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The fluid dynamics model was used to study the influence of the existence of the collisions on the dust particles in a dusty plasma sheath. The main collisions in this study consist of the ionization collision, the collision between electron and neutral particle, the collision between ion and neutral particle, the collision between electron and dust particle, the collision between ion and dust particle. Numerical calculation results are obtained by the fourth-order-Rung-Kutta method. It is shown that both the dust particles’ density and corresponding electricity quantity increase as the following collisions’ frequency enhances, such as ionization collision, the collision between electron and neutral particle, the collision between ion and neutral particle. The charge reduces due to the collisions concluding electron-dust particle and ion-dust particle. In addition, the effect produced by ions’ collision is much more obviously compared with electrons’ collision.     

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。     

New mechanism of atomic particle ionization in crystals

It is shown that at channeling in a crystal the electron loss by a fast ion due to “inelastic” collisions with the target electrons may be of importance as the “elastic” electron loss which is dominating in an amorphous target can be strongly reduced in a crystalline one.     

Low-pressure RF discharge in the free-flight regime

The self-consistent equations system for low-pressure RF discharge in the free-flight regime is formulated. The expressions for the electron energy diffusion coefficient due to electron-neutral collisions and to the electron collisions with the plasma-space charge moving boundary (stochastic heating) are derived. If the electron-neutral elastic collisions frequency exceeds the inelastic one, the conventional two-term approximation for the electron distribution function (EDF) can be generalized, and the space-time-averaged electron kinetic equation can be reduced to the one-dimensional energy diffusion one. The fast electrons attached to the electrode surface can also be accounted for in this equation. It is shown that in the cases of (a) spatially uniform ion profile, (b) for frequencies that are small compared with the electron bounce frequency, and (c) for frequencies exceeding the electron plasma one in the sheath, the stochastic heating vanishes     

Ion-acoustic waves in a dust-contaminated plasma

A self-consistent theory of ion-acoustic waves in dusty gas discharge plasmas is presented. The plasma is contaminated by fine dust particles with variable charge. The stationary state of the plasma and the dispersion and damping characteristics of the waves are investigated accounting for ionization, recombination, dust charge relaxation, and dissipation due to electron and ion elastic collisions with neutrals and dusts, as well as charging collisions with the dusts.     

Anomalous absorption of high-energy green laser light in high- z plasmas

We observe strong anomalous absorption of green laser light in mm-scale high-temperature gold plasmas. Both the laser light absorption and the resulting increase of the electron temperature, which was measured independently with Thomson scattering, have been successfully modeled by including enhanced collisions due to heat-flux driven ion acoustic fluctuations. Calculations that include only inverse bremsstrahlung significantly underestimate the experimental laser absorption and the electron temperature.     

Scattering of Low-Energy Electrons by Positive Ions in a Magnetic Field. I. Quantum Calculation of Transition Probabilities

We analyze electron–ion collisions in a magnetic field at a low temperature, for which the electron’s Larmor radius is less than the characteristic impact parameter of close collisions without the magnetic field. This ratio of spatial scales is realized in the photospheres of magnetic white dwarfs and in the experiments of antihydrogen creation. Under considered conditions, an electron transits from the initial to the final state via an intermediate quasibound state. We put forward an approximate analytical procedure for the quantum-mechanical calculation of the probabilities for an electron to transit between Landau levels due to a collision with an ion. We reduce the calculation to the inversion of finite-dimension matrices. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 6, pp. 512–525, June 2008.     

Damping of longitudinal plasma oscillations

Attenuation of electron oscillations in a fully ionized plasma is investigated by solving linearized kinetic equation without external fields. The general dispersion relation for longitudinal plasma oscillations is obtained using the BGK model. Damping due to electron ion collisions is obtained with a correction term. It is also observed that damping rate decreases ask increases, which is in agreement with McBride.     

Atomic collision processes relevant for heavy ion beam probes

Atomic collision processes of fast Tl and Cs ions with particles in a high temperature fusion plasma are investigated. At low beam energies (<5 MeV), ion impact collisions and charge exchange processes can be neglected compared to electron ionization processes. At beam energies above 5 MeV and high plasma ion temperatures, collisions with ions start to contribute significantly to signal generation and attenuation. Also, collisions with the neutral background gas in the beamlines can attenuate the ion beam significantly and lower the signal level, if the vacuum pressure is above 10^-4 Torr. For the heavy ion beam probes operating today, only electron impact ionization processes are important and accurate predictions of the secondary signal level and electron density profile measurements are possible because of the good knowledge of electron impact ionization cross sections for Cs ⁺ and Tl⁺ ions     

Influence of dynamic screening on the conductivity of hydrogen plasma including electron–electron collisions

We investigate the dynamical conductivity of dense hydrogen plasmas on the basis of the effective interaction potential (taking into account static or dynamic screening and diffraction effects). We apply a generalized Drude–Lorentz formula related to the dynamical conductivity with collision frequency. The influence of electron–ion collisions as well as the influence of both electron–ion and electron–electron collisions were taken into account via a renormalization factor. All calculations were performed on the basis of the effective potential with static or dynamic screening.     

电子发射对稳态等离子体鞘层影响的理论研究和数值模拟

 建立了一套非线性自洽的流体力学方程组,研究了电子发射对稳态等离子体鞘层的影响,并分别考虑了发射电子及离子同中性原子的弹性和非弹性碰撞过程。数值结果表明：发射电子的初始束流密度及中性气体密度是描述鞘层空间演化的两个最关键的物理量,特别是发射电子的存在使得鞘层厚度变薄。     

Three-dimensional PIC/MCC simulation of electron deposition in JAEA 10 A ion sources

A systematic research on the electron deposition process in the JAEA 10 A ion source is carried out by using a particle-in-cell/Monte Carlo collision simulation, which is based on a full three-dimensional self-developed code. Two parts are studied. One is the space and energy distribution of fast and slow electrons, the other is the vibration excitation collisions between electrons and hydrogen moleculars. The results show that the inhomogeneity of electrons comes from the Y direction drift of the fast electrons(Te 25 eV) due to the action of the magnetic fields. This drift also increases the number of vibration excitation collisions in the-Y direction, and results in the increase of Hain the-Y direction,eventually leading to the-Y drift of H-. It explains the spatial non-uniformity in the JAEA 10 A ion source.     

Resistive Electrostatic Ion Cyclotron Instability in Plasmas

The stability of electrostatic ion cyclotron waves propagating obliquely with respect to the background magnetic field is studied for collisional, fully-ionized plasmas in which there is a relative field-aligned streaming between electrons and ions. It is found that electron-ion collisions, in conjunction with electron streaming, provides a mechanism for instability. The role of electron streaming is to supply a source of free energy and the role of electron-ion collisions is to restrict the field-aligned mobility of the electrons, thus preventing them from establishing a Boltzmann equilibrium. Ion-ion collisions and finite ion Larmor radius are found to exert a stabilizing influence. The instability is analyzed for both current-carrying plasmas and counterstreaming-beam-plasma systems.     

蒙特卡罗碰撞算法在CHIPIC软件中的数值实现

分析离子源中电子所参与的碰撞,利用电子与其它粒子间的空碰撞模型,研究电子之间的库仑碰撞,采用不同的存储和调用机制研制了两种碰撞模型的蒙特卡罗碰撞处理模块,将数值模块添加到粒子模拟软件CHIPIC中,对离子源JAERI 10A进行模拟验证,通过对模拟结果的分析,表明所设计的三维MCC算法正确.     

Relaxation of bound electrons in elastic collisions with infinitely heavy particles

The recombination relaxation of bound electrons in collisions with infinitely rigid, infinitely heavy spheres is considered. The relaxation mechanism is due to a change in the electron scattering from the spheres. The distribution functions of bound electrons and the recombination time due to that mechanism are obtained. The characteristics of the relaxation are the same as for the Thompson recombination mechanism (caused by energy transfer from the electron to a third particle) to within replacement of the mass of the third particle by the ion mass.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 48–53, April, 1996.     

Nonlinear interaction phenomenon of dust acoustic solitary and shock waves in dusty plasma

The effects of head-on collision on dust acoustic (DA) solitary and shock waves in dusty plasma are investigated considering positively charged inertial dust, Boltzmann distributed negatively charged heavy ions, positively charged light ions, and superthermal electrons in the plasma system. The nonlinear Korteweg-de-Vries (KdV) Burger equations are derived taking the extended Poincaré-Lighthill-Kuo method into account to study the characteristic properties of nonlinearity and production of solitary shock due to collisions. The study reveals that the amplitudes and widths of the DA shock waves are decreasing with increasing viscosity, electron to dust density ratio, and dust to ion temperature ratio, while they are increasing due to the presence of superthermal electrons. The nonlinearity of DA waves are enhanced with increasing density ratio of electron to dust and temperature ratio of dust to ion and electron, respectively, but it is reducing with superthermal electrons. The phase shifts of DA solitary waves are found to decrease with rising superthermality of electrons and increase with the density ratio of electron to dust.     

Temperature Effects on the Beat Heating of a Collisional Magnetoplasma

The beat heating of a magneto-plasma by two antiparallel electromagnetic waves at different temperatures is examined. The effects of plasma temperature, plasma electron collisions, plasma ion collisions and magnitude and direction of the magnetic field on the excitation of plasma electron waves and plasma ion waves are studied. A formula for the power absorption density of the plasma by using Maxwell's equations in conjuction with continuity and momentum equation. including collisions and pressure tensor terms, is derived. The contribution of the plasma temperature to the power absorption density, both at low and high beat frequencies, of the collisional and the non-collisional magnetised plasmas is found very significant and is illustrated numerically. The inclusion of pressure tensor term in the momentum equation is also found to cause characteristic changes in the power absorption density of the plasma with the orientation of magnetic field.     

Plasma acceleration by area expansion

As the area of a plasma increases, the plasma can accelerate smoothly from subsonic to supersonic velocity. The singularity which ordinarily occurs at the sonic velocity is resolved not by charge separation, as is the case for a sheath, but rather by a zero in the numerator at the same spatial position as the zero in the denominator, the sonic point. That is, at the sonic point, the acceleration due to expansion just cancels out the deceleration due to ion and electron neutral collisions. It turns out that, in this configuration, the plasma can accelerate to about three times the ion sound speed. The electron temperature is determined by the geometry, gas species, and, mostly, by the gas pressure. Applications to the production of a stream of neutrals for etching, and to space plasma propulsion are discussed     

库仑碰撞截面在等离子体粒子模拟中的应用

在等离子体粒子模拟中,TA模型和NanBu模型被广泛用于处理库仑碰撞,这两种模型要求每个时间步长内全部粒子参与计算。为了降低参与碰撞的粒子数,提高库仑碰撞的计算效率,提出了一种基于截面的库仑碰撞模拟方法,并给出了库仑碰撞概率的计算公式。采用该方法对不同温度不同密度电子气的弛豫过程进行模拟,分别对比了电子速度分布函数、电子温度以及电子x、y方向上的温度与电子温度之比的模拟值与理论值,验证了该方法的准确性。在相同的小时间步长上,该方法相比TA模型计算效率提升可达40%以上。对于较大的时间步长,该方法仍能得到与理论解近似的模拟结果,相比Nanbu模型,在相同的精度下可取更大的时间步长,计算效率也有所提升。研究表明,该方法同样适用于电子-离子碰撞。因此在提高库仑碰撞计算效率上,该方法具有碰撞粒子数少以及适用于大时间步长的优势。     

Current-drive efficiency in a degenerate plasma

In a degenerate plasma, the rates of electron processes are much smaller than the classical model would predict, affecting the efficiencies of current generation by external noninductive means, such as by electromagnetic radiation or intense ion beams. For electron-based mechanisms, the current-drive efficiency is higher than the classical prediction by more than a factor of 6 in a degenerate hydrogen plasma, mainly because the electron-electron collisions do not quickly slow down fast electrons. Moreover, electrons much faster than thermal speeds are more readily excited without exciting thermal electrons. In ion-based mechanisms of current drive, the efficiency is likewise enhanced due to the degeneracy effects, since the electron stopping power on slow ion beams is significantly reduced.