Magnetized Plasma Sheath Research Articles

Magnetized multi-component plasmas sheath characteristics with three isothermal ion species

The dynamics of magnetized plasma sheath with three isothermal ions is studied numerically using the fluid model. The three ions ( Ar+,Kr+, and Xe+ ) are assumed to be singly charged and have the same temperature. In the beginning, the concentrations for Ar+ and Xe+ were taken in the same proportions, and then the Kr+ ion density is introduced slowly in the plasma. It is found that the presence of a third ion has changed the dynamics of ion densities inside the sheath and simultaneously their respective velocities. Ion density and electron density profiles were estimated inside the sheath region in the presence of a weak and strong magnetic field as well at different Kr+ ion concentrations. Further, the dependence of magnetic field obliqueness on the ion density profile and its velocities inside the sheath is also studied, and observed ion density bunching at different conditions. Based on the results, we have tried to introduce a concept of the derivation of system Bohm velocity by considering the ion mass as equivalent mass for the three interacting ion systems in the plasma. It is found that the system Bohm velocity with the equivalent mass effect is larger than their individual thermal velocities and close to Ar+ Bohm velocity, and higher than the system Bohm velocity with reference to the density ratio and their respective individual Bohm velocities in an isothermal multi-component plasma.

Polarization Characteristics Distortion for L-Band Fully Polarimetric Radar Subject to Magnetized Plasma Sheath

Polarization Characteristics Distortion for L-Band Fully Polarimetric Radar Subject to Magnetized Plasma Sheath

Properties of collisional plasma sheath with ionization source term and two-temperature electrons in an oblique magnetic field

A collisional magnetized plasma sheath with two groups of electrons has been studied using a fluid model including the effects of the ionization source term and the collisional force between ions and neutral atoms. Two kinds of non-Maxwellian descriptions of electron velocity distribution, non-extensive distribution and truncated distribution, are applied in the model, and the ionization effects of both kinds are considered. By applying Sagdeev potential, the modified Bohm sheath criterion is derived. The effects of ionization, magnetic field, and high-temperature electron concentration ratio on plasma sheath density, potential, sheath thickness, and ion kinetic energy are studied. In cases with high background gas density, ion density accumulates at the sheath edge position, forming a peak and manifesting as a rapid drop in the potential profile. The distribution characteristics of electrons have a significant impact on the transport properties of ions. Oscillations and non-monotonic characteristics of net charge near the sheath edge occur as the magnetic field angle increases, leading to an increase in the sheath layer width. It can be seen that in the case of a collisional sheath structure with high-temperature electrons, it is essential to consider the sheath changes induced by the ionization and the collisional force. Compared to a symmetric electron velocity distribution, the actual thickness of the sheath layer in a truncated electron distribution assumption could be significantly reduced.

Loss cone effects and monotonic sheath conditions of a partially magnetized plasma sheath

In this Letter, we propose the conditions for monotonic plasma sheaths adjacent to a floating wall in the presence of an applied, oblique magnetic field. The electron velocity distribution function (VDF) at the sheath edge obtained from a kinetic model exhibits a loss cone shaped truncation. Using an approximation of the truncated VDF, we derive an analytical framework of the sheath edge condition (i.e., Bohm condition), namely, the relation of ion injection velocity and sheath potential drop as a function of the magnetic field angle. The results show that the sheath edge velocity and total potential drop decrease for a steady-state sheath, which eventually collapses when the magnetic field lines become parallel to the wall.

Characteristics of the electromagnetic wave propagation in magnetized plasma sheath and practical method for blackout mitigation

“Magnetic window” is considered as an effective method to solve the communication blackout issue. COMSOL software package based on the finite element method is utilized to simulate the propagation of right-handed circularly polarized wave in the magnetized plasma sheath. We assume a double Gaussian model of electron density and an exponential attenuation model of magnetic field. The propagation characteristics of right-handed circularly polarized wave are analyzed by the observation of the reflected, transmitted and loss coefficient. The numerical results show that the propagation of right-handed circularly polarized wave in the magnetized plasma sheath varies for different incident angles, collision frequencies, non-uniform magnetic fields and non-uniform plasma densities. We notice that reducing the wave frequency can meet the propagation conditions of whistle mode in the weak magnetized plasma sheath. And the transmittance of whistle mode is less affected by the variation of the electron density and the collision frequency. It can be used as a communication window.

Generalized Hybrid Matrix Method Study on Vortical Differential Scattering of a Magnetized Plasma Sheath

Generalized Hybrid Matrix Method Study on Vortical Differential Scattering of a Magnetized Plasma Sheath

Effect of ion stress on properties of magnetized plasma sheath

In the plasma sheath, there is a significant gradient in ion velocity, resulting in strong stress on ions treated as a fluid. This aspect has often been neglected in previous sheath studies. This study is based on the Braginskii plasma transport theory and establishes a 1D3V sheath fluid model that takes into account the ion stress effect. Under the assumption that ions undergo both electric and diamagnetic drift in the presheath region, self-consistent boundary conditions, including the ion Bohm velocity, are derived based on the property of the Sagdeev pseudopotential. Furthermore, assuming that the electron velocity at the wall follows a truncated Maxwell distribution, the wall floating potential is calculated, leading to a more accurate sheath thickness estimation. The results show that ion stress significantly reduces the sheath thickness, enhances ion Bohm velocity, wall floating potential, and ion flux at the wall. It hinders the acceleration of ions within the sheath, leading to notable alterations in the particle density profiles within the sheath. Further research indicates that in ion stress, bulk viscous stress has the greatest impact on sheath properties.

The propagation of Alfvén wave in magnetized plasma sheath of hypersonic vehicles in near space

Hypersonic plasma sheath could shield communication signals, which results in the so-called “blackout.” Blackout is a major risk to the safety of re-entry vehicles and cruise hypersonic vehicles in near space. In this study, a propagation model of Alfvén waves in plasma sheaths is developed. The impacts of the external magnetic field, the wave frequency, and the boundary conductivity on the Alfvén attenuation were investigated. According to the simulation results, once the conductivity is close to the Alfvénic conductivity near the onboard antenna, the attenuation of Alfvén waves in the plasma sheath could reach its minimum. The total attenuation of the Alfvén wave in the plasma sheath decreases with the carrier frequency. Also, the attenuation decreases with increasing magnetic field strength.

Study of a collisionless magnetized plasma sheath with nonextensively distributed species

A weakly magnetized sheath for a collisionless, electronegative plasma comprising positive ions, electrons, and negative ions is investigated numerically using the fluid approach. The electrons are considered to be non-Maxwellian in nature and are described by Tsalli’s distribution. Such electrons have a substantial effect on the sheath properties. The study also reveals that non-Maxwellian distribution is the most realistic description for negative ions in the presence of an oblique magnetic field. In addition to the negative ion temperature, the sheath potential is also affected by the nonextensive parameters. The present research finds application in the plasma processing and semiconductor industry as well as in space plasmas.

Modeling of magnetized collisional plasma sheath with nonextensive electron distribution and ionization source

The properties of an atmospheric-pressure collisional plasma sheath with nonextensively distributed electrons and hypothetical ionization source terms are studied in this work. The Bohm criterion for the magnetized plasma is extended in the presence of an ion–neutral collisional force and ionization source. The effects of electron nonextensive distribution, ionization frequency, ion–neutral collision, magnetic field angle and ion temperature on the Bohm criterion of the plasma sheath are numerically analyzed. The fluid equations are solved numerically in the plasma–wall transition region using a modified Bohm criterion as the boundary condition. The plasma sheath properties such as charged particle density, floating sheath potential and thickness are thoroughly investigated under different kinds of ion source terms, contributions of collisions, and magnetic fields. The results show that the effect of the ion source term on the properties of atmospheric-pressure collisional plasma sheath is significant. As the ionization frequency increases, the Mach number of the Bohm criterion decreases and the range of possible values narrows. When the ion source is considered, the space charge density increases, the sheath potential drops more rapidly, and the sheath thickness becomes narrower. In addition, ion–neutral collision, magnetic field angle and ion temperature also significantly affect the sheath potential profile and sheath thickness.

Study of Fitted and Computed Plots in Magnetized Plasma Sheath

Velocity profile of ions at the sheath entrance position with various obliqueness of the magnetic field has been studied. The oscillation amplitude of the velocity decreases as time increases. The mean values of different component of velocity also changes. The computed and fitted values of the vector sum of oscillatory part of x, y and z-component of velocities of the ions are nearly matches. At angle 30°, damping rate of vector sum of oscillatory part of total velocity increases from 1 to 5 mT. On the other hand vector sum of oscillating part of initial velocity is almost equal for magnetic field 1 mT, 3 mT and 5 mT at the same angle.

Effect of Permittivity of Plasma Medium on the Particle Properties and Electric Field in a Magnetized Plasma Sheath

The plasma sheath, a thin layer having sharp gradients, is necessary to be formed at any material wall in exposure with plasma for its stability. Characteristics of magnetized plasma sheath formed in front of a material wall for different permittivity of plasma medium has been studies using the kinetic trajectory simulation (KTS) model. The electron density, ion density, electric field and potential decreases on moving away from the sheath entrance but total charge density increases. As plasma is composed of charged particles, any variation in the permittivity of the medium has significant effects on the sheath properties. It is found that on increasing the permittivity of the medium, the electric potential strength and hence electric field decreases because of increased shielding ability of the plasma. The results are in qualitative agreement with earlier studies based on the fluid approach but the kinetic approach is more accurate quantitatively providing a better perception of plasma-wall transition phenomena.

Study of magnetized multi-component plasma sheath containing charged dust particles in presence of oblique magnetic field: a fluid approach

The dynamics of low-temperature magnetized multi-component dusty plasma sheath structures have been investigated with finite ion temperature in presence of an oblique magnetic field using the one-dimensional multi-fluid model. The parametric changes inside the sheath are estimated in presence of charged dust species having nano-meter (nm) sizes. In presence of charged dust inside the sheath, the ions are found to get accumulated near the sheath edge, hence the ion density is decreased towards the wall. Further, with the increase in magnetic field strength, the peaking of ion densities near the sheath edge has been found to be intensified. The magnetic field orientation has also played a crucial role in the bunching of the ions near the sheath edge. An increase in the magnetic field obliqueness has also contributed to intensifying the ion bunching. It has also been observed that the sheath potential is substantially changed. In addition, we also investigated and presented the influence of dust species presence on the electron density inside the sheath. A qualitative explanation of the phenomenon that occurs due to the presence of dust species is presented.

Effect of Negative Ion Concentration and Magnetic Field on Electronegative Plasma Sheath

Plasma is the ionized state of matter and is of interest as it has found applications in diverse fields. In all practical applications of plasma, it interacts with the material surface via non-neutral region that is formed between bulk plasma and surface known as the sheath, which plays a vital role in overall plasma properties. In this work, the characteristics of electronegative magnetized plasma sheath have been presented employing the kinetic trajectory simulation method based on kinetic theory. It is found that magnetic field and volumetric composition of negatively charged particles have significantly affected the characteristics of electronegative plasma sheath. Although the particle densities deplete towards the wall, the decreasing rate of negative charged particles is steeper than that of positive ions. The magnitude of electric field slowly increases close to the sheath entrance, whereas it sharply increases close to the wall. The positive ion density decreases in both cases when the concentration of negative ion is increased or when the magnetic field is increased. On increasing the magnetic field from 0 to 250 mT, the ion density reaching the wall decreases from 0.331 to 0.305 n ps. The results are similar and agree with similar works following different models and our model provides a satisfactory basis for the study of electronegative plasma sheath.

Temporal Ion Velocity Variation with Obliqueness in Magnetized Plasma Sheath

A narrow region having sharp gradients in physical parameters is formed whenever plasma comes into contact with a material wall. In this work, the temporal velocity variation of ions in such a sheath has been studied in the presence of an external oblique magnetic field. The Lorentz force equation has been solved for the given boundary conditions using Runge-Kutta method. In order to satisfy the Bohm criterion, ions enter the sheath region with ion acoustic velocity. It is observed that all components of the velocity waves are damped in plasma in the time scale of one second. The computed oscillatory part of ion velocity match with the equation of the damped harmonic oscillator. Thus obtained damping constants as well as the frequency of all three components are nearly equal for obliqueness less than 600 after which they are distinctly different. This is due to the fact that the magnetic field becomes almost parallel to the wall. In earlier studies, only the final velocity profiles are reported and hence this study is useful in understanding how the ion velocities evolve in time as they move from sheath entrance towards the wall.

SO-FDTD analysis on transmission characteristics of terahertz wave in plasma

The propagation characteristics of terahertz waves in high-temperature magnetized inhomogeneous plasma sheath were investigated theoretically by the shift operator finite difference time domain method. Both the transmission characteristics of left and right circularly polarized terahertz waves propagating in uniform or non-uniform plasma were analyzed. Simulation results reveal that the transmission characteristics of terahertz waves in plasma will be influenced by plasma parameters and the external magnetic field. The plasma sheath has a high pass filtering characteristic to terahertz waves, which provides a significant theoretical basis, to a certain extent, for the “blackout” problem.

Analysis of Terahertz Wave on Increasing Radar Cross Section of 3D Conductive Model

Enhancing the frequency band of the electromagnetic wave is regarded as an efficient way to solve the communication blackout problem. In this paper, frequency of incident wave is raised to Terahertz (THz) band and the radar cross section (RCS) of the three-dimensional conductive model is calculated and simulated based on the Runge–Kutta Exponential Time Differencing–Finite Difference Time Domain method (RKETD-FDTD). Interaction of THz wave and magnetized plasma sheath is discussed. Attenuations in incident wave frequencies of 0.34 THz and 3 GHz and different plasma densities are analyzed. The monostatic RCS is used to compare the penetration in different incident wave frequencies while the bistatic RCS is fixed on 0.34 THz to study its characteristics. The simulation result has almost the same RCS as that of the model without coating plasma when the frequency of incident wave reaches 0.34 THz. The advantages of THz wave at 0.34 THz on increasing RCS and reducing the attenuation are demonstrated from different aspects including polarizations, incident angles, magnetization and anisotropy of plasma, thickness of plasma, scan planes and inhomogeneous distribution of plasma. It can be concluded that 0.34 THz has unique advantages in increasing the radar cross section and can be applied to solve the problem of communication interruption.

Effect of electron temperature in a magnetized plasma sheath using kinetic trajectory simulation

The understanding of the properties of magnetized plasma sheath has been various beneficial applications in surface treatment, electron emission gun, ion implantation, and nuclear fusion, etc. The effect of electron temperature on the magnetized plasma sheath has been studied for a fixed magnetic field and ion temperature. It has been observed that various plasma sheath parameters can be prominently altered by the varying temperature of the electron. The density of ion is influenced more by the change in electron temperature rather than the electron density. The temperature of the electron has a great effect at the wall, when electron temperature increases, the ion and electron densities at the wall decreases. This shows the potential at the wall also decreases follows the Poisson’s equation. Similarly, the electric field also decreases but total charge density increases when the electron temperature is increased.
 BIBECHANA 18 (2021) 58-66

Modulation frequency and velocity variation of ions in a magnetized plasma sheath for different obliqueness of the field

The understanding of ion dynamics in magnetized plasma sheath is crucial for all applications of plasma. The velocity variation as well as modulation frequency of ions in a magnetized plasma sheath has been studied for different obliqueness of the magnetic field. The governing Lorentz force equation has been solved numerically for the given boundary conditions as applicable in the kinetic simulation of the sheath. For different obliqueness of the magnetic field, the average values, maximum amplitude, damping factor as well as frequency of oscillation are studied. The oscillating velocity components change at different rates depending on their orientation with respect to the field direction. Significant changes in the damping factor and modulation frequency has been observed for all components of velocity; however, the frequency of oscillation remains the same. As the obliqueness increases, shoulder natures in the components of velocity are observed.
 BIBECHANA 18 (2021) 134-139

Characteristics of non-Maxwellian magnetized sheath with secondary electron emission

In this paper, the effects of non-Maxwellian distribution of electrons on the characteristics of magnetized plasma sheath with secondary electron emission are investigated by using a magnetic fluid model of one-dimensional velocity and three-dimensional space. The velocity of electrons follows the non-extensive distribution, and the ions are magnetized in a magnetic field with a certain tilt angle relative to the wall. The effects of the non-extensive electron distribution parameter <i>q</i> and the magnetic field strength and angle on the Bohm criterion, the floating wall potential, the secondary electron number density at the sheath edge, the sheath thickness and the ion velocity are studied by establishing the self-consistent equations. When the electron velocity distribution deviates from the Maxwellian distribution, the results show that as the <i>q</i>-parameter increases, the value of the Bohm criterion decreases, the floating wall potential increases, the number of secondary electrons at the sheath increases, the sheath thickness decreases, the number density of ions and electrons decline faster, the number density of ions near the wall is higher, and the velocities of the ions in the three directions are all reduced. In addition, as the magnetic field strength increases, the sheath thickness decreases, and the number density of ions and electrons in the sheath area decrease rapidly; the larger the magnetic field angle, the more significant the influences of the parameter <i>q</i> on the wall potential and the sheath thickness are, while the velocity component of the ion in the <i>x</i>-direction decreases with the increase of the magnetic field angle, but in the case of super-extensive distribution (<i>q</i> < 1), the velocity change near the wall presents an opposite trend, the increase of magnetic field angle causes wall velocity to increase; when it is close to Maxwellian distribution (<i>q</i> → 1), the velocity near the wall does not depend on the change of the magnetic field angle and basically tends to be identical; in the case of sub-extensive distribution (<i>q</i> > 1), the velocity near the wall decreases with the magnetic field angle increasing.