Time-resolved study of pulsed Ar–N₂and Ar–N₂–H₂microwave surfaguide discharges using optical emission spectroscopy

Abstract

Pulsed surfaguide microwave discharges operating at 2.45 GHz in several Ar-N 2 and Ar-N 2 -H 2 gas mixtures are studied using optical emission spectroscopy. Time-resolved measurements of Ar, N 2 , N + 2 , N, and H emission lines are presented. The gas temperature, and N 2 rotational and vibrational temperatures are also analyzed. Various discharge conditions, dependent on the applied power, discharge pressure, nitrogen and hydrogen content are examined. Time-resolved measurements confirm that N 2 dissociation in the discharge depends mainly on the presence of nitrogen ions (dissociative recombination). Gas temperature is found to be a power-dependent parameter, whereas vibrational temperature is mainly determined by nitrogen content and by the presence of H 2 in the mixture. Our data show that a negligible (∼0.2%) addition of H 2 dramatically changes the N 2 dissociation mechanism, as well as the time evolution of the emission lines during the pulse. These effects are explained by the disappearance of N + 2 generation due to the quenching of the N 2 (A) metastable level by molecular hydrogen.

Simple method for gas temperature determination in CO_2-containing discharges

“…These effects were observed previously for the other gas mixtures in the same type of discharges [19]. First effect corresponds to the gas heating at the beginning of the plasma pulse, whereas the second one reflects the equilibrium between the gas heating and heat dissipation and should be related to the vibrational-translational (VT) relaxation processes, as suggested in [19]. In our case, the saturation time of T gas is in a good agreement with the VT relaxation time (τ VT ) estimated for the symmetrical vibrational mode of CO 2 , whereas the asymmetric mode time constant appearing to be much larger (see [1,7]).…”

“…The uncertainty of the obtained temperature (which is about 11% in saturation) is still in the range of the errors described by expression (5) at T gas ∼ 800 K. The time-resolved temperature measurements performed using the three methods show clearly that, at a fixed energy delivered per plasma pulse (E p ), the T gas grows at the beginning of the pulse followed by a saturation after about 0.4 ms. These effects were observed previously for the other gas mixtures in the same type of discharges [19]. First effect corresponds to the gas heating at the beginning of the plasma pulse, whereas the second one reflects the equilibrium between the gas heating and heat dissipation and should be related to the vibrational-translational (VT) relaxation processes, as suggested in [19].…”

Plasma-based conversion of CO2: current status and future challenges

“…20 Figure 5 shows a comparison of the CO 2 conversion and energy efficiency in a MW plasma and DBD reactor as a function of SEI, as predicted by our model taking into account the CO 2 vibrational levels [49]. Note that the results of the MW plasma are obtained for a reduced pressure of 2660 Pa (20 Torr), as used in the experiments of [33,34], while the DBD results are for atmospheric pressure. Therefore, to compare both 25 discharges, we need to show them at the same SEI in eV/molec, because this is the most fundamental parameter for comparison.…”

Experimental and Theoretical Study of the Plasma Chemistry of Ethyl Lactate Plasma Polymerization Discharges

“…This strategy has already been used for studies of pure gas phase but has never been applied for plasma discharge . Additionally, FTIR spectroscopy has been used as a probe to measure the gas temperature of the plasma using the rotational bands of the CO molecules generated in the plasma . The latter parameter is of prime importance to validate our approach based on vibrational spectroscopy.…”