Kinetic modeling of positive ions in a low-pressure RF discharge

The evolution of the ion-velocity distribution function in a planar RF discharge is computed by numerically solving the Boltzmann equation in phase space. The electric field in this equation is computed with regard to the ion density, assuming Maxwellian electrons with a given uniform temperature. The collision term in the Boltzmann equation contains creation of ions by electron-impact ionization of the background gas and the effect of charge-exchange collisions. Examples are given of the behavior of discharges in argon at RF frequencies of 50 kHz, 300 kHz, and 15 MHz at a very low pressure and at a pressure of approximately 40 Pa. A good agreement is found with published experimental observations of the time-dependent behavior of the electric field profile in the RF sheath     

The space-time-averaging procedure and modeling of the RF dischargeII. Model of collisional low-pressure RF discharge

For pt.I see ibid., vol.19, p.130-40 (1991). A self-consistent equations system for the low-pressure RF discharge is formulated and qualitatively analyzed. If the plasma and sheath dimensions exceed the electron-energy relaxation length, a simple spatially averaged kinetic equation can be derived that resembles the conventional one for the local case. Since the energy-diffusion coefficient for the slow electrons that are trapped by the average electric field in the discharge center is small, the distribution function slope decreases significantly with the energy growth. Analytic estimates are derived and reasonable agreement with the experiments of Godyak (1976, 1979, 1986, 1990) is obtained     

Plasma and surface modeling of the deposition of hydrogenated carbon films from low-pressure methane plasmas

The elementary mechanisms are described which determine the plasma and surface processes during the plasma-enhanced chemical vapour deposition of hydrogenated carbon films from methane. Corresponding model calculations are reviewed and critically discussed in comparison to experimental results. A realistic modeling requires the simultaneous and self-consistent treatment of plasma and surface effects. Several experimental data sets on plasma parameters and the growth and the composition of the films have been reproduced successfully. However, a broader experimental data base is needed for more critical tests of the models. The reliability of the modeling, in particular of the surface effects, is still limited due to the poor availability of elementary data.     

Kinetics of an RF low-pressure discharge with a condensed phase

The electron energy distribution function in an RF low-pressure plasma is found in the presence of dust particles. The effect of microscopic objects on the electroneutrality of the plasma and the electron energy distribution is estimated.     

Ion kinetics in low-pressure, electropositive, RF glow dischargesheaths

Ion kinetics in low-pressure (e.g., 1 mtorr), electropositive, RF glow discharge sheaths are studied using a Monte-Carlo-based computer simulation. The numerical model integrates particle trajectories using a spatially nonlinear, time-varying model of the electric field in the RF sheath. A scaling relationship is then discussed, relating the normalized ion energy spread to the ratio of ion sheath transit time to the RF period. The scaled numerical data shows good agreement with existing numerical and experimental data     

Radial inhomogenity of plasma parameters in a low-pressure inductive RF discharge

This work is devoted to systematic investigation into the radial dependence of the plasma parameters of a low-pressure inductive radio-frequency (RF) discharge on pressure within a wide range of 0.8–1 Torr. Experimental results that were obtained under the considered pressures make it possible to analyze the patterns of the changes in plasma parameters upon both a nonlocal mode of discharge and a transition from a nonlocal to local mode of the RF power input. Discharges in helium, neon, argon, and krypton were considered. Experimental data were compared to the results of the numerical simulation of the inductive RF discharge using the particle-in-cell (PIC) method.     

Level populations in plasmas RF discharges and sonic channel

An absolute intensity calibration has been made to previously reported spectrographic measurements in an extensively studied argon rf discharge downstream of the exciting coil, and sonic afterglow. This calibration allows calculation of neutral argon atom density and of individual level population. Neutral atom densities were calculated from the electron density, the electron temperature, and Saha's equation, assuming that the electron temperatures were equal to the excitation temperatures. The densities calculated by these methods were far higher than those obtained from the perfect gas law, the gas temperature, and the pressure. The observed under- population of the ground level is shown to correspond to the “terminal non-equilibrium” defined by PARK.⁽³⁾ The present data are compared with two existing experiments to show that agreement exists among seemingly inconsistent and confusing reports, provided the non-equilibrium phenomena are properly accounted for.     

Determination of electron temperature in low-pressure plasmas by means of optical emission spectroscopy

A simple model, allowing to determine the electron temperature in a steady-state low-pressure plasma, is proposed. The model makes use of optical cross-sections and therefore takes into account direct and cascade excitation from ground and metastable states. Spectroscopic data from Mitic et al. (New J. Phys. 11, 083020 (2009)) are used to illustrate the performance of the method.     

Scaling characteristics of plasma parameters for low-pressureoxygen RF discharge plasmas

For a low-pressure (1-100 mtorr) oxygen RF discharge plasma, the scaling laws for the densities of charged species such as positive ion, negative ion, and electron are estimated in terms of external and internal plasma parameters for the ion-flux-loss-dominated region based on the global balance equations. The scaling formulas are compared with Langmuir probe measurement results performed on a planar inductively coupled oxygen plasma. The transition point from the ion-flux-loss-dominated region to the recombination-loss-dominated region moves to a lower pressure region as the absorbed power increases     

Spectral line shapes modeling in turbulent plasmas

In this work we investigate the influence of low frequency turbulence on Doppler spectral line shapes in magnetized plasmas. Low frequency refers here to fluctuations whose typical time scale is much larger than those characterizing the atomic processes, such as radiative decay, collisions and charge exchange. This ordering is in particular relevant for drift wave turbulence, ubiquitous in edge plasmas of fusion devices. Turbulent fluctuations are found to affect line shapes through both the spatial and time averages introduced by the measurement process. The profile is expressed in terms of the fluid fields describing the plasma. Assuming the spectrometer acquisition time to be much larger than the turbulent time scale, an ordering generally fulfilled in experiments, allows to develop a statistical formalism. We proceed by successively investigating the effects of density, fluid velocity and temperature fluctuations on the Doppler profile of a spectral line emitted by a charge exchange population of neutrals. Line shapes, and especially line wings are found to be affected by ion temperature or fluid velocity fluctuations, and can in some cases exhibit a power-law behavior. These effects are shown to be measurable with existing techniques, and their interpretation in each particular case would rely on already existing tools. From a fundamental point of view, this study gives some insights in the appearance of non-Boltzmann statistics, such as Lévy statistics, when dealing with averaged experimental data.     

Kr喷气箍缩等离子体的数值研究

 探讨了Z箍缩等离子体辐射磁流体模拟二维三温物理模型及其数值计算方法，针对“强光一号”加速器上Kr喷气实验的具体条件，利用辐射磁流体力学程序Z-pinch 2D-DG模拟了Kr喷气等离子体聚爆过程，分析了X射线辐射的特点，给出了等离子体密度和温度的演化图像以及喷气箍缩中一些带有普遍性的结论。     

A study of methods for moving particles in RF processing plasmas

Methods for moving charged particles in RF processing plasmas are investigated. These methods include varying RF power, varying chamber pressure, attraction and repulsion by an electrostatic probe, and movement with magnetic fields. Varying RF power changes the depth of the potential wells where particles are trapped. The RF power affects shape and location of the traps and the bulk plasma potential. Increasing the chamber pressure moves the sheath edge closer to the wafer being processed. Since particle traps are found at the plasma sheath edge increasing the chamber pressure will move the particle traps (and any trapped particles) closer to the wafer being processed. The Langmuir probe can repel particles when under negative bias and attract them when positively biased. This probe can also distort the sheath edge when the tip resides within the sheath. Applying a magnetic field can change the characteristics of the particle traps and produce a force on the charged dust particles     

射频功率对氢气与反式二丁烯的低压电感耦合等离子体的影响（英）

利用等离子体聚合技术制备的GDP壳层是目前ICF靶丸的主要烧蚀层材料。为了了解GDP薄膜沉积过程中的CH等离子体的状态,采用朗缪尔探针和质谱仪对C4H8/H2等离子体的组分和状态参数进行了诊断,并对等离子体的电子能量分布函数、电子密度、电子温度等进行了深入分析。同时讨论了等离子体状态与放电参数之间的关系。研究发现,射频功率对等离子体参数有明显的影响。从10 W到35 W,电子密度正比于射频功率。随着射频功率的增加,在两步电离机制作用下,电子温度和等离子体电势呈现先减小后增大的变化趋势。另外,在高气压下,质谱诊断中发现了大量的稳定的小质量碎片离子,这表明在高气压下等离子体气相中的离子碎片聚合反应被抑制。     

An experimental study of the plasma parameters of a hybrid low-pressure RF discharge

This paper presents an experimental study of the plasma parameters of a hybrid radio-frequency (RF) discharge, which is a new modification of an RF discharge. The discharge is maintained by both vortex and potential RF electrical fields. To generate a hybrid RF discharge, an RF power input unit is used in the form of a parallel-connected inductor and capacitor coatings. A blocking capacitor is included in the capacitive channel of the discharge. The paper presents data from the study of the influence of power coupled to the plasma, argon pressure, and blocking capacitance on the plasma parameters, i.e., the electron energy distribution, temperature, and density and plasma potential. The role of the capacitive channel in the variations in properties and the characteristics of the discharge are considered.     

射频功率对氢气与反式二丁烯的低压电感耦合等离子体的影响（英）

利用等离子体聚合技术制备的GDP壳层是目前ICF靶丸的主要烧蚀层材料。为了了解GDP薄膜沉积过程中的CH等离子体的状态,采用朗缪尔探针和质谱仪对C4H8/H2等离子体的组分和状态参数进行了诊断,并对等离子体的电子能量分布函数、电子密度、电子温度等进行了深入分析。同时讨论了等离子体状态与放电参数之间的关系。研究发现,射频功率对等离子体参数有明显的影响。从10 W到35 W,电子密度正比于射频功率。随着射频功率的增加,在两步电离机制作用下,电子温度和等离子体电势呈现先减小后增大的变化趋势。另外,在高气压下,质谱诊断中发现了大量的稳定的小质量碎片离子,这表明在高气压下等离子体气相中的离子碎片聚合反应被抑制。     

Numerical simulation of chemical processes in atmospheric plasmas

A model is built to study chemical processes in atmospheric plasmas at low altitude (high pressure) and at high altitude (low pressure). The plasma lifetime and the temporal evolution of the main charged species are presented.The electron number density does not strictly obey the exponential damping law in a long period. The heavy charged species are dominant at low altitude in comparison with the light species at high altitude. Some species of small amount in natural air play an important role in the processes.     

含氧等离子体中臭氧形成过程数值模拟

利用数值模拟程序对不同条件下氧等离子体和大气等离子体中臭氧的形成过程进行数值模拟. 结果发现：臭氧的形成与游离态氧原子密切相关;臭氧的最大数密度与初始电子数密度有关;臭氧最大数密度持续的时间与脉冲放电大气等离子体中放电间隔时间选取相关,最佳的放电间隔是游离态氧原子达到最大的时间. 关键词： 等离子体 数值模拟 臭氧产生     

Kr喷气箍缩等离子体的数值研究

探讨了Z箍缩等离子体辐射磁流体模拟二维三温物理模型及其数值计算方法,针对“强光一号”加速器上Kr喷气实验的具体条件,利用辐射磁流体力学程序Z-pinch 2D-DG模拟了Kr喷气等离子体聚爆过程,分析了X射线辐射的特点,给出了等离子体密度和温度的演化图像以及喷气箍缩中一些带有普遍性的结论。     

An adaptive line-by-line—statistical model for fast and accurate spectral simulations in low-pressure plasmas

An adaptive grid method is proposed for the simulation of low-pressure plasma radiation. The method relies on two complementary approaches which significantly reduce calculation times and the size of the obtained grids: Weak lines are calculated as a so-called “pseudo-continuum”, hence reducing the number of calculated lines, and a numerical algorithm has been developed for accurately calculating Voigt lineshapes using a minimum number of points. The method is fully user-parametric, allowing the choice of privileging calculation efficiency, or alternatively privileging the accuracy of the computed spectra. Sample radiative transfer calculations are presented, which show the efficiency of the method, also providing some guidelines on how to define lineshape calculation parameters, depending on the problem to be solved.