Dielectric Characteristics for Radio Frequency Waves in a Laboratory Dipole Plasma

Transverse and parallel dielectric permittivity elements have been derived for radio frequency waves in a laboratory dipole magnetic field plasma. Vlasov equation is resolved for both the trapped and untrapped particles as a boundary value problem to define their separate contributions to the dielectric tensor components. To estimate the wave power absorbed in the plasma volume the perturbed electric field and current density components are decomposed in a Fourier series over the poloidal angle. In this case, the dielectric characteristics can be analyzed independently of the solution of the Maxwell's equations. As usual, imaginary part of the parallel permittivity elements is necessary to estimate the electron Landau damping of radio frequency waves, whereas imaginary part of the transverse permittivity elements is important to estimate the wave dissipation by the cyclotron resonances. Computations of the imaginary part of the parallel permittivity elements are carried out in a wide range of the wave frequencies. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Propagation dynamics of relativistic electromagnetic solitary wave as well as modulational instability in plasmas

By one-dimensional particle-in-cell(PIC) simulations, the propagation and stability of relativistic electromagnetic(EM) solitary waves as well as modulational instability of plane EM waves are studied in uniform cold electron-ion plasmas.The investigation not only confirms the solitary wave motion characteristics and modulational instability theory, but more importantly, gives the following findings. For a simulation with the plasma density 10²³ m^-3 and the dimensionless vector potential amplitude 0.18, it is found that the EM solitary wave can stably propagate when the carrier wave frequency is smaller than 3.83 times of the plasma frequency. While for the carrier wave frequency larger than that, it can excite a very weak Langmuir oscillation, which is an order of magnitude smaller than the transverse electron momentum and may in turn modulate the EM solitary wave and cause the modulational instability, so that the solitary wave begins to deform after a long enough distance propagation. The stable propagation distance before an obvious observation of instability increases(decreases) with the increase of the carrier wave frequency(vector potential amplitude). The study on the plane EM wave shows that a modulational instability may occur and its wavenumber is approximately equal to the modulational wavenumber by Langmuir oscillation and is independent of the carrier wave frequency and the vector potential amplitude.This reveals the role of the Langmuir oscillation excitation in the inducement of modulational instability and also proves the modulational instability of EM solitary wave.     

Surface waves at the boundaries of relativistic plasma streams

A study is made of stable and unstable electromagnetic surface waves at the boundaries of the plane and cylindrical relativistic plasma streams in the frequency range corresponding to positive values of the plasma permittivity. It is demonstrated that there are critical parameters for the transition from slow to fast waves, namely, the angle between the velocity and the wave vector in plane geometry and the smallest mode number in cylindrical geometry. It is shown that the critical parameter for the onset of the firehose instability of an electron stream is the transverse size of the stream. Higher firehose modes of the stream are shown to be suppressed by applying a strong longitudinal magnetic field.     

Effect of viscous electron flow on THz plasma waves in field effect transistors

The instability of plasma waves is influenced by many factors, such as quantum effects and electrical thermal motion. However, in sufficiently small electronic devices, viscous electron flows can be generated from the electronic interactions and govern electronic transport. The strong influence of the viscous electron fluid on plasma wave instability in field effect transistors(FET) was analyzed in this study. The theoretical results show that the instability increment and radiation frequency are functions of the Mach number, and the instability increment. Further, the computer simulative data show that the radiation frequencies increase within a certain range and the instability increment decreases owing to the presence of viscous electron flows. Therefore, it can be concluded that the viscous electron flow FETs exerts considerable influence on the characteristics of the terahertz wave.     

Ion‐Acoustic Waves Instability in a Three Components Magneto‐Plasma with Nonthermal Electrons

A theoretical investigation has been made on obliquely propagating ion‐acoustic (IA) solitary structures in a three components magneto‐plasma containing cold inertial ions, Boltzmann distributed positrons, and hot non‐thermal electrons. The Zakharov‐Kuznetsov equation has been derived by the reductive perturbation method, and its solitary wave solution has been analyzed. Multi‐dimensional instability has also studied by the small‐k (long wave‐length plane wave) perturbation expansion technique, which is found to exist in such a plasma. The effects of the external magnetic field, nonthermal electrons, obliqueness and temperature ratio have significantly modified the basic properties of small but finite‐amplitude IA solitary waves, such as amplitude, width, instability criterion and the growth rate. The present investigation contributes to the physics of the nonlinear IA waves in space and laboratory electron‐positron‐ion magneto‐plasmas in which wave damping produces an electron tail. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Relativistic study of electromagnetic electron cyclotron instability based on trapped electrons in kappa-Maxwellian auroral plasmas

The presence of relativistic electrons in the Earth's magnetosphere may excite EMEC waves via resonant interaction. The understanding of EMEC waves induced by such electrons requires relativistic treatment. Therefore, we present here the investigation of EMEC waves based on relativistic trapped electrons represented by kappa-Maxwellian distribution in auroral plasmas. The analytical expressions of real frequency and relativistic growth rate are derived. Our numerical outcomes report that relativistic approximation increases the wave growth and causes reduction in the threshold value of drift velocity of trapped electrons for instability. The wave frequency that corresponds to the maximum growth decreases as we go from nonrelativistic limit to relativistic. The maximum growth increases with the increment in plasma frequency, perpendicular thermal velocity, drift velocity of trapped electrons, and Lorentz factor γ. Moreover, the relativistic effects on maximum growth are more pronounced for smaller values of drift velocity and perpendicular thermal velocity.     

Collisionless Drift Waves Ranging from Current‐Driven,Shear‐Modified,and Electron‐Temperature‐Gradient Modes

The specific history of collisionless drift waves is marked by focusing upon current‐driven, shear‐modified, and electron‐temperature‐gradient modes. Studies of current‐driven collisionless drift waves started in 1977 using the Innsbruck Q machine and was continued over 30 years until 2009 with topics such as plasma heating by drift waves in fusion‐oriented confinement and space/astrophysical plasmas. Superposition of perpendicular flow velocity shear on parallel shear intensively modifies the drift wave characteristics through the variation of its azimuthal structure, where the parallel‐shear driven instability is suppressed for strong perpendicular shears, while hybrid‐ion velocity shear cause unexpected stabilization of the parallel‐shear‐modified drift wave. An electron temperature gradient can be formed easily by control of thermionic electron superimposed on ECR plasma, and is found to excite low‐frequency fluctuation in the range of drift waves (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Self-Interaction of Electron Plasma Waves in a Planar Plasma-Filled Waveguide

Nonlinear behaviour of electron plasma waves propagating in a planar plasma-loaded waveguide immersed in an infinite magnetic field is analysed including finite temperature and mobile ion effects. It is shown that the wave becomes modulationally unstable if the wavenumber exceeds certain critical value K_c, which decreases with rise of temperature. The growth rate of instability is calculated and is found to increase with the rise of temperature.     

Effect of Particle Number Density on Wave Dispersion in a Two-Dimensional Yukawa System

Effect of the particle number density on the dispersion properties of longitudinal and transverse lattice waves in a two-dimensional Yukawa charged-dust system is investigated using molecular dynamics simulation. The dispersion relations for the waves are obtained. It is found that the frequencies of both the longitudinal and transverse dust waves increase with the density and when the density is sufficiently high a cutoff region appears at the short wavelength. With the increase of the particle number density, the common frequency tends to increase, and the sound speed of the longitudinal wave also increases, but that of the transverse wave remains low.     

On bending instability of a volumetrically charged capillary jet of dielectric liquids

It is shown that jets of volumetrically charged dielectric liquids in the vicinity of point k = 0 are characterized by a finite range of wavenumbers, in which a jet exhibits bending instability. The interval of wavenumbers corresponding to unstable waves with azimuth number m = 1, as well as the increment of the most unstable wave and its wavenumber, increase in proportional to the electric charge per unit length of the jet and the permittivity of the liquid.     

Langmuir probe study in the nonresonant current drive regime of helicon discharge

Characterization of the current drive regime is done for helicon wave-generated plasma in a torus, at a very high operating frequency. A radiofrequency-compensated Langmuir probe is designed and used for the measurement of plasma parameters along with the electron energy distributions in radial scans of the plasma. The electron energy distribution patterns obtained in the operational regime suggest that Landau damping cannot be responsible for the efficient helicon discharge in the present study. A typical peaked radial density profile, high plasma temperature and absence of an appreciable amount of energetic electrons for resonant wave-particle interactions, suggest that the chosen operational regime is suitable for the study of nonresonant current drive by helicon wave. Successful and significant current drive achieved in our device clearly demonstrates the capability of nonresonant current drive by helicon waves in the present operational regime.      

利用超快电子探针诊断受激拉曼散射静电波的数值模拟

利用二维粒子模拟程序EPOCH验证了超快电子束探针诊断受激拉曼散射产生的静电波的可行性。结果表明,电子束探针穿过静电波电场后会在电子束探针的横向上产生密度调制,密度调制呈周期性分布且沿静电波的传播方向移动,密度调制的波数对应静电波的波数且移动速度对应静电波的相速度,因此特定条件下可用于反推电子的温度、密度等信息。在诊断静电波的过程中,电子束探针的束长必须小于静电波的波长或者诊断设备的曝光时间必须小于静电波的周期。本研究提供了一种新型的直接诊断静电波和电子温度、密度的方法,对于推动受激拉曼散射等激光等离子体不稳定性的实验研究具有重要意义。     

Quantum collisionless damping of Langmuir waves in degenerate plasma

A new phenomenon, i.e., quantum damping of Langmuir waves in electron degenerate plasma was detected, studied, and explained. It was shown that quantum damping occurs in the short-wavelength spectral region, i.e., has a wavenumber threshold. Numerical solutions to the quantum dispersion relation were found for complex frequencies of Langmuir waves. Analytical expressions were derived for frequencies and wave damping decrements in various wavenumber ranges.     

Electron cyclotron wave propagation, absorption, and backscattermeasurements in a laboratory plasma

Broadband microwave propagation and absorption processes and backscatter from objects immersed in a magnetized, finite, warm plasma column is addressed. In particular, the propagation, absorption, and backscatter of electron cyclotron waves are measured and compared with bounded vacuum hot plasma wave propagation, absorption, and ray tracing theory. The nonreciprocal nature of the transmission and absorption in an anisotropic plasma is measured. A homodyne technique which isolates the scattering from a single object in the plasma from the scattering from all other objects in the plasma and the walls of the containment device is developed and utilized. The range of absorption frequencies and nonreciprocity of the transmission signal are shown to be well correlated with wave trajectories in the associated regions of the Clemmow-Mullaly-Allis (CMA) diagram. It is shown that quasi-parallel propagation of electron cyclotron waves near resonance is present and that the transverse effects of wavenumber on propagation in the cylindrical plasma are small     

On the stability of capillary waves on the surface of a space-charged dielectric liquid jet moving in a material medium

We have derived and analyzed the dispersion equation for capillary waves with an arbitrary symmetry (with arbitrary azimuthal numbers) on the surface of a space-charged cylindrical jet of an ideal incompressible dielectric liquid moving relative to an ideal incompressible dielectric medium. It has been proved that the existence of a tangential jump of the velocity field on the jet surface leads to a periodic Kelvin–Helmholtz- type instability at the interface between the media and plays a destabilizing role. The wavenumber ranges of unstable waves and the instability increments depend on the squared velocity of the relative motion and increase with the velocity. With increasing volume charge density, the critical value of the velocity for the emergence of instability decreases. The reduction of the permittivity of the liquid in the jet or an increase in the permittivity of the medium narrows the regions of instability and leads to an increase in the increments. The wavenumber of the most unstable wave increases in accordance with a power law upon an increase in the volume charge density and velocity of the jet. The variations in the permittivities of the jet and the medium produce opposite effects on the wavenumber of the most unstable wave.     

On the instability of electrostatic waves in a nonuniform electron–positron magnetoplasma

The dispersion properties of three-dimensional electrostatic waves in a nonuniform electron–positron (EP) magnetoplasma are analyzed. A new dispersion relation is derived by use of the electron and positron density responses arising from the electron and positron continuity and Poisson equations. In the local approximation, the dispersion relation admits two wave modes with different velocities. The growth rates of various modes are illustrated both analytically and numerically. Considering the temperature gradients produces a linearly stable transverse mode. The growth rate of the slow mode instability due to the density inhomogeneity only is the highest one, though it appears at higher thermal energy. The angle of the wave propagation affects drastically on the instability features in each case. The applications of the present analysis are briefly discussed.     

Langmuir探针诊断低压氢等离子体电子密度与温度

为研究实验参数对螺旋波诱导的低压氢等离子体状态的影响,用Langmuir探针对等离子体伏安特性曲线进行了原位诊断,采用双曲正切函数的指数变换模型拟合曲线,根据Druyvesteyn方法得到状态参数电子密度、有效电子温度和电子能量几率函数,分析了它们随实验参数的变化规律。结果表明:射频输入功率、气压和约束磁场对等离子体状态有较大影响。随着射频射入功率增大,放电模式发生转变,电子密度跳跃增长;随着气压增大,电子密度先增大后减小,1.5 Pa为最佳电离气压,随约束磁场的增强呈线性增长;有效电子温度随功率和气压的增大而下降,随约束磁场的增强线性降低,电子能量几率函数曲线峰位和高能部分都向低能移动,与有效电子温度变化规律吻合。     

热电子对低频等离子体漂移波的稳定作用

本文用磁流体理论导出了热电子等离子体中,等离子体密度梯度驱动的低频漂移波的色散关系,分析了热电子的稳定作用。热电子成分稳定等离子体低频扰动的物理机制是charge uncovering效应,它只依赖于热电子同等离子体的密度比α,而不依赖于热电子的β值。热电子能降低等离子体交换模和漂移波的增长率,减少漂移波引起的等离子体反常输运损失。稳定等离子体交换模要求α≈2％,稳定等离子体漂移波要求α≈40％。理论上预示了在热电子等离子体中,等离子体漂移波是最重要的低频不稳定性。 关键词：     

Filamentation instability of helicons

Nonlinear interaction of a large amplitude ducted helicon (whistler wave) with slow plasma motion is considered. The low-frequency response accounts for a finite ion gyroradius effect to the usual MHD Alfvén waves. It is found that this coupling leads to a filamentation instability which grows at a rate faster than those reported earlier.