The flute instability of a plasma driven by the electrostatic high-frequency eigenmodes

The stability problem of a plasma immersed in a high frequency field is studied on a simple model. It is supposed that the fundamental h. f. electrostatic eigenmode having the frequency lower than the electron cyclotron frequency is excited in a slab of a cold collisionless magnetized plasma with the symmetrical density profile. The stability of low-frequency short-wavelength flute perturbations is investigated. Averaging over fast time oscillations and by using the WKB method to cope with the problem of the space inhomogeneity we have obtained the expression for the electron drift velocity. Making use of this velocity and quasineutrality condition we have derived the local dispersion equation. It is shown how the growth rate depends on the amplitude of the h. f. mode and that h. f. eigenmodes having the frequency close to the plasma frequency in the middle of the slab can partially stabilize the gravitational flute instability.The authors wish to thank Dr. R.Klíma for helpful discussion.     

Resonant interaction of an electromagnetic wave with an inhomogeneous plasma slab

Resonant interaction at oblique incidence of an electromagnetic wave on an inhomogeneous plasma slab is studied. The time evolution of this interaction is solved numerically from two-fluid equations, adiabatic equation for electron pressure and from Maxwell equations. It is shown that the electromagnetic energy of an incident wave is transformed both into the heat energy and into the energy of plasma oscillations in the direction of density gradient. The distribution of the transformed energy between the heat energy and the energy of plasma oscillations is strongly dependent on the plasma temperature. The ratio of heat energy to the energy of plasma oscillations is growing with growing temperature. The plasma oscillations are generated by magnetic induction of the penetrating wave. In a cold plasma they are generated especially in the overdense region and their frequency is equal to local plasma frequency. The electric field in the direction of plasma gradient has a form of a wave packet whose envelope reaches a maximum at resonance. The characteristic wavelength in the wave packet decreases and the amplitude of the packet increases with the time.     

Interference simulation in a cold collisionless moving magnetized plasma slab and (free surface of plasma slab)

Abstract

The pattern of intensity due to the interference in a cold collisionless magnetized moving plasma slab is investigated. Theoretically, it is assumed the mentioned layer has been located as a thin layer in an etalon Fabry–Perot interferometer surrounded by vacuum. The direction of external magnetic field is normal to the plasma surface and the plasma slab moves parallel with external constant magnetic field. By taking into account the relativistic considerations, the functions of transmitted intensity are presented coincident with the Airy function form in laboratory and plasma slab frames, respectively. The effects of plasma frequency, cyclotron frequency, thickness of plasma slab, and velocity of the plasma slab on band width, finesse factor, and visibility are simulated. Finally with the assumption that there are two wavelengths near together in incident electromagnetic beam the power resolution for this configuration are analyzed. All studies mentioned above have been done for S-polarized and P-polarized electromagnetic beams separately.     

Generation of tunable electromagnetic radiation by a dust ripple in dusty plasmas

It is shown that a pre-existing dust ripple in a dusty plasma may excite tunable electromagnetic radiation. For our purposes, we use the Maxwell equation and the electron equation of motion to derive a Mathieu equation in the presence of a spatially oscillating dust ripple. The Mathieu equation admits instability of an electromagnetic wave. Criteria under which instability occurs are presented. Explicit expression for the electromagnetic radiation frequency and the growth rate are obtained. The possible relevance of our investigation to nonthermal electromagnetic radiation sources from laboratory and cosmic dusty plasmas is considered.     

Toward a theory of polarization processes produced by a fast charged particle passing through a plasma slab

The passage of a fast nonrelativistic charged particle through a plasma slab is considered. The temporal and spatial changes in the scalar potential and density of the surface charge induced by the particle and the change in the energy of the particle when it crosses plasma slab boundaries are analyzed in terms of a cold plasma model.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 4, pp. 446–457, April, 1996.In conclusion, we wish to express our gratitude to Professor L. M. Gorbunov (Lebedev Physical Institute, RAS) for useful discussions.     

Light collimation and focusing by a thin flat metallic slab

We present experimental and theoretical work showing that a flat metallic slab can collimate and focus light impinging on the slab from a point source. The effect is optimized when the radiation is around the bulk, not at the surface, plasma frequency. Also, the smaller the imaginary part of the permittivity is, the better the collimation. Experiments for Ag in the visible as well as calculations are presented. We also discuss the interesting case of Al, whose imaginary part of permittivity is very small at the plasma frequency in UV radiation. Generalization to other materials and radiations are also discussed.     

Behavior of an electron plasma in a thin metallic slab placed in a variable electric field

The response of an electron plasma in a thin metallic slab to a variable electric field applied normally to the slab surface is studied in the framework of the kinetic theory. The radiation power absorbed by a unit surface area is calculated under the assumption that the electric field frequency is small compared with the plasma frequency and that electron scattering by the metal surface is of a purely diffuse character.     

Simulation and analysis of interaction between oblique incidence electromagnetic wave and plasma slab

Numerical simulation of interaction between plasma slab and electromagnetic wave which has different incident frequency and incident angle is discussed in this paper. Some parameters contain reflection coefficient, transmission coefficient, reflectance, transmittance and phase are calculated by transfer matrix method. The relation of these parameters with incident frequency and incident angle is analyzed. The results show that the incident angle has low influence on the parameters when the angle varies from 0° to 30° and from 70° to 90°, but it has high influence on the parameters when it changes from 30° to 70°. These rules have certain directive significance to the research of interaction between oblique incidence electromagnetic wave and plasma slab and to the design of plasma layer.     

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.     

圆柱形等离子体中漂移波的稳定性

在平板模型下,所谓普适模是绝对稳定的。对于圆柱形等离子体,情形又如何呢?两者的主要差别在于:代替平板模型下的外行波边条件,在柱模型下则在r=0和r=∞处都没有波能外流。这可有效地改变模的稳定性。假设了指数型密度和电流分布,本文导出了漂移波的积分本征方程。在模径向慢变的情形下,它可变为二阶微分方程。对此方程作了数值计算,结果表明确实存在不稳定模。对两种模型(平板模型与柱模型)作了比较。 关键词：     

Modal analysis and cutoff frequencies of a doubly clad plasma loaded waveguide having a lemniscates of Bernoulli-type core cross-section

The modal dispersion characteristics of EM waves in a new unconventional plasma loaded doubly clad waveguide having a shape of the lemniscates of Bernoulli-type core cross-section have been studied analytically. The proposed waveguide has three parts namely the core with slighter high index, the inner cladding with plasma and the outer cladding with air. Now using the necessary orthogonal coordinates for the proposed structure and imposing the boundary conditions under the weak guidance condition, the modal characteristics equation has been obtained considering variations in plasma width and plasma frequency, the dispersion curves and cutoff frequencies have been obtained and presented in this paper. It is noted that as the width of plasma layer increases, the cutoff frequency also increases considerably in all considered cases. This shows that using plasma width as a new parameter we can control any particular mode on our wish.     

Evolution of a Cold Non-neutral Electron-Positron Plasma Slab

Evoiution of a non-neutral cold electron-positron plasma slab is investigated.Initially the slab consists of a quasineutral plasma core bounded on both sides by layers containing only positrons(or electrons).Results from a nonperturbative,or mathematically exact,analysis of the governing fluid conservation equations and the Poisson equation show that despite their equal mass and charge magnitude,the electron and positron fronts can expand separately as well as a single Quid,and that nonlinear surface oscillations can be excited on the expansion fronts.     

时变等离子体高功率微波频率上转换的粒子模拟

基于电磁波与时变介质相互作用能够实现电磁波频率上转换的原理,通过粒子模拟(PIC)方法对电磁波与时变等离子体薄层相互作用进行模拟,实现了频率由2.45 GHz提升至130 GHz,功率转化效率约为0.39%。探究了等离子体参数(包括等离子体密度、有限的等离子体上升时间以及等离子体薄层厚度)对频率上转换的影响。模拟结果验证了等离子体密度决定上转换频率,与理论结果相符。模拟结果表明,等离子体薄层厚度越大,得到的上转换波的能量越大;等离子体的上升时间越小,上转换波的转换效率和频谱纯度越高。采用等离子体密度21020 cm-3,等离子体厚度1 cm,等离子体上升时间0.04 ns 可以得到可观的130 GHz上转换波输出。     

On the frequency of oscillations in the pair plasma generated by a strong electric field

We study the frequency of the plasma oscillations of electron–positron pairs created by the vacuum polarization in a uniform electric field with strength E   in the range 0.2Ec<E<10Ec$0.2E_c<E<10E_c$. Following the approach adopted in Ruffini, et al. (2007) [1] we work out one second order ordinary differential equation for a variable related to the velocity from which we can recover the classical plasma oscillation equation when E→0$E\to 0$. Thereby, we focus our attention on its evolution in time studying how this oscillation frequency approaches the plasma frequency. The time-scale needed to approach to the plasma frequency and the power spectrum of these oscillations are computed. The characteristic frequency of the power spectrum is determined uniquely from the initial value of the electric field strength. The effects of plasma degeneracy and pair annihilation are discussed.     

Ambartsumian's principle of invariance and the reflection of radio waves from plane inhomogeneous slabs

Using Ambartsumian's principle of invariance we investigate for radio waves the reflection coefficient of a plane inhomogeneous slab. We find that the reflection coefficient, as a function of slab thickness, satisfies the Riccati equation. From this equation we deduce a geometric theorem on the upper and lower bounds of the reflection coefficient. We illustrate the theorem by applying it to several special cases.     

Electromagnetic Reflection from Conductive Plate Coated with Nonuniform Plasma

Based on the theories of electromagnetic (EM) field and generalized reflection coefficient, a simple method is put forward to deal with the EM reflection coefficient of conductive plate coated with nonuniform plasma. The plasma slab is modeled by a series of subslabs, in which the electron-number density is assumed to be constant. The overall number density profile across the whole slab follows any practical distribution function. The reflection coefficient is then deduced and its functional dependence on the number density, incident wave frequency, collision frequency, and background magnetic field is discussed.     

用共焦谐振腔法测量等离子体的电子迴旋辐射

本文中提出一个利用共焦谐振腔和扫频接收机测量等离子体的迴旋辐射的方案,推导出了在共焦谐振腔中一个均匀等离了体平板的辐射谱表式。分析表明,此法可独立地诊断托卡马克中等离子体的电子温度及其径向分布,同时具备准光学接收系统所特有的明确的空间分辨范围。 关键词：     

Anomalous modal structure in a waveguide with a photonic crystal core

We analyze a dielectric waveguide with a photonic crystal core. Using constant frequency contour analysis, we show that the modal behavior of this structure is drastically different from that of a conventional slab waveguide. In particular, at a given frequency the lowest-order guided mode can have an odd symmetry or can have more than one nodal plane in its field distribution. Also, there exist several single-mode regions with a different modal profile in each region. Finally, a single-mode waveguide for the fundamental mode with a large core and strong confinement can be realized. All these behaviors are confirmed by our three-dimensional finite-difference time-domain simulations.     

Study of the terahertz wave propagate in high temperature plasma band gap

In this paper, the phenomenon of band gap transmission in high temperature plasma is studied. Cold plasma has high pass property, so the low-frequency electromagnetic wave cannot penetrate plasma and propagate in it. Simulation results show that in high temperature plasma, a transmission peak will be produced in the low frequency band where the band gap is supposed to occur due to the influence of the external magnetic field and the electron temperature. Through the study of the frequency and the amplitude of the transmission peak, it is found that the frequency of the peak is related to the collision frequency and the magnetic field, and the amplitude of the peak is related to the electron temperature and the thickness of the plasma slab. The calculation formula of peak frequency is obtained by fitting the obtained data. The fitting formula is validated by the analytic solution, and the results show that the two methods are in good agreement.