Influence of diffusion of the electron energy distribution function in a low-temperature microwave discharge plasma

Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 2, pp. 235–241, February, 1989.     

基于流体模型和非平衡态电子能量分布函数的高功率微波气体击穿研究

用流体模型研究高功率微波气体击穿时, 电子能量分布函数常被假设为麦克斯韦分布形式, 此假设可能将给模拟结果带来较大的误差. 通过求解玻尔兹曼方程, 得到非平衡状态下的电子能量分布函数. 分别将上述两类分布函数引入到流体模型中, 对氩气击穿进行了数值模拟. 结果表明, 基于非平衡分布函数得到的击穿时间与粒子模拟结果符合得很好, 而当平均电子能量较低时, 麦克斯韦分布函数的高能尾部导致了较短的击穿时间. 最后, 采用非平衡分布函数计算了不同压强下的氩气击穿阈值, 发现其与实验结果基本符合. 关键词： 微波气体击穿 电子能量分布函数 流体模型 玻尔兹曼方程     

Investigation of the electron energy distribution function in a neon afterglow plasma

Probe measurements of the electron energy distribution function conducted in a neon afterglow plasma showed substantial deviations from a maxwellian distribution function in the high energy range. The differences result from Penning ionization and electron-metastable atom superelastic collisions.     

Apparatus for the electron energy distribution function measurement in the afterglow discharge

A method for measuring the second derivative of the Langmuir probe characteristic in plasma with fast varying parameters is described. Discussion about its applicability and the results of measurements in the Ne afterglow are given.The author wishes to acknowledge the support afforded him by Doc. Dr. M.ícha, CSc. and J.Glosík.     

Contribution to the electron energy distribution function measurement in the afterglow discharge

The measurement of the higher energy part of the electron distribution function in the neon afterglow is presented. A simple theory which enables us to estimate the error which arises by applying the Druyvesteynian theory to the transition regime is given. The numerical calculations of this error are presented to illustrate the dependence on the various plasma parameters.The author wishes to express his thanks to Doc. dr. M.ícha CSc and Dr. V.Hrachová CSc, for many helpful remarks.     

Analysis of electron energy distribution function in a magnetically filtered complex plasma

The electron energy distribution function (EEDF) for a magnetically filtered dusty plasma is studied in a dusty double plasma device where the electron energy can be varied from 0.15 eV to ～ 2.8 eV and plasma density from 10 6 cm-3 to 10 9cm-3 . The characteristics of EEDF for these ranges of plasma parameters are investigated in a pristine plasma as well as in a dusty plasma. The results show that in the presence of dust, there is a drastic modification in EEDF patterns in a plasma with higher electron temperature and density than those in a low temperature and low density plasma produced by the magnetic filter.     

On the electron energy distribution in the gas discharge positive column: Langmuir paradox

The results of calculations of electron drift characteristics in a dc spatially inhomogeneous periodic electric field are presented. It is shown that the effect of field inhomogeneities on the drift velocity and the average electron energy is insignificant under typical conditions of experiments with gas-discharge plasma at low gas pressures. However, the intensity of the processes of excitation, ionization, and plasma spatial distribution are strongly affected by the inhomogeneity (variance) and field variation behavior. It is shown that the electric field inhomogeneity in the gas discharge positive column leads to maxwellization of the electron energy distribution function.     

Investigation of the electron energy distribution function in an argon afterglow plasma

The electron energy distribution function in an argon afterglow plasma, measured by an electrical probe, substantially deviates from the maxwellian distribution in the energy range ε kT_e. The differences result from Penning ionization and electron-excited-atom superelastic collisions.     

Electron energy distribution function in a collisional plasma heated by an electron beam

The electron energy distribution function for the non-resonant electrons in a collisional weakly ionized plasma is found, provided that the intensity of the Langmuir oscillation is spatially dependent. It is assumed that electron-electron collisions are responsible for energy loss.     

Measurement of the electron energy distribution function in flame plasma at atmospheric pressure

The measurement of the electron distribution function in the lighting gas flame plasma at atmospheric pressure is described. The influence of the collision in the probe sheet and the ion current component is investigated. The experimental results show that the second derivative method for measurement of the electron distribution function is valid for sufficiently negative biassed probe.     

Dust particles in collisionless plasma sheath with arbitrary electron energy distribution function

Dust particles often appear in industrial plasmas as undesirable product of the plasma-wall interactions. Large particles of several micrometers in diameter are concentrated in a thin layer (the sheath) above the lower electrode of the rf driven parallel plate device, where the electric force is strong enough to compensate particle’s gravity. Experimental and theoretical uncertainties are significantly increased in the plasma sheath. Common models of dust charging in the plasma sheath suppose the Maxwellian electron energy distribution function (EEDF) in conjunction with a flux of cold ions satisfying classical Bohm criterion at the sheath edge. In this paper we generalize this model to arbitrary EEDF with adapted Bohm criterion. We limit our considerations to collisionless or slightly collisional plasma, where the EEDF inside the sheath is expressed through the EEDF in the plasma bulk. Derived theoretical formulas are incorporated into numerical model, describing collisionless radio frequency (rf) plasma sheath together with the electrical charge, various kinds of forces, balancing radius and oscillation frequency of particles.     

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.     

On non-hydrodynamic properties of the electron gas in the plasma of a DC discharge

The linearized one-dimensional Boltzmann equation was solved for the electron gas in the positive column of a low-current DC-discharge. A sinusoidal perturbation of the electric field was assumed in the column and the perturbed distribution function was found. The problem was solved both numerically and approximately. It is shown that in the absence of an electron-electron interaction strong deviations from the solution of the hydrodynamic quasihomogeneous equations appear for certain wavelengths, which were called resonant. These wavelengths almost exactly agree with the characteristic wavelengths of the ionization waves of the s- and p-variety. A physical interpretation of this resonant behaviour is given and its connection with the long correlation length in a plasma with non-interacting electons is pointed out.Na Slovance 2, Praha 8, Czechoslovakia.     

Determining the energy distribution function of electrons in the negative-luminescence plasma of a glow discharge from the line intensities

The energy distribution function of electrons (EDFE) in the negative luminescence of a glow discharge is found using, as well as the probe method, calculation from measured spectralline intensities. The measurements are made in a weakly anomalous discharge in helium at a pressure of 0.5 mm Hg. In the energy range from 0 to 35 eV, EDFE is determined by the second-derivative method, and in the range from 23 to 69 eV by derivation from the helium spectral-line intensities. Note that the nonmonotonic behavior of the distribution function due to inelastic collisions of electrons with gas atoms is clearly reflected both in the probe characteristics and in the radiation spectrum.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 71–76,. May, 1979.     

Beam electron energy distribution at a volume nanosecond discharge in atmospheric-pressure air

The energy distributions of beam electrons and x-ray photons in a volume nanosecond discharge on atmospheric-pressure air are studied. Several groups of elevated-energy electrons are found. It is shown that electrons with an energy from several tens to several hundreds of kiloelectronvolts (which is lower than a maximal voltage across the gap) make a major contribution to the beam current measured behind thin foils. It is corroborated that fast electrons (with an energy from several kiloelectronvolts to several tens of kiloelectron-volts) arise 100–150 ps before the basic peak of the beam current, elongating the current pulse and significantly increasing its amplitude. The contribution from electrons with an anomalously high energy (exceeding a maximal voltage across the gap) to the beam current is shown to be insignificant (less than 5%). The x-ray spectra in gas-filled diodes of different design are studied. Techniques of measuring the subnanosecond electron beam current and mechanisms generating fast and runaway electrons in volume high-pressure gas discharges are analyzed.     

Anomalous kinetic energy of a system of dust particles in a gas discharge plasma

The system of equations of motion of dust particles in a near-electrode layer of a gas discharge has been formulated taking into account fluctuations of the charge of a dust particle and the features of the nearelectrode layer of the discharge. The molecular dynamics simulation of the system of dust particles has been carried out. Performing a theoretical analysis of the simulation results, a mechanism of increasing the average kinetic energy of dust particles in the gas discharge plasma has been proposed. According to this mechanism, the heating of the vertical oscillations of dust particles is initiated by induced oscillations generated by fluctuations of the charge of dust particles, and the energy transfer from vertical to horizontal oscillations can be based on the parametric resonance phenomenon. The combination of the parametric and induced resonances makes it possible to explain an anomalously high kinetic energy of dust particles. The estimate of the frequency, amplitude, and kinetic energy of dust particles are close to the respective experimental values.     

测量电子气体的速度分布函数

利用夫兰克-赫兹实验仪测量了电子气体的速度分布函数,并分析了电子与氩原子碰撞的动力学过程.