Free‐Electron Gas Spectrum Uniqueness in the Mixture of Noble Gases

Gas mixtures can reach the Maxwell's specter shape in case of low‐ionized mono‐atomic mixtures in the weak electric field. The parameters pertaining to the Maxwell spectrum of free electrons' gas straightforwardly settle on the insulating characteristics of the examined gas mixture at the fundamental level. In this paper, a condition for breakdown has been accomplished taking as a starting point the ionization coefficients derived accordingly, as well as the conditions for breakdown in keeping with the Townsend mechanism. The dc breakdown voltage value of noble gases mixture has been measured in the experimental part of the paper. The hypothesis that the free‐electron gas spectrum is unique in the noble gas mixture and is of Maxwell's type has been verified. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

等离子体增强化学气相沉积中对尘埃颗粒诊断

采用SiH4,C2H4和Ar在射频容性耦合柱状放电室中产生了尘埃颗粒,利用发射光谱测得射频尘埃等离子体放电室中的一些基本碎片的发射光谱,并给出了这些碎片的光发射强度随着实验条件变化的曲线。随着功率和气压的增加,碎片的光发射强度逐步增加,尤其是随功率增加得更快,这说明功率对硅烷和乙烯的离解作用明显。随着硅烷和乙烯流量的增加,碎片的光发射强度随之下降。利用朗缪尔探针的实验结果得出尘埃密度的变化趋势,给出了尘埃密度随射频功率变化的曲线,其结果与硅烷和乙烯的离解变化趋势基本吻合。     

Langmuir Probe Measurement of the Electron Temperature in the Plasma Plume Formed by Pulsed Laser Deposition of Bi-Sr-Ca-Cu-O

The electron temperature of the plasma formed during pulsed laser deposition of Bi-Sr-Ca-Cu-O target was measured using Langmuir probe. The main parameters of the experiment were as follows: The distance of the probe from the target was in the range of (4-6) mm, the basic working pressure was 2×10^–3 Pa and the planar pulse energy density of laser beam was approximately 8 J/cm². The obtained values of electron temperature were in the range of (1.0-2.5) eV. Presented results are discussed from the point of view of different theories of plasma splitting.     

射频感应耦合低压等离子体特性分析

采用光谱诊断法和Langmuir单探针法对射频感应耦合Ar气等离子体特性进行分析。通过光栅光谱仪研究了低气压下Ar气等离子体的光谱强度的变化特性,采用Langmuir单探针法测量不同条件下电子密度和电子温度。等离子体发射光谱的光谱强度随着气压和功率的增加而增强,射频功率对光谱强度的影响较明显。当功率从120W增加到180W时,光谱强度将会迅速增加,等离子体发生E模向H模的模式转换。Langmuir单探针法测量的电子密度和电子温度在的变化规律符合E模向H模转换的变化规律。     

Langmuir Probe in Non‐Maxwellian Plasma: Correlation Between the Electron Energy Distribution Function,the Ion Energy at the Sheath Edge and the Floating Voltage

This work is devoted to the study of the Langmuir probe in non‐Maxwellian plasma, assuming mono‐energetic singly charged ions and a collisionless sheath. Using a general analytical equation for the Electron Energy Distribution Function (EEDF), we study the effect of the EEDF profile on: a) The ion energy at the sheath edge of a negatively biased collector, b) the I‐V probe characteristic and c) the floating voltage (V_p‐Vf). Different methods are used and compared to determine these parameters or characteristics. A correlation is given between the floating voltage, the ion energy at the sheath edge and the EEDF profile. The study is also extended to distribution functions with several components. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical Emission Spectroscopy Used to Study the Characteristics of the Capacitive Radio-Frequency Discharge in Argon

Capacitively coupled radio-frequency (13.56 MHz) glow discharge in argon at low pressure (200 mTorr) has been studied by optical emission spectroscopy (OES) and electrical probe. Increasing power density resulted in lowering of the electron temperature T _e and increase of the electron density n _e. The to transition in this case takes place smoothly. The intensity (I _750.4) of the emission line at 750.4 nm due to 2p₁1s₂ transition closely follows the variation of n _e with power density. Calculation of the electron-energy probability function shows that electron occupation mainly changes in the high-energy tail, which explains close resemblance of I _750.4 to n _e. At moderate pressures, only OES method was applied to observe - transition which is abrupt in this pressure range.     

同轴空心阴极氦等离子体的电子激发温度研究

利用同轴空心阴极放电装置,产生氦低温等离子体。通过对等离子体的发射光谱进行测量和计算,研究放电功率以及氦气压强对等离子体的电子激发温度的影响。结果表明:氦低温等离子体的发射光谱主要由连续谱和原子谱线构成,放电功率和压强对谱线的强度具有明显影响。压强的变化不仅影响电子从电场中获得的能量,还会影响电子与原子的碰撞频率,从而导致电子激发温度随着氦气压强的增大,出现先上升后下降的变化趋势。     

Effects of the System Temperature on Dust Cluster Formation in Plasma

Effects of the system temperature on dust aggregation in plasmas are investigated using two‐dimensional molecular dynamics simulations. It is shown that as the system temperature increases, the boundary of the clusters becomes gradually irregular (i.e., deviating from sphere‐like), and the cluster system gradually changes from solid to liquid and finally to gas state. The mean square displacement, mean nearest‐neighbor distance in the clusters, cluster size and coupling parameter of the system are obtained and the properties of the system structure and dynamics are investigated. The time τ needed for reaching equilibrium for different temperatures is obtained. It is shown that τ firstly decreases and then increases with the temperature, indicating that there is an optimum temperature allowing a dust aggregation to reach an equilibrium state most rapidly. The simulation results agree qualitatively with the experimental observations. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effects of Harmonic Modulation of Current in Glow Discharge Dusty Plasma with Ordered Structures

New method of disturbance by imposing harmonic signals on discharge current in DC glow discharge with ordered structures is studied at low values of disturbing amplitudes in molecular nitrogen. Influence of disturbing signals with frequencies from 10 Hz to 100 kHz is observed. New effects of changing vertical size and position of dusty structures in discharge space observed. Forced oscillations of dust particles and self‐oscillating crystals stabilizing effect under different conditions registered. Studied dusty structure's vertical size change dependencies on frequency and amplitude of disturbing signal (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of Negative Ions on Drift Waves in a Low‐Density Ar/O2‐Plasma

The effect of negative ions on the drift wave instability has been studied in detail in a linear device by means of Langmuir probes and cross‐correlation analysis. Drift waves are excited in low‐density (5 × 10¹⁴ m^–3) and strongly magnetized (0.5 T) pure argon plasmas and in the presence of an oxygen admixture. The radial density profile of negative ions is hollow. For increasing concentration of negative ions the wave frequency decreases by about 25%. Despite of an axial density gradient, a global wave frequency is established for the entire column length. While for the noble gas case the drift wave frequency is given by the equilibrium plasma parameters in the mid‐plane, there is no such relationship for the argon plasma with oxygen admixture. This different finding is attributed to the inhomogeneous distribution of the negative ions (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

13.56 MHz/2 MHz柱状感性耦合等离子体参数的对比研究

通过Langmuir双探针和发射光谱诊断方法,对比研究了驱动频率为13.56 MHz和2 MHz柱状感性耦合等离子体中电子密度和电子温度的径向分布规律.结果表明:在高频和低频放电中,输入功率的增加对等离子体参数产生了不同的影响,高频放电中主要提升了电子密度,低频放电中则主要提升了电子温度.固定气压为10 Pa,分别由高频和低频驱动时,电子密度的径向分布均为"凸型".而电子温度的分布差异比较明显,高频驱动时,电子温度在腔室中心较为平坦,在边缘略有上升;低频驱动时,电子温度随径向距离的增加而逐渐下降.为了进一步分析造成这种差异的原因,在相同放电条件下采集了氩等离子体的发射光谱图,利用分支比法计算了亚稳态粒子的数密度,发现电子温度的径向分布始终与亚稳态粒子的径向分布相反.继续升高气压到100 Pa,发现不论高频还是低频放电,电子密度的径向分布均从"凸型"转变为"马鞍形",较低气压时电子密度的均匀性有了一定的提升,但低频的均匀性更好.     

Influences of Temperature and Average Interparticle Distance on the Properties of Two-Dimensional Dusty Plasma

The structure and single-particle motion of a two-dimensional dusty plasma have been investigated. Pair correlation function, mean square displacement, velocity autocorrelation function, and the corresponding spectrum function have been computed by molecular dynamical simulation. The results show that the coagulation of a two-dimensional dusty plasma system is strongly affected by particle density and temperature, which are discussed in details.     

Electron Temperature Dependence of the Dissociative Recombination Coefficient of Molecular Argon Ions Ar+2 with Electrons

A dual mode (TM₀₁₀ cylindrical cavity/cylindrical waveguide) microwave apparatus is used to study the ion mobility and dissociative recombination of molecular argon ions with electrons in the afterglow period of a d.c. glow discharge as a function of electron temperature when electrons were heated by microwaves up to T_e ≤ 10300K, with T₊ = T_gas = 300K. The electron temperature dependence of the total rate coefficient of dissociative recombination may be represented by α (Ar⁺₂) = (8.1 ± 0.5) × 10^–7[300/T_e(inK)]^0.64cm³s^–1 which is in very good agreement with most previous experimental results but not with the recent theoretical calculations (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A Spectroscopic Investigation of Spatial Symmetry of Radiation in the U-shaped DC Argon Plasma with Aerosol Supply

Radial distributions of plasma parameters, temperature, and electron number density, together with radial distribution of analyte absorption and emission, were investigated in order to obtain insight into the radial symmetry of low-current (≤ 10 A), atmospheric pressure, argon stabilized arc with tangential introduction of the aerosol. For plasma diagnostics, several methods were used: measurements of H_β line profile, absolute intensity measurements of the argon 430.01-nm line, and of the spectrally adjacent continuum and power interruption technique. It was found that the inevitable asymmetry in aerosol introduction has negligible influence on basic plasma parameters but influences considerably the spatial distribution of the analyte particle spectral absorption and emission.     

Structural Characteristics and Equation of State of the Complex Plasmas

In this paper weakly and strongly non‐ideal plasmas are considered. In both cases the equations of state for hydrogen and dusty plasmas were studied on the basis of effective potentials. In the first case the thermodynamic properties for hydrogen plasmas were studied by the method of effective potentials taking into account quantummechanical diffraction, symmetry and screening effects. For strongly non‐ideal plasma or dusty plasma the equations of state were considered using radial distribution functions and effective interaction potential, which describes interactions of charged dust grains with dipole moments. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Dual Mode Microwave Afterglow Apparatus for Measuring the Electron Temperature Dependence of the Electron‐Ion Recombination

Three dual mode microwave apparatus (one using S ‐band and two using X ‐band) have been developed to determine ambipolar diffusion and electron‐ion recombination rates under conditions such that T_gas = 300K and T_e is varied from 300 K to 6300 K, in the afterglow period of the dc glow discharge. TheTM₀₁₀ cylindrical cavity (in S ‐band) and TM₀₁₁ open cylindrical cavity (X ‐band) are used to determine the electron density during the afterglow period and a non‐resonant waveguide mode is used to apply a constant microwave heating field to the electrons. To test the properties of the apparatus the neon afterglow plasma has been investigated. At T_e = 300 K a value of α (Ne⁺₂) = (1.7± 0.2) × 10^–7cm³/s is obtained which is in good agreement with values of other investigators. Also similar variations of α as T^–0.4_e (S ‐band) and as T^–0.42_e (X ‐band) obeyed over the range 300 ≤ Te ≤ 6300K are in good agreement with some other previous measurements. The simplicity of the X‐band microwave apparatus also allows the measurements of the gas temperature dependency and the study of electron attachment and may be used simultaneously with optical or mass spectrometry investigations. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of Particle＇s Size on the Structural and Dynamical Properties in 2D Dusty Plasma

In a two-dimensional （219） dusty plasma system, the size of particles is considered under two different interparticle potentials （Yukawa potential and Dressed potential）. The structural and dynamical characters are investigated by molecular dynamics simulation respectively. The results show that the 2D systems via Yukawa and Dressed potentials have a different critical coupling constant F corresponding to the systems beginning to coagulate and exhibit different crystal configurations. Also we find that the size of particles has little influence on the 2D system＇s structure characters.     

Effect of Analyte Concentration on the Laser-Induced Plasma Temperature and Electron Density in Liquid Matrix

In the present work, we report spectroscopic studies of laser-induced plasmas produced by focusing the second harmonic (532 nm) of a Nd:YAG laser onto the laminar flow of a liquid containing chromium. The plasma temperature is determined from the coupled Saha–Boltzmann plot and the electron density is evaluated from the Stark broadening of an ionic line of chromium [Cr(II)] at 267.7 nm. Our results reveal a decrease in plasma temperature with an increase in Cr concentration up to a certain concentration level; after that, it becomes approximately constant, while the electron density increases with an increase in analyte (Cr) concentration in liquid matrix.     

A Novel Measurement Method of the Emission Rules of Greenhouse Gases from Fertilized Soil Based on Fourier Transform Infrared Spectrometry with Long Optical Path

Farm soil is the main source of greenhouse gas emission. We developed an optical system for measuring nitrous oxide and carbon dioxide from soil using infrared spectrometer and long optical path gas cell based on multi-reflecting mirrors. The spectral characteristics of nitrous oxide at 2198–2223 cm^?1 and of carbon dioxide at 2258–2283 cm^?1 were observed with the system. We studied the rules of greenhouse gas emission and found that nitrous oxide increased with soil moisture whereas carbon dioxide showed no obvious relationship with moisture. We also studied the diurnal variation rules of nitrous oxide and carbon dioxide from fertilized soil. These results are consistent to the previous results obtained with other analytical methods. The results indicate that the infrared spectroscopy with long optical path is an effective way to measure greenhouse gas emission from soil.