介质阻挡放电中体放电和沿面放电的光谱线形研究

在放电间隙较大的介质阻挡放电中,利用高速照相机,同时观察到了体放电(VD)和沿面放电(SD)。采用光谱法,研究了VD和SD的光谱线形随放电参数的变化。在氩气介质阻挡放电中,测量了VD和SD的Ar Ⅰ(2P₂→1S₅)谱线展宽和频移随气压及放电间隙的变化。结果发现：SD的展宽和频移均比VD的大,说明SD的电子密度高于VD的电子密度;随着压强从40 kPa增大到60 kPa,VD和SD的谱线展宽及频移均增加,表明它们的电子密度均随压强的增大而升高;随着d值从3.8 mm增大到4.4 mm,VD和SD的谱线展宽也增加,反映它们的电子密度均随d值的增大而增加。     

针-板和针-水电极大气压直流辉光放电的光谱特性

利用光谱学方法,对针-水电极和针-板电极直流辉光放电特性进行了比较研究。结果发现两种装置产生的放电都有明显的分区现象, 从阴极到阳极分别为负辉区、阴极暗区、正柱区和阳极辉区。针-板电极放电中可以清晰地观测到阳极暗区, 而针-水电极放电阳极暗区不明显。对比两种放电的伏安特性曲线,发现放电电压均随电流增大而减小,但相同电流下针-水电极间的电压大于针-板电极间的电压。由于伏安特性具有负斜率,且放电电流密度介于10-5～10-4 A·cm-2,说明两种装置中的放电均处于正常辉光放电阶段。在正常辉光放电的范围内比较两种放电的发射光谱, 发现发射光谱中都包含N₂的第二正带系(含波长为337.1 nm的谱线)和N+₂的第一负带系(含波长为391.4 nm的谱线),但相对强度不同。利用光谱学方法对放电发射谱的谱线强度比I_391.4／I_337.1和振动温度进行了空间分辨测量,发现相同位置处针-水电极放电的谱线强度比要比针-板电极放电的大,并且相同位置处针-水电极放电的振动温度高。     

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.     

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。     

大气压He-Ar射频容性放电Ar亚稳态粒子数密度

利用发射光谱法测量大气压He-Ar混合气体射频容性放电中的Ar亚稳态1s5(3s23p54s［3/2］2)粒子数密度。在不同的放电功率和气体组分下测量放电等离子体中的重要参数:气体转动温度、电子激发温度和Ar亚稳态1s5粒子数密度。结果表明:气体温度在不同放电功率及Ar气压在5103 Pa以内时变化不大,范围为300~350 K;电子激发温度随着放电功率的增加而增加,并且在Ar气压为4103 Pa时最大,在放电功率为70 W时达到0.58 eV;1s5粒子数密度随着放电功率以及电子激发温度的增加而增加,在放电功率为70 W、Ar气压为4103 Pa时达到1.53109 cm-3。     

不同时空结构的四边形放电斑图等离子体参量研究

采用发射光谱法,研究了不同时空结构四边形斑图的等离子体参量。实验发现,在低气压区和高气压区,四边形斑图表现出不同的时空结构。利用N₂分子第二正带系的六条谱线强度计算了分子振动温度;利用第一负带系N+₂(391.4 nm)与第二正带系N₂(394.1 nm)谱线强度比,研究了电子能量的变化;利用Ar原子696.54 nm谱线的展宽和频移来反映电子密度;利用Ar原子特征谱线强度比法计算了电子激发温度。结果表明：低气压区四边形斑图的分子振动温度、电子激发温度和电子平均能量均大于高气压区四边形斑图,而电子密度小于高气压区四边形的电子密度。     

电子助进化学气相沉积金刚石中的光发射谱特性

采用蒙特卡罗方法,对以CH₄/H₂为源料气体的电子助进化学气相沉积(EACVD)金刚石中的氢原子(H_α, H_β, H_γ)、碳原子C(2p3s2p2∶λ=165.7 nm)以及CH(A2Δ→X2Π∶λ=420～440 nm)的光发射过程进行了模拟,气体温度随空间的变化采用温度梯度变化,研究了不同反应室气压及衬底温度下的光发射谱特性。结果表明,不同衬底温度下各谱线强度均随气压的增大先增大后减小; 当气压较低时,谱线强度随衬底温度的增大而减少,而气压较高时,谱线强度随衬底温度的增大而增大。     

Ar/CH4等离子体射流发射光谱诊断研究

为了更加深入的研究大气压条件下Ar/CH₄等离子体射流的放电机理和其内部电子的状态,通过自主设计的针-环式介质阻挡放电结构,在放电频率10 kHz、一个大气压条件下产生了稳定的Ar/CH₄等离子体射流,并利用发射光谱法对其进行了诊断研究。对大气条件下Ar/CH₄等离子体射流的放电现象及内部活性粒子种类进行诊断分析,重点研究了不同氩气甲烷体积流量比、不同峰值电压对大气压Ar/CH₄等离子体射流电子激发温度、电子密度以及CH基团活性粒子浓度的影响规律。结果表明,大气压条件下Ar/CH₄等离子体射流呈淡蓝色,在射流边缘可观察到丝状毛刺并伴有刺耳的电离声同时发现射流尖端的形态波动较大;通过发射光谱可以发现Ar/CH₄等离子体射流中的主要活性粒子为CH基团,C,CⅡ,CⅢ,CⅣ,ArⅠ和ArⅡ,其中含碳粒子的谱线主要集中在400~600 nm之间,ArⅠ和ArⅡ的谱线分布在680~800 nm之间;可以发现CH基团的浓度随峰值电压的增大而增大,但CH基团浓度随Ar/CH₄体积流量比的增大而减小,同时Ar/CH₄等离子体射流中C原子的浓度随之增加,这表明氩气甲烷体积流量比的增大加速了Ar/CH₄等离子体射流中C-H的断裂,因此可以发现增大峰值电压与氩气甲烷体积流量比均可明显的加快甲烷分子的脱氢效率,但增大氩气甲烷体积流量比的脱氢效果更加明显。通过多谱线斜率法选取4条ArⅠ谱线计算了不同工况下的电子激发温度,求得大气压Ar/CH₄等离子体射流的电子激发温度在6 000~12 000 K之间,且随峰值电压与氩气甲烷体积流量比的增大均呈现上升的趋势;依据Stark展宽机理对Ar/CH₄等离子体射流的电子密度进行了计算,电子密度的数量级可达1017 cm-3,且增大峰值电压与氩气甲烷体积流量比均可有效的提高射流中的电子密度。这些参数的探索对大气压等离子体射流的研讨具有重大意义。     

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。     

离子分子束源的浓度调制光谱研究

建立了一套交流放电产生离子分子束源的装置,以N₂为例,束流中N＋₂的发射谱强度远大于N₂的发射谱强度,N+₂(B)/N₂(C)高达6∶1。根据其发射谱,对交流放电过程和浓度调制光谱进行了测量研究,并计算了离子分子激发态振动温度和转动温度,分别为3 310和282 K。     

Measurements of argon metastable density using the tunable diode laser absorption spectroscopy in Ar and Ar/O_2

Densities of Ar metastable states 1s_5 and 1s_3 are measured by using the tunable diode laser absorption spectroscopy(TDLAS) in Ar and Ar/O2 mixture dual-frequency capacitively coupled plasma(DF-CCP). We investigate the effects of high-frequency(HF, 60 MHz) power, low-frequency(LF, 2 MHz) power, and working pressure on the density of Ar metastable states for three different gas components(0%, 5%, and 10% oxygen mixed in argon). The dependence of Ar metastable state density on the oxygen content is also studied at different working pressures. It is found that densities of Ar metastable states in discharges with different gas components exhibit different behaviors as HF power increases. With the increase of HF power, the metastable density increases rapidly at the initial stage, and then tends to be saturated at a higher HF power. With a small fraction(5% or 10%) of oxygen added in argon plasma, a similar change of the Ar metastable density with HF power can be observed, but the metastable density is saturated at a higher HF power than in the pure argon discharge. In the DF-CCP, the metastable density is found to be higher than in a single frequency discharge, and has weak dependence on LF power. As working pressure increases, the metastable state density first increases and then decreases,and the pressure value, at which the density maximum occurs, decreases with oxygen content increasing. Besides, adding a small fraction of oxygen into argon plasma will significantly dwindle the metastable state density as a result of quenching loss by oxygen molecules.     

Intensity of Ar spectral lines in an Ar-O2 glow discharge

Measurements of relative intensities of spectral lines and of plasma parameters have been carried out in an Ar-O₂ d.c. glow discharge under the following conditions: gas pressures of 1, 2 and 3 torr and partial pressures for O₂ of 0, 0.01, 0.02, 0.05 and 0.1 torr. Many of the Ar line intensities decreased when O₂ was added, while some were enhanced. Enhancement of the 6677A and 7504A lines has been most notable. The number density of metastable Ar atoms is decreased when O₂ is added. Upon addition of O₂, the electron temperature is decreased and the electron density increased, except at a gas pressure of 1 torr; the electric field strength in the positive column is also increased.     

Power Absorption in High Power Microwave Discharges

Measurements on RF power absorption in microwave discharges at 2.45 GHz, at pressures from 1 to 30 Torr in N2 and from 1 to 500 Torr in Ar, are described. A linear slow-wave structure of the strapped-bar type was employed for coupling RF energy to the plasma. From measurements on the plasma volume and on the total power absorbed, the variation with gas pressure of the RF power density in the plasma was obtained. For an incident power of 1 kW, power densities as high as 2-3 W/cm3 over relatively large plasma volumes could be achieved. The experimental data were used to calculate the pressure dependence of the electron density in an argon plasma, for an incident power of 1 kW.     

Space resolved density measurements of argon and helium metastable atoms in radio-frequency generated He-Ar micro-plasmas

Space resolved concentrations of helium He* (³S₁) and argon Ar* (³P₂) metastable atoms in an atmospheric pressure radio frequency micro-plasma jet were measured using tunable diode laser absorption spectroscopy. Even small absorptions down to 10^-4 could be measured using lock-in technique. The absolute density of metastable atoms densities at different rf-power, flow rate and gas mixture was deduced from measured absorption rates. Metastable concentrations range from 10⁹ to 10¹¹ cm^-3. Analysis of spectral profiles provided the pressure broadening coefficients of both metastable atoms by helium. The spatial distribution of metastable atoms in the plasma volume was obtained for various discharge conditions. Density profiles between the electrodes reveal the sheath structure and reflect the plasma excitation distributions in the discharge volume. It reveals the dominance of the α-mode discharge.     

Numerical study on the characteristics of nitrogen discharge at high pressure with induced plasma

Based on the fluid theory of plasma, a model is built to study the characteristics of nitrogen discharge at high pressure with induced argon plasma. In the model, species such as electrons, N2+, N4+, Ar+, and two metastable states (N 2(A3∑u+), N2 (a1 ∑u-)) are taken into account. The model includes the particle continuity equation, the electron energy balance equation, and Poisson抯equation. The model is solved with a finite difference method. The numerical results are obtained and used to investigate the effect of time taken to add nitrogen gas and initially-induced argon plasma pressure. It is found that lower speeds of adding the nitrogen gas and varying the gas pressure can induce higher plasma density, and inversely lower electron temperature. At high-pressure discharge, the electron density increases when the proportion of nitrogen component is below 40%, while the electron density will keep constant as the nitrogen component further increases. It is also shown that with the increase of initially-induced argon plasma pressure, the density of charged particles increases, and the electron temperature as well as the electric field decreases.     

Numerical study of the effect of gas flow in low pressure inductively coupled Ar/N<Subscript>2</Subscript> plasmas

The effect of gas flow in low pressure inductively coupled Ar/N₂ plasmas operating at the rf frequency of 13.56 MHz and the total gas pressure of 20 mTorr is studied at the gas flows of 5–700 sccm by coupling the plasma simulation with the calculation of flow dynamics. The gas temperature is 300 K and input power is 300 W. The Ar fractions are varied from 0% to 95%. The species taken into account include electrons, Ar atoms and their excited levels, N₂ molecules and their seven different excited levels, N atoms, and Ar⁺, N⁺, N₂ ⁺, N₄ ⁺ ions. 51 chemical reactions are considered. It is found that the electron densities increase and electron temperatures decrease with a rise in gas flow rate for the different Ar fractions. The densities of all the plasma species for the different Ar fractions and gas flow rates are obtained. The collisional power losses in plasma discharges are presented and the effect of gas flow is investigated.     

An investigation of high fractions of metastable helium atoms

Penning type discharge was adopted to excite helium atoms. It is suitable for generating high density metastables at a range from 0.1 mTorr to 0.5 Torr. The highest metastable density of 3.5 x 1010 cm-3 was observed at a static gas pressure of 0.5 Torr. The highest fraction of metastables (N12s/Nhe) of 10-3 in a low gas pressure was obtained. The variation of the magnetic field strength on the discharge does not result in a significant density change of the metastable helium atoms. When no magnetic field was applied, no discharge took place.     

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。     

Optical characterization of atmospheric‐pressure plasma needle

The atmospheric‐pressure plasma needle is a promising source that can be used efficiently for different industrial applications. A radio frequency (RF) (13.56 MHz) generator was used to generate a He–O₂/Ar mixture plasma. The ground‐state oxygen atomic density [O] was calculated as a function of discharge parameters by “actinometry”. The Ar‐I (2p₁ → 1s₂) line at 750 nm and the O‐I (³P → ³S) line at 844 nm were used to estimate the [O] atomic density. The rotational temperature T _R of He–O₂/Ar mixture was measured from the rotational levels of the “first negative system” (FNS) by using the “Boltzmann plot”. The effect of discharge parameters on the atomic oxygen density [O] and the gas temperature was monitored. These results show that [O] density increases with RF power and O₂ concentration, but decreases with the gas flow rate. Whereas the gas temperature increases with increase in the input RF power, it decreases with increase in the gas flow rate and O₂ concentration in the mixture. Since the [O] atomic density contributes to plasma‐based biomedical applications, the proposed optimum conditions for plasma‐based decontamination of heat‐sensitive materials in the present study are 0.6% oxygen, 500 sccm flow rate, and 26 W RF power.