Electric field characterization of plasma gun and multi-jet plasma arrays

Invited oralInternational audienceRoom temperature Pulsed Atmospheric Plasma Streams (PAPS) have already demonstrated their unique potential in biology and medicine. Lately, the validation of multi-jet plasmas resulting from metallic and dielectric assemblies-containing many orifices-plugged to a single Plasma Gun (PG) and operating at moderate feed gas flow rate (from hundreds to thousands standard cubic centimeters) has been demonstrated [1]. This technological improvement enhances the credibility of plasma jets to treat large areas and volumes being beneficial in biomedical and recently in agriculture applications. Although the role of reactive oxygen and nitrogen species (RONS) produced by plasma is currently under many investigations, the simultaneous contribution of intense pulsed electric fields (EF) in the activation of biological mechanisms still remains unclear. Therefore, in this work, the authors focus on the characterization of EF in PAPS applied to the treatment of cells and culture medium. EF maps [2] time and space resolved have been recorded with an electro optic sensors [3] and contribute to the interpretation of biological responses, e.g. electroporation, electropermeabilization and the impacts on cell viability. The controlled propagation of multi-jet plasmas depends on the nature of the assemblies and is observed by time resolved iCCD imaging as shown in Fig. 1 and Fig. 2. While the metallic one allows for simultaneous ignitions of multiple PAPS, the dielectric one leads to a controlled splitting of the PG ionization wave, inducing a propagation delay between each orifice. Effects of multi-jet plasmas on the hydrodynamic of the gas are studied together via fast-schlieren imaging and by EF characterization. The outcome of this work will be of significant interest towards the use of multiple jets in plasma treated cells, agriculture and biomedical applications. XD is supported with the grant INEL/Région Centre Val de Loire

Jets de plasmas atmosphériques pour des applications thérapeutiques de la décharge aux traitements : études, problèmes et enjeux

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Ionization wave propagation in an atmospheric pressure plasma multi-jet

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Numerical and experimental study on the dynamics of a µs helium plasma gun with various amounts of O2_2 admixture

International audienceThe use of admixtures (mostly O2 and N2) to a helium bu_er has been studied recently to tailor the generation of reactive species in plasma jets for biomedical applications. So far, most experiments have been dedicated to the study of the plasma plume. For endoscopic treatments, it is also important to better understand and optimize the propagation of discharges in long dielectric tubes as catheters. In this work, we present an experimental and numerical study on the dynamics of a microsecond helium plasma discharge with O2 admixture in a long dielectric tube. In simulations, a 2D fluid model is used. For comparison purposes, the geometries of the set-ups used for simulations and experiments are as close as possible. We compare experiments and simulations for di_erent amounts of O2 admixture added to the buffer gas and present results on the velocity of the discharge front for the various amounts of O2 and different applied voltages. In order to study the inuence of di_erent amounts of O2 admixture on the helium discharge dynamics, detailed kinetic schemes have been used. The influence of Penning and charge exchange reactions on the discharge structure and dynamics are studied, as well as the role of negative ions.P.V. is supported by an EDOM fellowship, and X.D. by an INEL/Region Centre-Val de Loire fellowship

Caractérisation d'un dispositif multijets plasma

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Numerical and experimental study on the dynamics of a μ\mus helium plasma gun with various amounts of O2_2 or N2_2 admixtures

International audienceRecently to tailor the generation of reactive species in plasma jets for biomedical applications, several research groups [1-5] have studied the use of admixtures (mostly O2 and N2) to the helium buffer. Furthermore, there exists also a recent interest for the consideration of electric field associated with the plasma plume delivery over tissues in comparison with the previously reported potent effects of the pulsed electric fields [6].So far, most experiments have been dedicated to the study of the plasma plume. For endoscopic treatments, it is also important to better understand and optimize the propagation of discharges in long dielectric tubes as catheters. In this work, we present an experimental and numerical study on the dynamics of a s helium plasma discharge with N2 or O2 admixture in a long dielectric tube. In a previous work [5] we have compared experiments and simulations for different amounts of nitrogen admixture added to the buffer gas at the inlet of the plasma gun. In this work, in experiments, we first compare with results obtained previously in N2 with results obtained with O2 admixture added in the helium buffer at the inlet of the plasma gun hollowed electrode but also alternatively downstream along the helium plasma propagation inside long dielectric capillaries to change the plasma jet properties. In simulations, a 2D fluid model is used. For comparison purposes, the geometries of the set-ups used for simulations and experiments are as close as possible and the same applied voltage waveforms are used with a 2 μs rise time and two peak voltages of 10 and 16 kV. In order to study the influence of different amounts of N2 and O2 admixture on the helium discharge dynamics, detailed kinetic schemes have been used. In both He/N2 and He/O2 mixtures, the influence of Penning and charge exchange reactions on the discharge structure and dynamics are studied. We present results on the comparison of experimental and numerical results obtained on the velocity of the discharge front for various amounts of N2 and O2 and different applied voltages.Second, we compare time-resolved measurements and simulations of longitudinal and radial electric fields associated with plasma propagation in the dielectric tube and in the plasma plume. AcknowledgmentsP.V. is supported by xxxxx fellowship, and X.D. by INEL/Region Centre-Val de Loire fellowship.References[1] T. Darny, E. Robert, S. Dozias and J.M. Pouvesle Proc. of the 5th Int. Conf. on Plasma Medicine, Nara, Japan (2014)[2] S. Iseni, S. Zhang, F. van Gessel, S. Hofmann, B. van Ham, S. Reuter, K.-D. Weltmann and P. Bruggeman New J. Phys. 16 123011 (2014)[3] Reuter S, Tresp H, Wende K, Hammer M, Winter J, Masur K, Schmidt-Bleker A and Weltmann K IEEE Trans. Plasma Sci. 40 2986–93 (2012)[4] van Gessel B, Brandenburg R and Bruggeman P Appl. Phys. Lett. 103 064103 (2013)[5]A. Bourdon, T. Darny, F. Pechereau, J.M. Pouvesle, P. Viegas, S. Ideni, E. Robert, Plasma Sources Sci. Technol 25 035002 (2016)[6] Zhang Q, Zhuang J, von Woedtke T, Kolb J F, Zhang J, Fang J and Weltmann K-D Appl. Phys. Lett. 105 104103 (2014

Determination of charge density in an atmospheric pressure plasma jet via electric field measurements and simulations

International audienceAtmospheric pressure plasma jets have been extensively studied for several years as theyshowed very promising results in numerous fields such as material processing or plasma medicine.What makes cold plasma interesting is the presence of electrons, ions, reactive oxygen andnitrogen species, visible and UV light and high transient electric fields (EF). Even if the latter playa key role, from the production and propagation of the plasma to the efficiency of applications,they are far from being fully understood. This work focuses on the comparison of measurementsof EF produced by a Plasma Gun (PG) discharge with an electro-optic probe based on Pockelseffect [1] with 2D simulations of atmospheric pressure discharges propagating in a geometry closeto the Plasma Gun’s one. Plasma Gun consists in a vertically downward oriented capillary with aninner high-voltage electrode and an outer grounded one. Plasma is powered with μs-durationvoltage pulses from single shot to 4kHz.In [2] the electric field is evaluated by the simulations inside the capillary, in the glass andoutside. The aim of this work is to compare the radial profile of the electric field outside thecapillary between experiments and simulations to get information on the plasma inside it. Theelectro-optic probe was placed at different levels alongside the capillary and was getting far fromit. Measurements were executed every 5mm over 5cm. At the middle of the capillary a decreaseinversely proportional to the distance has been found. It reminds the shape of an EF produced byan infinite uniformly charged cylinder. 2D simulations were in a good agreement finding also thesame slope for EF. But simulations permit also to get information on the distribution of chargedensity and especially to know if the main contribution is from volume or surface charge density.Results show that the radial profile of EF outside the tube is mostly determined by the volumecharge density in positive polarity while in negative polarity the surface charge density isdominant. Simulations have provided values of average volume charge density in the order of 7.5nC/cm3 in positive polarity and of average surface charge density around 1nC/cm² in negativepolarity. Near the electrodes, a decrease inversely proportional to the square of the distance hasbeen found, showing that there is an axial position dependence. A time dependence investigationwill also be presented.X.D. acknowledges his grant funding Thermofisher Scientific INEL/Région Centre Val de Loire.References[1] G. Gaborit et al., IEEE Trans. Plasma Sci., 42 (2014).[2] P. Viegas, F. Pechereau and A. Bourdon, Plasma Source Science and Technology, in press(2018

Numerical and experimental study on the dynamics of a micro-second helium plasma gun with various amounts of O2 or N2 admixtures

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Rare gas flow channeling in kHz plasma jet operation

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