高频诱导无极光源的发射光谱学诊断

【作者】 龙奇；

【导师】 陈大华；

【作者基本信息】 复旦大学 ， 物理电子学， 2008， 博士

【摘要】 论文围绕两个主要问题开展研究:1.射频诱导低气压无极光源的等离子体放电模式特性;2.微波诱导金属卤化物分子的辐射机理。通过对这两种实用高频诱导无极光源等离子体进行发射光谱学诊断,获得对其放电特性更深层次的物理认识。论文使用射频信号发射器和功率放大器提供可调制的射频功率输出,通过电感诱导的方式激发低气压Hg-Ar放电和Hg-Ke放电。通过改变射频功率或射频频率可观察到等离子体存在两种放电模式:静电放电模式（E放电）和感应放电模式（H放电）。E放电和H放电的启动条件是频率的函数,启动电场强度随频率的升高而降低。实验观察到H放电的启动电场要远高于其维持电场,即所谓的放电模式转变的滞后现象。通过启动过程的瞬态分析可知,工作在H放电的射频诱导无极光源启动必须经历E放电阶段。在E放电中,电子浓度逐渐增大,到达临界值时实现E放电向H放电的转变。启动过程中E放电持续时间和H放电达到稳定的时间随电路启动电压的增加而减少。通过对比Kr811.3nm和Hg435.8nm谱线以及Hg 365.0nm和Hg546.1nm谱线的相对强度变化,借助3电子温度电子能量概率分布函数（EEPF）模型可知:E放电向H放电转变时,随着电子浓度的提高,高能电子比例增加,中能电子和低能电子相对比例减少,EEPF逐渐逼近Maxwellian分布。通过对比Hg546.1nm与Hg435.8nm谱线相对强度的变化可知:在E放电中,原子亚稳态浓度随放电电流的增加而增加,而在H放电中趋势则相反。E放电向H放电转变过程中,方位角方向的感应电流明显增强,趋肤效应使得放电重新在H放电下达到平衡。实验表明:电子能量概率分布函数的改变、通过亚稳态的逐级电离、逐级激发和方位角方向的感应电场是射频诱导无极光源等离子体放电模式转变和滞后现象产生的重要原因。论文使用Abel转换和Boltzmann Plot方法确定微波诱导NaI等离子体的温度轮廓分布。在70W微波功率下,NaI等离子体中心温度为3609K,温度轮廓为典型的管壁稳定性分布。微波诱导NaI光谱中钠D线占主导地位,在300nm到600nm范围内可观察到NaI分子的连续光谱,但强度远远低于Na原子线。Na元素与泡壳材料的强烈化学反应决定了NaI分子不能单独的作为微波光源的填充物质。论文使用Barrels方法诊断了不同微波能量输入条件下,InI、InBr以及SnI₂泡壳的等离子体温度轮廓。实验表明:随着微波功率的上升,等离子体的温度先整体提升,到达某一功率时,泡壳中心温度降低而周边温度升高,温度轮廓变得更加平滑。在96W微波功率输入下,1号InI泡壳等离子体中心温度为4450K。误差分析表明,使用Bartels方法测量InI等离子体温度轮廓的误差为8.4%。微波诱导InI分子的连续光谱覆盖了整个可见光区域,光源的显色指数超过90,相对色温随微波功率的升高而下降,107W微波功率下1号InI泡壳的相对色温为6805K。维持放电区域的高温高压是实现微波光源高效光辐射的必要条件,在我们的实验条件下InI分子辐射效率随气压的增大而增大。InBr和GaI分子的辐射特性与InI分子类似,而AlI₃和InI₃分子由于受热离解而形成过量的碘分子,造成自由电子被吸收而使启动变得困难。SnI₂分子辐射连续光谱也覆盖了整个可见区域,连续谱强度最大值出现在660nm附近,74W微波功率时等离子体中心温度为4419K,光源相对色温为3274K。论文使用Morse势能曲线模拟InI分子各能级的结构,通过分子能级跃迁的选择规律和Franck-Condon原理对InI分子在微波诱导条件下的发射光谱的形成机理进行了物理解释。分析表明InI分子八个高能Rydberg态向低能级排斥态C态的跃迁是产生实验连续光谱的主要原因,其中InI分子的¹Σ₀₊⁺（Ⅲ）—¹Π₁跃迁在265nm到411nm间产生连续光谱,而InI分子³Π_0-（Ⅲ）—¹Π₁跃迁形成410nm到667nm之间的连续辐射。更多还原

【Abstract】 This thesis focuses on two main topics:1.the discharge modes of the RF induced low pressure electrodeless lamp;2.molecular radiation in microwave induced metal halide discharge.In order to get deeper physical understanding to these two practical electrodeless light sources,emission spectroscopic diagnostics is used in the experiments.By modulating the frequency and power of the RF signal,two discharge modes in the RF induced electrodeless lamp are observed:electrostatic discharge mode（so called E mode） and electromagnetic discharge mode（so called H mode）.The ignition conditions of E mode discharge and H mode discharge are functions of the frequency: the higher the frequency,the easier the ignition.The temporary study to the ignition process shows that the E mode discharge is a necessary precondition to ignite the H mode discharge.The duration of the E mode discharge and the stable time of the H mode discharge decrease as the ignition voltage increases.By comparing the spectral intensity ratios:Kr811.3nm/Hg436.8nm and Hg 365.0nm/ Hg546.1nm,we can know:during the transiton from E mode discharge to H mode discharge,the proportion of high energy electron is increased due to the frequent electron-electron collisions,which compensate the loss of high energy electrons in the inelastic collisions.The electron energy distribution function approaches the Maxwellian distribution.By comparing the spectral intensity ratio of Hg546.1nm line and Hg435.8nm line,it is observed that the density of metastable atom is increased as the current in the E mode discharge.The trend is opposite in H mode discharge. During the transition,the induced azimuthal current is enhanced greatly.The discharge returns to stable in the H mode due to skin effect.The temperature profile of microwave induced NaI plasma is determined by emission spectroscopy with Abel inversion and the Boltzmann Plot.The central temperature is determined to be 3609K at 70W microwave input.The temperature profile is a typical wall-stable type.The spectra of microwave induced NaI molecule are dominated by the renowned Na D lines,which locate at 589.0nm and 589.6nm.The continuous radiation between 300nm and 600nm is believed to be the molecular radiation of NaI, though very week.The chemical reaction between Na and the bulb material makes it impossible to fill NaI into a practical microwave lamp alone.Barrels method is employed to determine the temperature profile of microwave induced InI,InBr and SnI₂ plasma.As the increase of microwave power,the temperture profile becomes more even due to the slightly cooling down in the center and warming up in the outer of the plasma.The central temperature of InI plasma is 4450K at 96W microwave input.The error is less than 8.4%.The continuous radiation of microwave induced InI discharge covers the whole visible range,which makes the color rendering index more than 90.The corrected color temperature is 6805K at 107W microwave input.The spectra of InBr and GaI are quite similar to that of InI due to similar molecular structure.The ignitions of AlI₃ and InI₃ are more difficult than InI,because of the dissociation of metal trihalide into metal monohalide and halogen.Halogen is believed to quench the discharge by absorbing free electrons.The spectra of SnI₂ also cover the whole visible range,with the intensity peak at 660nm,resulting in lower color temperature than InI.The central plasma temperature is 4419K at 74W microwave input,while the corrected color temperature is 3274K.By simulating the Morse potential curve and using Franck-Condon principle,it is believed that the continuous radiation of microwave induced InI discharge originates from the transitions of 8 Rydberg states to the lower repulsive state:C state of InI molecule.The ¹∑₀₊⁺（Ⅲ）-¹∏₁ transition of InI molecule contributes to the continuous radiation between 265nm and 411nm,while the ³∏_0-（Ⅲ）-¹∏₁ transition results in the continuous radiation between 410nm and 667nm.更多还原