介质阻挡放电中单晶胞白眼斑图的光谱研究

Study on A White-Eye Pattern in Dielectric Barrier Discharge by Optical Emission Spectrum

在介质阻挡放电系统中,空气和氩气混合气体的实验条件下,第一次实现了只具有一个单元结构的白眼斑图。该斑图的结构从中心位置向外依次为:中心点,围绕中心点的环和环外六个点。由于出现该单晶胞白眼斑图时的电压较低,而本实验采用的水电极中的水的比热容大,具有良好的吸热性,这使斑图在放电过程中放电气隙间的气体的温度没有升高,并且放电现象没有发生变化。因此在实验过程中,单晶胞白眼斑图在长时间放电的情况下并没有使其等离子体状态发生改变。由普通照相机所拍摄的图片可以看到,单晶胞白眼斑图的中心点,围绕中心点的环和环外六个点的亮度有明显不同。在不同压强下该斑图的稳定性有所不同,并且中心点,围绕中心点的环和环外六个点的亮度随压强的变化有所不同。鉴于此,本实验采用了发射光谱法,研究了单晶胞白眼斑图中不同位置处(中心点、环及外围六个点)的等离子体温度随压强的变化关系。其中,分子振动温度使用氮分子第二正带系(C3Πu→B3Πg)的发射谱线来计算;电子激发温度利用氩原子763.26nm(2P6→1S5)与772.13nm(2P2→1S3)两条谱线强度值进行比较的方法进行研究;电子密度利用氩原子696.57nm(2P2→1S5)谱线的展宽来测量。发现在同一实验条件下,单晶胞白眼斑图的中心点的电子激发温度、电子密度和分子振动温度均最低,环外六个点相应的电子激发温度、电子密度和分子振动温度次之,环相应的电子激发温度、电子密度和分子振动温度均最高;随着气体压强从40kPa增大到60kPa,单晶胞白眼斑图不同位置处的电子密度增高但分子振动温度和电子激发温度均降低。本实验结果有助于进一步研究自组织斑图形成的机制。

The white-eye pattern was firstly observed and investigated in a dielectric barrier discharge system in the mixture of argon and air whose content can be varied whenever necessary,and the study shows that the white-eye cell is an interleaving of three different hexagonal sub-structures：the center spot,the halo,and the ambient spots.The white-eye pattern is observed at a lower applied voltage.In this experiment,the heat capacity of water is high so that the water in water electrode is good at absorbing heat.In the process of pattern discharging the gas gap didn＇t increase its temperature,and the discharging phenomenon of this pattern has not changed.The temperature of the water electrodes almost keeps unchanged during the whole experiment,which is advantageous for the long term stable measurement.Pictures recorded by ordinary camera with long exposure time in the same argon content condition show that the center spot,the halo,and the ambient spots og the white-eye pattern have different brightness,which may prove that their plasma states are different.And,it is worth noting that there are obvious differences of brightness not only on the center spot,the halo,and the ambient spots at the same pressure but also at the different pressure,which shows that its plasma state also changed with the variation of the pressure.Given this,in this experiment plasma temperatures of the central spot,halo,and ambient spots in a white-eye pattern at different gas pressure were studied by using optical emission spectra.The molecular vibration temperature is investigated by the emission spectra of nitrogen band of second positive system（C3Πu → B3Πg）.The electron excitation temperature is researched by the relative intensity ratio method of spectral lines of ArⅠ763.51nm（2P6→1S5）and ArⅠ772.42nm（2P2→1S3）.The electronic density is investigated by the broadening of spectral line 696.5nm.Through the analysis of experimental results,it is found that the molecular vibration temperature,electron excitation temperature and electronic density of the central spot are lowest,and the plasma parameters of the ambient spots are second,while the plasma parameters of the halo are highest at the same condition.The molecular vibration temperature and the electron excitation temperature of the three different parts of the pattern（central spot,halo,and ambient spots）decrease with the pressure increasing from 40 to 60kPa,but the electronic density increases.These results are of great important to the formation mechanism of the patterns in dielectric barrier discharge.