【作者】 杨晨光；

【导师】 左都罗；

【作者基本信息】 华中科技大学 ， 物理电子学， 2013， 博士

【摘要】 大气压纳秒脉冲放电作为一种有效的大气压非平衡等离子体产生方式,被广泛的应用于高能脉冲CO₂与准分子气体激光器泵浦、等离子体平板显示、等离子体医疗、环境治理、纳米材料合成、流动控制、等离子体隐身等诸多民用和军事领域。而且相对于其他放电方式,它还有紫外辐射以及氧原子、臭氧产率高,等离子体密度高,低能耗等优点。本论文将分从数值模拟与实验两个方面研究大气压纳秒脉冲放电等离子体。数值模拟研究通过自主编程,建立了一套适用于大气压纳秒脉冲放电模拟的PIC-MCC模型。为适应大气压纳秒脉冲放电的特点,该模型在传统PIC-MCC方法的基础上采用了隐式PIC格式和基于能量的带电粒子重整化方法。并针对大气压下电子极高的碰撞频率,提出了多MCC过程的处理方法。使用上述PIC-MCC模型,首先对大气压下氩气典型参数纳秒脉冲放电过程进行了详细的数值模拟研究。给出了等离子体特征物理量的的时间演化与空间分布结果。这些结果,证实了本论文PIC-MCC模型的准确性。依据有效电子温度的变化规律将大气压纳秒脉冲放电过程分成七个阶段,分析了各个阶段的等离子体的演化过程及形成机理。在此基础上,模拟二次电子发射率、放电电压、脉冲上升时间、初始电子密度以及中性气体温度这些放电参数对等离子体演化的影响。发现二次电子发射率在数纳秒脉冲范围内对等离子体的影响可以忽略不计；放电电压决定着最终的电子密度与最大电子温度；慢上升沿的脉冲放电电子密度、电子温度的增速也会减慢；初始电子密度仅影响等离子体鞘层形成的时间；中性气体温度影响电子密度增速、最大电子温度及鞘层形成时间。最后比较并深入分析了氦气、氖气放电与氩气放电的异同。由于正离子荷质比和碰撞截面的与氩气的不同不同,氦气、氖气放电鞘层附近电子峰值明显,电子能量分布在鞘层形成之前近似服从麦克斯韦分布。三者的整体演化过程和鞘层形成后的电子能量分布均相似。实验研究工作包括纳秒脉冲放电中性粒子温度测量与阴极鞘层能量注入比例测量两方面内容。首先详述了利用N2分子第二正带系光谱转动结构拟合中性气体温度的方法。在此基础上,分别使用低分辨率、高分辨率光栅光谱仪测量了实验室自制放电装置的时间分辨发射光谱。将低分辨率光谱强度与放电波形对照,发现在放电击穿前就有较强的发光。由高分辨率光谱观测结果可计算出两个时间段,四条振动带（0-0、0-1、0-2、0-3）的转动温度。对于方差可接受的拟合结果,同一时刻拟合的转动温度基本一致。为研究阴极鞘层注入能量比例,本论文提出了一种利用纳秒脉冲放电后阴极鞘层激波波速测量阴极鞘层温度、阴极鞘层与正柱区注入能量密度比的新方法。首先利用ICCD相机采集放电后时间序列的流场干涉图。然后从图像中提取激波波前位置并拟合阴极激波波速,进而计算出不同放电电压及工作气体气压下的阴极鞘层温度、阴极鞘层与正柱区注入能量密度比。阴极鞘层温度和阴极鞘层、正柱区注入能量密度比分别由放电过程中的总的注入能量密度与脉冲放电的击穿时间决定。这些实验工作直接或间接的反映了纳秒脉冲放电的过程以及相应的规律,为系统的进行更小空间尺度、更短时间尺度的大气压纳秒脉冲放电实验研究提供了方法与技术手段。更多还原

【Abstract】 As an effective method to generate atmospheric-pressure non-equilibrium plasma, atmospheric-pressure nanosecond-pulsed discharge has promising applications in pumping pulsed CO2laser and excimer laser, plasma display panel, plasma medicine, pollution control, nanofrabrication, flow control, plasma stealth, etc. Compared with other generation methods, it has higher yields of UV radiation, oxygen atom and ozone, higher plasma density and peak current, and lower energy comsuption. In this thesis, atmospheric pressure nanosecond pulsed discharge is investigated experimentally and simulatively.In simulation study, a PIC-MCC modeling, which is suitable for atmospheric-pressure nanosecond-pulsed discharge, is set up. In order to adapt the characteristics of atmospheric-pressure nanosecond-pulsed discharge, the special methods, implicit PIC algorithm and renormalization algorithm based on energy, have been utilized in the modeling. In addition, multiple MCC processes method is put forward to deal with the extremely high collision frequency of the electron in atmospheric pressure.Firstly, using the PIC-MCC modeling, the process of atmospheric-pressure argon nanosecond-pulsed discharge with typical parameters is studies in detail. The evolutions and distrubutions of plasma characteristics are reported. These results confirm the accuracy of the PIC modeling. Based on the evolution of effective temperature, the discharge process can be divided into seven phases, and the evolution and mechanism of the plamsa in seven phases are analysed.On the basis of discharge process analysis, the impact of discharge parameters, such as second electron emission ratio, plateau voltage, pulse rise time, initial charged particle density, and neutral gas temperature are studied simulatively. It is found that the impact of second electron emission ratio can be ignored in several nanoseconds pulse, and the plateau voltage in the pulse waveform is a major factor controlling the final charged particle density in the plasma bulk. The growth of electron density and effective electron temperature is slowing with longer pulse rise time, and the initial charged particle density can only affect the built-up time of cathode sheath. What is more, the neutral gas temperature influences the growth speed of electron density, maximum effective electron temperature, and the built-up time of cathode sheath. Finally, the similarities and differences of the nanosecond-pulsed discharges in three different noble gases (helium, neon and argon) are compared and analysed. The differences of specific charge and cross section lead to the quasi-Maxwell energy distribution of electron before the cathode sheath formation, and the electron peak near the cathode sheath in helium and neon. However, the evolution processes and the electron energy distributions after the cathode sheath formation are similar in these three gases.The experimental study contains the measurements of neutral gas temperature and energy injection ratio between cathode sheath and plasma bulk in atmospheric-pressure nanosecond-pulse discharge.In order to measure gas temperature during the discharge, the method of fitting plasma emission molecular spectra is adopted. Firstly, the nitrogen second positive spectra system is analyzed. On this basis, the time-resolved emission spectra are measured with low and high resolution grates. Compareing the spectra radiation intensity with the discharge voltage waveform, it can be found that high intensity radiation has appeared before discharge breakdown. The rotational temperatures of four vibration bands (0-0,0-1,0-2and0-3) in two different times can be fitted by the high resolution spectra, which coincide with each other.In order to study the injection energy ratio of cathode sheath, a new method, which using cathode shock wave velocity, is put forward to measure the cathode sheath temperature and the energy injection ratio between cathode sheath and plasma bulk. Firstly, the time sequence flow field interferograms after discharge are acquisited by the ICCD camera. After that, the cathode shock wave velocities in different discharge conditions are extracted from these interferograms to calculate the cathode sheath temperature and the energy injection ratio. It is found that the cathode sheath temperature and the energy injection ratio are determined by the specific energy deposition and the breakdown delay time respectively.These experiment studies reflect the process and law of the nanosecond-puled discharge, and offer the methods for systematic experimental study of atmospheric-pressure nanosecond-pulsed discharge with less special and temporal scale.更多还原