Etude et optimisation d'une décharge "Plasma Gun" à pression atmosphérique, pour des applications biomédicales

The use of plasmas, thermic or low pressure, in biomedical goes back up to 1970s. During these last years, atmospheric pressure cold plasma jets have been developed, allowed an increase of biomedical applications of plasmas. In GREMI, a plasma jet was developed : the Plasma Gun (PG). The plasma generated by the PG propagates on long distances inside capillaries. The optimization of the aimed treatments requires a detailed study of the discharges created by the PG. The characterization of the PG highlights the generation of Pulsed Atmospheric pressure Plasma Streams or PAPS, these last ones propagating from the reactor to the capillary outlet (ambient air) where they generate a plasma plume. These PAPS present two propagation modes, during which a connection between the ionization front and the reactor is present permanently. These two modes named respectively Wall-hugging and Homogeneous, differ mainly by the morphology and their propagation velocity. These modes have common characteristics, such as the possibility of division or meeting of PAPS, as well as the transfer of PAPS through a dielectric barrier or via a hollow metal capillary. The study of the plasma plume underlined the importance of the length of capillaries on the length of the plasma jet. Furthermore, the generation of the plasma has a very strong influence on the gas flow and the jet structuration during air expansion.L’utilisation de plasmas, qu’ils soient thermiques ou basse pression, dans le domaine biomédical remonte aux années 1970. Au cours de ces dernières années, les développements concernant des jets de plasma froid à pression atmosphérique, ont permis un élargissement des domaines d’applications biomédicales des plasmas. Au sein du GREMI, un type de jet de plasma a été développé : le Plasma Gun. Le plasma généré par le Plasma Gun se propage sur de longues distances à l’intérieur de capillaires. L’optimisation des traitements visés nécessite une étude approfondie des décharges créées par le Plasma Gun. La caractérisation du Plasma Gun a mis en évidence la génération de Pulsed Atmospheric pressure Plasma Streams ou PAPS, ces derniers se propageant du réacteur jusque dans l’air ambiant où ils génèrent une plume plasma. Ces PAPS présentent deux modes de propagation, au cours desquels une connexion entre le front d’ionisation et le réacteur est présente en permanence. Ces deux modes nommés respectivement Wall-hugging et Homogène, diffèrent principalement par la morphologie et la vitesse de propagation des PAPS qui leur sont associés. Chacun de ces modes présentent donc des caractéristiques qui leur sont propres mais certaines propriétés de propagation leur sont communes, telles que la possibilité de division ou de réunion de PAPS, ainsi que du transfert de PAPS à travers une barrière diélectrique ou via un capillaire métallique creux. L’étude de la plume plasma, propagation des PAPS dans l’air ambiant, a souligné l’importance de la longueur des capillaires sur la longueur du jet plasma. De plus, la génération du plasma a une très forte influence sur l’écoulement du gaz et la structuration du jet lors de son expansion dans l’air

Dynamics of ionization wave splitting and merging of atmospheric-pressure plasmas in branched dielectric tubes and channels

Atmospheric-pressure fast ionization waves (FIWs) generated by nanosecond, high voltage pulses are able to propagate long distances through small diameter dielectric tubes or channels, and so deliver UV fluxes, electric fields, charged and excited species to remote locations. In this paper, the dynamics of FIW splitting and merging in a branched dielectric channel are numerically investigated using a two-dimensional plasma hydrodynamics model with radiation transport, and the results are compared with experiments. The channel consists of a straight inlet section branching 90° into a circular loop which terminates to form a second straight outlet section aligned with the inlet section. The plasma is sustained in neon gas with a trace amount of xenon at atmospheric pressure. The FIW generated at the inlet approaches the first branch point with speeds of ≈10 8 cm s −1 , and produces a streamer at the inlet–loop junction. The induced streamer then splits into two FIW fronts, each propagating in opposite directions through half of the loop channel. The FIWs slow as they traverse the circular sections due to a shorting of the electric field by the other FIW. Approaching the loop–outlet junction, the two FIW fronts nearly come to a halt, induce another streamer which goes through further splitting and finally develops into a new FIW front. The new FIW increases in speed and plasma density propagating in the straight outlet channel. The electrical structure of the FIWs and the induced streamers during the splitting and merging processes are discussed with an emphasis on their mutual influence and their interaction with the channel wall. The FIW propagation pattern is in good agreement with experimental observations. Based on numerical and experimental investigations, a model for the splitting and merging FIWs in the branched loop channel is proposed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98591/1/0022-3727_45_27_275201.pd

Characterization of an atmospheric pressure pulsed plasma gun for biomedical applications

L’utilisation de plasmas, qu’ils soient thermiques ou basse pression, dans le domaine biomédical remonte aux années 1970. Au cours de ces dernières années, les développements concernant des jets de plasma froid à pression atmosphérique, ont permis un élargissement des domaines d’applications biomédicales des plasmas. Au sein du GREMI, un type de jet de plasma a été développé : le Plasma Gun. Le plasma généré par le Plasma Gun se propage sur de longues distances à l’intérieur de capillaires. L’optimisation des traitements visés nécessite une étude approfondie des décharges créées par le Plasma Gun. La caractérisation du Plasma Gun a mis en évidence la génération de Pulsed Atmospheric pressure Plasma Streams ou PAPS, ces derniers se propageant du réacteur jusque dans l’air ambiant où ils génèrent une plume plasma. Ces PAPS présentent deux modes de propagation, au cours desquels une connexion entre le front d’ionisation et le réacteur est présente en permanence. Ces deux modes nommés respectivement Wall-hugging et Homogène, diffèrent principalement par la morphologie et la vitesse de propagation des PAPS qui leur sont associés. Chacun de ces modes présentent donc des caractéristiques qui leur sont propres mais certaines propriétés de propagation leur sont communes, telles que la possibilité de division ou de réunion de PAPS, ainsi que du transfert de PAPS à travers une barrière diélectrique ou via un capillaire métallique creux. L’étude de la plume plasma, propagation des PAPS dans l’air ambiant, a souligné l’importance de la longueur des capillaires sur la longueur du jet plasma. De plus, la génération du plasma a une très forte influence sur l’écoulement du gaz et la structuration du jet lors de son expansion dans l’air.The use of plasmas, thermic or low pressure, in biomedical goes back up to 1970s. During these last years, atmospheric pressure cold plasma jets have been developed, allowed an increase of biomedical applications of plasmas. In GREMI, a plasma jet was developed : the Plasma Gun (PG). The plasma generated by the PG propagates on long distances inside capillaries. The optimization of the aimed treatments requires a detailed study of the discharges created by the PG. The characterization of the PG highlights the generation of Pulsed Atmospheric pressure Plasma Streams or PAPS, these last ones propagating from the reactor to the capillary outlet (ambient air) where they generate a plasma plume. These PAPS present two propagation modes, during which a connection between the ionization front and the reactor is present permanently. These two modes named respectively Wall-hugging and Homogeneous, differ mainly by the morphology and their propagation velocity. These modes have common characteristics, such as the possibility of division or meeting of PAPS, as well as the transfer of PAPS through a dielectric barrier or via a hollow metal capillary. The study of the plasma plume underlined the importance of the length of capillaries on the length of the plasma jet. Furthermore, the generation of the plasma has a very strong influence on the gas flow and the jet structuration during air expansion

Light hydrocarbons conversion in a pulsed DBD: Effect of temperature

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Experiments and modelling VOCs' removal in a DBD reactor

International audienceDielectric Barrier Discharges are commonly studied to remove Volatile Organic Compounds diluted in air at atmospheric pressure. Previously, we presented that a DBD heated up to 800 K lead to a high conversion rate at a total energy density lower than one at 300 K. Important effects of both temperature and energy density on produced species (nature and concentration) were observed. In this paper, we show that the discharge chemical effects can be described as chemical kinetics at 800 K. Streamer effects can be modeled as O-atoms generators. The DBD reactor is modeled by a successive elementary Plug Flow Reactors (PFR) distributed throughout the discharge tube. To simulate atomic oxygen production in streamers, O-atoms are injected at the inlet of each PFR. A combustion model is used to simulate the chemical kinetics. Taking into account both energy density and the PFR number a fitting variable, Fv, is introduced to fit the experimental results and data modelling

Diagnostic of the plasma gun operating condition : a pulsed plasma jet for biomedical applications

International audienceSince few years, cold atmospheric pressure plasma jets (C-APPJs) have recently attracted lots of attention and especially in a new field of plasma science: Plasma Medicine. C-APPJs have been used as a new tool for decontamination, therapeutic treatment… At GREMI, a new source has been developed, named Plasma Gun. The plasma gun is based on a high voltage dielectric barrier discharge, which works with rare gases at low flow rate (100 cm3.min-1). This device can generate plasma bullets which propagate at high velocity (108 cm.s-1) over one meter long flexible capillaries. These plasma bullets can be used for endoscopic treatment of tumors, as they can propagate in capillaries of few hundred micrometers inner diameter. In this work, time resolved ICCD imaging diagnostics of the plasma gun is described allowing the distinction between different bullet shapes along their propagation on a straight capillary. The dynamics of the bullet is directly connected with voltage and current measurements. Recently, a new property has been enlightened: the splitting of plasma bullets. Two symmetrical plasma bullets have been generated, and propagate similarly as in the straight capillary until meeting point. Their propagation is similar to the straight capillary. The mixing of two bullets induced a bullet with new property. This bullet can propagate in ambient air with high velocities.Cell treatments induce the necessity to generate particular species. These species has been generated by adding gases along the propagation of the bullets, or by using gas mixture to generate bullets. The evolution of the species has been performed by spectroscopic measurements.This work is supported through the APR Région Centre “Plasmed”, V.S. is supported by le Conseil Général du Loiret. D.R. is supported by Région Centre

Study of plasma bullets and microstructures generated by a pulsed plasma gun

International audienceA new plasma source, named Plasma Gun, has been developed in GREMI within the frame of the Plasmed project dedicated to plasma medicine applications. The Plasma Gun generates plasma bullets or bullet trains at very high velocities in dielectric tubes, connected to a HV DBD discharge reactor, over long distances that can exceed one meter in given discharge configurations. Bullet characterization has been performed using fast rise time HV probes, PIN photodiodes and ICCD camera. Measurements indicate that the plasma bullet generation occurred very early in the discharge formation, a priori during the risetime of the applied pulsed voltage. The bullets, which velocity decreases along their travel in the dielectric tube, are disconnected from the initial plasma source after a rather short distance (few cm) depending on discharge conditions. In some cases, we observed the formation of plasma microstructures around the dielectric tube probably due to intense electric field generated after the propagation of the plasma outside the initial discharge volume

Major challenges in the diagnostics of non thermal plasma sources relevant for biomedical applications

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Transfer of Pulsed Atmospheric-pressure Plasma Stream generated by a plasma gun

International audienceThe plasma gun, developed in GREMI, generates Pulsed Atmospheric-pressure Plasma Streams (PAPS) which propagate in dielectric capillaries or tubes. PAPS transfer can be induced by inserting metallic section along the plasma propagation path or via the plasma plume, generated at the capillary outlet, across the wall of rare gas flushed dielectric tube. Both electric field generated in the PAPS ionization front edge and charge transfer process are shown to be involved for PAPS transfer. Besides offering new insight in the PAPS propagation studies, these results open up new possibilities for non-thermal plasma delivery through dielectric or metallic or electrode-less capillaries

Atmospheric-pressure plasma transfer across dielectric channels and tubes

International audienceAtmospheric-pressure plasma transfer refers to producing an ionization wave (IW) in a tube or channel by impingement of a separately produced IW onto its outer surface. In this paper, we report on numerical and experimental investigations of this plasma transfer phenomenon. The two tubes, source and transfer, are perpendicular to each other in ambient air with a 4mm separation with both tubes being flushed with Ne or a Ne/Xe gas mixture at 1 atmosphere pressure. The primary IW is generated in the source tube by ns to μs pulses of ±25 kV, while the transfer tube is electrodeless, not electrically connected to the first and at a floating potential. The simulations are conducted using a two-dimensional (2D) plasma hydrodynamics model with radiation transport, where the three-dimensional tubes in the experiments are represented by 2D channels. Simulations and experiments show that the primary IW propagates across the inter-tube gap and upon impingement induces two secondary IWs propagating in opposite directions in the transfer tube. Depending on the polarity of the primary IW in the source tube, the secondary IW in the transfer tube can have polarities either the same or opposite to that of the primary IW. The speed and strength of both the primary and secondary IWs depend on the rate of rise of the voltage pulse in the source tube. The modelling results were found to agree well with the behaviour of plasma transfer observed using nanosecond intensified charge-coupled device imaging