Electric and plasma characteristics of RF discharge plasma actuation under varying pressures

The electric and plasma characteristics of RF discharge plasma actuation under varying pressure have been investigated experimentally. As the pressure increases, the shapes of charge–voltage Lissajous curves vary, and the discharge energy increases. The emission spectra show significant difference as the pressure varies. When the pressure is 1000 Pa,the electron temperature is estimated to be 4.139 e V, the electron density and the vibrational temperature of plasma are peak4.71×10~(11)cm~(-3) and 1.27 e V, respectively. The ratio of spectral lines I391.4/peak I380.5which describes the electron temperature hardly changes when the pressure varies between 5000–30000 Pa, while it increases remarkably with the pressure below 5000 Pa, indicating a transition from filamentary discharge to glow discharge. The characteristics of emission spectrum are obviously influenced by the loading power. With more loading power, both of the illumination and emission spectrum intensity increase at 10000 Pa. The pin–pin electrode RF discharge is arc-like at power higher than 33 W, which results in a macroscopic air temperature increase.     

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采用Langmuir探针法结合发射光谱法对螺旋波诱导的低压氢等离子体进行诊断,根据Druyvesteyn 方法和日冕模型分析电子能量几率函数(EEPF)、有效电子温度(Teff)、电子密度(ne)及激发态氢原子密度(nH*)随实验参数的变化规律.结果表明:随射频功率(Prf)、气压(p)和约束磁场(B)的增大,EEPF峰位由高能向低能移动,Teff 下降;当Prf从25W增大至35W左右时,ne发生跳跃增长,而nH*始终随Prf增大线性增长;随p增大,ne和nH*都呈现先增加后减小的变化规律;随B增强,ne线性增长,而nH*先增大后减小.     

空心针-板电极大气压氩气辉光放电的特性研究

大气压均匀放电等离子体在工业领域具有非常广泛的应用前景,它是利用直流电源激励的空心针-板放电装置,以氩气为工作气体在大气压空气中产生均匀稳定的放电。对氩气流量和气隙间距对辉光放电发光特性的关系进行了研究,结果表明放电所产生的等离子体柱连接两个电极,发光较为均匀(观察不到放电丝)。在板电极附近放电等离子体柱直径最大,最大直径随着电流和气流的增大而增大。放电伏安特性研究发现,与低气压辉光放电相类似,两电极间的电压随着电流的增大而减小,并且随气流和气隙间距的增大而增大。对该大气压直流均匀放电在扫描范围为330～450 nm的光学发射光谱进行分析,获得了放电等离子体的分子振动温度和谱线强度比I_391.4/I_337.1随氩气流量和气隙间距的变化关系。I_391.4/I_337.1均随流量和气隙间距的增大而降低。对等离子体柱的I_391.4/I_337.1沿气流方向(等离子体柱轴向)进行了空间分辨测量,并进行了定性分析,结果表明,振动温度及电子平均能量随着远离空心针口距离的增大而增大。这些结果对大气压辉光放电在工业中的应用具有重要意义。     

Field-free molecular orientation enhanced by tuning the intensity ratio of a three-color laser field

We theoretically study the field-free molecular orientation induced by a three-color laser field. The three-color laser field with a large asymmetric degree can effectively enhance the molecular orientation. In particular, when the intensity ratio of the three-color laser field is tuned to a proper value of I_3: I_2: I_1= 0.09 : 0.5 : 1, the molecular orientation can be improved by ～ 20% compared with that of the two-color laser field at intensity ratio I_2: I_1= 1 : 1 for the same total laser intensity of 2×10~(13)W/cm~2. Moreover, we investigate the effect of the carrier-envelope phase(CEP) on the molecular orientation and use the asymmetric degree of the laser field to explain the result. We also show the influences of the laser intensity, rotational temperature, and pulse duration on the molecular orientation. These results are meaningful for the theoretical and experimental studies on the molecular orientation.     

柱面天线射频感性耦合等离子体放电模式特性的实验研究

利用Z-scan、电流、电压探头,通过测量等离子体吸收功率、天线电流、电压、等离子体直流悬浮电位等多种参数,研究了匹配网络、天线耦合强度、导电地面积、气压等多种因素对E,H放电模式特性及模式转化行为的影响.基于Γ型阻抗匹配网络中串联电容对射频电源输出功率的影响,提出了E—H放电模式转化的正负反馈区概念.研究发现：在相同的其他放电条件下,处于正反馈区时等离子体放电易于产生跳变型模式转化,而且模式跳变的临界天线电流、回滞宽度、跳变临界功率、跳变功率差等参数均随阻抗匹配网络参数产生明显变化;在负反馈区内,模式转化过程趋于连续.由于阻抗匹配网络的影响,E—H模式的跳变电流并不是总大于H—E模式的跳变电流.在不同导电地面积、阻抗匹配网络、气压下,模式转化过程中等离子体直流悬浮电位的变化呈现多样性. 关键词： 射频等离子体 感性耦合 容性耦合 模式转化     

压强对介质阻挡放电中八边形结构等离子体温度的影响

利用水电极介质阻挡放电装置,在氩气和空气的混合气体中,首次观察到了由点和线组成的八边形结构。采用发射光谱法,研究了八边形结构中的点和线的等离子体温度随压强的变化关系。利用氮分子第二正带系(C3Π_u→B3Π几_g)的发射谱线,计算了点和线的分子振动温度;通过氮分子离子391.4 nm和氮分子394.1 nm两条发射谱线的相对强度比,研究了点和线的电子平均能量大小变化;利用氩原子763.26 nm(2P₆→1S₅)和772.13 nm(2P₂→1S₃)两条谱线强度比法,得到了点和线的电子激发温度。实验发现：在同一压强条件下,线比点的分子振动温度、电子平均能量以及电子激发温度均高;随着气体压强从40 kPa增大到60 kPa,点和线的分子振动温度、电子平均能量以及电子激发温度均减小。     

大面积沿面放电等离子体温度的光谱研究

设计了水电极放电装置,在空气/氩气混合气体中实现了大面积沿面放电。采用发射光谱法,对分子振动温度、电子平均能量和电子激发温度等随气压的变化进行了研究。根据氮分子第二正带系(C3Π_u→B3Π_g)的发射谱线计算出氮分子的振动温度;使用Ar 763.51 nm(2P₆→1S₅)和772.42 nm(2P₂→1S₃)的两条发射谱线的强度比得到电子激发温度;通过氮分子离子391.4 nm和氮分子337.1 nm两条发射谱线的相对强度之比得出了电子的平均能量的变化。实验研究了发射光谱随气压的变化,发现其强度随着气压的增加而增强,且其整个轮廓和谱线强度之比也发生变化。随着气压从0.75×105Pa升高到1×105Pa,分子振动温度、电子激发温度和电子能量均呈下降趋势。     

基于表面等离激元场的分子反射镜的理论研究

本文提出了一种基于微纳金属膜结构激发的表面等离激元场的分子反射镜新方案,利用中性分子与金属表面垂直方向上蓝失谐消逝波光场之间的偶极力相互作用,实现入射分子束的表面反射.理论计算了表面等离激元场的空间分布,用蒙特卡洛方法模拟了分子在该场中运动的动力学过程,得到了分子反射镜的反射率与相互作用时间和入射光强之间的关系.结果表明:当入射激光脉宽为10 ns,光强为I=1.0×109W/cm2时,纵向温度为10 mK,横向温度为1 mK的碘分子束反射效率达到55.89%,而且反射率随着入射光强的增大而增大.     

Experimental investigation of current modulation in a planar Cs-Batacitron

The Cs-Ba tacitron is being considered as a switch, or as an inverter consisting of two switches operating in a push-pull mode, for power conditioning of low voltage/high current dc power sources operating in high radiation/high temperature environment, beyond the limits of semiconductor switches. This paper presents new experimental results delineating the effect of the various operating parameters on the grid potential needed for ignition, V_g⁺, and extinguishing, V_g^-, during stable current modulation of a planar Cs-Ba tacitron. Parameters investigated are Cs pressure, emitter temperature, T_E, discharge current, I_C , and modulation frequency, f_g. The value of V_g ⁺, which is independent of T_E, decreases as Cs pressure increases, but increases as either I_C or f_g increases. Increasing the emitter temperature from 1100-1200°C only slightly decreases the forward voltage drop in the device by ~0.2 V. The value of |V_g^-| increases with Cs pressure, decreases with increased T_E, and is sensitive to changes in fg. At I_C=5 A, the value of |V_g ^-| for stable modulation shows a maximum between 8 kHz and 10 kHz. The Cs pressure, I_C, fg, and V_g⁺ all affect the ignition delay time; depending on the operating conditions, it increases from 5-30 μs to an equilibrium value of 10-45 μs during the first 2 ms in the pulse train     

高阻隔铝塑膜辉光放电发射光谱深度谱测量参数的优化

脉冲-射频辉光放电发射光谱(GDOES)深度剖析是一种基于辉光放电原理的原子光谱技术,广泛应用于薄膜材料与功能多层膜结构中成分随深度分布的表征.该技术具有真空度要求低,灵敏度高,溅射速率快等优点.同时脉冲-射频电源所采用的瞬间高功率模式可使得氩离子周期性轰击样品表面,避免了由于热量积累所导致的熔融或碳化,因此脉冲-射频...     

高气压空气环状感性耦合等离子体实验研究和参数诊断

等离子体的电子密度分布, 电子碰撞频率分布, 覆盖面积, 厚度是影响其覆盖目标电磁散射特征的关键属性. 对此, 本文开展了在20 cm×20 cm×7 cm石英腔内感性耦合等离子体(ICP)的放电实验, 观察了在高气压条件下, 空气ICP的环形放电形态, E-H模式跳变现象和分层结构, 测量了其电负性核心区和电正性边缘区宽度和厚度随功率、气压的变化趋势, 并通过COMSOL Multiphysics对平板线圈磁场强度分布的分析和电负性气体扩散理论给予上述现象合理的解释, 同时, 利用微波透射干涉法测量了核心区域的电子密度随功率和气压的变化曲线, 利用理论模型计算了边缘区域的电子密度分布, 最后通过辅助气体Ar发射谱线的玻尔兹曼图形法得到了核心区和边缘区的电子激发温度.     

氦氩射频容性放电发射光谱分析

光抽运亚稳态稀有气体激光器利用放电等离子体作为激光的增益介质.为掌握容性射频放电的放电参数对等离子体各项参数的影响的基本规律,利用等离子体发射光谱法研究了氦氩混合气体在不同装置、不同Ar组分、不同气压和不同射频注入功率下的等离子体参数.利用残留水蒸气产生的OH自由基A~2Σ~+→X~2Π的转动光谱分析获得气体温度;利用电子态光谱的玻尔兹曼做图法获得电子激发温度,利用Ar原子696.5 nm谱线的斯塔克展宽获得电子密度.结果表明:气体温度随气压增加略微上升,在一个大气压下改变组分和放电功率,气体温度变化不大;电子激发温度随总气压的下降而上升,且随着Ar组分的增加而略微下降;目前放电条件下的电子密度均在10~(15)cm~(-3)量级;长时间放电监测表明,残留的水蒸气会导致电子温度的下降,从而降低Ar亚稳态的产率.     

空气介质阻挡放电不同放电模式的光谱特性

采用光谱方法,研究了空气介质阻挡放电中流光向类辉光转变时电子能量的变化。利用氮分子第二正带系(C3Π_u→B3Π_g)的发射谱线,测量了氮分子(C3Π_u)的振动温度。通过考察氮分子离子391.4 nm谱线强度与氮分子337.1 nm谱线强度之比,研究了电子平均能量的变化。结果表明,流光向类辉光转变时,氮分子(C3Π_u)的振动温度激增,氮分子离子391.4 nm相对谱线强度突增,表明类辉光放电模式中电子能量比流光放电模式中电子能量高很多。实验还发现,气隙间距不同,这两种放电模式转变所对应的转变气压不同,但转变气压与气隙间距的乘积值保持不变。     

Thermal and induced flow characteristics of radio frequency surface dielectric barrier discharge plasma actuation at atmospheric pressure

Thermal and induced flow velocity characteristics of radio frequency(RF) surface dielectric barrier discharge(SDBD)plasma actuation are experimentally investigated in this paper. The spatial and temporal distributions of the dielectric surface temperature are measured with the infrared thermography at atmospheric pressure. In the spanwise direction, the highest dielectric surface temperature is acquired at the center of the high voltage electrode, while it reduces gradually along the chordwise direction. The maximum temperature of the dielectric surface raises rapidly once discharge begins.After several seconds(typically 100 s), the temperature reaches equilibrium among the actuator's surface, plasma, and surrounding air. The maximum dielectric surface temperature is higher than that powered by an AC power supply in dozens of k Hz. Influences of the duty cycle and the input frequency on the thermal characteristics are analyzed. When the duty cycle increases, the maximum dielectric surface temperature increases linearly. However, the maximum dielectric surface temperature increases nonlinearly when the input frequency varies from 0.47 MHz to 1.61 MHz. The induced flow velocity of the RF SDBD actuator is 0.25 m/s.     

液体电极上辉光放电丝的运动特性研究

大气压液体电极放电在生物医疗、化学降解、环境保护等众多方面具有广泛的应用前景,引起了研究者的关注.本文利用直流电压激励棒-水电极装置,在6 mm气隙间产生了大气压辉光放电.研究发现,随着电流的增大,放电由锥状转变成柱状,且此过程中水面上放电环的直径先增大后减小.利用高速照相机对放电进行研究,发现锥状放电是由单个放电丝旋转形成的.通过测量放电的伏安特性,表明放电处于正常辉光机理.利用光谱学方法,研究了不同电流下的振动温度、转动温度和谱线强度比I_(391.4)/I_(337.1),发现它们均随电流的增加而增大.根据气体放电理论,分析和解释了放电丝的运动机理,并对水面上放电环直径随电流的变化关系进行了解释.这些结果对于大气压液体电极放电的理论研究和实际应用均具有一定参考价值.     

Study on the transition from filamentary discharge to diffuse discharge by using a dielectric barrier surface discharge device

Discharge characteristics have been investigated in different gases under different pressures using a dielectric barrier surface discharge device. Electrical measurements and optical emission spectroscopy are used to study the discharge, and the results obtained show that the discharges in atmospheric pressure helium and in low-pressure air are diffuse, while that in high-pressure air is filamentary. With decreasing pressure, the discharge in air can transit from filamentary to diffuse one. The results also indicate that corona discharge around the stripe electrode is important for the diffuse discharge. The spectral intensity of N电介质 表面放电 扩散放电 发射光谱学dielectric barrier surface discharge, diffuse discharge, optical emission spectroscopyProject supported by the National Natural Science Foundation of China (Grant Nos 10575027 and 10647123), the National Science Foundation of Hebei Province, China (Grant No A2007000134), the Education Department of Hebei Province, China (Grant No 2006106),2006-10-24Discharge characteristics have been investigated in different gases under different pressures using a dielectric barrier surface discharge device. Electrical measurements and optical emission spectroscopy are used to study the discharge, and the results obtained show that the discharges in atmospheric pressure helium and in low-pressure air are diffuse, while that in high-pressure air is filamentary. With decreasing pressure, the discharge in air can transit from filamentary to diffuse one. The results also indicate that corona discharge around the stripe electrode is important for the diffuse discharge. The spectral intensity of N＋ （391.4nm） relative to N2 （337.1 nm） is measured during the transition from diffuse to filamentary discharge. It is shown that relative spectral intensity increases during the discharge transition. This phenomenon implies that the averaged electron energy in diffuse discharge is higher than that in the filamentary discharge.     

非平衡磁控溅射制备类石墨碳膜及性能研究

利用中频非平衡磁控溅射技术在单晶硅基底上沉积了类石墨碳膜, 采用Raman光谱、高分辨透射电子显微镜、原子力显微镜分析了薄膜微观结构和表面形貌; 采用纳米压痕仪和CSM摩擦磨损试验机测试了碳膜力学性能和摩擦学性能. 结果表明: 利用中频非平衡磁控溅射技术沉积的碳膜是一种以sp²键合碳为主、结构非晶、硬度适中、应力较低、表面粗糙度较大、摩擦性能优异的薄膜. 脉冲占空比对薄膜微观结构和性能有显著影响, 随着脉冲占空比的增大, Raman光谱D峰和G峰的强度比I_D/I_G先减小后增大, 而硬度随脉冲占空比的增大却呈现出相反的变化趋势, 即先增大后减小; 大气氛围中的摩擦性能测试表明, 本实验制备的薄膜具有优异的抗磨性能(～10^-11 cm³/N^-1. m^-1)和承载能力(～2.5 GPa). 随脉冲占空比的增大, 薄膜摩擦系数变化甚微而磨损率却呈现先显著减小后轻微增大的变化趋势. 类石墨碳膜优异的摩擦学性能主要归因于其独特的结构、较低的内应力及良好的结构稳定性.     

电场条件下氧化锌结晶特性及极化产物的拉曼光谱分析

开展高压电场调控纳米材料结构形貌和性能研究在功能材料领域具有重要的理论和实际意义.本文在高压电场条件下合成了氧化锌纳米粉体,并对粉末试片进行了后期电场极化处理,研究了电场对氧化锌的结构形貌、点缺陷、拉曼光谱的影响.以X射线衍射仪(XRD)、扫描电镜(SEM)和拉曼光谱仪对产物的结构形貌、拉曼位移、缺陷分布等进行了表征.结果表明,高压电场条件下氧化锌的完全晶化时间和温度比未施加电场时明显延长和升高,直流电场能够显著促进前驱物中氧化锌的形核,并降低晶化速度.不同电场强度下氧化锌具有不同的显微形貌.纳米氧化锌粉末试片在直流电场中极化后,其阴极面和阳极面的拉曼光谱表现出明显的差异.有明显漏电电流的情况下,阳极面在1050 cm~(–1)处的二级光学声子模A_1(LO)的强度显著提高,且拉曼强度I_1=438 cm~(–1)和I_2=1050 cm~(–1)的比值与极化电场的场强呈线性关系.当调转试片正反面进行二次极化时,原来在阳极面尖锐的1050 cm~(–1)峰经过阴极极化而消失.阳极面1050 cm~(–1)拉曼峰的锐化与氧化锌晶粒内的缺陷重新分布和双肖脱基势垒有关.     

光谱学方法研究介质阻挡沿面放电辉光模式的电场分布

利用介质阻挡沿面放电装置,在低气压空气中实现了辉光放电模式。利用光电倍增管对放电发光信号进行检测,发现外加电压每半周期出现一个发光脉冲,并且正负半周期的光脉冲是不对称的。利用Photoshop软件处理放电的照片,研究发现平行于高压电极不同位置的发光强度基本相同,然而距离高压电极越远,发光强度减小。放电中总电场由外加电场和电介质积累的壁电荷电场共同决定,确定该电场具有重要意义。通过分析放电的发射光谱中N+₂(B 2Σ+_u→X 2Σ+_g)谱线391.4 nm和N₂的第二正带系(C 3Π_u→B 3Π_g)谱线337.1 nm的比值,可以定性地说明电场的分布。研究发现电场在高压电极附近较大而远离高压电极处较小。这些研究结果对沿面放电的数值模拟和工业应用具有重要的价值。     

Local microstructural analysis for Y_2O_3/Eu~(3+)/Mg~(2+) nanorods by Raman and photoluminescence spectra under high pressure

In this paper, we investigate the Raman and photoluminescence spectra of Y_2O_3/Eu~(3+) and Y_2O_3/Eu~(3+)/Mg~(2+) nanorods under high pressures using 514-nm and 532-nm laser light excitation. We observe transitions from the initial cubic phase to amorphous at pressures higher than 24 GPa for both Y_2O_3/Eu~(3+) and Y_2O_3/Eu~(3+)/Mg~(2+) nanorods. In addition, Y_2O_3/Eu~(3+) and Y_2O_3/Eu~(3+)/Mg~(2+) nanorods exhibit different distorted states after the pressure has been raised to 8 GPa. The analyses of intensity ratios, I_(0-2)/I_(0-1) from ~5D_(0–)~7F2_to~5D_(0–)~7F_1and I_(0-2)A/B of ~5D_(0–)7F_2 transitions indicate that Y_2O_3/Eu~(3+)/Mg~(2+) nanorods exhibit stronger local micro-surrounding characteristics for Eu~(3+) ions in a pressuremodulated crystal field. The doped Mg2+ion results in reducing the crystal ionicity in the distorted lattice state under high pressures. The use of doped ions as an ion modifier can be applied to the study of small local microstructural changes through Eu~(3+) luminescence.