for excessively high seed fractions (over 5.0%). This result suggests that adding an excessive amount of Xe can reduce the uniformity of the plasma structure in the generator. On the other hand, at low load resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&lt;$</tex-math> </inline-formula> the appropriate load resistance) and high load resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$</tex-math> </inline-formula> the appropriate load resistance), a nonuniform plasma structure occurs for any seed fraction and results in the deterioration of generator performance. The electron temperature ranges for maintaining uniform plasma structure become narrower as the seed fraction increases which can be attributed to the low ionization potential of Xe and its large atomic weight.

Analysis of electromagnetic scattering from hypersonic vehicle coated with non-uniform plasma sheath based on FVTD method

The finite volume time domain (FVTD) method is proposed to accurately calculate the electromagnetic (EM) scattering of hypersonic vehicles coated with non-uniform plasma sheath. The plasma sheath in the actual flight environment is accurately established by solving the Navier–Stokes equations and combining appropriate thermochemical models. The radar cross section (RCS) of metal and uniform medium coated metal targets calculated by FVTD are in good agreement with those simulated by the software FEKO (MoM) and the Mie series. The calculated RCS of the vehicle under the reentry condition is consistent with the flight test data, too. The calculated electron number density distribution is consistent with the flight experiment results. The body fitted structure EM grid is adopted. The EM grid independence of the target coated with plasma sheath is studied. Then, the scattering and plasma EM parameters of the vehicle during the actual reentry are studied. The reentry altitude is from 78 to 55 km, and the reentry velocity is from 6406 to 6350 m/s. With the reentry altitude decreasing, the plasma angular frequency and collision frequency increased gradually. The scattering of different incident conditions and different wall catalytic conditions is analyzed in depth. This paper provides a valuable reference for vehicles' detection, recognition, and stealth during reentry flights.

Filamentation instability in the interaction of high-order Hermite cosh Gaussian laser beam and inhomogeneous plasmas

Based on high order paraxial theory and WKB approximation, filamentation instability in the interaction of high-order Hermite cosh Gaussian laser beam (HchG) and inhomogeneous plasma is studied. By changing the initial light intensity parameters and the non-uniformity of plasma density, the effect of different mode indices beams propagating in uniform and non-uniform plasmas on self-focusing filamentation structures is investigated. The results show that the HchG laser beam exhibits obvious self-focusing and filamentation phenomena along propagation distance in inhomogeneous plasma under the effect of the ponderomotive force. It is found that the mode index of HchG and plasma inhomogeneity have significant effects on filamentation instability, the higher order mode indices of HchG laser beam can strengthen filamentation instability, and plasma inhomogeneity also can enhance filamentation instability. The results provide a useful theoretical basis for effectively regulating the filamentation instability, increasing the peak laser power and designing narrower pulse width lasers.

Linear characteristics of dust acoustic waves in two dimensional inhomogeneous complex plasmas

This paper explores dust acoustic waves (DAWs)’ instability in two dimensional nonuniform complex plasmas. For this purpose, the dispersion relation is obtained using the method of separation of variables. In the process of linearizing the hydrodynamic equations describing the characteristics of two dimensional nonuniform complex plasma equations, the temporal and spatial dependence of all perturbations is assumed to be proportional to A1(x, y)exp[−iωt]. It is shown that the inhomogeneities in indifferent directions have different influences on the linear dispersion characteristics of DAWs. The numerical results show that the present research results are very important in the phenomenon of space astrophysical and experimental plasmas.

Flexible control over polarization tuning using electric wiggler during terahertz generation

Polarization of electromagnetic (EM) waves conveys remarkable information in sensitive terahertz (THz) measurements and communications. The conventional methods attain only limited performance over polarization control. Here, we report a powerful method for manipulation of THz polarization (linear-circular-elliptical) during the generation process. The THz wave is excited by photo-mixing of linearly polarized Gaussian lasers in a nonuniform plasma in the presence of external wiggler electric field. The state of THz polarization is tailored with electric wiggler biasing’s help. We find that emitted THz is linearly polarized for zero electric bias, circularly polarized for 15kV/cm wiggler field and elliptically polarized for 0−30kV/cm. We also find that direction of rotation of THz electric field vector depends on the polarity of electric wiggler. THz field ∼1.5×104kV/cm is obtained for laser intensity IL=2.98×1013W/cm2.

Propagation of dust-ion acoustic soliton in non-uniform plasma

Propagation of dust-ion acoustic soliton in non-uniform plasma

Research on Reflection Mechanism of Nonuniform Plasma

The surface of the near-space hypersonic vehicle is covered with a plasma sheath (PSh) with fluid properties. During the radar detection of hypersonic vehicles, the spatial distribution characteristics of PSh parameters affect the reflected wave intensity and the position of the maximum reflection layer of plasma in the vehicle’s different areas, resulting in significant differences in the intensity and frequency offset of echo signals in various areas. In order to further study the reflection characteristics of nonuniform plasma, this article uses the equivalent wave impedance method to calculate the reflection and transmission coefficients of each layer of plasma, analyzes the reflection intensity distribution mechanism of nonuniform plasma, and reveals the EM shielding effect (ES-effect) of plasma. Based on the typical carrier frequency, collision frequency, electron density, and electron density distribution gradient, the variation law of maximum reflection position and maximum reflection intensity in nonuniform plasma is revealed. The research results lay a theoretical foundation for analyzing echo signal characteristics of the PSh-covered target, radar detection anomaly suppression, and EM stealth.

Effects of a radial variation of surface coefficients on plasma uniformity in capacitive RF discharges

With the increasing demands toward large area plasma etching and deposition, the radial uniformity of capacitively coupled plasmas (CCPs) becomes one of the key factors that determine process performance in industrial applications. However, there is a variety of parasitic effects, e.g. electromagnetic and electrostatic edge effects, that typically lead to the formation of nonuniform radial plasma density profiles at various discharge conditions with a density peak appearing either at the center or near the edges of the electrodes. Moreover, in commercial CCPs different surface materials are in contact with the plasma at various positions as parts of boundary surfaces such as focus rings, masks, showerhead electrodes, wall and/or target materials. Via complex material specific plasma-surface interactions, the presence of such different surface materials affects plasma uniformity in a way that is typically not understood and, thus, not controlled. In this work, aided by 2d3v graphics processing unit accelerated particle-in-cell/Monte Carlo collision simulations, we study the effects of radial variations of electrode materials on the plasma via their different ion and electron induced secondary electron emission as well as electron reflection coefficients on the discharge characteristics. Based on such fundamental understanding we tailor the radial variation of boundary surface materials to improve plasma uniformity in low pressure CCPs. Such investigations are performed at different neutral gas pressures, where both center and edge high radial plasma density profiles form in the presence of radially uniform surface coefficients that resemble the presence of a single electrode material. It is demonstrated that by radially varying the surface coefficients at the grounded electrode, the radial plasma density profile can be finely adjusted and the plasma uniformity above the wafer placed at the powered electrode can be improved in both cases.

Localization of electron modes in nonuniform helicon plasma

New guided electrostatic and electromagnetic modes propagating in a nonuniform magnetized plasma with plane geometry are presented. The modes may arise in a plasma with a region of strong inhomogeneity leading to a concentration of wave energy and, thus, a localization of the modes. These localized modes can only propagate if the density gradient is sufficiently strong, whereas they do not exist in weakly nonuniform plasma. The eigenfunctions and the spectrum of the modes are found. In detail, the properties of the modes are studied for particular profiles in the transitional layer between two uniform plane plasma regions.

Exploring ultra-high-intensity wakefields in carbon nanotube arrays: An effective plasma-density approach

Charged particle acceleration using solid-state nanostructures has attracted attention in recent years as a method of achieving ultra-high-gradient acceleration in the TV/m domain. More concretely, metallic hollow nanostructures could be suitable for particle acceleration through the excitation of wakefields by a laser or a high-intensity charged particle beam in a high-density solid-state plasma. For instance, due to their special channeling properties as well as optoelectronic and thermo-mechanical properties, carbon nanotubes could be an excellent medium for this purpose. This article investigates the feasibility of generating ultra-high-gradient acceleration using carbon nanotube arrays, modeled as solid-state plasmas in conventional particle-in-cell simulations performed in a two-dimensional axisymmetric (quasi-3D) geometry. The generation of beam-driven plasma wakefields depending on different parameters of the solid structure is discussed in detail. Furthermore, by adopting an effective plasma-density approach, existing analytical expressions, originally derived for homogeneous plasmas, can be used to describe wakefields driven in periodic non-uniform plasmas.

Weak gravitational lensing by an ESTGB black hole in the presence of a plasma

This paper is devoted to studying the weak-field gravitational lensing properties of a 4D ESTGB black hole, which is surrounded by the plasma medium. The effects of the magnetic charges and the three plasma distribution models in the deflection of light around a 4D ESTGB black hole are investigated in detail. We find that the uniform plasma leads to a larger deflection of light rays in comparison with the singular isothermal sphere (SIS), the non-singular isothermal sphere (NSIS) models. Moreover, the deflection angle increases slightly as the absolute value of the magnetic charge decreases. Finally, we analyze the total magnification of image due to weak gravitational lensing around the black hole. The result shows that the presence of a uniform plasma medium remarkably enhances the total magnification whereas the non-uniform plasma reduces the total magnification.

Ammonia decomposition in a dielectric barrier discharge plasma: Insights from experiments and kinetic modeling

Utilizing ammonia as a storage medium for hydrogen is currently receiving increased attention. A possible method to retrieve the hydrogen is by plasma-catalytic decomposition. In this work, we combined an experimental study, using a dielectric barrier discharge plasma reactor, with a plasma kinetic model, to get insights into the decomposition mechanism. The experimental results revealed a similar effect on the ammonia conversion when changing the flow rate and power, where increasing the specific energy input (higher power or lower flow rate) gave an increased conversion. A conversion as high as 82 % was achieved at a specific energy input of 18 kJ/Nl. Furthermore, when changing the discharge volume from 31 to 10 cm3, a change in the plasma distribution factor from 0.2 to 0.1 was needed in the model to best describe the conversions of the experiments. This means that a smaller plasma volume caused a higher transfer of energy through micro-discharges (non-uniform plasma), which was found to promote the decomposition of ammonia. These results indicate that it is the collisions between NH3 and the high-energy electrons that initiate the decomposition. Moreover, the rate of ammonia destruction was found by the model to be in the order of 1022 molecules/(cm3 s) during the micro-discharges, which is 5 to 6 orders of magnitude higher than in the afterglows. A considerable re-formation of ammonia was found to take place in the afterglows, limiting the overall conversion. In addition, the model revealed that implementation of packing material in the plasma introduced high concentrations of surface-bound hydrogen atoms, which introduced an additional ammonia re-formation pathway through an Eley-Rideal reaction with gas phase NH2. Furthermore, a more uniform plasma is predicted in the presence of MgAl2O4, which leads to a lower average electron energy during micro-discharges and a lower conversion (37 %) at a comparable residence time for the plasma alone (51 %).

Zonal flow excitation in electron-scale tokamak turbulence

The derivation of an intermediate-scale gyrokinetic-electron theory in nonuniform tokamak plasmas (Chen et al 2021 Nucl. Fusion 61 066017) has shown that a Navier–Stokes type nonlinearity couples electron-temperature-gradient (ETG) modes and zonal flow (ZF) modes with wavelengths much shorter than the ion gyroradius but much longer than the electron gyroradius. This intermediate-scale ETG-ZF coupling is typically stronger than the Hasegawa–Mima type nonlinearity characteristic of the fluid approximation and is predicted to lead to relevant ZF generation and ETG mode regulation. Electron-scale, continuum, gyrokinetic simulation results are presented here which include both single-mode ETG and full-spectrum ETG turbulence. The ZF generation due to single ETG modes is investigated and the single-mode intermediate-scale results are found to be in agreement with theory. The full-spectrum results are then presented and explained qualitatively in terms of the single-mode results. It is found that the ETG-driven ZFs regulate intermediate-scale electron heat flux transport to levels in the predicted range.

Scattering characteristics of non-uniform dusty plasma targets based on Fokker-Planck-Landau collision model

Dusty plasma is a multi-particle system of dust particles suspended in plasma, which is generally composed of free electrons, ions, and dust particles. It is widely found in natural space and aerospace equipment, such as the Earth’s ionosphere, rocket tail flame, and sheath of the hypersonic vehicle. The dust particles will interact with free electrons and ions in the plasma so that the dust particles are charged. They also significantly change the characteristics of dusty plasma, showing some phenomena different from those in ordinary plasma, such as dust acoustic solitary waves and dust void. Electromagnetic (EM) waves will interact with dusty plasma, which results in the attenuation of EM wave signal and the change of phase and other serious effects, and the phenomenon of “blackout” appears. This is very unfavorable for the guidance and control system of the vehicle. The generation of “blackout” is related to the dynamics of dusty plasma and the analysis and research of EM characteristics, so studying the scattering characteristics of dusty plasma is of great significance. First, starting from the Boltzmann equation, the iterative expression of finite-difference time-domain under the Fokker-Planck-Landau (FPL) collision model of fully ionized non-uniform dusty plasma is derived. The expression of the conductivity of the fully ionized dusty plasma under the FPL collision model is obtained by combining the collision effect and charging effect of the dusty plasma. By using the &lt;i&gt;Z&lt;/i&gt;-transform finite-difference time-domain method, the radar cross section (RCS) of the dusty plasma coated metal blunt cone in two dimensions is calculated. The effects of dust particle density, dust particle radius, ratio of electron density to dust particle density, dust particle charging frequency, and EM wave incident angle on the scattering characteristics of the mental blunt cone are analyzed. The results show that the Debye shielding effect is weakened and RCS is increased with the increase of the radius of dust particles in the fully ionized non-uniform dusty plasma. In addition, it is affected by the collision effect and charging effect of dusty plasma, which will have a great influence on the RCS of the target. These results provide a theoretical basis for studying the EM waves scattering problem of fully ionized non-uniform dusty plasma and the communication problems in near space.

Quantum effects on the black hole shadow and deflection angle in the presence of plasma* *This research was partly supported by the following grants of the Uzbekistan Ministry for Innovative Development: Research Grant (FZ-20200929344 and F-FA-2021-510)

In this study, the optical properties of a renormalization group improved (RGI) Schwarzschild black hole (BH) are investigated in a plasma medium. Beginning with the equations of motion in a plasma medium, we aim to present the modifications in the shadow radius of the RGI BH. To this end, we compute the deflection angle of light in the weak gravity regime for uniform and non-uniform plasma media. Importantly, owing to the plasma media, we discover that the equations of motion for light obtained from the radiating and infalling/rest gas have to be modified. This, in turn, changes and modifies the expression for the intensity observed far away from the BH. Finally, we obtain the shadow images for the RGI BH for different plasma models. Although quantum effects change the background geometry, such effects are minimal, and practically detecting these effects using the current technology based on supermassive BH shadows is impossible. The parameter Ω encodes the quantum effects, and in principle, one expects such quantum effects to play significant roles only for very small BHs. However, the effects of plasma media can play an important role in the optical appearance of BHs, as they affect and modify the equations of motion.

Electron-acoustic solitons and double layers in a non-uniform plasma with field-aligned shear flow

Electron-acoustic solitary waves (EASWs) are investigated in a non-uniform electron plasma with field-aligned shear flow and two electron populations: hot and cold. Hot electrons are assumed to follow kappa distribution and temperature of cold electrons is considered to be less than those of hot electrons , whereas ions provide a stationary background of positive charge. Intermediate frequency drift wave couples with electron-acoustic wave (EAW) due to plasma density inhomogeneity. It is pointed out that the linear phase speed of the waves weakly depend upon the superthermality and temperature ratio of hot to cold electrons. Set of two fluid partial differential equations is reduced to an ordinary differential equation in a co-moving frame which has soliton solution in one limit. This ordinary differential equation can also be expressed in the form of an energy integral equation which admits double layer (DL) solution in another limit under appropriate boundary conditions. The results are applied to broadband electrostatic noise (BEN) in the dayside auroral zone of ionosphere.

Nonlinear excitation of geodesic acoustic mode by reversed shear Alfvén eigenmodes in non-uniform plasmas

Effects of plasma non-uniformities and kinetic dispersiveness on the spontaneous excitation of geodesic acoustic mode (GAM) by reversed shear Alfvén eigenmode (RSAE) are investigated numerically. It is found that, due to the turning points induced by the shear Alfvén continuum structure, the nonlinear excitation of GAM is a quasiexponentially growing absolute instability. As the radial dependence of GAM frequency and pump RSAE mode structure are accounted for, the radially inward propagating GAM is preferentially excited, leading to core localized thermal plasma heating by GAM collisionless damping. Our work, thus, suggests that GAM excitation plays a crucial role in not only RSAE nonlinear saturation, but also anomalous fuel ion heating in future reactors.