Non-Invasive Diagnostics of Molecular Gas Plasmas with Quantitative Optical Emission Spectroscopy

该项目旨在为特定类型的低压分子气体等离子体开发一种新的非侵入性且易于实现的电离气体-等离子体的光学诊断。涉及等离子体的工业过程为一长串的社会效益做出了贡献，这些社会效益继续快速增长。低压电离气体等离子体的独特性质使人们能够以其他方式无法实现的方式操纵材料。具体地说，它们的复杂动力学导致非平衡化学；高能离子、自由基(与衬底表面发生强烈反应的原子、分子或离子)，以及等离子体中通过与高能电子碰撞产生的光子在材料表面蚀刻、修饰或沉积薄膜。因此，工艺结果对不同能量的电子丰度和其他等离子体参数极为敏感。该项目还将庆祝等离子体技术，并通过开发一个新的实践推广展览来提高公众的“等离子素养”，突出用于航天器推进的等离子体推进器。展示的中心将是一个在大气压下工作的等离子体推进器。这个展示将与麦迪逊西部高中的火箭俱乐部合作创建，并将成为火箭俱乐部广受欢迎的巡回展览的一部分，每年有数千人在科学节和学校参观时观看。等离子体发出的光的光谱带有等离子体参数的编码地图。通过测量特征波长的等离子体光发射的强度来探测等离子体的性质，是通过一个模型来预测发射光谱的，该模型通过考虑控制等离子体光发射的激发和去激发过程来预测发射光谱。该项目的创新之处在于创建了以氧气为初始焦点的分子气体定量排放模型。通过仔细考虑已知的激发速率，这项研究将确定包含在模型中的光谱特征，选择一些对电子能量分布函数表现出强烈的量化依赖关系的光谱特征，以及另一些是解离分数的强函数，即分子分解成组成原子的分数。这种方法将允许等离子体参数被确定为模型产生的与使用光学发射光谱(OES)测量的观测光谱强度最匹配的值。为了展示和探索分子OES的诊断能力，它将被应用于选定的放电现象：(I)表现出尚未完全了解的复杂等离子体动力学的放电现象；(Ii)新的分子OES可能提供新见解的放电现象；以及(Iii)获得的新见解与工业过程发展相关的放电现象。

This project aims to develop a new non-invasive and easily-implemented optical diagnostic of an ionized gas, a plasma, for the particular class of low-pressure molecular gas plasmas. Industrial processes involving plasmas contribute to a long list of societal benefits that continues to grow at a rapid pace. The unique properties of low-pressure ionized gas plasmas enable the manipulation of materials in ways that cannot be achieved by other means. Specifically, their complex dynamics lead to non-equilibrium chemistry; energetic ions, radicals (atoms, molecules or ions that react strongly with substrate surfaces), and photons produced in the plasma through collisions with energetic electrons etch, modify or deposit thin films on materials surfaces. Process outcomes are thus critically sensitive to the abundances of electrons of different energies and other plasma parameters. This project will also celebrate plasma technology and enhance public 'plasma literacy' through the development of a new hands-on outreach exhibit highlighting plasma thrusters for spacecraft propulsion. The centerpiece of the display will be a working plasma thruster operating at atmospheric pressure. The display will be created in partnership with the Rocket Club at Madison West High School and will become part of the Rocket Club's popular traveling exhibit, viewed by thousands of people each year at science festivals and school visits.The spectrum of light emitted by the plasma carries an encoded mapping of plasma parameters. Probing plasma properties by measuring the intensity of plasma light emissions at characteristic wavelengths is made possible through a model that predicts emission spectra by accounting for the excitation and de-excitation processes that govern light emission by the plasma. This project's innovation is the creation of a quantitative emission model for molecular gases, with oxygen as an initial focus. Through careful consideration of known excitation rates, the study will identify spectral features for inclusion in the model, choosing some that show a strong quantitative dependence on the electron energy distribution function and others that are strong functions of the dissociation fraction, i.e., the fraction of molecules broken up into constituent atoms. This approach will allow plasma parameters to be determined as the values for which the model produces a best fit to the observed spectral intensities, measured using optical emission spectroscopy (OES). To demonstrate and explore the capabilities of the molecular OES diagnostic, it will be applied to selected discharge phenomena (i) that exhibit complex plasma dynamics not fully understood, (ii) for which new molecular OES is likely to contribute new insights and (iii) for which the new insights obtained have relevance for development of industrial processes.