Guy Parsey

Characterizing the dominant ions in low-temperature argon plasmas in the range of 1–800 Torr

The dominant ions in low-temperature rare gas plasmas can be either molecular ions or atomic ions depending on the discharge regime. In this paper, the dominant ions in low-temperature argon plasmas are characterized in a wide range of gas pressure (1–800 Torr). The channels for creation of molecular ions include atom assisted association, dissociative recombination, dissociation by atom impact (DAI), and dissociation by electron impact (DEI). The latter two were previously less often considered. It is found that the DEI reaction has a significant impact on the ion fractions, while the effect of the DAI reaction is much less important in the whole investigated gas pressure regime. As the gas pressure increases from 1 to 800 Torr, the atomic ion fraction drops rapidly in conjunction with an increase of the molecular ion fraction. This phenomenon confirms that in low-temperature argon plasmas the dominant ion will be the atomic ion in the low pressure regime but the molecular ion in the high pressure regime...

Global model capability study of EEDF modification of rare gas metastable laser reaction kinetics

Extending from revived interest in the study of diode-pumped alkali vapor lasers (DPAL), it was shown that optically pumping a rare gas metastable state can result in a population inversion with similar spectral characteristics to those making DPAL attractive1. Both systems can be pumped incoherently resulting in a temporally coherent output while a rare gas laser (RGL) does not suffer the extremely reactive behavior of alkali metals. Metastable species are produced under electric discharge and are relatively inert with respect to buffer gases and system construction. We propose using controlled electron energy distributions (EEDF) to modify RGL efficiency and to potentially drive the gain mechanism without the need for intense optical pumping. Formation of the EEDF is dependent on electric discharge conditions and introduction of electron sources.

General-purpose kinetic global modeling framework for multi-phase chemistry

Summary form only given. Spatially averaged (global) models are ubiquitous in plasma science, and the required data and equations are conceptually very similar for most applications. Unfortunately, it is common practice to implement a custom-developed software for each new global model; this unnecessary duplication of efforts negatively affects quality control and code maintenance. We present a general purpose kinetic global modeling framework (KGMf) designed to support plasma scientists in all modeling phases: collection and analysis of the reaction data, automatic construction of a system of ordinary differential equations (ODEs), time evolution of the system, and dynamical optimization of some target function. Alongside the description of the software, we present a few example tutorials.

Non-equilibrium kinetics of a microwave-assisted jet flame: Global model and comparison with experiment

Developing a systematic understanding of plasma driven chemical reaction pathways is difficult due to the stiffness and non-linear processes inherent with the involved physics. In the context of microwave-coupled plasmas within atmospheric pressure nozzle geometries, we have developed a kinetic global model (KGM) framework designed for quick exploration of parameter space. Our final goal is understanding key reaction pathways within non-equilibrium plasma assisted combustion (PAC), and their roles in the combustion process; of primary importance is the ability to determine possible system dependent reaction mechanism augmentation and specific reaction selectivity. In combination with a Boltzmann equation solver, kinetic plasma and gas-phase chemistry are coupled with a compressible gas flow model and solved with iterative feedback to match observed bulk conditions from experiments. We use a non-equilibrium electron energy distribution function (EEDF) to define electron-impact processes, allowing for demonstration of variation in reaction pathways due to changes in the EEDF shape. An Eulerian approach was developed as a purely steady-state flow model, followed by a Lagrangian time-dependent approach requiring knowledge of spatial electromagnetic field and flow profiles. Spatial profiles are converted into time-dependent envelopes affecting system parameters. The KGM is first applied to argon and air (N2-O2, N2-O2-Ar) systems as a means of assessing the soundness of the assumptions inherent in any global model. The simplified nature of the gas-phase chemistry and the availability of cross-sectional data reduce the sources of uncertainty in the model, which can be validated against the experimental measurements of electron density, emission spectrum and gas temperature. The test with air greatly increases the complexity by incorporating a plethora of excited states, providing new energy sink mechanisms (e.g. translational and vibrational excitation) and reaction pathways. The KGM is then applied to plasma driven combustion mechanisms (e.g. H2 or CH4 with an oxidizer source), which increases the importance of flow treatment and the range of gas-phase chemistry time-scales. As the reaction mechanisms become more complex, the limits of available data will begin to hinder model physicality, requiring analytical and/or empirical treatment of gaps in data to maintain completeness of the reaction mechanisms. Due to the relative simplicity of simulations with global models, the KGM can also be used to provide a sensitivity analysis to errors and variations within available data.