The collision frequency of electron-neutral-particle in the weakly ionized plasma with the power-law velocity distribution

We study the collision frequency of electron-neutral-particle in the weakly ionized plasma with the power-law velocity q-distribution and derive the formulation of the average collision frequency. We find that the average collision frequency in the q-distributed plasma also depends strongly on the q-parameter and thus is generally different from that in the Maxwell-distributed plasma, which therefore modifies the transport coefficients in the previous studies of the weakly ionized plasmas with the power-law velocity distributions.     

弱电离大气等离子体电子碰撞能量损失的理论研究

在前期计算电子能量分布函数的基础上, 求出弱电离大气等离子体中各碰撞反应过程的电子能量损失. 由于在弹性碰撞中电子-重粒子能量交换很少, 同时氮气、氧气分子又有很多能量阈值较低的转动、振动能级存在, 因此在大气等离子体中弹性碰撞电子能量损失所占份额很小(直流电场下小于6%). 研究发现, 弱电离大气等离子体中在不同能量区间占主导的能量损失过程不同. 随着有效电子温度(或约化场强)增加, 占主导的电子能量损失过程依次为转动激发、振动激发、电子态激发、碰撞电离、加速电离产生的二次电子. 在约化场强E/N=1350 Td (或有效电子温度为14 eV)附近, 平均电离一个电子所需的能量最小, 约为57 eV. 因此可以根据不同的需求调节电场强度, 从而达到较高的能量利用率. 关键词： 弱电离大气等离子体 碰撞反应过程 电子能量损失     

Nonlinear Landau damping of high frequency waves in non-Maxwellian plasmas

Space plasmas often possess non-Maxwellian distribution functions which have a significant effect on the plasma waves.When a laser or electron beam passes through a dense plasma,hot low density electron populations can be generated to alter the wave damping/growth rate.In this paper,we present theoretical analysis of the nonlinear Landau damping for Langmuir waves in a plasma where two electron populations are found.The results show a marked difference between the Maxwellian and non-Maxwellian instantaneous damping rates when we employ a non-Maxwellian distribution function called the generalized(r,q)distribution function,which is the generalized form of the kappa and Maxwellian distribution functions.In the limiting case of r=0 and q→∞,it reduces to the classical Maxwellian distribution function,and when r=0 and q→κ+1,it reduces to the kappa distribution function.     

弱电离大气等离子体电子能量分布函数的理论研究

使用球谐展开的方法求解玻尔兹曼方程,得到了弱电离大气等离子体(79％氮气和21％的氧气)的电子能量分布函数(EEDF).发现当约化电场较小时(E/N＜100 Td),EEDF在2-3 eV急剧下降,在此情况下,高能尾部比麦氏分布要小;当约化电场增加,E/N＞ 400 Td,分布函数趋近于麦氏分布;当约化电场进一步增加,E/N＞ 2000 Td,EEDF的高能尾部(超过200 eV)相对于麦氏分布增加,在高频场作用下,EEDF更倾向于麦氏分布.当ω》vm时,有效电子温度只依赖于E/ω,而与碰撞频率无关;当ω《vm时,有效电子温度只依赖于E/N,与微波频率无关.与一些单原子分子等离子体中电子-电子碰撞在电离度大于10-6时就会影响EEDF不同,空气等离子体中,只有当电离度大于0.1％时,电子-电子碰撞才会对EEDF有明显影响.     

Heat conductivity and Dufour effect in the weakly ionized,magnetized, and kappa-distributed plasma

By using the generalized Boltzmann equation of transport and the first-order approximation of Chapman-Enskog expansion on the κ-distribution function, we study the thermal conductivity and Dufour effect in the weakly ionized and magnetized plasma. We show that the thermal conductivity and Dufour coefficient in the κ-distributed plasma are significantly different from those in the Maxwell-distributed plasma, and the transverse thermal conductivity and Dufour coefficient in the κ-distributed plasma are generally greater than those in the Maxwell-distributed plasma, and the Righi-Leduc coefficient and Hall Dufour coefficient in the κ-distributed plasma are also generally greater than those in the Maxwell-distributed plasma.     

弱电离等离子体对电磁波吸收的物理模型和数值求解

从物理基本方程、理论证明和数值分析三方面说明了在一维平板模型中，含时波动方程和亥 姆霍兹方程是等价的，即使电磁波波长小于等离子体的尺度，电磁波的全波解也具有简谐形 式. 对电磁波在弱电离强碰撞等离子体中的传播特性进行了数值研究，结果表明，弱电离强 碰撞等离子体对电磁波具有很强的吸收特性. 关键词： 电磁波 弱电离等离子体 过阻尼     

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     

粒子束在气体系统中的碰撞频率和反应速率系数

利用统计的方法,系统研究了粒子束与气体系统中粒子的碰撞频率分布和总碰撞频率;分析了气体系统粒子间的碰撞频率以及反应速率系数与特征速率的关系.     

Ion velocity shear-induced drift wave and momentum transport in non-Maxwellian magnetoplasma flows

We have investigated the diamagnetic flow in a non-uniform partially ionized plasma with non-Maxwellian electron population to explain the dynamics of ion velocity shear-induced low-frequency drift mode and associated instabilities. The dispersion relations are found, and instability threshold conditions are pointed out along with ion-parallel momentum transport due to drift motion with relative phase shift of fluctuating quantities in a non-conservative system. The real frequencies and instability growth rates are studied numerically and illustrated for typical space and laboratory plasmas. This study should be useful in understanding some aspects of low-frequency time-delayed perturbations with sheared flow leading to drift instabilities and cross-field parallel ion momentum transport in nonuniform magnetoplasmas containing a non-Maxwellian electron population.     

Hall推力器内饱和鞘层下电子与壁面碰撞频率特性

利用二维粒子模拟方法研究Hall推力器内电子与壁面的碰撞频率.研究发现,饱和鞘层状态下的电子与壁面的碰撞频率较经典鞘层下大大增加,甚至高出经典鞘层状态下电子与壁面碰撞频率两个数量级,这样饱和鞘层状态下电子与壁面的碰撞频率对近壁电流的贡献将不容忽略.进一步分析造成饱和鞘层状态下电子与壁面碰撞频率增加的原因后认为,饱和鞘层状态下电子与壁面碰撞频率的增加是鞘层电势降过低和壁面发射的二次电子回流造成的. 关键词： 饱和 鞘层 碰撞 频率     

弱电离尘埃等离子体层反射与透射的SO-FDTD方法分析

将弱电离尘埃等离子体复介电常数表示以jω 为自变量的分式多项式形式, 利用移位算子时域有限差分(SO-FDTD)方法, 给出了弱电离尘埃等离子体频域本构关系的时域形式. 推导了弱电离尘埃等离子体电磁特性的时域递推关系式. 用SO-FDTD方法计算了弱电离尘埃等离子体层的反射和透射系数, 分析了尘埃粒子浓度和尘埃粒子半径的变化对反射系数和透射系数的影响. 结果表明: 有尘埃粒子时的反射系数比没有尘埃粒子时反射系数小, 而透射系数要比没有尘埃粒子时的透射系数大; 当尘埃粒子浓度或尘埃粒子半径增大时, 其反射系数均减小.     

非磁化等离子体中的电子碰撞频率

电子碰撞频率是非磁化等离子体的一个重要参数,它对等离子体与电磁波相互作用的性质具有较大影响。基于产生等离子体的气压条件不同,其电子碰撞频率具有较大变化范围。研究了它对非磁化等离子体吸波能力的影响,得出了当电子碰撞频率与等离子体频率和入射波频率相当时,等离子体对电磁波具有较大吸收的结论,给出了对应于最大吸收的最佳碰撞频率值。分析了通过选择放电气体来调整等离子体的电子碰撞频率。     

Modification of the electron velocity distribution function in weakly ionized plasmas by nonisotropic elastic-scattering processes

Summary After a brief presentation of a technique for solving Boltzmann's equation in multiterm approximation in the presence of nonisotropic elastic and (conservative) inelastic collisions of the electrons with gas atoms or molecules, we report the results of a systematic study of the impact of a nonisotropic scattering in elastic collisions. By using an appropriate distribution for the scattering angle, the effects on isotropic (i.e. energy) distribution, total anisotropy of the velocity distribution and some transport and rate coefficients are investigated for a model plasma, from mainly forward to mainly backward scattering. The results are then compared with those found for isotropic scattering. A particularly large impact has been found, for instance, on energy distribution and some macroscopic quantities for narrow forward scattering, while the classical two-term approximation especially is found to fail for backward scattering. The results are qualitatively explained by considering the balance between energy gain by the field and collisional dissipation and the modifications produced when changing the anisotropy of elastic scattering.

---

Riassunto Dopo una breve presentazione di una nuova tecnica per la risoluzione dell'equazione di Boltzmann in approssimazione ?multi-term? in presenza di urti elastici non isotropi e urti anelastici conservativi da parte di elettroni con atomi o molecole del gas, vengono riportati i risultati di uno studio sistematico dell'effetto dell'anisotropia dello scattering elastico. Facendo ricorso ad appropriate distribuzioni dell'angolo di scattering, si studia l'effetto su distribuzione energetica, anisotropia della distribuzione delle velocità ed alcuni coefficienti del trasporto utilizzando un conveniente gas modello e variando lo scattering da ?prevalentemente in avanti? a ?prevelentemente all'indietro?. I risultati sono poi confrontati con quelli ottenuti con la comune assunzione di scattering isotropo. Si è potuto così mettere in luce che esiste un effetto particolarmente pronunciato dello scattering in avanti su distribuzione energetica ed alcune importanti grandezze macroscopiche e, contemporaneamente, anche osservare che la convenzionale approssimazione a due termini tende a divenire inadeguata particolarmente in presenza di scattering all'indietro. Tutti i risultati ottenuti sono qualitativamente spiegati considerando il bilanciamento tra guadagno di energia dovuto al campo elettrico e dissipazione dovuta agli urti e, in particolare, analizzando gli effetti che sono prodotti quando l'anisotropia dello scattering elastico viene alterata.

---

Резюме Сначала обсуждается техника решения уравнения Больщмана в многочленном приближении в присутствии неизотропных упругих и (консервативных) неупругих соударений электронов с атомами или молекулами газа. Затем мы приводим результаты систематического исследования влияния неизотропного рассеяния в упругих соударениях. Используя соответсвующее распределение для угла рассеяния, для модельной плазмы исследуются влияние на изотропное (т.е. энергетическое) распределение, полная анизотропия распределения по скоростям и некоторые транспортные и вероятностные коэффициенты. Полученные результаты сравниваются с результатами вычислений для изотропного рассеяния. Обнаружено особенно большое влияние, например, на энергетическое распределение и на некоторые макроскопические величины для узкого угла рассеяния вперед, хотя классическое двух-членное приближение не обнаруживает изменения для рассеяния назад. Полученные результаты качественно обьясняются с помощью рассмотрения баланса между приращением энергии из-за полевой и столкновительной диссипации и изменениями, связанными с изменением анизотропии упругого рассеяния.

     

Propagation of dust-acoustic waves in weakly ionized plasmas with dust-charge fluctuation

For an unmagnetized partially ionized dusty plasma containing electrons, singly charged positive ions, micron-sized massive negatively charged dust grains and a fraction of neutral atoms, dispersion relations for both the dust-ion-acoustic and the dustacoustic waves have been derived, incorporating dust charge fluctuation. The dispersion relations, under various conditions, have been exhaustively analysed. The explicit expressions for the growth rates have also been derived. International Conference on the Frontiers of Plasma Physics and Technology, 9–14 December 2002, Bangalore, India.     

强激光部分离化等离子体成丝不稳定性

从部分离化等离子体和通常的全离化等离子体的差异是存在束缚电子出发,分析强激光在部分离化等离子体中的传播和折射指数,其束缚电子加强成丝不稳定性的发展.对钕玻璃三倍频激光金靶等离子体的原子成丝不稳定性进行了计算和分析.结果表明强激光部分离化等离子体的原子成丝不稳定性显著高于相对论成丝不稳定性. 关键词： 激光等离子体相互作用 部分离化等离子体 成丝不稳定性     

Impact of nonisotropic elastic and inelastic scattering on the electron velocity distribution in weakly ionized plasmas

Summary By using appropriate angular distributions for elastic and inelastic scattering of electrons with gas atoms, the effect of nonisotropic elastic and/or inelastic collision processes on electron velocity distribution and corresponding macroscopic quantities, and also on their variations when increasing the approximation orders, is studied for a convenient model plasma. The study is made possible by the use of a new technique for the solution of the Boltzmann equation at elevated orders of approximation based on an appropriate Legendre polynomial expansion of the velocity distribution function. It is found that large variations of the distribution function and relevant macroscopic quantities occur when passing from isotropic scattering to narrow angular distributions of forward scattering in elastic collisions or in both kinds of collision processes. The simultaneous action of the two anisotropies leads to a pronounced amplification of the effect while backward scattering produces less important changes. The effects remarkably increase when decreasing the energy loss per inelastic collision. A microphysical interpretation of the impact of nonisotropic scattering is given in terms of the competing actions of field acceleration and collisional dissipation, which is modified by nonisotropic scattering, and of the reflections on the structure of the hierarchy of equations describing the electron behaviour.

---

Riassunto Facendo ricorso ad appropriate distribuzioni angolari relative allo scattering elastico ed anelastico di elettroni da parte degli atomi di un conveniente gas modello, è stato studiato l’effetto che processi di collisione elastici e/o anelastici anisotropi hanno su distribuzione elettronica delle velocità e corrispondenti parametri macroscopici, nonché sulle variazioni che dette grandezze macroscopiche subiscono quando viene elevato l’ordine di approssimazione. Lo studio è stato reso possibile dall’uso di una nuova tecnica che permette la soluzione dell’equazione di Boltzmann ad elevati ordini di approssimazione con un’opportuna espansione in polinomi di Legendre della distribuzione delle velocità. è stato così possibile osservare che grandi variazioni sia della distribuzione delle velocità che delle grandezze macroscopiche si hanno allorché si passa da scattering isotropo a scattering marcatamente in avanti nelle collisioni elastiche o in entrambi i tipi d’urto. La simultanea azione delle due anisotropie porta ad una pronunciata amplificazione dell’effetto mentre lo scattering all’indietro produce cambiamenti meno importanti. è stato anche messo in luce come l’effetto dipenda dall’energia persa negli urti anelastici e come esso generalmente aumenti considerevolmente se la perdita anelastica decresce. Viene anche data una interpretazione fisica dell’effetto prodotto dall’anisotropia dello scattering in termini delle azioni competitive del campo e degli urti e dei riflessi che lo scattering anisotropo ha sulla struttura della gerarchia di equazioni che descrivono il comportamento elettronico.

---

Резюме Используя соответствующие угловые распределения для упругого и неупругого рассеяния электронов на атомах газа, для обычной модельной плазмы исследуется влияние процессов неизотропных упругих и/или неупругих соударений на распределение электронов по скоростям и на соответствующие макроскопические величины, а также их изменение при увеличении порядка аппроксимации. При исследовании используется новая техника решения уравнения Больцмана в соответствующих порядках аппроксимации, основанная на разложении по полиномам Лежандра функции распределения электронов по скоростям. Получено, что больщие изменения функции распределения и соответствующих макроскопических величин возникают при переходе от изотропного рассеяния к узким угловым распределениям рассеяния вперед в упругих соударениях или в обоих типах процесса соударения. Одновременное действие двух анизотропий приводит к заметному усилению эффекта, тогда как рассеяние назад вызывает менее существенные изменения. Эффект значительно увеличивается при уменьшении энергетических потерь в неупругом соударении. Предлагается микрофизическая интерпретация влияния неизотропного рассеяния в терминах конкурирующих процессов ускорения полем и столкновительной диссипации, которые изменяются за счет неизотропного рассеяния, а также изменений структуры иерархии уравнений, описывающих поведение электронов.

     

Computer simulation of the collision frequency of two particles in optical tweezers

Optical tweezers have been successfully used in the study of colloid science. In most applications people are concerned with the behaviour of a single particle held in the optical tweezers. Recently, the ability of the optical tweezers to simultaneously hold two particles has been used to determine the stability ratio of colloidal dispersion. This new development stimulates the efforts to explore the characteristics of a two-particle system in the optical tweezers.An infinite spherical potential well has been used to estimate the collision frequency for two particles in the optical trap based on a Monte Carlo simulation. In this article, a more reasonable harmonic potential, commonly accepted for the optical tweezers, is adopted in a Monte Carlo simulation of the collision frequency. The effect of hydrodynamic interaction of particles in the trap is also considered. The simulation results based on this improved model show quantitatively that the collision frequency drops down sharply at first and then decreases slowly as the distance between the two particles increases. The simulation also shows how the collision frequency is related to the stiffness of the optical tweezers.     

Power dependence of terahertz carrier frequency in a plasma-based two-color generation process

We conduct a frequency spectrum experiment to investigate terahertz（THz） emissions from laser-induced air plasma under different laser incident powers. The frequency spectra are measured using both air-biased-coherent detection and a Michelson interferometer. The red-shift of the THz pulse carrier frequency is observed as a response to increased pump power. These phenomena are related to plasma collisions and can be explained by the plasma collision model. Based on these findings, it is apparent that the tuning of the THz carrier frequency can be achieved through regulation of the pump beam.     

Slowing down of charged particles in dusty plasmas with power‐law kappa‐distributions

We study the slowing down of a particle beam passing through the dusty plasma with power‐law κ‐distributions. Three plasma components, electrons, ions, and dust particles, can have a different κ‐parameter. By using Fokker‐Planck theory, the deceleration factor and slowing down time are derived and expressed by a hyper‐geometric κ‐function. Numerically, we study the slowing down property of an electron beam in the κ‐distributed dusty plasma. We show that the slowing down in the plasma depends strongly on the κ‐parameters of plasma components, and dust particles play a dominant role in the deceleration effects. We also show dependence of the slowing down on mass and charge of a dust particle in the kappa‐distributed plasma.     

Propagation features of head-on collision dust acoustic solitary waves in four-component quantum plasmas

ABSTRACT

In framework of the extended Poincaré–Lighthill–Kuo, the properties of dust acoustic (DA) solitary wave’s interaction are investigated in four-component quantum dusty plasma. Two Korteweg–de Vries equations describing the colliding DA solitary waves are derived by eliminating the secularities. By knowing the explicit form of the solitary wave solutions, the leading phase changes, trajectories and phase shifts are obtained, accordingly. The effects of various physical parameters such as the quantum mechanical parameters, the charge ratio between positive and negative dust particles, the mass ratio between negative and positive dust particles and the ratio of electron to ion temperatures are studied extensively. Our findings showed that these parameters play a significant role on the characteristics and basic features of DA solitary waves such as phase shifts in trajectories due to collision. The obtained results may be beneficial to understand well the collision of DA solitary waves that may occur in laboratory plasmas, space plasma as well as in plasma applications.