大气等离子体中负氧离子产生和演化过程数值模拟

文章利用数值模拟程序对不同条件下大气等离子体中负氧离子的形成及演化过程进行数值模拟.结果发现:负氧离子数密度衰减过程中出现拐点,进入一个较为平稳的状态;平稳期负氧离子数密度与初始电子数密度近似成线性关系;水分含量对负氧离子的演化过程具有重要影响,水分含量越高,负氧离子或其团簇数密度平稳期后的衰减越缓慢. 关键词： 等离子体 数值模拟 负氧离子     

不同初始温度下H2/O2混合物等离子体的演化

本文对不同初始温度下,H₂/O₂混合物等离子体中主要粒子随时间发展的演化规律进行了数值模拟,得到了放电后等离子体中主要带电粒子和中性粒子密度随时间的变化规律.计算结果表明,H₂/O₂混合物等离子体中主要活性粒子密度随时间的增加减小,化学反应达到平衡所需的时间随初始温度升高逐渐减少. 关键词： 等离子体 化学过程 数值模拟 演化     

不同电离度下大气等离子体粒子行为的数值模拟

利用一个空间零维大气等离子体模型对其中的主要粒子在不同电离度情况下的变化规律进行了研究.得到放电后不同初始电子密度下的电子寿命,同时给出了主要带电粒子和中性粒子密度随时间的演化.结果表明,电子密度随时间快速衰减,电子寿命随电离度的增大而减小.对一些重要的中性粒子(如O,N,O₃和NO)随电离度增大的行为进行了分析. 关键词： 电离度 大气等离子体 数值模拟     

一维大气等离子体化学过程数值模拟

用数值模拟方法研究了低空及高空环境下，大气等离子体的化学反应及一维扩散过程. 推导了三组分(电子和正负离子)的双极扩散公式，观察了扩散过程中不同组分的空间分离，以及扩散和化学反应对电子数密度演化的贡献. 关键词： 大气等离子体 化学过程 数值模拟     

不同初始温度下H2/O2混合物等离子体的演化

本文对不同初始温度下,H₂/O₂混合物等离子体中主要粒子随时间发展的演化规律进行了数值模拟,得到了放电后等离子体中主要带电粒子和中性粒子密度随时间的变化规律.计算结果表明,H₂/O₂混合物等离子体中主要活性粒子密度随时间的增加减小,化学反应达到平衡所需的时间随初始温度升高逐渐减少.     

充气型放电毛细管的密度测量及磁流体模拟

在激光尾波场电子加速机理中,为了有效地加速电子,需要抑制衍射散焦等造成的激光传输不稳定性问题. 激光脉冲的稳定传输不仅有利于能量耦合给等离子体波,而且对电子束的注入及稳定加速有着重要影响,具有一定横向密度分布的充气型放电毛细管可以有效引导激光脉冲的传输. 利用等离子体的Stark展宽效应对毛细管产生的等离子体进行密度测量,给出了等离子体密度与充气压强之间的关系. 利用磁流体程序CRMHA对毛细管的放电特性进行了模拟,研究了毛细管引导效应的形成机理. 关键词： 充气型放电毛细管 Stark展宽 磁流体模拟 引导     

大气压脉冲放电等离子体射流特性及机理研究

通过实验和数值模拟研究了大气压脉冲放电等离子体射流,其中在脉冲电压上升沿阶段的放电中形成等离子体子弹并向接地电极输运,其传播速度在10⁴ m·s^–1量级.数值模拟研究还发现等离子体子弹邻近区域内增强的电场强度可达到10⁶ V·m^–1,说明等离子体子弹的形成主要由放电空间局域增强的电场导致,在接地电极附近会得到进一步增强.放电空间的电子密度时空演变过程揭示了等离子体子弹经过的区域会保持较高的电子密度,说明等离子体子弹的拖尾现象;而等离子体子弹头部增强的电子产生率与局域增强的电场强度对应,这说明了等离子体子弹产生的动力学过程.该大气压脉冲放电等离子体射流中等离子体子弹的特性和机理研究为发展大气压等离子体射流提供了理论和技术基础.     

相位反射产生的激光场空洞现象及其与激光等离子体参数相关性研究

理论研究和数值模拟研究表明激光在等离子体中诱导的等离子体密度调制可以起类似布拉格反射镜的作用，使得后面的入射光在等离子体平均密度远低于临界密度的区域就对入射光产生相位反射.相位反射的发生会影响激光在等离子体中的传播，例如激光在等离子体中相对传播时会出现激光场空洞现象.进一步的理论和数值模拟研究表明，相位反射持续发生的时间以及反射率的高低与等离子体的密度、等离子体区域的长度、激光强度以及脉宽等因素密切相关，这些都会对激光在等离子体中的传输产生影响. 关键词： 相位反射 密度调制 激光等离子体 粒子模拟     

约化场强对氮-氧混合气放电等离子体演化特性的影响

采用零维等离子体动力学模型,计算了不同约化场强条件下N₂/O₂放电等离子体的演化特性.结果表明,平均电子能量与约化场强有着近似的线性关系,在约化场强为100 Td时,平均电子能量约为2.6 eV、最大电子能量达35 eV;约化场强是影响电子能量函数分布的主要因素.气体放电过程结束后,振动激发态氮分子的粒子数浓度不再变化,电子激发态的氮分子、原子和氧原子的粒子数浓度达到一峰值后开始降低;放电结束后的氧原子通过复合反应生成臭氧.约化场强升高,由于低能电子减少的影响,振动激发态氮分子的粒子数浓度降低,当约化场强由50 Td增加75 Td,100 Td时,粒子数浓度由3.83×10¹¹ cm^-3降至1.98×10¹¹ cm^-3和1.77×10¹¹ cm^-3,其他粒子浓度则相应增大. 关键词： 等离子体 约化场强 粒子演化 数值模拟     

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     

Ozone generation in oxygen-fed wire-to-cylinder ozonizer: effect of CH2Cl2, CHCl3 and CCl4 diluents

The inhibition effect of methylene chloride CH₂Cl₂, chloroform CHCl₃ and carbon tetrachloride CCl₄ on the ozone generation process from oxygen by negative corona discharge was experimentally investigated. The experiments were performed in a system of coaxial cylindrical electrodes at total gas pressure of 900 mbar and ambient temperature of gaseous mixtures. The rate of ozone generation as well as ozone concentration apparently decreases with a rising number of substituted chlorine atoms in the methane molecule at constant specific energy consumption dissipated in the discharge and at constant concentration of gaseous impurities in oxygen. In addition to experimental results, the paper presents theoretical considerations aimed at identifying the main process responsible for inhibition of ozone generation. The consumption of considerable fraction of oxygen atoms by CH _x Cl _y–1 radicals formed in discharge, is likely the most important mechanism responsible for the deleterious effect of such compounds on the efficiency of ozone production.     

Analysis of sterilization effect by pulsed dielectric barrier discharge

Atmospheric pressure (AP) plasmas can sterilize against almost all kinds of bacteria because many ions and reactive species, such as oxygen atoms and ozone, etc., are generated during AP plasmas. So AP plasmas are proper processes for application to air cleaners and sterilizers. The aim of this paper is to evaluate a germicidal effect caused by pulsed plasma system in air utilizing a dielectric barrier discharge (DBD) type reactor incorporating alumina, glass, etc. Escherichia coli, Bacillus subtilis and Pseudomonas aeruginosa bacteria were used for this sterilization experiment. For analysis of the relationship between sterilization results and chemical species generated in the discharge, we used optical emission spectroscopy and we checked emission spectra by atomic oxygen (394.2 and 436.8 nm) and second positive system of nitrogen (337.1 nm). Experimental results showed that DBD treatment during 70 s sterilized E. coli with 99.99% effectively and ozone molecules were the dominant germicidal species. From these results we concluded that the pulsed DBD system is very effective for sterilization.     

Experimental investigations and modelling studies of ozone producing corona discharges

The ozone generation by negative corona discharge in coaxial cylindrical system of electrodes have been studied experimentally in Ar+O₂ and N₂+O₂ mixtures. Both in argon and nitrogen mixtures with oxygen the monotonous decrease in ozone concentration [O₃] was observed at decreasing oxygen content in mixtures and the constant input energy density η. The rate coefficients for the ozone generation and ozone decomposition were obtained by fitting experimentally measured data [O₃]=f(η) with Vasiljev-Eremin formula. The calculated rate coefficient for ozone generation in N₂+O₂ mixtures at low content of oxygen (below 20%) was found considerably higher than that in Ar+O₂ mixtures. Increase in the rate coefficients for ozone generation and decomposition was observed with decreasing content of oxygen in both mixtures. The experimental results are in qualitative agreement with the simple model incorporating five main chemical processes in mechanism of ozone generation. The research was partially supported by Slovak Grant Agency under project 1/765920 The UK EPSRC (Grant GM/98944) and NATO Joint Project PST CLG 976544.     

Numerical modeling of ozone production in a pulsed homogeneousdischarge: a parameter study

The pulsed volume discharge is an alternative for the efficient generation of ozone in compact systems. This paper presents a parameter study of the reactions in this kind of homogeneous discharge by using a numerical model which solves plasma chemical kinetic rate and energy equations. Simulations are performed for 10^-9-10^-5 s single pulses and oxygen gas density in the range 10<300 K and normalized electric field of 1000 decreased. The maximum concentration is 3% at 10 amagat and 100 K. The results on ozone accumulation in multiple pulse discharges are presented. In contrast to the single pulse case, higher efficiency is achieved at lower gas density. This scaling can be explained by losses due to ion currents     

相对湿度和氧气浓度对滑动弧放电特性影响研究

本文通过检测背景气体不同含氧量和相对湿度下的放电电流强度和臭氧浓度,分析氧气和水汽对滑动弧放电特性的影响.结果表明,背景中氧气是臭氧的主要发生源,臭氧随氧气浓度的增大而增大.水汽的离解反应与臭氧发生反应存在竞争关系,同时其生成的OH粒子会与臭氧发生反应,因此水汽对臭氧的产生起抑制作用.由于氧气和水的电子结合系数都很高,水与电子还会发生离解结合反应,因此背景气体氧气浓度和水汽含量增大会减少等离子体区域的电子数量,降低放电电流强度.     

大气压等离子体辅助多晶硅薄膜化学气相沉积参数诊断

本文采用发射光谱法诊断了大气压下Ar气、SiCl₄及H₂气混合气体（Ar/SiCl₄/H₂）射频放电等离子体射流特性.利用Si原子谱线强度计算了电子激发温度并以此估算了Si原子数密度,研究了射频功率及气体流量对电子激发温度和Si原子数密度以及SiCl₄解离率的作用.     

大气压等离子体辅助多晶硅薄膜化学气相沉积参数诊断

本文采用发射光谱法诊断了大气压下Ar气、SiCl₄及H₂气混合气体（Ar/SiCl₄/H₂）射频放电等离子体射流特性.利用Si原子谱线强度计算了电子激发温度并以此估算了Si原子数密度,研究了射频功率及气体流量对电子激发温度和Si原子数密度以及SiCl₄解离率的作用. 关键词： 大气压等离子体射流 发射光谱 电子激发温度 多晶硅薄膜沉积     

Laser-induced plasmas in liquids for nanoparticle synthesis

Spatially and temporally resolved emission spectroscopy is used to study the major features of the onset and evolution of plasmas created by pulsed laser irradiation of targets immersed in liquids. It is shown that double pulse operation provides an enhanced rate of nanoparticle formation and increases the emission signal from the plasma atoms and ions owing to more efficient ablation of the target material. The main parameters (density of atoms, electron temperature and density) of laser-induced plasmas in liquids are estimated. The prospects of laser ablation in liquids as a method for producing nanoparticles are analyzed.     

Metastable argon atoms under significant neutral depletion in helicon plasmas by laser-induced fluorescence

We study the spatial distribution of the metastable-state argon atoms in high density helicon plasmas by means of laser-induced fluorescence. It is observed that the neutral argon in metastable-state has an anomalous radial distribution in density; it has a caldera-like shape radially, which is rare in typical low-temperature plasmas such as inductively coupled plasmas wherein the density increases toward the discharge center, as previously reported. The formation of the distribution can be explained as it forms by the combined effects of significant neutral depletion in high plasma density, off-axis electron-density distribution, and increasing diffusive loss toward the wall. To establish the assertion with the underlying physics, we calculate a simple global model and obtain the neutral density distribution in metastable-state under various conditions. The calculated results qualitatively agree with the experimental results.