Measurement of reactive species absolute concentrations in N2, Ar/N2, He/N2 and H2/N2 microwave flowing afterglows at reduced pressure

J.-P. Sarrette (1) , Valentin Ferrer (1) , André Ricard (1) , J.P. Gardou (1) , Frédéric Marchal (1)

1 LAPLACE-PRHE - Plasmas Réactifs Hors Equilibre

Reduced pressure (2-20 Torr) flowing afterglows initiated in N2 and in mixtures of N2 with rare (Ar,He) or molecular (H2) gases generate and transport high concentrations of active species (atoms, metastable states, …) that can be used in many applications including surface sterilization or surface treatments. In the present paper, N2, Ar/N2, He/N2 and H2/N2 microwave flowing afterglows were characterized by Optical Emission Spectroscopy (OES). The discharge was generated by a surfatron cavity (2.45 GHz) in a 5 mm i.d. quartz tube enlarging to a 50 cm in length and 18 mm i.d. tube. N2 1+ (11-7), N2+ 1- (0-0), N2 2+ (1-0), NO β (0-8) and NH A-X (0-0) band intensity ratios were used to obtain absolute concentrations of N, O (oxygen been present as gas impurity) and H atoms, of N2(A) and N2(X,<13) metastable states and of N2+ ions and NH molecules, assuming a simplified set of chemical reactions in the afterglow [1]. Active species densities measured up to 50 cm from the surfatron gap in a N2 (0.5 slpm, 4 Torr) afterglow are shown Fig.1. In parallel with OES, absolute atomic densities of N and H atoms were also measured using a two-photon laser induced fluorescence technique (TALIF). In this experiment, a tunable dye laser pumped by a the second harmonic of a Nd:YAG laser was operated in the red spectral range, from 591 to 636 nm. The output beam was frequency doubled by a BBO crystal and the resulting UV beam was frequency mixed with the residual dye laser beam in a second BBO crystal. The UV laser radiations are located in the UV-C wavelength range, from 202 to 212 nm. The laser beam was focused at a constant position on the axis of the 18 mm afterglow tube while the surfatron was moved on the 5 mm tube to vary the distance between the discharge and the measuring point. Calibration of TALIF signals was performed in situ but without afterglow, using the same gas mixture containing krypton.

Mots clés: plasmas; flowing afterglows; N atom; H atom; TALIF; optical emission spectroscopy; plasmas

Domaines: Plasmas

J.-P. Sarrette, Valentin Ferrer, André Ricard, J.P. Gardou, Frédéric Marchal. Measurement of reactive species absolute concentrations in N2, Ar/N2, He/N2 and H2/N2 microwave flowing afterglows at reduced pressure. PLATHINIUM, Sep 2021, Antibes, France. ⟨hal-02997653⟩