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Title:Characterization Of Hybrid Ns Pulse/rf Plasmas And Atmospheric Pressure Plasma Jets
Author(s):richards, caleb
Contributor(s):Adamovich, Igor V.; Mignogna, David Kyle; van den Bekerom, Dirk; Jans, Elijah R.
Subject(s):Dynamics and kinetics
Abstract:Strong vibrational nonequilibrium is sustained in nitrogen and nitrogen/carbon dioxide “hybrid” plasmas, generated by a ns pulse train overlapping with a sub-breakdown RF waveform. \chem{N_2} vibrational level populations in the plasma are measured by broadband Coherent Anti-Stokes Raman Spectroscopy (CARS). Vibrationally excited \chem{CO_2} and CO in the plasma are detected by Quantum Cascade Laser Absorption Spectroscopy (QCLAS). The plasma is generated using a custom-designed external circuit which overlaps a ns pulse train and a sine-wave RF waveform, generated by two different power supplies, in plane-to-plane, double dielectric barrier discharge configuration. The results show that the sub-breakdown RF waveform, which does not produce ionization but heats the electrons generated by the ns pulses, has a strong effect on vibrational excitation of molecules in the plasma. This enables isolating and quantifying the contribution of reactions of vibrationally excited molecules in plasmachemical and plasma-catalytic processes. Specifically, the effect of the excitation of \chem{CO_2} asymmetric stretch vibrational mode on the dissociation of carbon dioxide is studied by QCLAS measurements of \chem{CO_2} vibrational level populations and CO product. In a closely related study, a quasi-two-dimensional atmospheric pressure plasma jet in a noble gas/nitrogen mixture, impinging on a dielectric plate (glass or quartz), is interrogated by Coherent Anti-Stokes Raman Spectroscopy (CARS). The experiments are made in \chem{N_2}/Ar, \chem{N_2}/He, and \chem{N_2}/Ne plasma jets powered by a ns pulse train or an RF waveform. Strong \chem{N_2} vibrational nonequilibrium is measured in the jet, and found to increase as the mole fraction of nitrogen in the mixture is reduced. This suggests that \chem{N_2} vibrational excitation is produced by the energy transfer from metastable electronically excited atoms to the nitrogen vibrational mode, possibly via the metastable excited electronic state, N$_2(A^3\Sigma_u^+$). To quantify the role of electronically excited nitrogen in this energy transfer processes, the number density of N$_2(A^3\Sigma_u^+$) molecules in the plasma is measured by Tunable Diode Laser Absorption Spectroscopy.
Issue Date:2021-06-23
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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