ELECTRON TRANSPORT BEHAVIOR IN NORMAL AND ABNORMAL DIRECT CURRENT DISCHARGE CATHODE SHEATH

This paper studies the electron transport behavior in normal and abnormal helium direct current (dc) glow discharges using a Monte Carlo simulation, in which the influences of the electron initial energy and cathode surface reflection on the electron swarm behavior are considered. The electron-neutral atom collision processes and the electron swarm parameters (such as the number of collisions, collision rates, ionization coefficient, mean drift velocity, electron density, etc.) are analyzed. The results show that the variations of the initial energy of the electron emitted from the cathode and the cathode reflection cause a weak effect on the electron transport parameters in the two discharges. The results also indicate that the electron transport parameters are quite different in normal and abnormal discharges.     

直流辉光等离子体阴极鞘层电子的输运过程

采用蒙特卡罗方法对氦直流辉光放电平板电极等离子体阴极鞘层内电子的输运过程进行了研究。利用实验数据拟合得到的电子与中性粒子的碰撞截面,计算了电子的平均能量及能量分布的空间变化,同时研究了电子的其它参数分布.     

THEORETICAL INVESTIGATION OF ELECTRON-NEUTRAL ATOM COLLISION PROCESS AND ELECTRON TRANSPORT PARAMETERS IN DC GLOW DISCHARGE OF PLASMA WITH A TRANSVERSE MAGNETIC FIELD

A Monte Carlo simulation (MCS) technique is used to simulate the cathode sheath region of a helium dc glow discharge. In such a simulation, a nonuniform electric field and a transverse uniform magnetic field are considered. When the magnetic field intensity increases from 0 to 800 G, all types of collision considered in this paper are enhanced. This result is in agreement with the experimental result. The results also show that with the increase of magnetic field intensity, the electron transport time, the electron density increase, and the electron mean energy decreases.     

横向磁场对辉光等离子体阴极区电子输运过程的影响

本文动用改进的蒙特卡罗技术，研究了横向磁场对氦气直流辉光放电阴极区电子输运过程的影响。     

随机磁场中的双极电场与双极扩散

等离子体中存在随机场输运时,必然会导致双极电场。本文给出了存在电场时,粒子在随机场中的转移几率,由此可计算输运流、双极电场等。算出的双极电场与碰撞的关系是不灵敏的((|e|E)/T_e=-A1/n_e(dn_e)/(dx),A与碰撞有关,但A～1)。并指出,此双极电场可作为判断随机场是否重要的必要条件(但非充分条件)。在随机场双极扩散中,杂质流速大于氢离子流速(V_I/V_i≈(m_i/     

直流空心阴极放电中鞘层区电子的输运过程

采用蒙特－卡洛方法对空心阴极放电中鞘层区电子的输运过程进行了研究，电子在鞘层区被非均匀电场加速，两次碰撞之间的步长是由电子与中性粒子的碰撞频率确定。模型中三种碰撞截面积是由实验和理论数据拟合而来。研究了电子平均能量、电子密度和电离系数在径向的分布。电子能量的空间分布结果与实验很好地符合。 关键词：     

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。     

Transport phenomena in a partially lonized Lorentzian magnetoplasma

Some transport coefficients are evaluated for a homogeneous, partially ionized Lorentzian plasma in the presence of a uniform external magnetic field. The electronion collisions are taken into account by means of the modified Fokker-Planck equation and the electron-neutral collision frequency, ν_en is taken as velocity (ω) dependent or velocity independent, depending on the energy range under consideration. The variation of the transport coefficients with magnetic field is determined for ν_en ∝ ω^s (s being a positive or negative integer) and one finds that qualitatively this behavior does not change by changing either the collision frequency or the velocity dependence of the collision frequency; however for weak magnetic fields the magnitudes of these transport coefficients increase with the decrease in ν_en or s, whereas for strong magnetic fields the transverse components of the transport coefficients decrease and the Hall components tend to saturate with the decrease of either the collision frequency or s.     

Most electron heat transport is not anomalous; it is a paleoclassical process in toroidal plasmas

It is hypothesized that radial electron heat transport in magnetically confined toroidal plasmas results from paleoclassical Coulomb collision processes (parallel electron heat conduction and magnetic field diffusion). In such plasmas the electron temperature is equilibrated along magnetic field lines a long length L (> poloidal periodicity length piR0q), which is the minimum of the electron collision length and an effective field line length. Thus, diffusing field lines induce a radial electron heat diffusivity M identical with L/(piR0q) approximately 10>1 times the magnetic field diffusivity eta/mu0 approximately nue(c/omegap)2.     

随机磁场对静电波驱动的速度扩散的影响

随机磁场改变了波与粒子之间的耦合关系。因而使波驱动的速度扩散受到影响。其结果是:波电场的横向分量可以对纵向速度扩散有贡献;∈<<1情形,扩散系数的共振峰被展宽;∈>>1情形,扩散系数的振荡效应被削弱。当随机磁场的关联时间与波的特征时间之间相对大小不同时,随机磁场产生影响的具体机制不完全相同,所造成的后果也有差别。对于接近于在垂直方向传播的波,随机磁场对速度扩散的影响一般是重要的。     

Benchmark calculations for Monte Carlo simulations of electrontransport

Benchmark calculations have been performed for electron transport coefficients with an aim to produce a body of data required to verify the codes used in plasma modeling. The present code for the time resolved Monte Carlo simulation (MCS) was shown to represent properly DC transport coefficients in a purely electric field, in crossed electric and magnetic fields, and in the presence of nonconservative collisions, ionization, and attachment. In addition, we have suggested tests of the time dependent solutions. Relaxation of the initial transport coefficient may serve as an accurate test of the code as well as the input data for some fluid codes. In this paper, we show only one example, but several different sets of conditions and cross sections should be used as well. Finally, we propose application of the quasi-steady state results in RF fields. As an example we suggest calculation of the components of diffusion tensor showing anomalous longitudinal diffusion and calculations made with nonconservative collisions (ionization in this case). We also check the application of approximate formulas to determine drift velocity on the basis of total collision frequency and to determine a diffusion coefficient by using the Einstein relation. Other tests required to verify the transport data calculations are discussed as well     

感生电场与动生电场的等效性探究

本文认为在感生电场的情况下,磁场的强弱变化可以引起磁场自身的横向运动,使得线圈中电子相对于磁场发生运动,从而等效为一个动生电场,受到洛伦兹力的作用.借助磁感线模拟磁场的运动方式,得到圆形回路中任意一点与磁场相对运动速度的表达式,进而推得该＂等效动生电场＂中的洛伦兹力.以螺线管为例,验证该方法可以解释感生电场所满足的规律.将感生电场与动生电场的产生原因统一为导体中电子与磁场的相对运动,相应电动势的非静电力统一为洛伦兹力.     

Effect of E × B electron drift and plasma discharge in dc magnetron sputtering plasma

Study of electron drift velocity caused by Etimes B motion is done with the help of a Mach probe in a dc cylindrical magnetron sputtering system at different plasma discharge parameters like discharge voltage, gas pressure and applied magnetic field strength. The interplay of the electron drift with the different discharge parameters has been investigated. Strong radial variation of the electron drift velocity is observed and is found to be maximum near the cathode and it decreases slowly with the increase of radial distance from the cathode. The sheath electric field, E measured experimentally from potential profile curve using an emissive probe is contributed to the observed radial variation of the electron drift velocity. The measured values of the drift velocities are also compared with the values from the conventional theory using the experimental values of electric and magnetic fields. This study of the drift velocity variation is helpful in providing a useful insight for determining the discharge conditions and parameters for sputter deposition of thin film.     

射频辉光放电CH4等离子体中电子的能量分布

通过求解Lorentz简化的玻尔兹曼方程,得到射频放电CH₄等离子体中电子的能量分布函数.求解过程中使用一个简化的射频电场模型代替泊松方程求解放电电场.共计包含6类环境气体及27种电子碰撞反应.通过EEDF对等离子体中的电子反应率系数、电子平均能量、电子的传输率系数等进行求解分析.结果表明,在等离子体鞘层区域电子能量具有Maxwell分布形式,在正柱区域具有Druyvesteyn分布形式.最高电子能量和最大反应率系数出现在鞘层区域.电子的迁移率系数和扩散率系数随射频周期的演化时空分布不均匀.     

Magnetfeldabhängige Mikrowellen-Absorption und -Dispersion zur Bestimmung von Stoßfrequenz und Stoßmodell bei Flammenplasmen

At atmospheric pressure acetylene-oxygen and acetylene-air flames were burning through anX-band waveguide resonator parallel to the microwave electric field vector and perpendicular to an external magnetic field in the Voigt-geometry commonly used to study electron cyclotron resonance. However, because the electron collision frequency is greater than the angular microwave frequency, absorption and dispersion are merely slowly decreasing functions of the magnetic field strength. They depend—besides on collision frequency—on the nature of the electron collisions. Both, absorption and dispersion were evaluated independently for different classical collision models. Taking into account the tensor-property of conductivity, closest agreement of the two results for the collision frequency and best coincidence of measurement and theory was obtained for the model of an electron-polarizable molecule collision, which corresponds to a collision frequency independent of electron velocity. The collision frequency amounts to 210±4 GHz for our acetylene-oxygen-flames and 249 ± 4 GHz for the acetylene-air-flames.     

Solving the Boltzmann equation in a 2-D-configuration and2-D-velocity space for capacitively coupled RF discharges

A new kinetic scheme, the generalized Monte Carlo flux (GMCF) method, provides the electron particle distribution function in phase space, f(ν, μ, r, z, t) (ν: speed, μ: velocity angle, r: radial position, z: axial position, and t: time), for solving the Boltzmann equation in modeling capacitively coupled RP discharges. For a simulation with spatial- and temporal-varying fields in RF discharges, the GMCF method handles the collision terms of the Boltzmann equation by using one transition matrix to compute the collision transition between velocity space cells. An anti-diffusion flux transport scheme is developed to overcome the numerical diffusion in the velocity and configuration spaces. The major advantages of the GMCF method are the increase in resolution in the tail of distribution functions and the decrease of computation time. The GMCF calculation results in terms of microscopic electron distribution function and macroscopic quantities of density, electric field and ionization rate, are presented for RF discharges and compared with other kinetic and fluid simulation and experimental results. The effects of the induced radial electric field in the sheath close to the radial wall in a cylindrically symmetric parallel-plate geometry are discussed     

随机磁场中的反常扩散效应

本文讨论了随机磁场中反常扩散效应的特征,导出了扩散流及电场随时间变化的公式,指出,趋向于稳态所需的时间远小于粒子约束时间,因而反常扩散基本上是准稳态的形式。此时,存在明显的双极电场,而双极扩散流基本上是离子扩散的量级。 关键词：     

Excited atoms in argon gas discharge plasma

General principles are discussed for a gas discharge plasma involving excited atoms where electron-atom collision processes dominate. It is shown that an optimal kinetic model of this plasma at not large electric field strengths can be based on the rate constants of quenching excited atom states by electron impact. The self-consistent character of atom excitation in gas discharge plasma is important and results in the tail of the energy distribution function of electrons being affected by the excitation process, which in turn influences the excitation rate. These principles are applied to an argon gas discharge plasma where excitation and ionization processes have a stepwise character and proceed via formation of argon atom states with the electron shell 3p ⁵4s.     

托卡马克电场电子注入的漂移电子束研究

 研究了漂移电子束中电子的运动规律, 得到了电子在外加电场、纵磁场和电子束自场中的运动轨迹和漂移速度表达式, 并就它们的成束条件、成束形状和电压要求以及束的稳定性条件进行了比较和讨论, 认为阴极垂直于纵磁场放置更好一些。