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Accueil > Séminaires et conférences > Séminaires, soutenances de thèses et HDR précédents > 2018 > Soutenances de thèses et HDR 2018 > Le vendredi 4 mai 2018 à 10h

Le vendredi 4 mai 2018 à 10h

Soutenance de thèse de Yifei Zhu - Numerical study of nanosecond capillary and surface dielectric barrier discharges : kinetics, transport and fluid responses

The presentation will be in English. The defense will be on 4th of May 2018 in Ecole Polytechnique, amphi Gregory at 10:00.

Abstract :

Nanosecond pulsed discharges are characterized by high reduced electric fields (hundreds of Td) and strong nonequilibrium. They have characteristic electron energies of a few to tens of eV and specific energy deposition ranging from 10−3 eV/mol to a few eV/mol. The energetic electrons can efficiently generate chemical active species, lead to fast gas heating. These discharges are found in a growing list of successful practical applications : gas pollution control, surface treatment, plasma assisted aerodynamics, plasma assisted biology and medicine and plasma assisted combustion.

Two particular configurations are studied in present work : (i) nanosecond capillary discharge (nCD) operated at moderate pressures and high specific deposited energy, and (ii) nanosecond surface dielectric barrier discharge (nSDBD) operated at atmospheric or higher pressures and relatively low specific deposited energy.

Nanosecond capillary discharge is an experimental tool to analyse nanosecond plasma in some limit extreme conditions. Recent nCD experiments revealed that, plasma kinetics changes dramatically at high specific energy deposition. One of the aims of the present work, is to study numerically the effects of the changed kinetics to the classical actinometry measurement technique, and the spatial-temporal evolution of plasmas during discharge and afterglow.

Nanosecond surface dielectric barrier discharge has been widely studied in the community of aerodynamics. However, at the moment of starting the thesis, the parameters of nSDBD plasma were not yet clearly understood, detailed comparison of numerical calculations and experiments were not available. Therefore, modelling of nSDBD and comparison with experiments performed for the same parameters is another object of the presented thesis.

The results in the thesis are presented in three parts. In the first part, numerical modelling and experiment of Ar-based actinometry are used to study the atomic oxygen density in nanosecond capillary discharge. A kinetic scheme describing consistent behavior of the set of the experimental data is developed. The main processes responsible for population and decay of the three species of interest are selected on the basis of sensitivity and rate analysis. The role of the reactions between excited species and electrons in early afterglow for pulsed discharges at high electric fields and high values of specific deposited energy is discussed. Density of O-atoms in the ground state is obtained from the calculations.

The second part is devoted to study, analyse and predict the features of the discharge and afterglow of nCD under different specific energy deposition based on a two–dimensional self-consistent code, nonPDPsim. Propagation of the discharge have been modelled. Two modes of propagation were identified, three shapes of ionization waves are found with various tube radius. The decay rate and radial distribution of electrons and N2(C3Πu) in the afterglow are studied with respect to specific energy deposition.

Finally, a two–dimensional parallel PASSKEy (“PArallel Streamer Solver with KinEtics”) code coupling plasma and hydrodynamics has been developed and validated to model nSDBD. Series of numerical calculations for a single pulse nSDBD in atmospheric pressure air at 24 kV voltage amplitude has been performed, the results were compared with experiments in the same conditions. Calculated and measured velocity of the discharge front, electrical current, 2D map of emission of N2(C3Πu) → N2(B3Πg), and hydrodynamic perturbations caused by the discharge on the time scale 0.2 − 5 µs are analysed. The effect of different kinetics processes in 2D distribution of heat release is studied. The data are presented and analyzed for negative and positive polarity of voltages. A set of parametric calculations with different dielectric permittivity, the thickness of dielectric and ambient pressures are presented.


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Tutelles : CNRS Ecole Polytechnique Sorbonne Université Université Paris Sud Observatoire de Paris Convention : CEA
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Exploitant du site : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Hébergeur : Laboratoire de Physique des Plasmas, Ecole Polytechnique route de Saclay F-91128 PALAISEAU CEDEX
Directeur de la publication : Pascal Chabert (Directeur)