空间尘埃等离子体结构的模拟

尘埃等离子体是一种高温带电气体，它们通常存在于星际空间，在地球上空，在闪电区，一般也会产生这种气体．由于在等离子体中的尘埃都是带电的，因此它们之间存在着静电相互作用．但尘埃等离子体空间内有着各种不同的间隔区，有的间隔区内尘埃间是相互吸引的，而在另一些间隔区内，尘埃间是相互排斥的．因此近年来德国马普研究所的地球外物理研究中心和悉尼大学的科学家们一直在探寻在等离子体内混合有多少尘埃时就会产生相互作用．他们的研究方法主要是计算机模拟．     

高密度尘埃等离子体的非相干散射理论研究

将带电尘埃粒子的影响引入到非相干散射理论中,建立了包含电子、离子和尘埃组分的尘埃等离子体非相干散射理论模型.对火箭喷焰高密度尘埃等离子体条件下,离子谐振区和尘埃谐振区的非相干散射谱线进行了计算,讨论了尘埃粒径、温度和密度对谱线结构的影响,获得了尘埃颗粒影响非相干散射回波特征的基本物理规律.     

碰撞对尘埃等离子体鞘层中尘埃颗粒影响

在一维平板鞘层中应用流体模型研究了尘埃等离子体鞘层中碰撞对尘埃颗粒密度和带电量的影响。 研究所涉及的碰撞主要有电离碰撞,电子、离子分别与中性粒子的碰撞,以及电子、离子分别与尘埃颗粒的碰撞。通过采用四阶龙格库塔法,得到了数值解。结果表明,随着电离碰撞或者电子、离子分别与中性粒子碰撞的频率 增加,都将导致鞘层中尘埃颗粒的数密度增大,数密度的极值位置向鞘边位置靠近,尘埃颗粒带电量增多。电子、离子与尘埃颗粒的碰撞,使得尘埃带电量减小。此外,从研究的结果来看,由离子产生的碰撞要比电子产生的碰 撞对尘埃颗粒的影响明显得多。     

聚变等离子体中尘埃杂质的带电和运动特性及温度变化研究

研究了在磁约束聚变环境中不同等离子体参数下尘埃粒子的带电、运动及温度特性.研究表明:电子温度与离子温度比对尘埃带电量有明显的影响;二次电子发射会显著减少尘埃带电量;尘埃充电的弛豫时间比在实验室加工等离子中要短得多.在考虑离子拖曳力作用下,尘埃粒子的速度可达102m·s-1的量级;针对碳材料计算得到粒子的寿命达毫秒量级.这些数值研究结果与实验观测结果相一致.     

调制磁场清除柱形等离子体发生器中的尘埃颗粒

利用流体模型，计算了调制磁场作用下，圆柱形等离子体发生器中电子、离子及尘埃的运动情况．数值模拟结果表明，尘埃颗粒随着调制磁场频率的改变，产生两种不同的运动方式：pulse运动和除尘运动．解释了pulse运动产生的机理，并提出了柱形等离子体发生器中利用调制磁场清除尘埃颗粒的方法． 关键词： 尘埃颗粒 调制磁场     

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研究了强耦合尘埃等离子体的尘埃声波的线性色散关系和尘埃声孤波的非线性传播。考虑一个包含电子、离子、正电扰动尘埃颗粒的完全电离的三成分模型等离子体。假定其电子、离子数密度服从玻尔兹曼分布,而大质量的尘埃成分用一组经典流体方程描述,对系统方程进行线性化,得到了尘埃声波的线性色散关系,发现离子的集中参数对色散关系的影响很大。用约化摄动法对系统方程进行展开,得到了描述小振幅孤波的伯格斯方程。基于伯格斯方程研究了尘埃声孤波的基本特性,发现尘埃颗粒的强耦合效应对尘埃声孤波有很大的修正作用。该研究结果有助于理解尘埃空间等离子体中局域波的一些特性。     

强耦合尘埃等离子体中正电扰动下的尘埃声激波

研究了强耦合尘埃等离子体的尘埃声波的线性色散关系和尘埃声孤波的非线性传播。考虑一个包含电子、离子、正电扰动尘埃颗粒的完全电离的三成分模型等离子体。假定其电子、离子数密度服从玻尔兹曼分布,而大质量的尘埃成分用一组经典流体方程描述,对系统方程进行线性化,得到了尘埃声波的线性色散关系,发现离子的集中参数对色散关系的影响很大。用约化摄动法对系统方程进行展开,得到了描述小振幅孤波的伯格斯方程。基于伯格斯方程研究了尘埃声孤波的基本特性,发现尘埃颗粒的强耦合效应对尘埃声孤波有很大的修正作用。该研究结果有助于理解尘埃空间等离子体中局域波的一些特性。     

量子尘埃等离子体中尘埃充电对尘埃声波的影响

采用流体动力学方程组和尘埃充电方程组成的自洽模型系统,对量子尘埃等离子体中的尘埃声波波动性质进行了研究。通过线性理论分析方法得到系统的尘埃声波波动方程及其色散关系,并对色散关系进行了数值分析。研究表明:充电效应定性地修正了尘埃声波的色散特性,引起尘埃声波的耗散,其耗散强度主要与尘埃等离子体的参数有关。最后,分析了引起尘埃声波耗散的物理原因。     

绝热电荷扰动对非均匀热尘埃等离子体中三维孤波的影响

尘埃颗粒上不断有电子流和离子流的出入以及二次电离、光电离等因素,所以尘埃颗粒上的带电量不是一个常量而是随着时间和空间变化的,因此尘埃电荷成为尘埃等离子体中的一个新的动力学变量,研究其对等离子体中各类非线性过程的作用成为尘埃等离子体物理中的一个重要课题.当今对于非均匀尘埃等离子中非线性波的研究大多数都集中于一维,对于三维非线性波的研究非常少.基于这种情况,在考虑非均匀性、尘埃颗粒绝热电荷扰动以及外部磁场等物理因素的情况下,运用约化摄动方法得出描述三维孤波的变系数的Korteweg-de Vries(KdV)方程.由结果可以看出,非均匀性、电荷扰动、外部磁场、斜向传播、尘埃温度对三维非线性波的传播有着极大的影响.利用适当的变换,得到了变系数方程的近似解.     

离子与尘埃相互作用对离子声波和尘埃声波的影响

基于流体力学方程和与时间相关的线性微扰理论,分析了尘埃等离子体环境中离子与尘埃粒子的相互作用对离子声波和尘埃声波的影响,结果表明两者间的相互作用使得离子声波变得稳定而使尘埃声波变得不稳定。     

Fundamentals and applications of ion-ion plasmas

Ion-ion plasmas can form in the late afterglow of pulsed discharges or downstream of continuous wave discharges in electronegative gases. In ion-ion plasmas, negative ions replace electrons as the negative charge carriers. In the absence of electrons, ion-ion plasmas behave quite differently compared to conventional electron-ion plasmas. Application of a radio frequency bias to a substrate immersed in an ion-ion plasma can be used to extract alternately positive and negative ions, thereby minimizing charging on device features during micro-device fabrication. Ion-ion plasmas are also important in negative ion sources, dusty plasmas, and the D-layer of the earth's atmosphere.     

Nonlinear dust-ion-acoustic waves in a multi-ion plasma with trapped electrons

A dusty multi-ion plasma system consisting of non-isothermal (trapped) electrons, Maxwellian (isothermal) light positive ions, warm heavy negative ions and extremely massive charge fluctuating stationary dust have been considered. The dust-ion-acoustic solitary and shock waves associated with negative ion dynamics, Maxwellian (isothermal) positive ions, trapped electrons and charge fluctuating stationary dust have been investigated by employing the reductive perturbation method. The basic features of such dust-ion-acoustic solitary and shock waves have been identified. The implications of our findings in space and laboratory dusty multi-ion plasmas are discussed.     

Linear propagation of dust acoustic modes in the presence of an electron beam

The physical and optical properties of plasmas are depended on dynamics of species in the discharge volume. Then, the presence of an electron beam, as a separate component, in a dusty plasma can modify the plasma structures through altering the discharge parameters. In this report, the linear propagation of acoustic modes in a collisionless dusty plasma contains electrons, ions and charged dust grains is investigated in the presence of an electron beam. Our analysis indicates that the electron beam can modify the dispersion relations of dust acoustic modes which resulted different data transportation in dusty plasmas. The obtained results are also examined for negative and positive charged dust grains with different number densities. The charge of dust grains represents an important role in the dynamics of the low frequency waves. Additionally, our findings reveal that the propagation of acoustic waves in dusty plasmas can be controlled by adjusting the electron number density of the beam and the cathode potential. Lastly, we obtian the destabilizing effects, originated from dust charge fluctuation, by reconsidering the dispersion relations of both dust acoustic modes.     

Effect of dust size distribution and dust charge fluctuation on dust ion-acoustic shock waves in a multi-ion dusty plasma

The effects of dust size distribution and dust charge fluctuation of dust grains on the small but finite amplitude nonlinear dust ion-acoustic shock waves, in an unmagnetized multi-ion dusty plasma which contains negative ions, positive ions and electrons, are studied in this paper. A Burgers equation and its stationary solutions are obtained by using the reductive perturbation method. The analytical and numerical results show that the height with polynomial dust size distribution is larger than that of the monosized dusty plasmas with the same dust grains, but the thickness in the case of different dust grains is smaller than that of the monosized dusty plasmas. Furthermore, the moving speed of the shock waves also depend on different dust size distributions.     

Dust-ion-acoustic shock waves due to dust charge fluctuation

A dusty plasma system containing Boltzmann electrons, mobile ions and charge fluctuating stationary dust has been considered. The nonlinear propagation of the dust-ion-acoustic waves in such a dusty plasma has been investigated by employing the reductive perturbation method. It has been shown that the dust charge fluctuation is a source of dissipation and is responsible for the formation of the dust-ion-acoustic shock waves. The basic features of such dust-ion-acoustic shock waves have been identified. The implications of our results in space and laboratory dusty plasmas are discussed.     

Obliquely propagating dust-acoustic solitary waves in magnetized dusty plasmas with two-temperature Maxwellian ions

The nonlinear propagation of dust-acoustic waves in an obliquely propagating magnetized dusty plasma, containing Maxwellian distributed ions of distinct temperatures (namely lower and higher temperature Maxwellian ions), negatively charged mobile dust grains, and Maxwellian electrons, is rigorously investigated and analyzed by deriving the Zakharov-Kuznetsov equation. It is investigated that the characteristics of the dustacoustic solitary waves are significantly modified by the external magnetic field, relative ion and electron temperature-ratio, and respective number densities of two population of ions. The implications of the results obtained from this analysis in space and laboratory dusty plasmas are briefly discussed.     

Streaming instability in quantum dusty plasmas

By using a quantum hydrodynamic (QHD) model, we derive a generalized dielectric constant for an unmagnetized quantum dusty plasma composed of electrons, ions, and charged dust particulates. Neglecting the electron inertial force in comparison with the electron pressure, and the force associated with the electron correlations at a quantum scale, we discuss two classes of electrostatic instabilities that are produced by streaming ions, and dust grains. The effects of the plasma streaming speeds, the thermal speed of electrons, and the quantum parameter are examined on the growth rates. The relevance of our investigation to dense astrophysical plasmas is discussed.     

Streaming instability of dust-acoustic mode with helical wavefronts

Making use of the kinetic approach for plasma species, the electrostatic twisted dust-acoustic (DA) waves are studied in a collisionless unmagnetized multi-component dusty plasma consisting of electrons, singly ionized positive ions and charged massive dust grains. The Vlasov-Poisson equations are coupled together to obtain a generalized response function by using the Laguerre-Gaussian (LG) perturbed electrostatic potential and distribution function in the paraxial limit. The dispersive properties and growth rate instability of twisted DA waves are examined with distinct OAM states in a multi-component dusty plasma. Various significant modifications associated with the real wave frequency and growth rate are shown with respect to twist parameter and dust concentration. It is examined that dust concentration enhances the growth rate of twisted DA waves, whereas an increase in twist parameter reduces the growth rate instability. The excitation of twisted DA mode is also found to enhance with streaming speed of inertialess electrons. Our results may be useful for particle transport and trapping phenomena due to wave excitation in laboratory dusty plasmas.     

Collision and recombination driven instabilities in variable charged dusty plasmas

The dust-acoustic instability driven by recombination of electrons and ions on the surface of charged and variably-charged dust grains as well as by collisions in dusty plasmas with significant pressure of background neutrals have been theoretically investigated. The recombination driven instability is shown to be dominant in the long wavelength regime even in the presence of dust-neutral and ion-neutral collisions, while in the shorter wavelength regime, the dust-neutral collision is found to play a major role. In an earlier research work, the dust-neutral collision was neglected in comparison to the effect due to the recombination for estimating the dust-acoustic instability; later the other report shows that the recombination effect is negligible in the presence of dust-neutral collisions. In line of this present situation our investigation revealed that the recombination is more important than dust-neutral collisions in laboratory plasma and fusion plasma, while the dust-neutral collision frequency is dominant in the interstellar plasmas. The effects of ion and dust densities and ion streaming on the recombination and collision driven mode in parameter regimes relevant for many experimental studies on dusty plasmas have also been calculated.