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Accueil > A propos du LPP > Communication > Actualités archivées > 2018 > New experiments and simulations developed at the LPP study the spatio-temporal evolution of a plasma jet impacting a target

New experiments and simulations developed at the LPP study the spatio-temporal evolution of a plasma jet impacting a target

Helium plasma jets at atmospheric pressure are applied on targets for surface treatment and biomedical applications. When a Helium plasma jet impinges on a dielectric target, the discharge front spreads over the target surface and charges its surface. The spatial and temporal evolution of the electric field induced in the target is then crucial for the applications. At LPP, both experimental and modelling teams study this type of discharge propagation and interaction with targets.

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Séquence d’imagerie rapide de l’émission lumineuse visible obtenue expérimentalement lors de la propagation de la décharge entre l’extrémité du tube capillaire (en haut) et la cible (couche grise inférieure), visualisant l’impact sur la surface de la cible, à plusieurs délai td par rapport au front de l’impulsion de tension

Experimentalists at LPP, Elmar Slikboer and Olivier Guaitella, collaborating with Enric Garcia-Caurel at LPICM in École Polytechnique and Ana Sobota at TU/e in Eindhoven, use an electro-optic BSO crystal as target. The refractive index of electro-optic crystals changes linearly with the applied electric field induced by surface charges, according to the Pockels effect. Thus, using Mueller polarimetry, the electric field induced inside the target by the charges deposited on its surface by the discharge propagation is experimentally obtained. This field is of paramount importance in plasma jet applications. The measured field reaches maximum values of 5 kV/cm, lower than those reported for the discharge front of the order of 20 kV/cm.
In a recently published paper, these measurements have been complemented by the numerical calculations of modellers at LPP, Pedro Viegas and Anne Bourdon, collaborating with Zdenek Bonaventura and Adam Obrusník at the Masaryk University in Brno. A 2D fluid model is used to study separately the contribution of volume charges and surface charges to the spatio-temporal evolutions of the electric field during the plasma–surface interaction. Simulations show that during the plasma–surface interaction indeed two effects sequentially determine the electric field inside the target : Firstly, a relatively high electric field is observed due to the proximity of the ionization front ; Afterwards, in longer timescales, lower electric fields, of the same order of magnitude as those measured, are induced due to the contribution of both leftover volume charges close to the target and surface charges deposited on its surface. The experimental technique provides a unique way to examine this second phase of the plasma–surface interaction.

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Distribution spatiale de la magnitude du champ électrique [kV.cm-1] obtenue numériquement après l’impact de la décharge sur la cible. La cible est placée entre z=-0,5 mm et z=0

More details in P. Viegas et al., Plasma Sources Sci. Technol. 27 (2018) 094002.


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Tutelles : CNRS Ecole Polytechnique Sorbonne Université Université Paris Sud Observatoire de Paris Convention : CEA
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Directeur de la publication : Pascal Chabert (Directeur)