大直径射流的放电特性及其等离子体参数和活性粒子分布的光谱诊断

Study on Spectral Characteristics of Large Diameter Plasma Jet

大气压等离子体射流因其产生的等离子体羽富含活性粒子而在废水净化、元素探测、材料处理等方面具有良好的应用前景。通常等离子体羽的直径较小,限制了其工作效率。针对于此,利用交流电压激励大气压氩气等离子体射流,产生了直径约为14 mm的大尺度均匀等离子体羽。采用发射光谱法对电子密度和氧原子浓度随不同实验参数的变化关系进行了研究。光电测量结果表明,当外加电压峰值或氩气流量增加时,等离子体羽发光亮度增加。当电压峰值较低时,等离子体羽的上下游在电压的每个周期均有两个光脉冲信号,且上游光信号强度比下游的大。随着电压峰值增大,上下游等离子体羽的光信号强度都增大。当电压峰值较高时,上下游等离子体羽的光信号在每个电压周期呈现三个放电脉冲。不论每个电压周期放电脉冲数目多少,上下游等离子体羽的发光信号均具有同步性。利用光谱仪采集了300~800 nm范围内上下游等离子体羽的发射光谱,发现它们中均含有OH和N 2的谱线及ArⅠ和OⅠ谱线。其中,上游等离子体羽的ArⅠ谱线强度比下游的大,但OH和N 2的谱线强度比下游的小。利用谱线强度比对上、下游等离子体羽的电子密度进行了研究。结果表明,上游等离子体羽的电子密度在10^(14) cm^(-3)量级,高于下游羽的电子密度(10^(13)~10^(14) cm^(-3)量级)。并且,上游和下游等离子体羽的电子密度均随外加电压峰值的升高而增加,随氩气流量的增加而增加。利用光化线强度法,研究了下游羽中氧原子浓度随实验参数的变化规律。结果表明,氧原子浓度沿气流方向降低;对于一个等离子体羽,平均而言氧原子浓度随外加电压峰值升高而增加,随氩气流量增加而增加。对于以上实验现象,利用气体放电的基本理论进行了定性解释。

Atmospheric pressure plasma jet which can generate a plasma plume has good application prospects in wastewater purification,element detection,material treatment and so on,because the plasma plume is rich in abundant active species.In addition,the diameter of the plasma plume is usually small,which limits its work efficiency.In view of this,in this work,a large scale uniform plasma plume with a diameter of about 14 mm is produced in a plasma jet excited by an AC voltage in Ar at atmospheric pressure.The electron density and the concentration of oxygen atom as a function of different experimental parameters are studied by means of emission spectroscopy.Photoelectric measurement results show that the luminance of plasma plume increases when applied peak voltage or argon flow increases.There are two optical emission pulses per voltage cycle both in upstream and downstream regions of the plasma plume when the peak voltage is low,and the intensity of optical emission signal in the upstream is higher than that in the downstream.Both optical signal intensities of plasma plumes in the upstream and downstream increase with the increasing of peak voltage.There are three optical emission pulses at each voltage period in the upstream and downstream when the peak voltage is high.Regardless of the number of discharge pulses per voltage cycle,the optical emission signals for the upstream and downstream of the plasma plume are synchronous.OH,N 2,Ar,and OⅠspectral lines can be observed from emission spectrum in the range of 300~800 nm both in the upstream and downstream discharge collected by a spectrometer.The emission intensity of Ar upstream is higher than that downstream,while the emission intensity of OH and N 2 is lower than that in the downstream.The electron densities for the upstream and downstream of the plasma plume are measured by spectral line intensity ratio.The results show that the electron density in the upstream discharge is on the order of 10^(14) cm^(-3),which is higher than that in the downstream plume(10^(13)~10^(14) cm^(-3)).In addition,the electron densities of the plasma plume increase with the increase of peak voltage and argon flow both upstream and downstream.In addition,The variations of concentration of oxygen atom with different experimental parameters are studied by using optical actinometry.It is shown that the concentration of oxygen atom decreases along the flow direction.For the plasma plume,the oxygen concentration increases with the peak voltage and the argon flow,averagely.The experimental phenomena mentioned above are explained qualitatively based on the theories of gas discharge.