【作者】 熊青；

【导师】 卢新培；

【作者基本信息】 华中科技大学 ， 电气工程， 2013， 博士

【摘要】 大气压低温等离子体射流是近年来蓬勃发展的一种新型大气压低温气体放电技术，是目前国际上等离子体科学和技术领域的重要研究热点之一。大气压低温等离子体射流在开放空间中产生，由于其气体温度低、化学活性强、无污染等独特的技术优势，在众多领域（生物医学、材料、环境等）有着广阔的应用前景。本文以大气压低温等离子体射流为研究对象，在以下几个方面开展了研究工作：1.适合于生物医学领域的大气压低温等离子体射流发生装置的研制。（i）研制了两种适合于生物医学等需要低温处理领域的大气压低温等离子体射流发生装置，采用介质阻挡放电结构将高电压电极与放电区域、以及工作区域在空间上隔离，避免了电弧放电的产生以及提高了装置的使用安全性，产生的射流可长达11cm，这是当时国际上报道的最长等离子体射流，同时人体的手指能够直接安全地与等离子体射流接触；（ii）通过等效电路分析发现，其中一种射流发生装置在施加40kHz、峰值7kV交流电压时，射流与人体的手指接触时手指承受的电压在安全范围内（<36V），证实了该装置在临床医学应用的安全性；（iii）同时，基于多气流通道的结构，实现了同时产生多个等离子体射流的技术，有效地扩大了射流处理面积。2.等离子体射流长度的可控制性研究。通过改变放电条件，研究了外部空间的空气、电源参数（电压幅值、电压脉宽、频率）、工作气体流速等对等离子体射流长度的影响。（i）研究结果表明外部空间的空气对射流的延伸有明显的负面影响，在纯工作气体环境中产生的射流长度要远大于外部空间中的射流，分析发现主要是由于空气分子能够有效促使射流中储能粒子，例如激发态或亚稳态的He或Ar原子（工作气体为氦气或氩气）、以及高能电子的快速消失而导致；（ii）建立流体模型并模拟工作气体的流场发现，在层流状态下射流顶端的工作气体最低含量必须达到一定值时射流才能继续延伸，这导致了当射流顶端的工作气体含量低于产生等离子体的最低值时，升高施加电压幅值不能有效地增大射流的长度；（iii）通过流体模拟发现，工作气体流速对射流长度的影响可分为三个阶段，层流、层流向湍流转化、湍流阶段，射流长度在气流开始从层流向湍流状态转化时达到最大；（iv）通过分析不同阶段的等离子体射流长度，得到射流长度和喷嘴直径的比值，与气流雷诺数的分布趋势，该分布趋势有助于我们对射流发生装置的设计，以及在不同工作气体流速、不同喷嘴尺寸时对射流流场状态的预测以及射流长度的控制。3.等离子体射流产生机理的研究。采用高速拍摄以及时空分辨光谱技术对等离子体射流的产生过程进行了研究，获取了等离子体子弹的时空动态传播行为的详细信息。（i）研究发现等离子体子弹的传播速度与N+2391.4nm谱线强度在相近空间位置达到最大，表明等离子体子弹的传播速度直接与其中的电荷量相关；（ii）首次发现当等离子体子弹在接触一根空心绝缘介质管、介质管中通有工作气体时能够在介质管中产生另一个快速向外部空间传播的等离子体子弹的现象，进一步分析表明第二个等离子体子弹的产生是由第一个等离子体子弹中的电荷积累在介质管表面形成的强空间电场导致；（iii）研究结果表明等离子体子弹的产生和传播直接与其中的电荷量相关，电荷量越高，等离子体子弹在前方形成的局部空间电场越强，子弹的传播速度越高、传播距离越大，最终形成的等离子体射流越长。4.等离子体射流基本参数（电子温度和电子密度）的诊断研究。通过绝对辐射光谱和高分辨率光谱测量，对等离子体射流的电子温度和电子密度进行了诊断研究。（i）由氦原子能级密度的分布趋势发现射流等离子体处于极度非热平衡状态，首次得到对应于氦原子低能级区域的电子激发温度高达1.2eV，远高于高能级区域的电子激发温度（0.3eV）；（ii）同时研究表明氦原子高能级区域的密度分布处于萨哈热平衡状态，低能级区域的密度分布远偏离于萨哈平衡状态；（iii）建立了一种谱线轮廓的组合拟合方法，针对射流中的氦原子和氢原子谱线轮廓进行了分析以及拟合，首次获得了射流电子密度的空间分布非均匀特性，其中射流中心区域的电子密度可达1.2×10²¹m^-3，比射流边缘区域高一个量级。5.等离子体射流化学特性的诊断研究。采用激光诱导荧光技术，定量确定了等离子体射流中OH分子和O原子的绝对密度及其空间分布。（i）通过考虑激光诱导荧光测量中重要的分子转动和振动能量传输过程，建立了更加准确的定量诊断射流等离子体中OH分子密度的方法；（ii）研究结果表明，随着工作气体中水分子或者氧气含量的增加，射流中OH分子或者O原子的产生逐渐向靠近出气端口的强放电区域集中，强放电区域中OH分子或O原子的密度呈现先增加、后减小的变化趋势；（iii）当工作气体中混合0.3%H2O或0.3%O2时，射流中OH分子或O原子密度达到最高，分别为5.5×10¹⁹m^-3和2.4×10²²m^-3。更多还原

【Abstract】 As a new gas discharge technology generating low-temperature plasmas at atmosphericpressure, atmospheric pressure low-temperature plasma jets have received vigorous devel-opments in recent years, and become one of the hot research issues in plasma science andtechnology. As some unique technical advantages of this type of gas discharge, such as gen-eration in open space, low gas temperature, advanced plasma chemistry, pollution-free andetc., it has great application potentials in various fields, like biomedicine, material science,environment, etc. In this dissertation, comprehensive investigations of atmospheric pressurelow-temperature plasma jets are carried out and the details are presented as follows:1. Development of atmospheric pressure low-temperature plasma jet setups for biomed-ical applications.（i） Two different types of plasma jet setups are developed for plasma treat-ments in biomedical field （or other fields need low-temperature processing）. Based on themechanism of dielectric barrier discharge, the high-voltage electrode is covered by dielectricmaterial, which successfully avoids the generation of arc discharge and greatly improves theoperation safety of plasma jet setups. One of the setups is able to generate a plasma jet witha length up to11cm, which is the longest plasma jet generated in open air ever reported inthe world at that time. Human fingers can directly contact with the plasma jets generated bythese setups;（ii） Through analyzing the equivalent circuit of the case when a human finger iscontacting with the plasma jet generated by sine-wave high-voltages with frequency40kHzand amplitude7kV, it is found that the voltage dropped on the human body is at the safetyrange （<36V）, which proves that the safety of the plasma jet is high enough for biomed-ical applications;（iii） A setup which can simultaneously generate multiple plasma jets isdeveloped based on the configuration with multiple gas channels, which greatly increasesthe treatment area of plasma jets.2. Investigations of the control of plasma jet length. Experimental research on theeffects of the air in open space, parameters of power supply （applied voltage amplitude,pulse duration, frequency）, and gas velocity on the plasma jet length is carried out.（i）It is found out that the diffused air has a significant adverse influence on the generationof plasma jet in open space. The jet length generated in a pure working gas environmentis much larger than that of the jet in open air. Analysis shows that the adverse effect ofdiffused air is resulted by the fast quenching of energy-saving species, such as excited ormetastable He or Ar atoms （with helium or argon working gas） and high-energy electronsby air molecules;（ii） Through the fluid simulation of working gas, it is found out that when the gas flow is at laminar mode, the plasma jet can continue propagating in the open spaceonly when the working gas in the top-area of plasma jet achieves a specific ratio. Whenthe ratio of working gas is lower than the specific value, the length of plasma jet will notperform an obvious rise when the applied voltage is increased.（iii） The fluid simulationshows that the change of plasma jet length can be divided into three regimes with the riseof the working gas velocity, namely the laminar regime, transition regime from laminar toturbulent, and turbulent regime. The plasma jet achieves its maximal length when the gasflow starts to change to the turbulent mode from laminar mode;（iv） Based on the analysisof the influence of gas velocity on the plasma jet length, it is found out that the curvesof jet length versus gas velocity at different diameters of setup nozzles can be unified ina map of the jet Reynolds number versus the dimensionless ratio between jet length andnozzle diameter. The map is helpful for the design of jet setups and allows us to predict theflow pattern of plasma jet in order to estimate and control the plasma jet length at differentgeometrical size of setup nozzles.3. Research on the generation mechanisms of plasma jets. Detailed information of thegeneration processes of plasma bullet are obtained through high-speed nanosecond imagingtechnology and time-and-space resolved optical emission spectroscopy measurements.（i）It is found out that the plasma bullet achieves its maximal propagation velocity at a similarposition in the open space where the emission intensity of N+2391.4nm line also gets itspeak. This demonstrates that the propagation velocity of plasma bullet is directly related tothe density of charged particles inside the bullet;（ii） When the plasma bullet contacts witha dielectric tube and the tube is fed with working gas, a second plasma bullet is generatedinside the tube and propagating fast toward the open space. Analysis shows that the gen-eration of the second plasma bullet is induced by the strong space electric-field formed bythe charged particles of the first plasma bullet accumulated on the tube surface;（iii） Theseresults demonstrate that the generation and propagation of the plasma bullet is directly in-duced by the strong local space electric-filed in front of the bullet-like ionization volume,the more charged particles inside the volume, the stronger the local space electric-field isformed, and the faster and larger distance the bullet can propagate, and finally the longerplasma jet is generated.4. Diagnostic investigations on the basic parameters, namely the electron temperatureand electron density of the plasma jet, are carried out through absolute and high-resolutionoptical emission spectroscopy measurements.（i） It is found out that the electron excitationtemperature for the low-part of helium atomic state distribution function （ASDF） is around1.2eV, much higher than that of the high-part of helium ASDF （0.3eV）. The jet plasma isworking at an extreme non-equilibrium state;（ii） Meanwhile, it shows that the high-part of helium ASDF is almost following the Saha equilibrium, but the low-part is far away fromthe Saha equilibrium;（iii） The plasma electron density is determined by profile-fitting ofthe helium and hydrogen lines through a composition profile-fitting method. The spatiallynon-uniform characteristic of electron density in the plasma jet is studied. A high electrondensity up to1.2×10²¹m^-3is characterized for the discharge core in the jet center, whichis of an order of magnitude larger than that of the discharge area in the jet edge.5. Diagnostic investigations of the plasma jet chemistry are performed through theadvanced laser-induced fluorescence （LIF） spectroscopy measurements. The absolutedensities of OH and O radicals, and their spatial distribution in the plasma jet are deter-mined.（i） A calculation model is developed in this dissertation for determining the OHdensity in plasma jet with a higher accuracy. The model includes several important physicalmechanisms affecting the generation of LIF photons and is able to provide a true OHdensity in plasma sources.（ii） It shows that with increase of the admixtures of water oroxygen molecules, the distribution of OH or O radicals in the plasma jet gradually shrinkto the discharge core close to the gas outlet. The generation of OH or O radicals performa up-and-down behavior with the rise of the contents of water or oxygen molecules inworking gas;（iii） The density of OH or O radicals achieve their maximum densities of5.5×10¹⁹m^-3and2.4×10²²m^-3respectively when the admixtures of water or oxygenmolecules are both of0.3%.更多还原