Abstract:

Understanding molecular energy transfer and chemical reactions in nonequilibrium reactive flows and nonequilibrium plasmas is critical for a number of applications, such as hypersonic aerothermodynamics and propulsion, high-speed flow control, plasma-assisted combustion, and plasma-enhanced catalysis. Energy partition, chemical reaction pathways, and rate of energy thermalization in nonequilibrium plasmas are strongly affected by the applied electric field and by the number densities of excited metastable molecular and atomic species. This talk presents an overview of time-resolved electric field and excited species measurements in high-pressure (up to 1 bar) molecular plasmas, using laser diagnostics. These diffuse and stable plasmas are sustained by a ns pulse discharge operated at a high pulse repetition rate, combined with DC or RF voltage waveforms. This approach improves the plasma stability at high pressures and enables selective generation of vibrationally and electronically excited molecules, as well as atomic species and radicals. Electric field, gas temperature, vibrational level populations of diatomic molecules, and number densities of metastable excited electronic states are measured by Electric Field Induced Second Harmonic (EFISH) generation, Coherent Anti-Stokes Ramas Scattering (CARS), Cavity Ring Down Spectroscopy (CRDS), and Tunable Diode Laser Absorption Spectroscopy (TDLAS). The results demonstrate considerable potential of laser diagnostic techniques for characterization of high-pressure nonequilibrium transient plasmas, where they provide detailed insight into kinetics of ionization, vibrational relaxation, quenching of excited electronic states, molecular dissociation, energy thermalization (“rapid heating”), plasma chemical reactions, and their coupling to the reacting flow.

Bio: