直流激励的大气压氩气喷枪的光谱研究

利用正高压驱动空心针-板喷枪装置,通入工作气体氩气,在大气压空气中产生了均匀稳定的喇叭状等离子体羽。电学和光学测量结果表明,放电虽然是在直流电源驱动下工作,但放电为周期性的脉冲。通过对等离子体羽发光信号进行空间分辨测量,研究了脉冲的形成机理,发现除针尖附近的电晕放电外,等离子体羽是以正流光(等离子体子弹)从针尖向着接地电极方向传播的。采用光谱学方法,对电子激发温度随电压的变化及其空间分布进行了测量。结果表明,电子激发温度(约为3 eV)随电压的增大而升高,在一定电压下,电子激发温度沿气流方向也在升高。     

大气压空气等离子体羽的振动温度研究

利用三电极介质阻挡放电装置,在大气压空气中产生了较大体积的等离子体羽。采用光学方法对该等离子体羽的特性进行了研究。发现随着外加电压峰值增加,每个外加电压周期的放电脉冲个数增加。通过采集等离子体羽的发射光谱,空间分辨地研究了放电等离子体羽的振动温度。结果表明等离子体羽的振动温度随着外加电压峰值的增加而减小;随着远离喷嘴的距离的增加,等离子体振动温度先增加后减小,当距离喷嘴5.4 mm时振动温度达到最高值。对上述现象进行了定性分析。研究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。     

Laser-induced fluorescence measurements of velocity within a Hall discharge

The results of a study of laser-induced fluorescence velocimetry of neutral and singly ionized xenon in the plume and interior portions of the acceleration channel of a Hall thruster plasma discharge operating at powers ranging from 250 to 725 W are described. Axial ion and neutral velocity profiles for four discharge voltage conditions (100 V, 160 V, 200 V, 250 V) are measured as are radial ion velocity profiles in the near-field plume. Ion velocity measurements of axial velocity both inside and outside the thruster as well as radial velocity measurements outside the thruster are performed using laser-induced fluorescence with nonresonant signal detection on the xenon ion 5d[4]_7/2–6p[3]_5/2 excitation transition while monitoring the signal from the 6s[2]_3/2–6p[3]_5/2transition. Neutral axial velocity measurements are similarly performed in the interior of the Hall thruster using the 6s[3/2]⁰ ₂–6p[3/2]₂transition with resonance fluorescence collection. Optical access to the interior of the Hall thruster is provided by a 1-mm-wide axial slot in the insulator outer wall. While the majority of the ion velocity measurements used partially saturated fluorescence to improve the signal-to-noise ratio, one radial trace of the ion transition was taken in the linear fluorescence region and yields a xenon ion translational temperature between 400 and 800 K at a location 13 mm into the plume. Received: 27 September 2000 / Revised version: 2 March 2001 / Published online: 9 May 2001     

Analysis on plasma chemistry and particle growth in corona discharge process for NO/sub x/ removal using discrete-sectional method

The particle formation and growth combined with plasma chemistry in the pulsed corona discharge process (PCDP) to remove NO/sub x/ were analyzed by the discrete-sectional model. In the PCDP, most of the NO is converted into NO/sub 2/ and, later, into HNO/sub 3/ which reacts with NH/sub 3/ to form the NH/sub 4/NO/sub 3/ particle. In the beginning of the reactor, we have the high concentration of small size particles and, later, the particle size distribution in the reactor becomes bimodal with the large size and small size particles and, finally, becomes monodisperse with the large size particles. As the average electron concentration increases, it takes a shorter reactor length to remove the NO/sub x/. As the initial NO and H/sub 2/O concentrations decrease, the NH/sub 3/ is consumed more slowly to form the ammonium nitrates particles. As the averaged electron concentration and initial H/sub 2/O concentration increase, the large size particles grow more quickly and the particle size distribution becomes bimodal earlier. As the initial NO and NH/sub 3/ concentrations increase, the diameter of large size particles becomes larger by the faster coagulation between particles. The predicted NO/sub x/ conversion and particle size distribution were in close agreements with the published experimental results at the averaged electron concentration of 2/spl times/10/sup 5/ cm/sup -3/ in this study.     

Supersonic flow of a nonequilibrium gas-discharge plasma around a body

The flow of a nonequilibrium gas-discharge plasma around a semicylindrical body is studied. The aim of the study is to see how a change in the degree of nonequilibrium of the incoming plasma changes the separation distance between a shock wave and the body. Experiments are carried out with a supersonic nozzle into which a semicylindrical body is placed. The inlet of the nozzle is connected to a shock tube. In the course of the experiment, electrodes built into the wall of the nozzle initiate a gas discharge in front of the body to produce an additional nonequilibrium ionization in the stationary incoming supersonic flow. The discharge parameters are selected such that the discharge raises the electron temperature and still minimizes heating of the gas. The degree of nonequilibrium of the flow varies with gas-discharge current. Diagnostics of the flow is carried out with a schlieren system based on a semiconductor laser. The system can record flow patterns at definite time instants after discharge initiation.     

Modeling refraction characteristics of silicon nitride film deposited in a SiH/sub 4/-NH/sub 3/-N/sub 2/ plasma using neural network

Silicon nitride has been deposited using plasma-enhanced chemical deposition (PECVD) equipment. The PECVD process was characterized by conducting a 2/sup 6-1/ fractional factorial experiment on six experimental factors, including substrate temperature, pressure, radio frequency (RF) power, ammonia NH/sub 3/, silane SiH/sub 4/, and nitrogen N/sub 2/ flow rates. Refractive characteristics of the deposited film were examined by modeling the refractive index as a function of experimental factors. A helium-neon laser with a wavelength 6328 /spl Aring/ was used to measure the refractive index. To evaluate the appropriateness of the model, the network trained with 32 experiments was then tested with 12 experiments not pertaining to the training data. Several learning factors involved in training neural networks were optimized and an accurate prediction model with the root mean-squared error of 0.018 was achieved. Compared to statistical regression model, the neural network model demonstrated an improvement of more than 65%. Using various three-dimensional plots, underlying deposition mechanisms were qualitatively estimated. For the limited experimental ranges, the index increased with increasing SiH/sub 4/ flow rate. With an increase in either NH/sub 3/ or N/sub 2/, meanwhile, the index decreased consistently. The index also increased with increasing substrate temperature or pressure. The effects of the temperature were very complex as it interacted with other factors.     

光纤激光气体氮化钛合金发射光谱及等离子体研究

激光气体氮化工艺可在钛合金表面快速生成氮化层,提高钛合金表面硬度和耐磨性,促进钛合金应用.采用光纤激光气体氮化Ti-6Al-4V合金,为了明确氮化过程光谱发射区是否形成等离子体,采用探针法检测了光谱发射区导电性;为了研究工艺参数对光谱特性、光谱发射区温度及等离子数量的影响,采用光谱仪采集了氮化过程发射光谱,并采用高速摄...     

采用态-态模型的热化学非平衡喷管流数值研究

数值求解耦合态-态模型的N₂/N准一维喷管非平衡流方程,获得驻室温度3 000 K~10 000 K,压力1 atm~10 atm条件下的流场参数分布和详细的振动能级分布,分析喷管流动中的宏观和微观特性,并对这类复合占优的流动考察双温度模型中假设的合理性.     

光谱方法研究大气压氩气等离子体喷枪的放电特性

利用同轴介质阻挡放电喷枪,通过氩气的流动在大气压空气中产生了均匀的等离子体羽。等离子体羽沿气流方向较为均匀,但在喷嘴处为白色且亮度较高,远离喷嘴处为蓝色,亮度较低。研究了等离子体羽长度与外加电压幅值、驱动频率和气体流速的关系,气流小于4 L·min-1时等离子羽的长度随气流的增大而增大,而当气流大于4 L·min-1时长度随气流的增大而减小。当气流保持恒定时,等离子体羽的长度随外加电压幅值或驱动频率的增大而增大。结合气体放电理论以及分析湍流和平流对放电的影响,对等离子体羽长度随实验参数的变化进行了定性解释。光学方法研究发现在外加电压正半周期等离子羽有一个发光脉冲,而负半周期没有发光信号。同轴介质阻挡放电正半周期有两个发光脉冲,负半周期有一个发光脉冲。通过对该N₂现象的分析,为等离子体羽的产生机制提供了一种可能的解释。采集了同轴介质阻挡放电和等离子体羽的发射光谱,研究发现除等离子体羽存在明显的OH和N₂的发射谱线外,其发射光谱没有明显差别。利用光学发射谱N+₂第一负带系,对等离子体羽转动温度进行了测量,发现转动温度沿远离喷嘴的方向逐渐降低,且转动温度随电压幅值的增大而增大。     

HL-2A 装置的边缘参数测量

HL-2A 装置中平面边缘的等离子体特性通过磁力传动的马赫/ 雷诺协强/ 朗缪尔10 探针组进行了研究。10 探针组安装在可径向向里和向外移动, 并可绕轴旋转360^o 的传动杆上, 用于测量主等离子体边缘的温度、密度、悬浮电位、空间电位、径向和极向电场、湍流的雷诺协强、径向和极向等离子体流速及其径向分布。HL- 2A 装置的实验结果表明, 边缘等离子体扰动诱发的雷诺协强产生了边缘极向流; 雷诺协强的径向梯度驱动带状流抑制了湍流输运。     

Ar/H2O大气压等离子体射流放电特性

为了研究水蒸气体积分数对大气压等离子体射流放电机理及放电效率的影响,进而产生高活性低温等离子体并优化其效率。通过对大气压氩水等离子体射流的电压电流波形和Lissajous图形等电气特性的测量及发射光谱和发光图像等光学特性诊断,研究了不同水蒸气体积分数时,等离子体射流的放电特性。通过计算放电功率、传输电荷量、电子激发温度、分子振动温度和分子转动温度等主要放电参量,研究了它们随水蒸气体积分数的变化趋势,并结合放电机理对所得实验结果进行分析。结果表明,Ar/H2O等离子体射流除了产生N2和Ar,还有OH和O,气体温度在525~720 K之间变化,为典型的低温等离子体;随着水蒸气体积分数的增加,等离子体羽喷出管口的长度减小,放电功率减小,发光强度减弱,转动温度和振动温度增加;相同功率下,水蒸气体积分数为0.5%时,产生的OH达到最大。     

发射光谱研究大气压等离子体射流的气体温度

采用介质阻挡放电等离子体喷枪装置,在大气压下流动氩气中产生了射流等离子体。利用光电倍增管,对射流等离子体进行了时空分辨测量,分析了等离子体喷枪内介质阻挡放电和外部等离子体羽的放电特性。利用高分辨率光谱仪采集等离子体羽处的发射光谱,通过对发射光谱中OH(A2Σ+→X2Π,307.7～308.9nm)及N2+的第一负系(B2Σ+u→X2Π+g,390～391.6nm)谱线拟合得到了射流等离子体的转动温度,拟合得到的转动温度分别为443和450K。在5%的误差范围内,这2种方法得到的结果是一致的。由于在大气压下,转动温度近似等于产生气体放电的气体温度,所以可以确定大气压射流等离子体气体温度。利用该方法研究了不同电压下的气体温度,发现气体温度随着外加电压增加而增大。     

Industrial-scale experiments of desulfuration of coal flue gas using a pulsed corona discharge plasma

The flow rate of flue gas in the industrial experiments was 3000 Nm/sup 3//h. The flue gas from the boiler burning coal was used. The influences of operating parameters on the efficiency of desulfuration (DeSO/sub 2/) were studied, which include the retention period of flue gas in the reactor, the initial concentration of SO/sub 2/ in flue gas, a mole ratio of NH/sub 3/ to SO/sub 2/ in the gas, the temperature of the gas, as well as the power consumption of pulsed corona discharges. The experimental results shown that the efficiency of DeSO/sub 2/ was above 80%, when the initial concentration of SO/sub 2/ was 1000 /spl sim/ 2000 ppm, the gas temperature was 60 /spl deg/C /spl sim/ 75 /spl deg/C, the retention period was more than 5.8 s, a mole ratio of NH/sub 3/ to SO/sub 2/ was 2 : 1, the water content in flue gas was above 6%, and he consumption was 2.5 /spl sim/ 3.5 Wh/Nm/sup 3/.     

Influence of the composition of a plasma-forming gas on nitriding in a non-self-maintained glow discharge with a large hollow cathode

The article presents the results of an investigation into the influence of the composition of a plasma-forming gas (N₂, Ar, He) on nitriding of VT1-0 grade titanium (0.25%-Fe; 0.1%-Si; 0.2%-O) and commercial 40X steel (0.4%-C; 1.0%-Cr) in the plasma of a non-self-maintained glow discharge with a large hollow cathode. It is shown that the efficiency of nitriding of 40X steel weakly depends on the composition of the plasma-forming gas mixture, whereas nitriding of VT1-0 titanium in a helium-nitrogen mixture leads to a noticeable increase in the microhardness of the specimen’s surface in comparison with nitriding in an argon-nitrogen gas mixture.     

HL-2A等离子体边缘的快速单探针测量

介绍了对HL-2A装置中平面边缘等离子体的单探针测量。单探针是安装在可径向移动、并可绕轴旋 转360o的传动杆上的。在1MHz的快速采样频率下,测量了主等离子体边缘的温度、密度、悬浮电位、空间电位、极 向等离子体流速的径向分布。测量的结果表明,利用单探针测量的主等离子体边缘参数与朗缪尔四探针测量结果 基本一致。     

Efficient extracavity generation of radially and azimuthally polarized beams

We demonstrate an efficient transformation of a linearly polarized Gaussian beam to a radially or an azimuthally polarized doughnut (0,1)* Laguerre-Gaussian beam of high purity. We use a spatially variable retardation plate, composed of eight sectors of a lambda/2 retardation plate, to transform a linear polarization distribution to radial/azimuthal distribution. We transformed an Nd:YAG Gaussian beam with M(2)=1.3 to a radially and azimuthally polarized (0,1)* Laguerre-Gaussian beams with M(2)=2.5 and degree of radial/azimuthal polarization of 96-98%.     

Production of a large area diffuse arc plasma with multiple cathode

An arc channel at atmospheric pressure tends to shrink generally. In this paper, a non-transferred DC arc plasma device with multiple cathode is introduced to produce a large area arc plasma at atmospheric pressure. This device is comprised of a 42-mm diameter tubular chamber, multiple cathode which is radially inserted into the chamber, and a tungsten anode with a nozzle in its center. In argon/helium atmosphere, a large area and circumferential homogenous diffuse arc plasma, which fills the entire cross section surrounded by the cathode tips, is observed. Results show that the uniformity and stability of diffuse arc plasma are strongly related to the plasma forming gas. Based on these experimental results, an explanation to the arc diffusion is suggested. Moreover, the electron excitation temperature and electron density measured in diffuse helium plasma are much lower than those of constricted arc column, which indicates the diffuse helium plasma probably deviates from the local thermodynamic equilibrium state. Unlike the common non-transferred arc plasma devices, this device can provide a condition for axial-fed feedstock particles. The plasma device is attempted to spheroidize alumina powders by using the central axis to send the powder. Results show that the powder produced is usually a typical hollow sphere.     

大气条件等离子体针处理Enterococcus faecalis菌

自行研制的等离子体针在大气压下通过介质阻挡放电产生的等离子体,再由喷嘴处安装的漏斗形装置聚焦形成针状等离子体. 然后对针状等离子体的基本特性和杀Enterococcus faecalis（E. faecalis）菌进行了研究,E. faecalis菌是一种引起完善充填根管再感染的主要微生物. 当等离子体针功率为5—28?W时,对等离子体的温度进行了测量,表明它不同于其他热杀菌方式. 通过改变等离子体针内电极末端注入的氧气量,发现适当的氧气量,不仅增加等离子体内含氧粒子的浓度而且对等离子体的长度影响也不明显. 实验表明最佳参数为功率15?W,0.1?m³·h^-1氦和2.5%氧气,间距12?mm,处理时间30 s. 为了找出杀菌的关键粒子,进一步比较了大气压下的等离子体针的发射光谱与agar（琼脂）2?mm下的光谱并找出关键粒子. 关键词： 大气压等离子体 介质阻挡放电 E. faecalis菌')" href="#">E. faecalis菌 光谱     

Spectroscopic measurements of excited particles in a N2 gas RF plasma-assisted carbon laser ablation

In this work, we investigated a carbon plasma plume produced by laser ablation of a graphite target in a nitrogen gas environment. The spatial distributions of C and N atoms were measured by time-resolved absorption spectroscopy. The spatial distributions of the relative densities of CN radicals, C₂, and C₃ molecules were measured using time-resolved emission spectroscopy. We determined that nitrogen gas produced an increase in carbon atom and molecule densities in the ablation plume. It was observed that the addition of RF plasma to the plume increased the CN radicals and C atom densities, and decreased the C₂ and C₃ molecule densities. The RF plasma changed the evolution of various fractional species of C, N, CN, C₂, and C₃ in the ablation plume. The chemical reactions with and without RF plasma were explained using the evolution and density of the fractional species of C, N, CN, C₂, and C₃in the plume. PACS 52.38.Mf; 42.62.Fi; 33.20.-t; 81.05.Uw     

Optical diagnostics for temperature measurement in a DC arcjet reactor used for diamond deposition

2 a-state in this plume. LIF measurements of CH are complicated by the presence of C₃ and we discuss strategies to deal with this interference. The gas temperature describing the rotational distributions obtained for NO, C₂ and CH agree within experimental error. Optical emission measurements indicate that the rotational and vibrational distributions of the excited A-state of CH and a-state of C₂ are characterized by vibrational and rotational populations which are at least 1000 K above the ground state distributions. The excited states are collisionally quenched before their population distributions equilibrate with the gas temperature. We also determine relative populations of the ground and excited states along the axis of the plume between the arcjet nozzle and the substrate and relative populations for a cross section of the jet, midway between the nozzle orifice and the substrate. The measured relative ground and excited state populations for both CH and C₂ show different trends along the plume axis, indicating that the ground and excited states of these molecules are products of different chemical mechanisms; such mechanisms are discussed. Received: 16 July 1996/Revised version: 24 September 1996