非均匀磁场尘埃等离子体中颗粒的复杂运动

本文研究了在非均匀磁场尘埃等离子体中不规则尘埃颗粒的复杂运动, 包括圆滚运动、尖头圆滚运动、圆周运动以及波浪运动等. 放置在电极上的圆柱形磁铁的主要作用是改变鞘层的径向分布, 进而对颗粒产生径向约束, 使尘埃颗粒悬浮于圆柱形磁铁周围, 其磁场并不足以磁化颗粒使其做圆滚运动. 通过与球形尘埃颗粒的对比实验发现, 圆滚运动是不规则尘埃颗粒在等离子体中特有的一种运动. 我们提出了一种新的机理: 由于不规则颗粒的自旋而引起的横向反Magnus力对颗粒的圆滚运动起了重要的作用. 文中通过受力分析定性地对实验中观察到的非球形颗粒的各种运动给出了合理的解释.     

尘埃颗粒在射频等离子体鞘层中的非线性共振现象的理论研究

一种自洽的理论模型用于研究尘埃颗粒在射频鞘层中垂直方向的非线性共振现象.利用射频鞘层动力学模型，研究了鞘层电场和尘埃颗粒的充电过程.考虑作用在尘埃颗粒上的各种作用力(如重力、电场力、离子拖拽力、中性气体摩擦力及探针的扰动力)，并通过数值求解颗粒运动方程，模拟了该尘埃颗粒在探针扰动下的非线性振荡过程.所得结果不仅很好地再现了最近的实验观察，同时还发现这种非线性振动过程与等离子体参数、施加的射频偏压的功率、探针的扰动电位和位置等有着密切的联系. 关键词： 射频鞘层 尘埃颗粒 尘埃充电 非线性共振 迟滞     

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.     

等离子体通道中的自生磁场

研究了超短脉冲强激光在等离子体通道中传播时产生的自生磁场．利用相对论动量方程和泊松方程及安培定律得出自生磁场的一个基本公式，在此基础上解析并数值研究了通道中产生的自生磁场的特性和结构，初步探讨了超短脉冲强激光在等离子体中传播时形成的排空效应对自生磁场的影响，并分析了产生自生磁场的机制 关键词：     

对含有非热力学平衡离子的尘埃等离子体中孤波特性的理论研究

得到了描述由尘埃颗粒电荷变化、非热力学平衡分布的离子和Boltzmann分布的电子组成的未磁化的热尘埃等离子体中的尘埃声波的修正的KdV (mKdV) 方程. 并对诸多的尘埃等离子体参数对尘埃声孤波结构的影响进行了理论研究，结果表明，尘埃等离子体参数决定着尘埃声孤波结构，且只在这些参数特别选定的一些区域，才会出现稳定的孤波. 关键词： 非热力学平衡离子 尘埃颗粒电荷变化 尘埃声孤波     

反应等离子体中尘埃空洞形成的实验研究

利用气体合成（乙烯和硅烷，氩气是载气）的方法，产生尘埃粒子，并在此基础上研究了悬 浮在射频等离子体鞘层上方的尘埃云及尘埃空洞.实验结果给出了尘埃云和尘埃空洞与射频 功率和气压等参数的关系曲线. 关键词： 尘埃等离子体 尘埃空洞 尘埃云     

尘埃等离子体

尘埃等离子体物理是近十年里等离子体学科中一个活跃的分支领域之一，带电尘埃广泛存在于空间等离子体、实验室聚变装置、低温等离子体工业应用等众多小同的环境中，并且呈现出相同或相似的性质．这是一种部分或完全电离的等离子体，其基本成分除了电子和离子外，还有（通常）带负电的、且电荷不是常数的微粒．带电颗粒有着与电予和离子完全不同的动力学行为，其与等离子体的相互作用呈现出许多新的物理现象．文章介绍了尘埃等离子体物理的简要发展历史、基本性质和主要研究方向以及最近一些热点问题．     

弱电离尘埃等离子体的介电张量研究

忽略磁场作用,通过求解含BGK碰撞项的Boltzmann方程和尘埃粒子充电方程导出了弱电离尘埃等离子体介电张量的表达式.证明了“冷”尘埃等离子体的纵向介电张量系数与横向介电张量系数相等.完善了弱电离尘埃等离子体电磁特性的理论模型. 关键词： 弱电离尘埃等离子体 Boltzmann方程 充电方程 介电张量     

两种带电尘埃颗粒的等离子体鞘层玻姆判据

采用流体方程和尘埃充电自洽模型研究了鞘边含有两种尘埃颗粒的等离子体玻姆判据. 通过拟牛顿法数值模拟了鞘边两种尘埃颗粒的存在对尘埃自身充电以及离子马赫数的影响. 两种尘埃颗粒中含量较少的尘埃颗粒数密度的增加, 导致两种尘埃颗粒表面悬浮势一个降低, 一个升高. 含量较少的尘埃颗粒的数密度越多和半径越小, 都会导致离子马赫数增大. 另外鞘边无论何种尘埃颗粒的速度增加, 鞘边离子马赫数都将减小. 关键词： 等离子体鞘层 尘埃颗粒 玻姆判据     

聚变等离子体中杂质离子对尘埃颗粒电势的影响

用粒子轨道理论研究了多电荷正离子对聚变等离子体中尘埃颗粒充电过程以及充电平衡时表面电势的影响。模拟结果表明,在氢等离子体中,多电荷正离子的浓度越大、电荷数越多以及离子质量数越大,都将使得尘埃颗粒在充电过程中迅速携带较多的负电荷,且充电平衡时具有更大的负电性。此外,充电平衡时,尘埃颗粒表面电势与氢等离子体中另一种多电荷正离子的浓度呈负线性相关,多电荷正离子对随氢离子温度变化的尘埃颗粒表面势的极值也产生影响。     

Electrodynamics and dispersion properties of a magnetoplasma containing elongated and rotating dust grains

The electrodynamics and dispersion properties of a magnetized dusty plasma containing elongated and rotating charged dust grains are examined. Starting from an appropriate Lagrangian for dust grains, a kinetic equation for the dust grain and the corresponding equations of motion are derived. Expressions for the dust charge and dust current densities are obtained with the finite size (the dipole moment) of elongated and rotating dust grains taken into account. These charge and current densities are combined with the Maxwell-Vlasov system of equations to derive dispersion relations for the electromagnetic and electrostatic waves in a dusty magnetoplasma. The dispersion relations are analyzed to demonstrate that the dust grain rotation introduces new classes of instabilities involving various low-frequency waves in a dusty magnetoplasma. Examples of various unstable low-frequency waves include the electron whistler, the dust whistler, dust cyclotron waves, AlfvÉn waves, electromagnetic ion-cyclotron waves, as well as lower-hybrid, electrostatic ion cyclotron, modified dust ion-acoustic waves, etc. Also found is a new type of unstable waves whose frequency is close to the dust grain rotation frequency. The present results should be useful in understanding the properties of low-frequency waves in cosmic and laboratory plasmas that are embedded in an external magnetic field and contain elongated and rotating charged dust grains.     

Attractive potential around a thermionically emitting microparticle

We present a simulation study of the charging of a dust grain immersed in a plasma, considering the effect of thermionic electron emission from the grain. It is shown that the orbit motion limited theory is no longer reliable when electron emission becomes large: screening can no longer be treated within the Debye-Huckel approach and an attractive potential well can form, leading to the possibility of attractive forces on other grains with the same polarity. We suggest to perform laboratory experiments where emitting dust grains could be used to create nonconventional dust crystals or macromolecules.     

Effect of radiation on dust particles in orbital resonances

The effect of electromagnetic radiation on the dynamics of arbitrarily shaped cosmic dust particles is investigated. The paper concentrates on the motion of dust grains near commensurability resonances with a planet—mean-motion resonances—and possible capture of the grains in the resonances. A particle is in resonance with a planet when the ratio of the mean motions of the two objects is a ratio of two small integers.

The most fundamental properties of the orbital evolution of spherical dust particles in the mean-motion resonances are shortly rederived: the solar wind effect is also included and the existing result is improved. The results for spherical particles are compared with the detailed numerical calculations for nonspherical particles. It is shown that the fundamental results valid for spherical grains do not hold, in general, for nonspherical particles. While spherical particles are always characterized by the secular decrease of the semi-major axes near mean-motion resonances, this may not be true for nonspherical particles. Nonspherical grains may exhibit an increase of the semi-major axes before capturing in the mean-motion resonances. This is caused by the effect of electromagnetic radiation on nonspherical dust grains. The eccentricities of spherical particles in the exterior resonances approach a limiting value, but nonspherical grains may not follow this behaviour. The interior resonances are characterized by a systematic decrease of eccentricity for spheres, but various behaviours exist in the case of irregularly shaped particles.

The motion of a nonspherical dust particle under the action of electromagnetic radiation may be characterized by a small change of the semi-major axis during a long-time interval, but the particle is not captured in any mean-motion resonance. This kind of motion does not exist for spherical grains.     

Growth and form of planetary seedlings: results from a microgravity aggregation experiment

The outcome of the first stage of planetary formation, which is characterized by ballistic agglomeration of preplanetary dust grains due to Brownian motion in the free molecular flow regime of the solar nebula, is still somewhat speculative. We performed a microgravity experiment flown onboard the space shuttle in which we simulated, for the first time, the onset of free preplanetary dust accumulation and revealed the structures and growth rates of the first dust agglomerates in the young solar system. We find that a thermally aggregating swarm of dust particles evolves very rapidly and forms unexpected open-structured agglomerates.     

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.     

Rotational properties of annulus dusty plasma in a strong magnetic field

The collective dynamics of an annulus dusty plasma formed between a co-centric conducting (non-conducting) disk and ring configuration is studied in a strongly magnetized radiofrequency (rf) discharge. A superconducting electromagnet is used to introduce a homogeneous magnetic field to the dusty plasma medium. In the absence of the magnetic field, the dust grains exhibit thermal motion around their equilibrium position. The dust grains start to rotate in the anticlockwise direction with increasing magnetic field (B > 0.02 T ), and the constant value of the angular frequency at various strengths of the magnetic field confirms the rigid body rotation. The angular frequency of dust grains linearly increases up to a threshold magnetic field (B > 0.6 T ) and after that its value remains nearly constant in a certain range of magnetic field. Further increase in magnetic field (B > 1 T ) lowers the angular frequency. Low value of the angular frequency is expected by reducing the width of the annulus dusty plasma or the input rf power. The azimuthal ion drag force due to the magnetic field is assumed to be the energy source which drives the rotational motion. The resultant radial electric field in the presence of a magnetic field determines the direction of rotation. The variation of floating (plasma) potential across the annular region at given magnetic field explains the rotational properties of the annulus dusty plasma in the presence of a magnetic field.     

Theoretical model for the effect of dust grains on self‐filamentation of a gaussian electromagnetic beam in a fully ionized plasma

A theoretical model for the effect of dust grains on the self‐filamentation of a Gaussian electromagnetic beam propagating in a fully ionized plasma has been developed by employing the energy balance of the plasma constituents, perturbed electron and ion concentrations, and temperature. In this model, neutral atom ionization, re‐integration and accumulation of electrons and ions, photoelectric emission of electrons from the surface of dust grains, as well as elastic and charging collisions have also been considered. The effective dielectric constant in the presence of dust grains has been constructed. The effect of temporal growth of dust grains on various plasma parameters for different values of the dust density has been explored. The variation of the beam width with the normalized channel of propagation has been observed for distinct dust densities and dust charge states. It is observed that the non‐linearity induced by the effective dielectric constant in the presence of dust grains increases the self‐filamentation of the beam, thus enhancing the effective critical power with the dust density. Some of the outcomes of our approach are in line with experimental observations. These outcomes may be useful for explaining space and laboratory plasma experiments as well as for future studies in complex plasmas.     

The dust emission law in the wind erosion process on soil surface

The dust emission models to date cannot describe the relation between the transport rate of different sized grains and their grain size composition in soil surface, so Aeolian grain transport on a soil-like bed composed of fine sand and silt powder was measured in a wind tunnel. Six types of soil-like beds with different silt fractions have been tested in this experiment. The mass flux profiles of silt dust and sand grains are much different due to their different motion modes. Analysis of the vertical distribution of the powder and sand grains reveals that for a given soil bed, the ratio of the horizontal dust flux to the horizontal sand flux is directly proportional to their mass ratio in the bed. The dust flux is closely linked to the sand flux by the bombardment mechanism. For a given wind velocity and grain size of the bed, the slopes of the vertical mass flux profiles of sand grains larger than 100 μm are nearly equal in a log-linear plot and the ratio between the fraction of transport rate of each size group to the whole transport rate and the mass fraction of each size group in the bed is a constant only dependent on grain size. With this law, the transport rate of dust and different sized grains can be related with the grain size composition in the soil surface. Supported by the National Natural Science Foundation of China (Grant No. 50706031) and the Natural Science Foundation of Shanxi Province of China (Grant No. 2008021005)     

竖直振动管中颗粒的上升运动

通过实验和数值模拟研究了竖直振动管中颗粒的受激运动.将一直管插入静止的颗粒料层中,并在管内预填充一定高度的颗粒,对直管施加竖直振动.振动强度较弱时,管内的颗粒在重力作用下向下运动;当振动达到一定的强度时,管内颗粒不下降反而克服重力的作用向上运动,随着振动强度的进一步提高,即使不在管内预填充高于颗粒床层的颗粒,颗粒也会沿着振动管逆重力向上运动.颗粒的上升高度与运动速度强烈依赖于振动强度.通过高速相机记录颗粒和直管在单个振动周期内的运动,并结合离散元(DEM)法模拟管内颗粒的受力变化规律,给出了颗粒上升的机理.此研究对实现散体物料的定向输运提供了一种新方法.