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Accueil > A propos du LPP > Communication > Actualités archivées > 2020 > Marlous Hofmans has defended her PhD on "Experimental characterization of helium plasma jets”

Marlous Hofmans has defended her PhD on "Experimental characterization of helium plasma jets”

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Marlous Hofmans has defended her PhD on "Experimental characterization of helium plasma jets” on Thursday October 15, 2020 at 4pm at the Eindhoven University of Technology in the Netherlands.

During her PhD, Marlous has spent half of the time at LPP and at the Eindhoven University of Technology.

The defense ceremony in Eindhoven has a different structure than the PhD defenses at Ecole Polytechnique : it lasts for strictly 1 hour in which Marlous has given a presentation of 10 minutes and has answered questions of the jury for the rest of the hour.

Abstract :
This thesis studies an atmospheric pressure helium plasma jet that is powered by positive, unipolar pulses at a kHz frequency. Experiments are performed that focus on the propagation dynamics, flow structure and temperature in a freely expanding jet, as well as the influence of a metallic target on the plasma.
Stark polarization spectroscopy yields an axial electric field of around 10 kV/cm in the capillary of the jet and an increase up to 20 kV/cm in the plume, which is constant for different amplitudes and durations of the applied voltage pulse. Thomson and rotational Raman scattering are used to determine the electron density and electron temperature, at different axial and radial positions, as well as the gas temperature and the density of N2 and O2 that are mixed into the helium from the surrounding air.
Quantitative comparison of these experimental results with results from a 2D fluid model show a good agreement and allow for a better understanding of the obtained results, namely that the electric field in the ionization front depends linearly on the flow composition at that location. Schlieren imaging shows the onset of turbulent structures at high applied flow rates and at the application of the voltage pulses. The gas temperature, as measured by a temperature probe, is found to increase by around 12°C when the plasma is ignited and by around 25°C when a metallic target is placed in front of the jet.

Jury :
Prof.dr.ir. Gerrit Kroesen (Eindhoven University of Technology (EPG), Pays-Bas) PhD supervisor
Dr. Olivier Guaitella (École Polytechnique (LPP), France) co-supervisor
Dr.Dipl.-Ing. Ana Sobota (Eindhoven University of Technology (EPG), Pays-Bas) co-supervisor
Prof.dr. Deborah O’Connell (University of York, Royaume-Uni) Referee
Prof.dr. Uros Cvelbar (Jožef Štefan Institute, Slovénie) Referee
Dr. Svetlana Starikovskaia (École Polytechnique (LPP), France) member
Dr. Richard Engeln (Eindhoven University of Technology (PMP), Pays-Bas) member

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Directeur de la publication : Anne Bourdon (Directrice)

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