For the first time, absolute
densities of atomic nitrogen in its ground state (N4S) have been
measured in hot dry and humid air plasma columns under post-discharge regime.
The determination of space-resolved absolute densities leads to obtain the
dissociation degrees of molecular nitrogen in the plasma. The hot plasmas are
generated inside an upstream gas-conditioning cell at 600 mbar when the air gas
flow is directly injected at 10 slm in a microwave resonant cavity (2.45GHz, 1
kW) placed in the downstream side. Density measurements based on laser induced
fluorescence spectroscopy with two-photon excitation (TALIF), are more
particularly performed along the radial and axial positions of the plasma
column. Calibration of TALIF signals is performed in situ (i.e. in the same gas-conditioning cell
but without plasma) using an air gas mixture containing krypton. Optical
emission spectroscopy is considered to estimate the rotational gas temperature
by adding a small amount of H2 in dry air to better detect OH (A-X)
spectra. The rotational temperatures in humid air plasma column (50% of
humidity) are larger than those of dry air plasma column by practically 30%
near the nozzle of resonant cavity on the axis of the plasma column. This is
partly due to attachment heating processes initiated by water vapor. A maximum
of the measured absolute nitrogen density is also observed near the nozzle
which is also larger for humid air plasma column. The obtained dissociation
degrees of molecular nitrogen in both dry and humid air plasma along the air
plasma column are lower than the cases where only thermodynamic equilibrium is
assumed. This is characteristic of the absence of chemical and energetic
equilibria not yet reached in the air plasma column dominated by recombination
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Marchal, F., Yousfi, M., Merbahi, N., Wattieaux, G. and Piquemal, A. (2016) Quantitative Determination of Density of Ground State Atomic Oxygen from Both TALIF and Emission Spectroscopy in Hot Air Plasma Generated by Microwave Resonant Cavity. Plasma Science and Technology, 18.
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