Characteristics of parallel-plate and planar-surface dielectric barrier discharge at atmospheric pressure

Experiments are performed to investigate and compare the characteristics of stable parallel-plate and planar-surface dielectric barrier discharge in helium gas at atmospheric pressure. The evolution of applied electric field profile and the discharge initiation processes are found quite different for both electrode geometries. Further discharge voltage, discharge current, power densities etc. are compared. The differences of basic plasma properties are presented for both the electrode configurations.     

Simulation of transition from Townsend mode to glow discharge mode in a helium dielectric barrier discharge at atmospheric pressure

The dielectric barrier discharge characteristics in helium at atmospheric pressure are simulated based on a one-dimensional fluid model. Under some discharge conditions, the results show that one discharge pulse per half voltage cycle usually appears when the amplitude of external voltage is low, while a glow-like discharge occurs at high voltage. For the one discharge pulse per half voltage cycle, the maximum of electron density appears near the anode at the beginning of the discharge, which corresponds to a Townsend discharge mode. The maxima of the electron density and the intensity of electric field appear in the vicinity of the cathode when the discharge current increases to some extent, which indicates the formation of a cathode-fall region. Therefore, the discharge has a transition from the Townsend mode to the glow discharge mode during one discharge pulse, which is consistent with previous experimental results.     

常压He气和N$lt;sub$gt;2$lt;/sub$gt;气均匀介质阻挡放电的伏安特性

对带有多电流峰的常压He气均匀介质阻挡放电与常压N₂气均匀介质阻挡放电的伏安特性进行了实验分析. 分析结果表明：实验结果与模拟结果相符. 在带有多电流峰的常压He均匀介质阻挡放电中,辉光放电模式和汤森放电模式可以共存于一个多电流放电序列内. 此外,在放电电流增长阶段,可以根据常压均匀介质阻挡放电的伏安特性曲线的微分电导来判断均匀介质阻挡放电的放电模式. 在放电电流增长阶段,如果电流脉冲的伏安特性曲线呈现负微分电导,则电流脉冲为辉光放电模式;如果呈现正微分电导,则为汤森放电模式. 由此可以判断,常压N₂气均匀介质阻挡放电为汤森放电模式. 关键词： 伏安特性 辉光放电模式 汤森放电模式 常压均匀介质阻挡放电     

Characterizing uniform discharge in atmospheric helium by numerical modelling

One-dimensional fluid model of dielectric barrier discharge (DBD) in helium at atmospheric pressure was established and the discharge was numerically simulated. It was found that not only the spatial distributions of the internal parameters such as the electric field, the electron density and ion density are similar to those in a low-pressure glow discharge, but also the visually apparent attribute (light emission) is exactly the same as the observable feature of a low-pressure glow discharge. This confirms that the uniform DBD in atmospheric helium is a glow type discharge. The fact that the thickness of the cathode fall layer is about 0.5mm, much longer than that of a normal glow discharge in helium at atmospheric pressure, indicates the discharge being a sub-normal glow discharge close to normal one. The multipulse phenomenon was reproduced in the simulation and a much less complicated explanation for this phenomenon was given.     

Observation of self-organized square lattice pattern formation in surface barrier discharge plasma

The experimental observation of a two-dimensional self-organized square lattice pattern in a planar surface barrier discharge is reported. The discharge was operated near atmospheric pressure in helium gas. The transition from irregular plasma spot pattern to a square lattice pattern is achieved by reducing the discharge driving frequency. On increasing the driving frequency the regular lattice pattern is destroyed and again transforms to an irregular plasma spot pattern. Dielectric degradation and powder formation is also observed after discharge process. Spatio-temporal behavior of observed plasma pattern is presented.     

大气压氦气介质阻挡放电中的周期一不对称放电实验研究

大气压介质阻挡放电不仅具有对称周期一的放电形式, 还会在一定参数下呈现不对称周期一(AP1)放电. 本文采用具有平行电极结构的介质阻挡放电装置, 分别在气隙宽度1 mm, 3 mm, 7 mm和10 mm下的大气压氦气中进行了一系列放电实验, 研究了气隙宽度和外施电压频率对周期一放电对称性的影响. 实验结果表明: 在较宽的气隙宽度和外施电压频率参数区间内可以观察到显著的AP1放电; 气隙宽度越大越容易产生AP1放电, 同一气隙宽度下外施电压频率较高时则相对更容易观察到AP1放电; 随着气隙宽度增加, 首次击穿即呈现AP1 放电的外施电压频率临界值逐渐减小. 本文的研究初步验证了之前关于气隙宽度对AP1放电影响的数值仿真结果, 由此可以推测AP1放电并不只是由系统参数的不对称引起的, 也很可能是一种在一定的气隙宽度和外施电压频率下系统固有的、内在的高频不稳定放电行为. 关键词： 介质阻挡放电 不对称放电     

Concentric-ring structures in an atmospheric pressure helium dielectric barrier discharge

This paper performs a numerical simulation of concentric-ring discharge structures within the scope of a two-dimensional diffusion--drift model at atmospheric pressure between two parallel circular electrodes covered with thin dielectric layers. With a relative high frequency the discharge structures present different appearances of ring structures within different radii in time due to the evolvement of the filaments. The spontaneous electron density distributions help understanding the formation and development of self-organized discharge structures. During a cycle the electron avalanches are triggered by the electric field strengthened by the feeding voltage and the residual charged particles on the barrier surface deposited in the previous discharges. The accumulation of charges is shown to play a dominant role in the generation and annihilation of the discharge structures. Besides, the rings split and unify to bring and annihilate rings which form a new discharge structure.     

大气压Ar／NH3介质阻挡辉光放电的仿真研究

为了研究火气压下氩气（Ar）中掺杂氨气（NH3）的Ar／NH3介质阻挡辉光放电的放电机理,通过建立一‘个多粒子的自洽耦合流体模型,采用有限元方法进行数值计算,得到了气体间隙压降、介质表面电荷密度、放电电流密度随时间的周期变化波形,以及带电粒子、中性粒子与空间电场强度的时空分布．仿真计算结果表明：气体间隙的周期击穿过程主要由气隙电压控制,并受气隙两侧介质极板上积聚的表面电荷的影响．气隙间带电粒子密度和电场强度的时空分布表明本文的放电过程存在阴极位降区、负辉区、法拉第暗区、等离子体正柱区等辉光放电的典型区域,放电模式为大气压辉光放电．在Ar/NH3等离子体中,主要的正离子为NH＋,其次为Ar2＋,主要的负离子为NHi：NH3分解产生的主要的激发态分子为NH,NH2和N2H3,而最终的稳态产物主要是N2和H2．     

Coaxial rf atmospheric pressure dielectric barrier air-helium plasma characteristics

The electrical and optical characteristics of a coaxial rf atmospheric pressure dielectric barrier discharge (DBD) with one electrode covered with glass and with helium in air were investigated. Optical measurements with an intensified charge coupled device (ICCD) camera combined with the voltage and power vs. current data provided identification of the α to γ mode transitions. The coaxial design allowed operation with very low power density plasmas (0.18 W/cm³) and a much larger plasma size (13 mm) than the parallel plate designs.     

大气压氩气介质阻挡辉光放电的一维仿真研究

为了研究氩气(Ar)中介质阻挡大气压辉光放电(APGD)的放电机理, 通过建立一个一维的多粒子自洽耦合流体模型, 采用有限元方法进行数值计算, 得到了气体间隙压降、介质表面电荷密度、放电电流密度随时间的周期变化波形, 以及电子、离子、亚稳态粒子密度和空间电场强度的时空分布. 仿真计算结果表明：介质表面积聚的电荷对于放电的过程的起始及熄灭具有重要作用;当增大外施电压时, 放电击穿时刻提前, 放电电流密度和介质表面电荷密度峰值增大, 表明放电过程更加剧烈;随着阻挡介质相对介电常数的增大, 放电电流密度也随之增大. 各粒子密度及电场的时空分布表明放电过程在外施电压半个周期中只有一次放电, 且存在明显的阴极位降区、负辉区、等离子体正柱区等辉光放电的典型区域, 为大气压辉光放电(APGD).     

大气压氦气介质阻挡放电倍周期分岔及混沌现象的实验验证

采用具有平行电极结构的介质阻挡放电装置,在大气压氦气条件下进行了一系列放电实验,观察了放电波形并对其进行了频谱分析.结果表明,在一定条件下随外施电压幅值的增加,大气压氦气均匀介质阻挡放电会由周期一态放电经周期二态、周期四态放电进入混沌态放电.研究验证了大气压氦气介质阻挡放电经倍周期分岔路径通向混沌的现象,不仅仅出现在数值仿真中,在现实实验中也是确实存在的.     

Surface modification of polypropylene non-woven fabric using atmospheric nitrogen dielectric barrier discharge plasma

In this paper, a dielectric barrier discharge operating in nitrogen at atmospheric pressure has been used to improve the surface hydrophilic property of polypropylene (PP) non-woven fabric. The changes in the hydrophilic property of the modified PP samples are investigated by the contact angle measurements and the variation of water contact angle is obtained as a function of the energy density; micrographs of the PP before and after plasma treatment are observed by scanning electron microscopy (SEM) and the chemical composition of the PP surface before and after plasma treatment is also analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results show that the surface hydrophilic property of the PP samples is greatly improved with plasma treatment for a few seconds, as evidenced by the fact that the contact angle of the treated PP samples significantly decreases after plasma treatment. The analysis of SEM shows that the surface roughness of the treated PP samples increases due to bonding and etching in plasma processing. The analyses of FTIR and the C1s peak in the high-resolution XPS indicate that oxygen-containing and nitrogen-containing polar functional groups are introduced into PP surface in plasma processing. It can be concluded that the surface hydrophilic property of the modified PP samples has been obviously improved due to the introduction of oxygen-containing and nitrogen-containing polar groups and the increase of the surface roughness on the PP surface.     

Numerical studies of atmospheric pressure glow discharge controlled by a dielectric barrier between two coaxial electrodes

The glow discharge in pure helium at atmospheric pressure, controlled by a dielectric barrier between coaxial electrodes, is investigated based on a one-dimensional self-consistent fluid model. By solving the continuity equations for electrons, ions, and excited atoms, with the current conservation equation and the electric field profile, the time evolution of the discharge current, gas voltage and the surface density of charged particles on the dielectric barrier are calculated. The simulation results show that the peak values of the discharge current, gas voltage and electric field in the first half period are asymmetric to the second half. When the current reaches its positive or negative maximum, the electric field profile, and the electron and ion densities represent similar properties to the typical glow discharge at low pressures. Obviously there exist a cathode fall, a negative glow region, and a positive column. Effects of the barrier position in between the two coaxial electrodes and the discharge gap width on discharge current characteristics are also analysed. The result indicates that, in the case when the dielectric covering the outer electrode only, the gas is punctured earlier during the former half period and later during the latter half period than other cases, also the current peak value is higher, and the difference of pulse width between the two half periods is more obvious. On reducing the gap width, the multiple current pulse discharge happens.     

大气压下多脉冲均匀介质阻挡放电的研究

基于一维流体力学模型，数值计算研究了大气压下氦气中多脉冲均匀介质阻挡放电的形成原因和性质，分析讨论了所加电压频率、幅值及介质板性质等对多脉冲均匀放电的影响. 模拟结果显示，当放电间隙较小时，由于介质表面积累电荷增加，感应电场增强，在外加电压的每半个周期内，可以形成多个放电脉冲，这些脉冲相应于等时间间隔的分立击穿. 放电间隙越窄，半个周期内形成的脉冲数目越多. 所加电压频率和幅值的变化不仅影响脉冲的幅度，同时也使放电脉冲的数目发生变化，而介质层厚度及介电常数的变化对放电脉冲数目没有明显的影响. 关键词： 大气压均匀放电 介质阻挡放电 数值模拟 等离子体     

常压介质阻挡放电间隙的选择及其在材料表面改性中的应用

使用自制介质阻挡放电装置，分析了常压等离子体放电电流和放电功率与放电间隙的变化关系，提出了“放电临界间隙”的概念，并应用该装置对PBT熔喷非织造布进行表面改性，讨论了放电间隙和放电气体等因素对改性效果的影响．     

Glow discharge in helium at atmospheric pressure as a source of spectrum excitation

Self-maintained glow discharge at atmospheric pressure in a helium flow is used as an excitation source of spectra for analysis of the metals Na, Ca, Pb, Cd, and Zn in aqueous solutions of their salts. The intensities of the analytical lines of these metals are obtained as a function of the concentration, and the detection limits for each element are determined. Deceased. Institute of Molecular and Atomic Physics, Academy of Sciences of Belarus, 70, F. Skorina Ave., Misnk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 6, pp. 711–715, November–December, 1997.     

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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。     

介质阻挡均匀大气压氮气放电特性研究

基于一维流体力学模型，对介质阻挡均匀大气压氮气放电特性进行了数值计算研究.模型中考虑了氮气中主要的电离、激发过程，所包含的粒子种类为e，N₂，N⁺₂，N⁺₄，N₂(a¹∑^-_u)，N₂(A³∑⁺_u).模拟结果显示，氮中的放电具有低气压下汤生放电的特性.放电电流幅度较小，放电过程中气体电压变化缓慢，电子密度远低于离子密度，而且最大值出现在阳极，电子不能在放电间隙中被俘获，不存在中性等离子体区，气体中的电场趋于线性变化.亚稳态N₂(A³∑⁺_u)和N₂(a¹∑⁺_u)在整个放电空间都具有非常高的密度，比电子密度高三个量级以上，亚稳态密度的最大值出现在阳极，这样的分布决定了放电的空间结构.放电所需的种子电子主要由亚稳态之间潘宁电离提供，这种机理使放电的电离水平较低，导致氮气中的放电只能是汤生放电.随着放电参数的变化，多电流峰放电也可在氮气中获得. 关键词： 大气压均匀放电 介质阻挡放电 数值模拟 氮气     

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。     

空气中大气压下均匀辉光放电的可能性

利用介质阻挡电极结构,对101325×105Pa气压下空气间隙中的放电进行了实验研究,数值模拟计算了实验条件下电子雪崩的发展过程.结果表明:对于长度不大于2mm的空气间隙,可能实现辉光放电.对于长度不小于5mm的空气间隙,如果不能设法降低放电场强,放电必然是流注形式,不可能实现辉光放电.另外,实验结果未能验证“离子捕获”机理降低放电场强而实现辉光放电的正确性 关键词： 大气压辉光放电 电子雪崩 流注