Kinetic modeling is used to analyze energy partition and energy transfer in nanosecond pulse discharges sustained between two spherical electrodes in nitrogen and air. The modeling predictions are compared with previous time-resolved temperature and ( ) Σ = − +

The present kinetic modelling calculation results provide key new insights into the kinetics of vibrational excitation of nitrogen and plasma chemical reactions in nanosecond pulse, 'diffuse filament' discharges in nitrogen and dry air at a moderate energy loading per molecule, ∼0.1 eV per molecule. It is shown that it is very important to take into account Coulomb collisions between electrons because they change the electron energy distribution function and, as a result, strongly affect populations of excited states and radical concentrations in the discharge. The results demonstrate that the apparent transient rise of N 2 'first level' vibrational temperature after the discharge pulse, as detected in the experiments, is due to the net downward V-V energy transfer in N 2-N 2 collisions, which increases the N 2 (X 1 , v = 1) population. Finally, a comparison of the model's predictions with the experimental data shows that NO formation in the afterglow occurs via reactive quenching of multiple excited electronic levels of nitrogen molecule, N * 2 , by O atoms.

Femtosecond, two-photon-absorption laser-induced fluorescence (fs-TALIF) is employed to measure space-and time-resolved distributions of atomic hydrogen and oxygen in moderatepressure, non-equilibrium, nanosecond-duration pulsed-discharge plasmas. Temporally and spatially resolved hydrogen and oxygen TALIF images are obtained over a range of low-temperature plasmas in mixtures of helium and argon at 100 Torr total pressure. The high-peak-intensity, low-average-energy fs pulses combined with the increased spectral bandwidth compared to traditional ns-duration laser pulses provide a large number of photon pairs that are responsible for the two-photon excitation, which results in an enhanced TALIF signal. Krypton and xenon TALIF are used for quantitative calibration of the hydrogen and oxygen concentrations, respectively, with similar excitation schemes being employed. This enables 2D collection of atomic-hydrogen and -oxygen TALIF signals with absolute number densities ranging from 2 × 10 12 cm −3 to 6 × 10 15 cm −3 and 1 × 10 13 cm −3 to 3 × 10 16 cm −3 , respectively. These 2D images are the first application of TALIF imaging in moderatepressure plasma discharges. 1D self-consistent modeling predictions show agreement with experimental results within the estimated experimental error of 25%. The present results can be used to further the development of higher fidelity kinetic models while quantifying plasmasource characteristics.

Time-resolved and spatially resolved temperature measurements, by pure rotational picosecond broadband coherent anti-Stokes Raman spectroscopy (CARS), and kinetic modeling calculations are used to study kinetics of energy thermalization in nanosecond pulse discharges in air and hydrogen-air mixtures. The diffuse filament, nanosecond pulse discharge (pulse duration ∼100 ns) is sustained between two spherical electrodes and is operated at a low pulse repetition rate to enable temperature measurements over a wide range of time scales after the discharge pulse. The experimental results demonstrate high accuracy of pure rotational ps CARS for thermometry measurements in highly transient non-equilibrium plasmas. Rotational-translational temperatures are measured for time delays after the pulse ranging from tens of ns to tens of ms, spanning several orders of magnitude of time scales for energy thermalization in non-equilibrium plasmas. In addition, radial temperature distributions across the plasma filament are measured for several time delays after the discharge pulse. Kinetic modeling calculations using a state-specific master equation kinetic model of reacting hydrogen-air plasmas show good agreement with experimental data. The results demonstrate that energy thermalization and temperature rise in these plasmas occur in two clearly defined stages, (i) 'rapid' heating, caused by collisional quenching of excited electronic states of N 2 molecules by O 2 , and (ii) 'slow' heating, caused primarily by N 2 vibrational relaxation by O atoms (in air) and by chemical energy release during partial oxidation of hydrogen (in H 2-air). The results have major implications for plasma assisted combustion and plasma flow control.