大气压等离子体针产生空气均匀放电特性研究

大气压空气放电由于脱离了真空装置,易于实现流水线生产,因而在工业上具有广泛的应用. 采用等离子体针装置在空气中产生了稳定的大气压均匀放电. 利用光谱法对等离子体的相关参数进行了空间分辨率测量,并通过光学方法对放电机理进行了研究. 结果表明,等离子体针产生的放电存在电晕放电和等离子体羽放电两种模式. 在稳定的等离子体羽放电模式中,发光分为强光区和弱光区. 弱光区放电的发展速度远大于强光区的发展速度,电子能量和电子密度均是弱光区比强光区大. 对均匀放电的气体温度和振动温度的研究表明,强光区放电遵循汤生击穿机理而弱光区为流光放电. 这些结果对大气压空气放电的工业应用具有重要意义. 关键词： 大气压均匀放电 等离子体针 发射光谱 放电机理     

仪器展宽对大气压等离子体电子密度测量的影响

实验使用两台不同的单色仪,采用光谱线型法测量了大气压氩气介质阻挡放电中的电子密度.诊断结果表明,由于不同的单色仪其仪器加宽不同,仪器加宽对总的光谱线型有较大影响.通过考虑等离子体中的各种加宽机制,采用卷积和反卷积的方法对氩原子发射谱线线型进行了分析,从整个光谱线型中分离出Stark线型,排除了仪器加宽对最终诊断结果的影响.从而最终测量了大气压氩气介质阻挡放电中的电子密度.测量得到在大气压氩气介质阻挡放电中单个放电丝存在时,电子温度为10000K时,电子密度约为3.05-3.26×1021 m-3.此方法不仅可以应用在大气压介质阻挡放电中,还可以用于测量其它大气压等离子体电子密度.     

等离子体羽中氧原子的光谱强度分布

大气压等离子体羽放电产生的低温等离子体由于不需要真空装置,可以对复杂材料进行三维处理等,在工业上具有广泛的应用前景。本工作利用等离子体针放电装置在大气压空气中产生了稳定的等离子体羽。通过光谱测量,发现等离子体羽发射谱中存在777.5和844.6nm的氧原子谱线。这表明在大气压空气放电中产生了具有高化学活性的氧原子。通过光谱学方法研究了氧原子谱线强度的空间分布,发现靠近电极处氧原子谱线强度远大于其他位置。为了对这一现象进行解释,利用光电倍增管对等离子体羽的发光信号进行了空间分辨测量,发现靠近电极处发光信号宽度远大于其他位置的发光信号宽度。这些结果对大气压空气等离子体羽在杀菌消毒等领域的应用具有重要意义。     

介质阻挡放电点燃大气压直流均匀放电的光谱研究

由于大气压均匀放电等离子体在工业领域具有广泛的应用前景,为了获得大尺寸的大气压均匀等离子体,采用氩气作为工作气体,在大气压空气环境中利用同轴介质阻挡放电点燃了针-板电极间的大气隙(气隙宽度达到5 cm)直流均匀放电。研究发现,同轴介质阻挡放电能够有效降低针-板电极间的击穿电压。该均匀放电由等离子体柱、等离子体羽、阴极暗区和阴极辉区组成。其中等离子体柱和阴极辉区都是连续放电。而等离子体羽不同位置的放电是不同时的。事实上,等离子体羽放电是由从阴极向着等离子体柱移动的发光光层(即等离子体子弹)叠加而成。利用电学方法测量了放电的伏安特性曲线,发现其与低气压正常辉光放电类似,均具有负斜率。采集了放电的发射光谱,发现存在N₂第二正带系、氩原子和氧原子谱线。通过Boltzmann plot方法对放电等离子体电子激发温度进行了空间分辨测量,发现等离子体柱的电子激发温度比等离子体羽的电子激发温度低。通过分析放电机制,对以上现象进行了定性解释。这些研究结果对大气压均匀放电等离子体源的研制和工业应用具有重要意义。     

大气压氩气针-板介质阻挡放电的光电诊断

利用针-板介质阻挡放电装置,在4 mm长的气隙中产生了大气压氩气射流等离子体。利用电学方法实现了对放电电流和电荷量的同时测量,并且对放电脉冲数和放电功率进行了研究;利用发射光谱法对放电等离子体进行了空间分辨测量,并根据ArⅠ696.54 nm的Stark展宽计算了等离子体的电子密度。结果发现:随着外加电压的增加,每个周期内的放电脉冲数增加,放电功率也增加。随着针头距离的增加,电子密度由2.94×1015cm-3逐渐减小到2.28×1015cm-3。实验结果表明:电场强度对放电脉冲数和电子密度的空间分布起重要作用。     

介质阻挡均匀大气压辉光放电数值模拟研究

通过数值求解一维电子、离子连续性方程和动量方程，以及电流连续性方程，计算了氦气介 质阻挡大气压辉光放电电子、离子密度和电场在放电空间的时空分布，以及放电电流密度和 绝缘介质板充电电荷密度随时间的变化. 分析讨论所加电压频率、幅值及介质板性质等对均 匀大气压辉光放电性质的影响. 当外加电压频率足够高时，大量离子被俘获在放电空间，空 间电荷场又引起足够多的电子滞留在放电空间. 这些种子电子使得在大气压下发生汤森放电 ，放电空间结构类似于低气压辉光放电，即存在明显的阴极位降区、负辉区、法拉第暗区和 等离子体正柱 关键词： 大气压辉光放电 介质阻挡 数值模拟 等离子体     

较大体积的大气压空气介质阻挡放电特性研究

利用三电极介质阻挡放电装置, 在主放电区产生了较大体积的大气压空气均匀放电. 利用光学与电学方法, 对主放电特性进行了研究, 发现随驱动功率的不同, 主放电存在等离子体羽和等离子体柱两种模式, 等离子体羽的击穿电压随外加电压峰值的增加而减小. 利用光电倍增管对两种放电模式进行了空间分辨测量, 发现等离子体羽是以发光光层的形式传播, 而等离子体柱是连续放电. 通过采集两种放电的发射光谱, 对其振动温度和转动温度进行了测量. 发现两种放电模式的振转温度均随着U_p的增大而降低. 关键词： 介质阻挡放电 等离子体羽 等离子体柱 发射光谱     

����ѹ�����赲�����ŵ������ٶȷֲ��IJ���

通过测量大气压介质阻挡放电等离子体辐射信号,建立偶极子辐射模型,利用快速傅立叶变换,计算了大气压介质阻挡放电等离子体中离子速度分布。计算结果表明,速度分布偏离麦克斯韦分布,并且随着放电过程的进行,离子速度及相对离子数进行有规律的变化。     

大气压介质阻挡射流放电离子速度分布的测量

通过测量大气压介质阻挡放电等离子体辐射信号,建立偶极子辐射模型,利用快速傅立叶变换,计算了大气压介质阻挡放电等离子体中离子速度分布。计算结果表明,速度分布偏离麦克斯韦分布,并且随着放电过程的进行,离子速度及相对离子数进行有规律的变化。     

等离子体电极普克尔盒电光开关单脉冲过程数值模拟

采用流体模型对等离子体电极普克尔盒(PEPC)电光开关单脉冲过程进行了数值模拟分析.模型包括带电粒子连续性方程、动量守恒方程、电子平均能量方程及空间电位泊松方程.分别采用隐式指数差分格式，超松弛迭代法(SOR)和经典四阶龙格-库塔法(R-K)对带电粒子连续性方程，泊松方程和电子平均能量方程进行数值求解.模拟分析了PEPC单脉冲过程中的带电粒子浓度、电子温度、空间电场、PEPC的放电电流、晶体两侧电压和开关效率的时间演化特性.模型得出了PEPC中气体放电等离子体的微观物理过程与PEPC宏观参量的关系，对设计 关键词： 等离子体电极普克尔盒 电光开关 数值模拟 气体放电     

非对称磁镜场电子回旋共振氧等离子体刻蚀化学气相沉积金刚石膜

分别应用郎缪尔双探针和离子灵敏探针对非对称磁镜场电子回旋共振氧等离子体的电子参数、空间分布和离子参数进行了测量,分析了气压对等离子体参数及空间分布的影响。利用该等离子体在优化的气压条件下对化学气相沉积金刚石膜进行了刻蚀,并研究了刻蚀机理。结果表明:电子温度为5~10 eV,离子温度为1 eV左右,而等离子体数密度在1010cm-3数量级。随气压的升高,电子和离子温度降低,而电子数密度先增大后减小。在低气压下等离子体数密度空间分布更均匀,优化的刻蚀气压为0.1 Pa。刻蚀过程中,离子的回旋运动特性得到了加强,有利于平行于金刚石膜表面的刻蚀,有效地保护了金刚石膜的晶界和缺陷。     

PIC/MCC Simulation of Electron and Ion Currents to Spherical Langmuir Probe

The Particle In Cell/Monte Carlo Collisions (PIC/MCC) simulation was used for the calculation of electron and ion currents to a spherical Langmuir (electrostatic) probe. This simulation took into account the collisions of collected charged particles with neutral gas particles around the probe and it can calculate the probe currents at higher neutral gas pressures. The improvements of usual simulation techniques enabled to speed up the simulation and to calculate the probe current even for neutral gas pressures above 1 kPa. The simulations were carried out for two cases: i) probe with radius of 0.5 mm in non‐thermal plasma with high electron temperature, ii) probe with radius of 10 µm in afterglow plasma with low electron temperature. The influence of probe radius on electron probe current was also studied. The simulations showed that thick sheath limit of OML theory provides incorrect values of probe current for probes with radii larger than 200 µm at plasma parameters considered even at very low neutral gas pressures. The probe characteristics were calculated for probe with 0.5 mm radius for pressures up to 500 Pa and for probe with 10 μm radius for pressures up to 3 kPa. The influence of collisions on electron and ion probe current was demonstrated and the procedure for determination of electron and ion densities from the probe measurement at higher pressures was developed. The results from PIC/MCC simulations were compared with results from continuum theory. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Self-consistent modelling of plasma-solid interaction

In the paper the transport of electrons and ions in plasma is studied by computer simulation. The main goal of the modelling was to establish an exact form of energy distributions of charged particles near the metal substrates immersed into plasma and to analyse changes in their distributions during the transport through both the presheath and the sheath for various voltage biases and substrate geometries. Further results concern the probe characteristics both in inert gas and chemically active plasma and the distribution of potential and space charge in the vicinity of metal electrodes. As a simulation technique the combination of molecular dynamics and Monte Carlo methods was used. The movement of charged particles in self-consistent electric field was studied under the assumption of internal symmetry of the problem, which enabled to reduce the number of necessary coordinates to four (either 1d3v or 2d2v).     

Probe Measurements of Wave Fluctuations Excited in Glow Discharges

Fluctuations of the electric field, the charged particle density, the electron temperature and the plasma potential are simultaneously measured by a probe in the positive column of helium glow discharge at a few torr gas pressure by exciting a small amplitude ionization wave. It is proposed that these values can be determined by analyzing the probe current.     

Probe Measurements of Wave Fluctuations Excited in Glow Discharges

Fluctuations of the electric field, the charged particle density; the electron temperature and the plasma potential are simultaneously measured by a probe in the positive column of helium glow discharge at a few torr gas pressure by exciting a small amplitude ionization wave. It is proposed that these values can be determined by analyzing the probe current.     

Studies on the Measuring Method of Number Density of Ions in the High Speed Flow Field

At present, the method of using a parallel-plate probe to measure the number density of ions at atmosphere has some limitations such as big size of probe, low velocity of gas flow allowed to measure, and low accuracy. In this paper, a detector with a spherical probe is fabricated and is used to measure the number density of ions. The diameter of probe can be reduced to 6 mm. The highest velocity that can be measured is extended to 28 m/s, and the collecting rate is up to 100%. The spatial distribution diagram of ion number density is also given, with a cross section of 0.36 $hbox{m}^{2}$. Then, an effective method is provided to measure the number density of ions generated from the miniature ion source or in the gas flow with high velocity.      

Formation of a volume discharge at a subnanosecond rise time of the voltage pulse

A study is made of the formation of a volume discharge in atmospheric-pressure air in a nonuniform electric field without additional preionization. It is shown that the spatial distribution of the plasma glow between a plane and a spherical (as well as a point) electrode at a subnanosecond rise time of the high-voltage pulse is volumetric in character. The change of the voltage polarity does not qualitatively affect the character of the glow. The propagation of a spherical ionization wave in nitrogen is calculated in the drift-diffusion approximation. The fact that the character of the discharge glow is essentially independent of the voltage polarity is explained by the multiplication of the background electrons in the dense working gas.     

Modelling of fusion-reaction protons measurements within TEXTOR facility

This paper describes the computation of fusion protons detection efficiency, which has been carried out by means of the known GOURDON code. For this purpose an analytical model of the tokamak magnetic field has been used. Computer simulations of different trajectories of charged particle, on the basis of the motion equations, have been performed with the GOURDON code. Detection efficiency, defined as the ratio of the number of detected particles to that of particles emitted from plasma, has been calculated. The transparency function of the detector system has been derived for given geometry of the ion-pinhole camera. Calculations have been carried out for the detector position used in recent experiments. The poloidal-and toroidal-symmetry of plasma and standard fusion-product source profile have been assumed. The computed detection efficiency is presented as a function of the main radius and particle pitch-angle for different spatial orientations of the detector head.     

Parameters of the Plasma Sheet Generated by a Sheet Beam in the Range of Forvacuum Pressures

Results of experimental investigations into the spatial distribution of the parameters of the plasma (electron concentration and temperature) generated by a sheet beam with energy up to 2 keV in argon at pressures from 6 to 9 Pa are presented. The electron beam was produced by a source with a plasma cathode specially designed for emission of beams in the range of forvacuum pressures. It is demonstrated that the character of distribution of the plasma parameters is caused by the corresponding distribution of the electron current density over the beam cross section, and the plasma parameters themselves also noticeably depend on the gas pressure and the magnetic field. A model of ionization processes that provides satisfactory agreement between the calculated and experimental dependences is suggested.     

Particle‐in‐cell/Monte Carlo simulation of electron and ion currents to cylindrical Langmuir probe

Electron and ion currents to a cylindrical Langmuir (electrostatic) probe were calculated using the particle‐in‐cell/Monte Carlo (PIC/MC) self‐consistent simulation for a neutral gas in the pressure range 2–3,000 Pa. The simulation enables us to calculate the probe currents even at high neutral gas pressures when the collisions of collected charged particles with neutral gas particles near the probe are important. The main aim of this paper is the calculation of probe currents at such high gas pressures and the comparison of the results with experimentally measured probe currents. Simulations were performed for two cases: (a) probes with varying radii in a non‐thermal plasma with high electron temperature at low neutral gas pressure of 2 Pa (in order to verify the correctness of our simulations), and (b) probe with the radius of 10 μm in the afterglow plasma with low electron temperature and a higher neutral gas pressure (up to 3,000 Pa). The electron probe currents obtained in case (a) show good agreement with those predicted by the orbital motion limited current (OMLC) theory for probes with radii up to 100 μm for the given plasma conditions. At larger probe radii and/or at higher probe voltages, the OMLC theory incorrectly predicts too high an electron probe current for the plasma parameters studied. Additionally, a formula describing the spatial dependence of the electron density in the presheath in the collisionless case is derived. The simulation at higher neutral gas pressures, i.e. case (b), shows a decrease of the electron probe current with increasing gas pressure and the creation of a large presheath around the probe. The simulated electron probe currents are compared with those of measurements by other authors, and the differences are discussed.