Nonuniform Plasma Slab Research Articles

Electrostatic shock waves driven by electron vortices in laser–plasma interactions

Nonlinear structures such as shock waves and vortices widely exist in nature and the Universe. They have also been separately observed in laser–plasma interactions. We show for the first time that two perpendicularly propagated collisionless electrostatic shock waves (CESs) can be excited by a moving electron vortex (EV). The latter is driven by an ultrashort intense laser pulse propagating through a sandwich nonuniform underdense plasma slab and is found to move perpendicularly to the density gradient. Two CESs are observed on both sides of the passing route of the EVs. The left-side CES is induced by a high-density electron layer, which originates from the vortex front and is compressed and accelerated during the EV motion. The right-side CES is induced by supersonic ions accelerated by the EVs directly. Ion acceleration by such CESs along the directions perpendicular to the vortex propagation is also observed. This study reveals the transformation of nonlinear structures and provides new routes for laser energy dissipation in plasmas.

Propagation of terahertz waves in nonuniform plasma slab under “electromagnetic window”

The application of magnetic fields, electric fields, and the increase of the electromagnetic wave frequency are up-and-coming solutions for the blackout problem. Therefore, this study considers the influence of the external magnetic field on the electron flow and the effect of the external electric field on the electron density distribution, and uses the scattering matrix method (SMM) to perform theoretical calculations and analyze the transmission behavior of terahertz waves under different electron densities, magnetic field distributions, and collision frequencies. The results show that the external magnetic field can improve the transmission of terahertz waves at the low-frequency end. Magnetizing the plasma from the direction perpendicular to the incident path can optimize the right-hand polarized wave transmission. The external electric field can increase the transmittance to some extent, and the increase of the collision frequency can suppress the right-hand polarized wave cyclotron resonance caused by the external magnetic field. By adjusting these parameters, it is expected to alleviate the blackout phenomenon to a certain extent.

Attenuation properties of EM wave by magnetized nonuniform plasma slab coated on perfect conductor plane

AbstractThe total amplitude reflection coefficient of EM wave in a nonuniform plasma slab coated on perfect conductor plane is newly derived by using the scattering matrix method (SMM), and the attenuation is calculated. Three types of plasma electron density profile, that is the hyperbolic, sinusoidal, and linear profiles, are used. The external magnetic field and plasma parameters such as the maximum electron density and collision frequencies are discussed to calculate the attenuation of EM wave. The calculation results show that the plasma electron density profile and maximum electron density exert a large effect to the attenuation of EM wave and the attenuation under the uniform external magnetic field is taken place by the electron cyclotron resonance absorption, the up hybrid resonance absorption and geometric resonances absorption.

Effects of Nonuniform Moving Plasma on the Polarization Properties of Obliquely Incident EM Waves

The effects of nonuniform moving plasma on the polarization properties of electromagnetic (EM) waves were theoretically studied. Taking the ${L}$ -band right-hand circularly polarized (RHCP) wave as an example, based on the nonuniform moving plasma slab moving perpendicularly to the incident wave, the relationship between the polarization properties of the transmitted wave and the normalized velocity of the nonuniform plasma slab was analyzed. The results indicate that the polarization state of the transmitted wave is closely related to the normalized velocity of the nonuniform plasma slab. When the plasma slab approaches to the incident wave, its influence on the polarization properties is greater than that away from the incident wave. In addition, when the change of the polarization state reaches the maximum, the corresponding normalized velocity is mainly determined by the incident angle and the collision frequency. Various interesting features regarding polarization properties were obtained. The results are very important for applications in space exploration.

Numerical calculation of the reflection, absorption and transmission of a nonuniform plasma slab based on FDTD

In this paper, reflection, absorption and transmission characteristics of nonuniform plasma layer with varying electron number density are analyzed. The plasma number density profile is parabolic. Finite-difference time-domain (FDTD) and subslabs approximation methods are utilized and the results are validated. In FDTD, we use auxiliary differential equation (ADE) to simulate the plasma dispersive characteristics. In subslabs method, the plasma layer is divided into several thin subslabs with constant electron number density in each subslab. Partial reflection coefficients at each subslab boundary with different electromagnetic parameters are calculated. The total reflected and transmitted coefficients are then deduced using transmission line method. The reflected, transmitted and absorption power ratio with respect to the incident power is acquired. Their functional dependence on the number density, collision frequency and the distribution of number density, collision frequency is studied.

Study on the attenuation characteristic of terahertz wave through a non-uniform magnetized plasma

In this paper, the interaction between terahertz wave and a non-uniform magnetized plasma slab is investigated. The electric field distribution in non-uniform plasma is presented and used to calculate the attenuation of the electromagnetic wave through plasma. Several types of electron density profiles are proposed and discussed. Effects of different plasma parameters (electron density, collision frequency, plasma thickness) and magnetic field amplitudes on THz wave attenuation characteristic are investigated. The transmission ratios at several typical THz signal frequencies in both unmagnetized and magnetized plasma are presented as well. These simulation results are meaningful for the flight communication.

Effects of magnetized plasma on the propagation properties of obliquely incident THz waves

In this paper, the propagation of obliquely incident terahertz (THz) wave in a non-uniform magnetized plasma slab is investigated. The electron density and the collision frequency across the plasma are assumed to have a Gaussian profile. To deal with the non-uniform profile, the plasma slab is divided into a series of subslabs. For more accuracy, twice reflection between the interfaces of each subslab is considered, and the corresponding transmitted and reflected power are derived. Effects of collision frequency, magnetic field amplitude and incident angle on THz wave propagation characteristics are investigated. Specifically, the refraction angles in each subslab are presented. These simulation results are meaningful for the hypersonic flight communication.

Absorption of electromagnetic waves by a moving non-uniform plasma

The absorption coefficient of electromagnetic waves by a moving non-uniform plasma slab is investigated theoretically. Two cases of movement are considered: (1) the plasma slab moves parallel to the interface and (2) the plasma slab moves perpendicular to the interface. In both the cases, the influences of six typical plasma parameters on the absorption coefficient are discussed in detail by analyzing the relativistic model. It has been obtained that the absorption coefficient is strongly affected by the velocity of the moving plasma. Various interesting features concerning the variation of the absorption coefficient are obtained, which are very important for applications in space exploration.

An iterative method to include spatial dispersion for waves in nonuniform plasmas using wavelet decomposition

A novel method for solving wave equations with spatial dispersion is presented, suitable for applications to ion cyclotron resonance heating. The method splits the wave operator into a dispersive and a non-dispersive part. The latter can be inverted with e.g. finite element methods. The spatial dispersion is evaluated using a wavelet representation of the dielectric kernel and added by means of iteration. The method has been successfully tested on a low frequency kinetic Alfven wave with second order Larmor radius effects in a nonuniform plasma slab.

Effects of magnetic field on the interaction between terahertz wave and non-uniform plasma slab

In this paper, the interaction between terahertz electromagnetic wave and a non-uniform magnetized plasma slab is investigated. Different from most of the published literatures, the plasma employed in this work is inhomogeneous in both collision frequency and electron density. Profiles are introduced to describe the non-uniformity of the plasma slab. At the same time, magnetic field is applied to the background of the plasma slab. It came out with an interesting phenomenon that there would be a valley in the absorption band as the plasma's electromagnetic characteristic is affected by the magnetic field. In addition, the valley located just near the middle of the absorption peak. The cause of the valley's appearance is inferred in this paper. And the influences of the variables, such as magnetic field strength, electron density, and collision frequency, are discussed in detail. The objective of this work is also pointed out, such as the applications in flight communication, stealth, emissivity, plasma diagnose, and other areas of plasma.

Ultra-intense attosecond pulses emitted from laser wakefields in non-uniform plasmas

AbstractA scheme of generating ultra-intense attosecond pulses in ultra-relativistic laser interaction with under-dense plasmas is proposed. The attosecond pulse emission is caused by an oscillating transverse current sheet formed by an electron density spike composed of trapped electrons in the laser wakefield and the residual transverse momentum of electrons left behind the laser pulse when its front is strongly modulated. As soon as the attosecond pulse emerges, it tends to feed back to further enhance the transverse electron momentum and the transverse current. Consequently, the attosecond pulse is enhanced and developed into a few cycles later until the density spike is depleted out due to the pump laser depletion. To control the formation of the transverse current sheet, a non-uniform plasma slab with an up-ramp density profile in front of a uniform region is adopted, which enables one to obtain attosecond pulses with higher amplitudes than that in a uniform plasma slab.

Numerical analysis of the reflection and absorption of electromagnetic wave in nonuniform magnetized plasma slab

In this paper, a model for calculating the reflection and absorption powers of electromagnetic wave (EM wave) in nonuniform magnetized plasma slab is given out based on layer propagation theory. The effects of various plasma parameters and different values of magnetic field intensity on the reflected and absorbed powers are discussed. The results illustrate that the thickness of plasma seldom affects the reflection of radar wave, but it can broaden or reduce the absorption width. Meanwhile, the background magnetic field intensity has an influence upon the results, and it could change the resonance spectrum of magnetized plasma. We also find out that, with appropriate plasma density, collision frequency and magnetic field intensity, more than 90% of radar wave power can be absorbed and the resonant absorption band is about 2 GHz.

Effect of High-Frequency Electric Field on Propagation of Electrostatic Wave in a Non-Uniform Relativistic Plasma Waveguide

The effect of a high frequency (HF) electric field on the propagation of electrostatic wave in a 2D non-uniform relativistic plasma waveguide is investigated. A variable separation method is applied to the two-fluid plasma model. An analytical study of the reflection of electrostatic wave propagation along a magnetized non-uniform relativistic plasma slab subjected to an intense HF electric field is presented and compared with the case of a non relativistic plasma. It is found that, when the frequency of the incident wave is close to the relativistic electron plasma frequency, the plasma is less reflective due to the presence of both an HF field and the effect of relativistic electrons. On the other hand, for a low-frequency incident wave the reflection coefficient is directly proportional to the amplitude of the HF field. Also, it is shown that the relativistic electron plasma leads to a decrease in the value of reflection coefficient in comparison with the case of the non relativistic plasma.

Reflection, absorption and transmission of TE electromagnetic waves propagation in a nonuniform plasma slab

A numerical scheme is described to compute the reflection, absorption, and transmission coefficients of TE m , 0 and plane electromagnetic waves propagating in a nonuniform plasma slab. The numerical solutions are in good agreement with theoretical solutions for two different kinds of electron density profiles. The solutions for various electron density profiles will be shown in TE m , 0 mode. The method has applications to predicting the fields in plasmas where the density is profile is known, such as in microwave breakdown in a waveguide.

Interaction of electromagnetic waves with a magnetized nonuniform plasma slab

The absorption, reflection, and transmission of electromagnetic waves by a nonuniform plasma slab immersed in an ambient uniform magnetic field of various strengths are studied in this paper. The effects of the plasma parameters and magnetic field strength on the absorbed, reflected, and transmitted power are discussed. The magnetized nonuniform plasma slab is modeled by a series of magnetized uniform plasma subslabs. The calculation results show that the effects of the magnetic field strength and density gradient on the absorbed power, as well as the frequency band of resonant absorption, are significant. A complete analysis utilizing the scattering matrix method is also used to compare the above calculation results which neglect multiple reflections between subslab interfaces. Broadband absorption of electromagnetic waves can be achieved by changing the magnetic field strength and plasma density. More than 90% of the electromagnetic wave power can be absorbed in a magnetized nonuniform plasma slab with width of 12 cm and the absorption bandwidth can range from 1 to 20 GHz with different plasma parameters and external magnetic field strengths.

Nonuniform non-neutral plasma in a trap.

An analytical model for breathing oscillations in a nonuniform non-neutral plasma slab is developed. The plasma is relatively small and warm with the smallest dimension only of several Debye lengths. Nonuniformity in the equilibrium results in a frequency shift associated with pressure and boundary effects. The plasma size and temperature, being related to the frequency shift, can therefore be evaluated from frequency measurements. In particular, for small nonuniform plasmas the frequency of the breathing mode is twice that predicted by the cold fluid theory. Nonlinear oscillations are also considered and the pressure is shown to have an important effect on the dynamics. Analytical solutions for linear and nonlinear oscillations are obtained and compared with that from one-dimensional particle-in-cell simulations. Good agreement is found.

SMM analysis of reflection, absorption, and transmission from nonuniform magnetized plasma slab

An new analytical technique for obtaining a complete set of reflection, absorption, and transmission coefficients for a stratified plasma slab is presented, named the scattering matrix method (SMM). The nonuniform magnetized plasma slab is modeled by a number of subslabs. Each subslab has a fixed electron density. The overall density profile across the whole slab follows any practical distribution function. Because the field in each subslab can be represented by the sum of the reflected and incident components, the partial reflection and transmission coefficients can be obtained by successively matching boundary conditions at all interfaces. The partial and total reflected, absorbed, and transmitted powers as the functions of the electron density, collision frequency, and electron cyclotron frequency for typical parabolic and exponential density profiles are investigated.

Electron surface waves in a nonuniform plasma slab

Electron surface waves in a nonuniform, metal bound, thermal plasma slab have been analyzed and detected. Measurements of the dispersion relations of these waves, as well as the eigenstructure of the perturbed electron density, reveal a spectrum of waves with frequencies above and below the peak electron plasma frequency in the slab. These waves are analogous to the Gould–Trivelpiece and Tonks–Dattner waves found in dielectric bound plasma columns. Measurements have been made using particle-in-cell simulation of an argon plasma and are compared with linear fluid theory in which the adiabatic approximation is made for the perturbed pressure. The presence of the metal boundary leads to regions near the plasma sheaths in which the fluid theory breaks down; we explore the differences between theory and measurement in this region.

The Effect of a HF Electric Field on the Propagation of anElectrostatic Wave in a Nonuniform Plasma Waveguide

An analytical study of the reflection of an electrostatic wavepropagating along a magnetized nonuniform plasma slab subject to anintense HF electric field is presented. It is found that when thefrequency of the incident wave ωg is close to theelectron plasma frequency ωPe, the plasma is lessreflective due to the presence of the HF field. On the other hand, fora low-frequency incident wave(ωg ∼ ωPi), the reflectioncoefficient is directly proportional to the amplitude of the HFfield.

Numerical calculation of the reflection, absorption, and transmission of microwaves by a nonuniform plasma slab

The reflection, absorption, and transmission of microwaves by a magnetized, steady-state, two-dimensional, nonuniform plasma slab is studied. A discussion on the effect of various plasma parameters on the reflected power, absorbed power, and transmitted power is presented. The nonuniform plasma slab is modeled by a series of subslabs. Even though it is assumed that the number density is constant in each subslab, the overall number density profile across the whole slab follows a parabolic function. The partial reflection coefficient at each subslab boundary is computed along with the absorption at each subslab. The total reflected, absorbed, and transmitted powers are then deduced and their functional dependence on the number density, collision frequency, and angle of propagation is studied. >