棒-环电极大气压等离子体射流的光谱特性

通过设计新型的交流电压激励的氩气等离子体射流,在棒电极的上游与下游区域均产生了大气压非平衡态等离子体羽。该射流与平行场射流和交叉场射流不同,它的电场与气流方向的夹角可以在一定范围内变化。结果表明,随着外加电压或夹角的增加,上游羽的长度增加而下游羽的长度减小。利用光学和电学的方法,研究发现随着外加电压的增加,上下游放电脉冲的个数均增加。利用放电的光学发射谱,发现上游羽有Ar和OH的谱线,而下游羽除了Ar和OH的谱线外,还可以观察到N₂的谱线。并且下游羽的谱线强度比上游羽的略高。基于碰撞辐射模型,通过谱线强度比的方法研究了上下游羽的电子密度和电子激发温度。结果表明上下游羽的电子密度随着外加电压的增加而增加。上下游羽的电子激发温度也随着外加电压的增加而增加。并且,在同一外加电压时下游羽的电子密度和电子激发温度均比上游羽的高。此外,利用OH发射光谱研究了上下游羽的气体温度,发现下游羽的气体温度也比上游羽的略高。     

大气压氩气射流等离子体的光谱特性研究

等离子体喷枪是一种重要的等离子体源,已成为近几年低温等离子体研究的一个重要课题。本文利用钨针-钨丝网电极制作了直流喷枪装置,在大气压空气中产生了稳定的等离子体羽,并采用发射光谱的方法,对等离子体羽的等离子体参数进行了研究。在钨针电极与钨丝网电极之间放出耀眼的白光,钨丝网电极出口的气流下游有火苗形状的等离子体羽喷出。在电压保持不变的条件下(13.5 kV),等离子体羽长度随气体流量增加而增大;在气体流量保持不变的条件下(10 L·min-1),羽长度随外加电压的增大而增大。在气体流量一定的条件下,放电电压和放电电流呈反比例关系,即电压随着电流的增大而减小,说明放电属于辉光放电。采集了该喷枪在300～800 nm范围内的放电发射光谱,通过玻尔兹曼方法对放电等离子体电子激发温度进行了测量。结果表明,电子的激发温度随外加电压的增大而降低,随着工作气体流量的减小而升高。利用放电的基本理论对上述现象做了解释。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。     

三种电极的大气压氩等离子体射流光学特性

采用铜片-单匝线圈电极、螺旋缠绕电极和双铜片电极3种结构的放电装置,以氩气作为工作气体,在正弦波激励下获得了大气压等离子体射流。利用电学方法测量了放电电流以及电荷量,并对放电脉冲和放电功率进行了研究;利用发射光谱法对射流的等离子体参量进行了空间分辨测量,并根据ArⅠ 763.5 nm和Ar Ⅰ 772.4 nm的光强计算了电子激发温度。结果发现：在外加电压的正负半周期内,电流脉冲的个数和幅值呈现非对称的变化趋势;随着外加电压的增加,3种结构电极的放电功率从1.7 W逐渐增加到6.0 W;在相同的外加电压情况下,电极面积越小,等离子体射流的长度越长;3种等离子体射流的电子激发温度在1 348.5~3 212.1 K之间,并且随着气体流量的增加,各位置的电子激发温度总体上呈下降趋势,而等离子体的电子密度呈上升趋势。实验结果表明：外加电压对放电功率有一定影响;射流长度与电极面积有关;气体流量对电子激发温度和电子密度的空间分布起重要作用。     

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。     

Model of pulsed electric discharge expansion in dense gas taking into account electron and radiative thermal conductivities. I. Expansion mechanism

Using an ionization sensor, it was found that weakly ionized plasma with an ionization degree larger than 10^?6 is formed under exposure to UV radiation of a high-current pulsed electric discharge in gas (air, nitrogen, xenon, and krypton) at atmospheric pressure at a distance of ～1.2–2.5 cm from the discharge boundary. It was shown that the structure of such discharge includes, in addition to the discharge channel, a dense shell and a shock wave, also a region of weakly ionized and excited gas before the shock wave front. The mechanism of discharge expansion in dense gas is ionization and heating of gas involved in the discharge due to absorption of the UV energy flux from the discharge channel and the flux of the thermal energy transferred from the discharge channel to the discharge shell due to electron thermal conductivity.     

Model of pulsed electric discharge expansion in dense gas, taking into account electron and radiative thermal conductivities. IV. Limiting brightness of discharge radiation

Based on the relation between the radiation brightness B _R of the pulsed high-current electric discharge in dense gas (Xe, Kr, Ar, Ne, He, N₂, and air at atmospheric pressure and above) and its temperature, the dependence of the limiting brightness B _LIM of discharge channel radiation on ionization potentials of atoms of mentioned gases was obtained, and the condition under which the brightness saturation is achieved was determined. It was shown that this dependence is in agreement with experimental data of various researchers.     

Model of pulsed electric discharge expansion in dense gas taking into account electron and radiative thermal conductivities. II. Energy balance and equation

Using an ionization sensor, it was found that weakly ionized plasma with an ionization degree larger than 10⁻⁶ is formed under exposure to UV radiation of a high-current pulsed electric discharge in gas (air, nitrogen, xenon, and krypton) at atmospheric pressure at a distance of ∼1.2–2.5 cm from the discharge boundary. It was shown that the structure of such discharge includes, in addition to the discharge channel, a dense shell and a shock wave, also a region of weakly ionized and excited gas before the shock wave front. The mechanism of discharge expansion in dense gas is ionization and heating of gas involved in the discharge due to absorption of the UV energy flux from the discharge channel and the flux of the thermal energy transferred from the discharge channel to the discharge shell due to electron thermal conductivity.     

大气压直流微等离子体射流研究

介绍了一种结构简单、 制作方便的微米量级大气压等离子体射流。这种微等离子体射流由直流电源驱动,可在多种工作气体(如Ar,He,N₂等)中实现大气压放电,产生高电流密度的辉光放电。为了确定微等离子射流产生的激发物种成分,测量了以Ar和N₂为工作气体的等离子体发射光谱。利用发射光谱相对强度比值法测量了氩气微等离子体射流的电子激发温度。实验显示,其电子激发温度约为3 000 K,这远低于大气压等离子体炬的电子激发温度。利用N₂的二正带发射光谱得到微等离子体的振动温度约为2 500 K;利用其电学参数估算电子密度在1013cm-3量级。利用此微等离子体射流进行了普通打印纸表面处理的应用实验。结果显示,这种微等离子体射流能够明显的提高普通打印纸的亲水性。     

Spectroscopic diagnostics of barrier discharge plasmas in mixtures of zinc diiodide with inert gases

The spectral characteristics of the emission of gas discharge atmospheric pressure plasmas in mixtures of zinc diiodide vapor with inert gases (He, Ne, Ar, Kr, and Xe) are investigated. The formation of a gas discharge plasma and the excitation of the components of a working mixture were performed in a high-frequency (with a repetition frequency of sinusoidal voltage pulses of 100 kHz) barrier discharge. The gas discharge emission was analyzed in the spectral range 200–900 nm with a resolution of 0.05 nm. Emission bands of ZnI(B-X) exciplex molecules and I₂* excimer molecules, lines of inert gases, and emission bands of XeI* exciplex molecules (in Xe-containing mixtures) were revealed. It is ascertained that the strongest emission of ZnI* molecules is observed in ZnI₂/He(Ne) mixtures. The regularities in the spectral characteristics of the gas discharge plasma emission are considered.     

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。     

Theoretical analysis of ion kinetic energies and DLC film deposition by CH4＋ Ar （He） dielectric barrier discharge plasmas

The kinetic energy of ions in dielectric barrier discharge plasmas are analysed theoretically using the model of binary collisions between ions and gas molecules. Langevin equation for ions in other gases, Blanc law for ions in mixed gases, and the two-temperature model for ions at higher reduced field are used to determine the ion mobility. The kinetic energies of ions in CH4 ＋ Ar（He） dielectric barrier discharge plasma at a fixed total gas pressure and various Ar （He） concentrations are calculated. It is found that with increasing Ar （He） concentration in CH4 ＋ Ar （He） from 20% to 83%, the CH4＋ kinetic energy increases from 69.6 （43.9） to 92.1 （128.5）eV, while the Ar＋ （He＋） kinetic energy decreases from 97 （145.2） to 78.8 （75.5）eV. The increase of CH4＋ kinetic energy is responsible for the increase of hardness of diamond-like carbon films deposited by CH4 ＋ Ar （He） dielectric barrier discharge without bias voltage over substrates.     

Power Consideration for Pulsed Discharges in Potassium Seeded Argon

Minimization of energy consumed in plasma generation is critical for applications, in which a large volume of plasmas is needed. We suggest that a high electron density atmospheric pressure plasmas can be generated by pulsed discharges in potassium seeded argon at an elevated temperature with a very small power input. The ionization efficiency and power budget of pulsed discharges in such plasmas are analytically studied. The results show that ionization efficiency of argon, especially at small reduced electric field E/N （the ratio of the electric field to the gas number density）, is improved effectively in the presence of small amount of potassium additives. Power input of pulsed discharge to sustain a prescribed average level of ionization in potassium seeded argon is three orders of magnitude lower than that in pure argon. Further, unlike in pure argon, it is found that very short high-voltage pulses with very high repetition rates are unnecessary in potassium seeded argon. A pulse with lOOns of pulse duration, 5kHz of repetition rate, and 2Td （1 Td = 1 × 10^-21 Vm^2） of E/N is enough to sustain an electron density of 10^19 m^-3 in 1 arm 1500K Ar＋0.1% K mixture, with a very small power input of about 0.08 × 10^4 W/m^3.     

Changes in Properties of Dielectric Barrier Discharge Plasma Jets for Different Gases and for Insulating and Conducting Transfer Plates

Dielectric barrier discharge (DBD) plasma jets have been studied extensively in recent years because of its wide range of applications. DBD plasmas can be produced using many different gases and can be applied to a broad variety of surfaces and substrates. This work provides comparisons of DBD plasmas generated using argon (Ar), helium (He), and nitrogen (N₂), as well as their mixtures with water vapor in order to know how some plasma properties are affected by the use of different gases. All plasmas were studied in two different conditions: using a transfer plate made of a conductive material and using a transfer plate made of an insulating one. It was observed that the process of Penning ionization of nitrogen molecules by direct collisions with metastable atoms and molecules is evident and significant only in plasmas that use He as the working gas, which means that He atoms in metastable states have greater ability to transfer energy to molecules of nitrogen in the plasma. The collisions of metastable He with N₂ molecules determine the vibrational temperature (T _vib) values in He plasmas, while in Ar and N₂ plasmas, the T _vib values are determined mainly by collisions of electrons with N₂ molecules. It was noticed that the use of an insulating or a conducting transfer plate as the sample holder affects the results of adhesion between poly(dimethylsiloxane) samples, and it is mainly due to the differences in the plasma power, with a higher plasma power leading to better adhesion.     

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。     

不同电极结构下介质阻挡放电电离特征的试验研究

由于具有工作气压高、放电均匀等特点,大气压介质阻挡放电成为近年来非平衡等离子体领域研究的主要技术。电极结构是电离特性的主要影响因素之一,因此,通过电极结构优化来改善电离特性,对等离子体放电设备的应用领域拓展及性能优化至关重要。为改善大气压介质阻挡放电的电离特性,产生高活性、高均匀性的低温等离子体,基于自主设计的同轴介质阻挡放电装置进行了不同电极结构的电离试验及参数诊断;在一个标准大气压、放电频率11.4 kHz、放电峰值电压5.4～13.4 kV条件下进行了氩气电离试验;采用原子发射光谱法（AES）对氩等离子体谱线的激发、分光进行了检测分析;研究了螺纹电极、齿状电极、圆柱电极放电的特征光谱参数及外施电压对介质阻挡放电特征参数的影响。结果表明,齿状电极放电所形成等离子体的放电强度更大且放电效果显著,电子平均能量利用率低,电子激励温度弱于圆柱电极;圆柱电极放电强度较弱,但易形成大面积均匀性等离子体;大气压环境下电子激励温度不因外源电压的升高而单调递加,这表明通道内微放电的主要特征并不依赖于外施电压的供给,而是取决于电极结构、气体组份、气体压强;增大外施电压仅能增加单位时间内微放电的数量,经整合电子激励温度可达3 500 K,符合典型的低温等离子体特征。     

Model of pulsed electric discharge expansion in dense gas taking into account electron and radiative thermal conductivity. III. Limit discharge temperature

Based on the energy conservation law for the shell of a pulsed high-current electric discharge in dense gas (Xe, Kr, Ar, Ne, He, N₂, air) an equation for the relative temperature of the discharge channel was derived taking into account electron and radiative thermal conductivities and the energy expended to ionization of gas involved in the discharge. The condition under which the limit channel temperature T _LIM is achieved was determined by solving this equation, and the universal dependence between the temperature T _LIM and the ionization potentials of the above gas atoms was obtained. It was shown that this universal dependence is in agreement with experimental data.     

Shielding gas influences on laser weldability of tailored blanks of advanced automotive steels

The effects of shielding gas types and flow rates on CO₂ laser weldability of DP600/TRIP700 steel sheets were studied in this work. The evaluated shielding gases were helium (He), argon (Ar) and different mixtures of He and Ar. Weld penetration, tensile strength and formability (Erichsen test) of laser welds were found to be strongly dependent upon the shielding gas types. The ability of shielding gas in removing plasma plume and thus increasing weld penetration is believed to be closely related to ionization potential and atomic weight which determine the period of plasma formation and disappearance. It was found that the higher helium shielding gas flow rate, the deeper weld penetration and the lower weld width.     

极板电压与间距对大气压射频氩等离子体放电参数的影响

 基于1维流体力学模型,对大气压射频裸露金属电极氩气放电过程进行了研究。模型中考虑了氩等离子体放电过程中主要发生的激发和电离等7个反应过程,对等离子体反应产生的主要粒子,包括电子、氩原子离子Ar⁺、氩分子离子Ar2⁺和氩激发态Ar^*等,建立连续性方程、动量方程和电流平衡方程。分析了极板电压、极板间距对上述粒子数密度分布的影响。给出了电子,Ar⁺,Ar^*和Ar₂⁺密度随极板电压及间距变化的时空演化过程。得出极板电压或极板间距的改变会使放电空间的电场发生改变,对应一定的极板间距,极板电压有一个最佳值,极板电压和间距的变化会使对应的极板间有一个最佳电场值,而对应最佳电场有一个等离子体气体间最佳反应系数,从而使放电空间粒子数密度发生改变。     

Experimental studies of the Bohm criterion in a two-ion-species plasma using laser-induced fluorescence

The Bohm criterion is studied experimentally in the case of a two ion species plasma. Measurements are carried out in Ar and Ar+He plasmas (PA(r I) approximately 0.1 mtorr, 0< or =P(He)/P(Ar)< or =25, and 0< or =n(+)(He)/n(e)< or =0.5, T(e)< or =2 eV) created in an unmagnetized dc hot filament discharge confined by surface multidipole magnetic fields. Laser-induced fluorescence (LIF) measurements of Ar II ion velocity distribution functions (ivdfs) within the presheath up to the sheath edge show that the ions reach the sheath edge traveling faster than their individual Bohm speed by more than 75%, approaching a speed equal to the ion sound speed of the system.     

Electromagnetic interaction between local surface plasmon polaritons and an atmospheric surface wave plasma jet

We analyze the electromagnetic interaction between local surface plasmon polaritons （SPPs） and an atmospheric surface wave plasma jet （ASWPJ） in combination with our designed discharge device. Before discharge, the excitation of the SPPs and the spatial distribution of the enhanced electric field are analyzed. During discharge, the critical breakdown electric field of the gases at atmospheric gas pressure and the surface wave of the SPPs converted into electron plasma waves at resonant points are studied. After discharge, the ionization development process of the ASWPJ is simulated using a two- dimensional fluid model. Our results suggest that the local enhanced electric field of SPPs is merely the precondition of gas breakdown, and the key mechanism in maintaining the discharge development of a low-power ASWPJ is the wave-mode conversion of the local enhanced electric field at the resonant point.