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International audience; The breakdown voltage (Vb) of gases can be reasonably estimated using Paschen's law, which is based on assumptions such as a perfectly uniform electric field, and infinite electrode size. This analytical approach has demonstrated remarkable capability in redicting Vb in numerous cases, by scaling it by the product of pressure and nter-electrode distance (p·d). This description is quite efficient and convenient over wide ranges of pressure and gap distance. However, the robustness of Paschen's law in predicting consistent values of Vb is severely compromised at gap distances shorter than typically 1 micrometer at atmospheric pressure. Several studies have provided experimental, theoretical, and simulation evidences highlighting these limitations. This raised significant concerns, both theoretical and practical, about the insulation properties of gases at short distances. This study focuses on experimentally investigating Vb of air in short electrode gaps, ranging from 100 nm to 6 μm. The electrode system consists of a silicon wafer coated with gold, connected to ground. The anode connected to high voltage is a sharp CuBe needle coated with gold, with 20 μm tip radius of curvature. The gap distance is controlled by a piezoelectric actuator. Ambient air is used at atmospheric pressure, allowing for comparisons with data from existing literature. Complementary experiments are also performed in a closed chamber allowing to vary the pressure from 10-4 mbar to 3.0 bar, and control the gas purity and water content.

The simulation of corona discharges usually requires an excessive amount of time. The objective of this work is therefore to reduce the CPU time of corona discharges. The profound disparity between physical time scales in a gas discharge renders explicit time integration impractical in large time scale applications, for example in flow controls. We propose an implicit time strategy in the scope of the Local Field Approximation plasma model. We investigate some algorithms to solve the discretized plasma model, which are adapted to take into consideration a constraint on the electron density. The constraint is introduced to compensate for unaccounted sources of electrons; it is expressed by a minimum/floor density imposed on the electrons. Therefore, simplified plasma models can be employed for discharge simulations, for instance a four-specie, four-reaction model is used in this article. The investigation is done on a one-dimensional wire-to-wire corona discharge. After having identified the most suitable algorithm, we carry on to two-dimensional wire-to-wire discharges and compare the numerical results with experiment data for different floor densities.

International audience; This paper is a broad overview and a summary of the recent progress achieved in Ion Cyclotron Range of Frequency (ICRF) Systems, Experiments and Modeling during the last twenty years in magnetic confinement fusion experiments. It has been written mainly for students or newcomers in this exciting field and introduces the different applications and lists the main detrimental effects associated with the use of ICRF in magnetic fusion experiments. Modelling techniques and state-of-the-art ICRF systems are described. Recent results obtained with ICRF in fusion plasma experiments are summarised. Planned ICRF projects such as ITER or future fusion reactors and the remaining issues that remain to be solved are detailed.

The size of a hard Kα x-ray source ($${\mathrm{E}}_{{\rm{K}}_{\rm{\alpha }}}$$ E K α = 17.48 keV) produced by a high intensity femtosecond laser interacting with a solid molybdenum target is experimentally investigated for a wide range of laser intensity (I ~ 1017–2.8 × 1019 W/cm2) and for four values of the temporal contrast ratio (6.7 × 107 10). Results point out the size enlargement of the x-ray source with the increase of laser intensity and with the deterioration of temporal contrast. It amounts up to sixteen times the laser spot size at the highest laser intensity and for the lowest temporal contrast ratio. Using hydrodynamic simulations, we evaluate the density scale length of the pre-plasma L/λ just before the main pulse peak. This allows us to show that a direct correlation with the laser absorption mechanisms is not relevant to explain the large size broadening. By varying the thickness of the molybdenum target down to 4 µm, the impact of hot electron scattering inside the solid is also proved irrelevant to explain the evolution of both the x-ray source size and the Kα photon number. We deduce that the most probable mechanism yielding to the broadening of the source size is linked to the creation of surface electromagnetic fields which confine the hot electrons at the solid surface. This assumption is supported by dedicated experiments where the evolution of the size enlargement of the x-ray source is carefully studied as a function of the laser focal spot size for the highest contrast ratio.

International audience; The frequency-resolved terahertz (THz) beam profile characteristics of a two-color air-plasma THz source were investigated in the broadband frequency range (1-15 THz). The frequency resolution is achieved by combining THz waveform measurements and the knife-edge technique. Our results show that the THz focal spot size is strongly frequency dependent. This has important implications on nonlinear THz spectroscopy applications where accurate knowledge of the applied THz electrical field strength onto the sample is important. In addition, the transition between the solid and hollow beam profile of the air-plasma THz beam was carefully identified. Far from the focus, the features across the 1-15 THz range have also been carefully examined, revealing the characteristic conical emission patterns at all frequencies.

International audience; Knowledge of thermodynamic properties as well as parameters such as energy density and power flow isimportant for modeling thermal plasmas of fluoroalkylamine-air mixtures. In this paper, these thermodynamic properties of fluoroalkylamine-air mixture plasmas are calculated in a temperature range of 500 K to 20,000 K at atmospheric pressure and local thermodynamic equilibrium (LTE). The Gibbs free energy minimization method is used to determine the chemical equilibrium compositions of the plasmas that are needed to calculate the thermodynamic properties. These thermodynamic properties are then used to calculate the energy density and power flow of these plasmas. The variation of the energy density is related to the variations of the density and mass enthalpy. We notice that, this energy density increases with the percentage of air in the mixture for temperatures higher than 7000 K. The power flow, which depends also on density, enthalpy mass and sound speed, increases with the percentage of air in the same temperature range. Energy density and power flow results show that increasing air percentage in the mixture can be more interesting for damaging gaseous chemical species such as CF2, CO, HCN, and HF appearing at low temperatures with high concentrations.

International audience; Methods to follow in real time complex processes occurring along living cell membranes such as cell permeabilization are rare. Here, the terahertz spectroscopy reveals early events in plasma membrane alteration generated during photodynamic therapy (PDT) protocol, events which are not observable in any other conventional biological techniques performed in parallel as comparison. Photodynamic process is examined in Madin-Darby canine kidney cells using Pheophorbide (Pheo) photosensitizer alone or alternatively encapsulated in poly(ethylene oxide)-block-poly(ε-caprolactone) micelles for drug delivery purpose. Terahertz spectroscopy (THz) reveals that plasma membrane permeabilization starts simultaneously with illumination and is stronger when photosensitizer is encapsulated. In parallel, the exchange of biological species is assessed. Over several hours, this conventional approach demonstrates significant differences between free and encapsulated Pheo, the latter leading to high penetration of propidium iodide, Na+ and Ca2+ ions, and a high level of leakage of K+, ATP, and lactate dehydrogenase. THz spectroscopy provides, in a single measurement, the relative number of defects per membrane surface created after PDT, which is not achieved by any other method, providing early, sensitive real-time information. THz spectroscopy is therefore a promising technique and can be applied to any biological topic requiring the examination of short-term plasma membrane permeabilization.

International audience; Pulsed gas injection in a plasma can affect many fundamentals, including electron heating and losses. The case of an asymmetric RF magnetron plasma with a pulsed argon injection is analyzed by optical emission spectroscopy of argon 2p-to-1s transitions coupled with collisional-radiative modeling. For a fully detailed population model of argon 2p levels accounting for direct and stepwise electron-impact excitation in optically thick conditions, a rapid decrease in the electron temperature, Te, is observed during each gas injection with the sudden pressure rise. The opposite trend, with unrealistic Te values before and after each pulse, is observed for analysis based on simple corona models, thus emphasizing the importance of stepwise excitation processes and radiation trapping. Time-resolved electron temperature variations are directly linked to the operating parameters of the pulsed gas injection, in particular the injection frequency. Based on the complete set of data, it is shown that the instantaneous electron temperature monotonously decreases with increasing pressure, with values consistent with those expected for plasmas in which charged species are produced by electron-impact ionization of ground state argon atoms and lost by diffusion and recombination on plasma reactor walls.

Sander Bekeschus and Sylvain Iséni equally contributed to this work as first authors.; International audience; Parameter studies of plasma treatment are informative about the optimal use of this technology in biomedical applications such as the argon radio-frequency plasma jet kINPen. However, the interdependence of the plasma-dissipated power in relation to input current and feed gas modulation on the resulting biological consequences has not been studied so far. To this end, a parameter study is presented, and the effect on human immune cell viability was investigated across different input current power and argon with oxygen/nitrogen feed gas admixture settings. It was found that with both nitrogen and oxygen admixtures, a concentration-dependent change in plasma-dissipated power emerged, which converged at 27.5 mA and 26.5 mA, respectively. The extent of cytotoxicity in immune cells confirmed the relevance of these findings, which were in congruency with the plasma dissipated powers identified. These findings underline the critical role and input parameter-dependent action of plasma sources for biomedical application.Dr Sander Bekeschus and Dr Sylvain Iséni equally contributed to this work as first authors.

Non-thermal plasma is widely considered as an effective technology for applications in agriculture. Particularly, numerous reports studies have highlighted the role of plasma-activated water (PAW) for seeds germination, plant growth, stress tolerance, and antibacterial ability. The present study investigated the effects of PAW on lettuce (Lactuca Sativa L.) seed germination and seedling growth. PAW was achieved by using an atmospheric pressure dielectric barrier discharge in Ar (50%) –N2 (40%)–O2 (10%) gas mixture for treatment time ranging from 5 to 30 mn. The physicochemical properties of PAW (temperature, pH, electrical conductivity, concentrations of nitrate, nitrite, and hydrogen peroxide) were evaluated. Results show that water-activated during moderate time, 10 to 20 mn, contains reactive oxygen and nitrogen species at relevant concentration levels to have active impacts on seed germination and seedling growth. Germination potential significantly increased by about 117%, 56%, and 77% after 15 mn of treatment, for the first 3 days, respectively, compared to control. For long time PAW (25–30 mn), the germination rate is either constant or decreases. Positive effects of PAW treatments were registered on the growth parameters of seedling including stem and root length, leaf weight, leaf area and chlorophyll content, and the vigor of seedlings. Chlorophyll content significantly increased by 220% for PAW-treated 15 mn and by about 165% for PAW-treated 20 mn, respectively, compared with control. Additionally, PAW induce morphological changes on lettuce seeds which are associated with oxidizing species leading to better water and nutrients uptake.

International audience; In this chapter, we focus on the application of plasma structures to realize reconfigurable antennas. Several approaches are presented to dynamically control the beamwidth and radiation gain of circularly polarized helical antennas based on plasma reflectors. Ideas and design principles were discussed and confirmed by full-wave simulations and measurements of realized prototypes. It is shown that plasma reflectors can be effectively used to design reconfigurable helicone antennas with controllable gain and beamwidth. The chapter also presents a reconfigurable slotted antenna using a plasma tube inside the metallic waveguide. It is shown that the radiation pattern of the antenna can be readily reconfigured by changing the state of the plasma column. In short, it is shown that in contrast to conventional methods based on electronic or mechanical devices, reconfigurable antennas based on plasma media benefit from simple and relatively low-cost structures as well as high performance.

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The reactivity of platinized ultramicroelectrodes (Pt-black UMEs) towards superoxide anion O2.−, an unstable Reactive Oxygen Species (ROS), and its relatives, H2O2 and O2, was studied. Voltammetric studies in PBS demonstrate that Pt-black UMEs provide: i) a well-resolved reversible redox signature for O2.− detected in both alkaline and physiological buffers (pH 12 and 7.4); ii) irreversible oxidation and reduction waves for H2O2 at pH 7.4. The oxygen reduction reaction (ORR) at Pt-black surfaces solely yields H2O2 (2 electrons/2 H+) at physiological pH. Consequently, Pt-black UMEs allow to sense different ROS including superoxide anion for future biomedical or physico-chemical investigations.

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International audience; The high-dimensional and multiscale nature of fusion plasma flows require the development of reduced models to be implemented in numerical codes capable of capturing the main features of turbulent transport in a sufficiently short time to be useful during tokamak operation. This paper goes further in the analysis of the dynamics of the κ − ε model based on the turbulent kinetic energy κ and its dissipation rate ε [Baschetti et al., Nuc. Fus 61, 106020 (2021)] to improve the predictability of the transverse turbulent transport in simulation codes. Present 1D results show further capabilities with respect to current models (based on constant effective perpendicular diffusion) and on the standard quasi-linear approach. The nonlinear dependence of D in κ and ε estimated from two additional transport equations allow to introduce some non-locality in the transport model. This is illustrated by the existence of parameter ranges with turbulence spreading. The paper also addresses another issue related to the uncertainties on the inherent free parameters of such reduced model. The study proposes a new approach in the fusion community based on a variational data assimilation involving the minimisation of a cost function defined as the distance between the reference data and the calculated values. The results are good, and show the ability of the data assimilation to reduce uncertainties on the free parameters, which remains a critical point to ensure the total reliability of such an approach.

International audience; Plasma micro reactors are in their whole elaborated in clean room by MEMS fabrication techniques. They are usually made on silicon platform and constituted by SiO2 dielectric grown by thermal oxidation and nickel coated by PVD process. Electrical and optical characterizations are the main diagnostics used to determine the properties of the discharge and the robustness of the device. SEM images are also made before and after plasma operation. These DC microdischarges can operate continuously during more than 24 hours in stable regime from 100 Torr up to the atmospheric pressure. In these conditions, a high density of reactive species is produced and can be used for gas, liquid or surface treatment.

This paper investigated thin films deposition processes of silica-like based on the injection of liquid droplets in Atmospheric Pressure Plasma Jet–APPJ operated in open air. An aerosol of hexamethyldisilane is produced by a syringe-pump and injected in a nitrogen post-discharge for different liquid precursor and carrier gas flow rates. For high carrier gas flow, this process enables to form silica-like without addition of oxygen in the plasma phase. Furthermore, this process offers a thin film dynamic deposition rate from 500 to 1400 nm.m.min−1 depending on the carrier gas flow and the film structure departs from silica-like to organosilicon layers for the lowest flow rates. These evolutions are attributed to plasma–droplets interactions related to the transport of droplets, the evaporation of liquid and plasma polymerization.

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National audience; Climate change is predicted to cause severe loss in agricultural production by increasing disease epidemics and intensifying abiotic stresses. Therefore, there is a need for sustainable methods to alleviate plant stress, such as non-thermal plasma. Here we review the role of non-thermal plasma for plant treatment, with focus on the control of viruses, bacteria, fungi and other diseases. We present factors influencing the microbicidal activity of non-thermal plasma. Application of non-thermal plasma for combating abiotic stresses such as drought, metal toxicity, nanoparticles and salinity are discussed. Plasma-generated reactive species trigger the activity of stress-responsive genes in plants. The hypothetical mechanisms involved in triggering the activity of different stress-responsive genes controlling diseases as well as abiotic stresses, are also presented and discussed. The mechanism of plant-plasma interaction is similar to priming, hormesis or adaptive response, and resembles vaccination in animals and humans.

Plasma-Assisted Combustion (PAC) has shown potential in improving the ignition, extinction, and dynamic performance of combustion systems. In this work, nanosecond repetitively pulsed (NRP) spark discharges are applied to extend the lean blow out (LBO) limit of the SICCA-Spray burner. This laboratory-scale atmospheric test rig is equipped with a swirl spray injector representing in an idealized fashion a single sector of a gas turbine. Three fuels and injection conditions are considered: perfectly premixed methane–air, liquid heptane, and liquid dodecane injected as hollow cone sprays. The optimal electrode position that extends the LBO limit is found to be near the external edge of the outer recirculation zone (ORZ). Spectroscopic measurements show that the NRP sparks produce atomic species and heat the gas above the adiabatic flame temperature. High-speed chemiluminescence images of blow out sequences indicate that the flame evolves similarly for all three fuels from “M” or “V” shapes prevailing at ϕ = 0.9 to a configuration where chemical conversion also takes place in the ORZ at ϕ = 0.63 . A low frequency combustion oscillation arises near the LBO limit ( ϕ = 0.57 ). Spray flames blow out at this point, while the plasma-assisted ones continue to burn. It is shown that PAC provides a significant improvement of the extinction performance, in particular when operating with liquid fuel spray injection.

International audience; Platinum (Pt), platinum-bismuth (PtBi), platinum-copper (PtCu) and platinum-bismuth-copper (PtCuBi) clusters were grown in a gas aggregation source (GAS) equipped with three in-plane plasma magnetrons located in a single region of the gas aggregation zone. The X-ray diffraction results have shown that PtCu clusters form alloys as the decrease of the lattice parameter occurs when the Cu atomic content increases. PtBi clusters do not form alloys, but the presence of secondary Bi oxide phases was detected. Scanning transmission electron microscope mapping images revealed that simultaneously adding Bi and Cu to Pt leads to PtCu alloyed clusters decorated with Bi or CuBi species on the surface. The electrochemical results indicated that the shell might be composed of a metastable CuBi phase. Electrochemical measurements have shown that the addition of Bi or Cu to the Pt clusters enhances the catalytic activity for glycerol oxidation by decreasing the oxidation onset potential.

In order to mitigate debris in the low Earth orbit and to avoid dramatic collisions on Earth after atmospheric reentry at its end of life, the spacecraft mission has to take into account the influence of reentry on the spacecraft survivability. In this way, oxidation in air plasma conditions was studied on metallic alloys such as TA6V to obtain oxidation kinetic laws at high temperature and for short time duration (few minutes). Experimental results obtained for the oxidation of TA6V at high temperature and low pressure in air plasma conditions together with microstructural characterization using SEM and XRD are presented. For a constant holding time of oxidation of 300 s for two total air pressures (300 and 2000 Pa) in the temperature range 1300–1900 K, the mass variation versus reciprocal temperature follows an Arrhenius law that gives a same activation energy of around 62–64 kJ/mol showing the low influence of pressure. Then kinetics laws were obtained for a constant temperature of 1830–1840 K for 3 pressures (300, 2000 and 5000 Pa) in the short time interval 50–470 s. The oxidation of the TA6V alloy by atomic oxygen leads to the spallation of the oxide layers even for short duration, and thus, the space debris during its atmospheric reentry will lose very few mass and the debris will reach the Earth only partially destroyed. The mass loss was calculated, and finally, it was shown that it represents only 0.5‰ of the initial mass of the TA6V alloy.

International audience; A new low-Mach algorithm for the thermal lattice Boltzmann method (LBM) is proposed aiming at reducing the computational cost of thermal flow simulations in the low Mach number limit. The well-known low Mach number approximation is adopted to accelerate the simulations by enlarging the time step through re-scaling the psuedoacoustic speed to the same order of the fluid motion velocity. This specific process is inspired by the similarity between the artificial compressibility method and the isothermal LBM and is further extended to its thermal counterpart. It must be emphasized that such low-Mach acceleration strategy is in a general form, thus can be easily applied to other compressible LB methods. The present method overcomes the drawback of the classical pressure gradient scaling method due to the pressure gradient changing. The new algorithm is validated by various well-documented academic test cases in laminar [one dimensional gravity column, 2D (two dimensional) rising thermal bubble, and 2D differentially heated square cavity] and turbulent [3D (three dimensional) Taylor–Green vortex and 3D heated cylinder] regimes. All the results show excellent agreement with the reference data and high computational efficiency.

7èmes Journées Scientifiques 2022 GT Matériaux Diélectriques, GdR SEEDS, Grenoble"Décharges électriques et matériaux isolants : Phénomènes et Applications"; National audience; La rupture dielectrique d’un gaz est un aspect critique pour les applications reposant sur l’isolation électrique telles qu’utilisée dans les dispositifs de coupures électriques ou autres systèmes de contact. La tension de claquage peut elle, être estimée en bonne approximation grâce à la loi de Paschen établie il y a plus d’un siècle. Cette dernière est basée sur des fondements théoriques simples moyennant un certains nombres d’hypothèses (champ électrique rigoureusement uniforme, dimensions infinies des électroqdes, rugosité de surface nulle…). Cette approche analytique a montré sa capacité remarquable de prédiction de la tension de claquage pour un nombre incalculable de systèmes non-idéaux. S’artilant autour du produit pression·distance (p·d), la loi de Paschen s’exploite sur une large échelle de pression couplée à des distances relativement adaptées à leurs utilisations; des distances macroscopiques. Indépendament des incertitudes autours des constantes présentes dans formalisme mathématique, la fiabilité que l’on connait de cette loi faillie dès lors que les distances inter-électrodes se rapprochent du micromètre et en dessous. Plusieurs études ont téhoriques et expérimentales ont déjà mis en évidence cette limitation qui remet en question le caratère isolant d’un gaz même à des préssions de lors de l’atmosphère ou au-dessus.Cette contribution rapporte les premiers résultats du d’étude expérimentale visant à mieux comprendre les mécanismes de claquages lors de très faibles distances inter-électrodes. Les distances typiques sont de l’ordre de la centaine de nanomètres entre une pointe de rayon de courbure de quelques micromètres et un plan de faible rugosité relativement au gap. Des conditions expérimentales spécifiques permettront de mettre en évidence la possibilité d’initier un claquage à des tensions de 30V ce qui ouvre de nouvelles perspectives notamment dans le domaine de microsystèmes de type MEMS.

International audience; In this study, the SPS of 0.1 µm zirconia has been performed and shows high densification rate behavior in the final stage. This work consists of modeling the densification behavior of this powder especially at the intermediate/final stage transition. To model this, a Master Sintering Curve (MSC) is combined with an analytic model to identify the activation energy and the sintering moduli. The modeling of the behavior of the powder during the sintering tests is done via the Skorohod-Olevsky model. It appears from this study that the modeling of final stage sintering requires a regime transition to model the exceptionally high densification rate of the powder. The final stage grain growth seems not to decrease the final stage sintering kinetics.

In the present work we investigate for the first time the 2D fluid transport of the plasma in WEST during an entire discharge from the start-up to the ramp-down (shot #54487). The evolution of density profile, electron and ion temperatures together with the experimental magnetic equilibrium, total current and gas-puff rate is investigated. Comparisons with the interferometry diagnostic show a remarkable overall qualitative agreement during the discharge that can be quantitative at some locations in the plasma core. If at the onset of the X-points during the ramp-up the electron heat flux is dominant at the target, present results show that the ion heat flux becomes dominant during the stationary phase of the discharge. Using a simple model for erosion, present results assess the tungsten sputtering due to deuterium ions during the start-up and ramp-up phases of the discharge and confirm the need to consider full discharge simulation to accurately treat the W source of contamination. This work also demonstrates the interest of developing magnetic equilibrium free solver including efficient time integration to step toward predictive capabilities in the future for fusion operation.

A low-temperature plasmas jet is generated by a dielectric barrier discharge powered by a pulsed high voltage in helium flow (3 L min−1) at atmospheric pressure in the presence of different targets (a glass slide, ultra-pure water and a grounded metal plate) positioned perpendicular to the plasma propagation axis. Experimental electrical characterizations such as discharge current, voltage and power, and optical characterizations such as intensified camera ICCD, Schlieren imaging and emission spectroscopy to follow specific excited species have been achieved. The transition from laminar to turbulent regime was observed during the discharge ignition with a larger spreading of the plasma on the surface target with lower dielectric permittivity. The generation of two discharges during each voltage pulse is highlighted during the propagation of the ionization wave which has a variable speed along the plasma axis not depending on the target kind. The evolution of some active species (such as OH, O and excited nitrogen and helium) are investigated using time resolved mapping of the emissions of radiative excited species propagating in ambient air between the plasma jet output and the target. For a low relative permittivity target (glass), the volume ionization wave at its arrival on the target spreads on its surface thus behaving as a surface ionization wave. For the highest relative permittivity (metal), a conductive channel appears between the target surface and the plasma jet during the first discharge, followed by a diffuse plasma plume from the target surface towards the plasma jet after the impact of the ionization wave on the target. A hybrid behavior is highlighted for the ultra-pure water which leads to a short spreading of the ionization wave on the target surface, the formation of a conductive channel in ambient air between tube output and target and the formation of a plasma plume on the target surface.

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Introducción. Dentro de las cámaras de alto vacío de los inyectores de partículas neutras al plasma de los futuros reactores de fusión nuclear, como el ITER o DEMO, se producen las llamadas “corrientes parásitas” que, con el tiempo, provocan el deterioro de diferentes componentes. A pesar de que esta emisión típica tiene una explicación sobre la base de la teoría de emisión de campo, aún quedan muchas interrogantes por ser descritas. El objetivo fue utilizar la Teoría del Funcional de la Densidad, como base principal para la descripción de algunos aspectos de la emisión electrónica desde superficies contaminadas o con irregularidades nanométricas. Métodos. Los estudios fueron realizados en superficies de tungsteno y carburo de tungsteno contaminadas con carbono, así como en superficies corrugadas de tungsteno limpio. Resultados. Se generaron nuevos conocimientos sobre el origen de las “corrientes parásitas” y su relación con diferentes irregularidades de las superficies de los cátodos.

This work investigates the effects of process parameters on thin-film deposition by direct liquid injection in a low-frequency dielectric barrier discharge. The precursor, hexamethyldisiloxane, is introduced as micrometer-size liquid droplets with nitrogen carrier gas in a pulsed mode and the discharge is produced at atmospheric pressure in a pulsed regime. No significant deposit is observed during plasma-off time and outside the discharge region. Despite the pulsed injection, this reveals that the precursor content in the plasma zone remains constant over much longer time scales and that thin-film deposition results from droplets charging and their transport towards the dielectrics by the low-frequency electric field. Over the range of experimental conditions investigated, it is found that pulsed, aerosol-assisted plasma deposition is limited by the amount of energy provided to precursor droplets, and not by precursor insufficiency.

International audience; Discharging of dust particles in an argon plasma afterglow is investigated using different approaches. First, the dust charge distribution function (DCDF) is obtained by solving numerically the master equation describing dust discharging as a one-step stochastic process. Second, the DCDF is calculated as a Gaussian distribution with mean dust charge and variance, which are functions of time. Additionally, the time-dependencies for the mean dust charge are obtained assuming that the charge changes continuously in the afterglow plasma. Calculation results are compared with available experimental data and are found to be in good qualitative agreement if the dust discharging model accounts for the emission of electrons in the collisions of excited argon atoms with dust particles. This study is carried out taking into account the transition from ambipolar to free diffusion as well as multistep ionization, excitation, and deexcitation of argon atoms in the plasma afterglow.

Transport processes around the magnetic X-point of tokamaks, such as turbulence and mean-field drifts, are scarcely understood. The assessment of the capability of turbulence codes to quantitatively reproduce these dynamics has been hampered by limitations in computational power and available experimental data. In this paper, we present a rigorous validation of full-scale simulations of a newly developed X-point scenario in the basic toroidal plasma device TORPEX, performed with the four state-of-the-art codes FELTOR, GBS, GRILLIX, and STORM. High-resolution Langmuir probe array measurements of various time-averaged and fluctuating quantities and across the entire cross section of TORPEX show that this X-point scenario features the key ingredients of X-point dynamics, such as small-scale fluctuations and background drifts. The codes are able to qualitatively reproduce some characteristics of the time-averaged fields, such as the ion saturation current profiles at mid-height, the plasma up-down asymmetry, and the blob trajectories. A quantitative agreement is found for the background E × B velocity pattern, while the fluctuation levels are generally underestimated typically by factors of 2 or more, and thus, background fluxes are found to dominate over turbulent ones in simulations. The sensitivity of the simulation results on the plasma collisionality and on the position of the sources is tested in GBS, showing a mild effect on the overall quantitative agreement with the experiment. Overall, this validation reveals the challenges to reproduce the plasma dynamics near an X-point and provides a clear path to a quantitative and computationally relatively inexpensive assessment of future developments in turbulence codes.

International audience; The properties of an Ar/C2H2 dusty plasma (neutral, ion and electron densities, effective electron temperature and dust charge) are studied using a volume-averaged model. The steady-state plasma is considered, as well as the case when the dust radius varies with time in the same way as in our experiments. It is analysed how different process conditions (absorbed power, input flux of acetylene, electron energy distribution function and nanoparticle density) affect the plasma properties. The results of our calculations are compared with our experimental results on growth of nanoparticles in an Ar/C2H2 plasma and the results are found to be in a good qualitative agreement.

Time-resolved optical emission spectroscopy of nanosecond-pulsed discharges ignited in liquid nitrogen between two bismuth electrodes is used to determine the main discharge parameters (electron temperature, electron density and optical thickness). Nineteen lines belonging to the Bi I system and seven to the Bi II system could be recorded by directly plunging the optical fibre into the liquid in close vicinity to the discharge. The lack of data for the Stark parameters to evaluate the broadening of the Bi I lines was solved by taking advantage of the time-resolved information supported by each line to determine them. The electron density was found to decrease exponentially from 6.5 ± 1.5 × 1016 cm−3 200 ns after ignition to 1.0 ± 0.5 × 1016 cm−3 after 1050 ns. The electron temperature was found to be 0.35 eV, close to the value given by Saha’s equation.

International audience; This work examines the combination of pulsed direct-liquid injections with dielectric barrier discharge at atmospheric pressure for the deposition of organosilicon coatings using hexamethyldisiloxane (HMDSO) as the precursor and nitrogen as the carrier gas. In such conditions, deposition relies on the charging of micrometer droplets and their transport toward the substrate by the Coulomb force. The thin-film morphology and extent of precursor fragmentation are strongly linked to the amount of energy provided by the filamentary discharge to HMDSO droplets. While cross-linked and smooth coatings were achieved at low energies as in standard gas phase plasma polymers, viscous and droplet-like structured thin films were deposited at higher energies. The latter material is attributed to the soft polymerization of HMDSO droplets related to plasma–droplet interactions.

International audience; The main objective of this study is to show that the abnormally high mass of some ancient bones from archaeological sites could be due to chronic ingestion of large amounts of fluoride that would have led to a serious condition called skeletal fluorosis.Fluorine being a difficult element to quantify by standard analytical methods and especially by those using portable equipment, we have evaluated the potential of LIBS in a bioarchaeological study of samples from the sites of Cumae and Pompeii in Italy.However, fluorine atomic emission lines are generally not detected in LIBS spectra of bone samples and therefore the molecular bands of CaF were exploited in our study. A regression model was established between the LIBS signal of CaF and the fluorine concentration from PIXE-PIGE analyses from a dedicated batch of bone samples.The results obtained show that the performance of fluorine quantification in bones by LIBS is very satisfactory and that it is thus possible to distinguish bones from individuals suspected to have skeletal fluorosis from those that are not.All spectra were recorded with a portable LIBS instrument and processed with software developed at IRAMAT-CRP2A laboratory.

The invention relates to electrical engineering, namely to high and ultrahigh pressure gas-discharge lamps. The invention encompasses high power short arc xenon lamps, high pressure mercury short arc lamps, and all other short arc lamps with a cathode doped with an easily ionizable additive and an anode with a diameter larger than that of the gas discharge arc. The technical and economic efficiency of the claimed invention consists in increasing the efficiency of generation of optical radiation in the selected region of the spectrum. The effect is achieved by an appropriate choice of the shape of the working surface of the anode facing the cathode.

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International audience; Abstract Dielectric nanocomposite materials are now involved in a large panel of electrical engineering applications ranging from micro-/nano-electronics to power devices. The performances of all these systems are critically dependent on the evolution of the electrical properties of the dielectric parts, especially under temperature increase. In this study we investigate the impact of a single plane of silver nanoparticles (AgNPs), embedded near the surface of a thin silica (SiO 2 ) layer, on the electric field distribution, the charge injection and the charge dynamic processes for different AgNPs-based nanocomposites and various temperatures in the range 25°C–110°C. The electrical charges are injected locally by using an Atomic Force Microscopy (AFM) tip and the related surface potential profile is probed by Kelvin Probe Force Microscopy (KPFM). To get deeper in the understanding of the physical phenomena, the electric field distribution in the AgNPs-based nanocomposites is computed by using a Finite Element Modeling (FEM). The results show a strong electrostatic coupling between the AFM tip and the AgNPs, as well as between the AgNPs when the AgNPs-plane is embedded in the vicinity of the SiO 2 -layer surface. At low temperature (25°C) the presence of an AgNPs-plane close to the surface, i.e., at a distance of 7 nm, limits the amount of injected charges. Besides, the AgNPs retain the injected charges and prevent from charge lateral spreading after injection. When the temperature is relatively high (110°C) the amount of injected charges is increased in the nanocomposites compared to low temperatures. Moreover, the speed of lateral charge spreading is increased for the AgNPs-based nanocomposites. All these findings imply that the lateral charge transport in the nanocomposite structures is favored by the closely situated AgNPs because of the strong electrostatic coupling between them, additionally activated by the temperature increase.

International audience; As plasma processes are atomic and molecular by nature, simulations at the molecular level will be relevant for providing us with insights into core and interface plasma chemistry basic phenomena. Moreover, statistical averaging allows to provide/predict macroscopic data as reaction rates, diffusion coefficients, ... directly comparable with experiment outputs. Among all the available molecular simulation tools, (reactive) molecular dynamics (MD) simulation technique is a good compromise between quantum mechanical and kinetic Monte-Carlo methods, especially due to the availability of robust and accurate reactive force fields [1]. Moreover, such reactive forcefields are also calculating partial chages at any relevant times using charge equilibration algorithm. In the context of plasma chemistry this will allow to address charge transfer mechanisms. Using this forcefields, MD simulations are able to calculate the trajectories of a set of particles, by solving the appropriate set of Newton equations of motion. For realistic comparisons with experiments, inputs of MD simulations have to be selected for matching experimental conditions. Addressing reactive plasma processes remains a quite challenging and useful task. Two examples nicely illustrate the interest of carrying out reactive molecular dynamics simulations: i) Hydrocarbon plasma deposition, including plasma phase reactivity [2] and ii) plasma-liquid interaction, especially effects of plasma produced reactive oxide and nitride species on organic molecules in water [3]. Both methodological aspects of MD simulation implementation for these plasma processes and determination of statistical data directly comparable with experiments will be reviewed.[1] E. C. Neyts, P. Brault, Plasma Process. Polym. 14 (2017) 1600145[2] D. Graves, P.Brault, J. Phys. D: Appl. Phys. 42 (2009) 194011 [2] P. Brault et al, J. Appl. Phys. 129 (2021)

International audience; This article reports on the characterization of a laboratory model 100 A-class hollow cathode with a sintered lanthanum hexaboride (LaB6) emitter for high-power Hall thrusters. The cathode has been fired up to 70 A with xenon as working gas. The cathode architecture, test setup, ignition procedure, and power consumption are described first. The second part of this contribution comments on the current–voltage characteristics and the discharge modes obtained for discharge currents in the 30–70 A range and flow rates in the 15–30 SCCM range. The cathode operates in a spot mode at high discharge currents and in a plume mode with large oscillations at low currents and low gas flow rate. Spectral analysis shows that most frequencies reside in the 10–200 kHz range with flat and sharp distributions in plume and spot modes, respectively. Finally, we present electron temperatures and densities measured in the cathode plasma plume by means of incoherent Thomson scattering. The two quantities decrease along the axis. The density is large (up to ∼1019m−3) and increases with both the ion current and the gas flow rate. The electron temperature increases with the current and decreases with the gas flow rate. The temperature remains relatively low (

Denture stomatitis is a disease involving C. albicans, which can affect elderly and immuno-compromised people. To avoid any recurrence of this pathology, it is necessary to treat patients regularly and disinfect dentures. However, the denture cleansers’ efficacy is not optimal and often leads to adverse color effects on the denture base resins. The aim of this study was to investigate the efficacy of a low-pressure non-thermal O2 plasma (NTP) treatment on C. albicans seeded on ProBase®Hot resin (Ivoclar Vivadent). The viability reduction of C. albicans was assessed by colony forming units (CFU) analysis and by scanning electron microscopy (SEM). The effect of repeated treatments on the resin color was evaluated by spectrophotometry. The resin samples were placed in a sealed bag in which O2 plasma was generated in low-pressure conditions. The results showed that a 120-min O2 NTP treatment led to a 6-log reduction of C. albicans viability (p &lt, 0.05) and to yeasts’ major alterations observed by SEM. Furthermore, significant slight color changes of the resin (∆E00 = 1.33) were noted only after six plasma treatments (p &lt, 0.05). However, the denture aesthetic was preserved, as the color changes were not perceptible and remained below the acceptability threshold (∆E00 &lt, 4).

International audience

International audience; This paper addresses simulation of heat dominated compressible flows in a closed cavity using a pressure-based lattice Boltzmann (LB) method, in which thermal effects are modeled by applying a pressure-featured zero-order moment of distribution functions. A focus is made on the conservation of mass at boundary nodes, which is a challenging issue that significantly complicated by the density-decoupled zero-order moment here. The mass leakage at boundary nodes is mathematically quantified, which enables an efficient local mass correction scheme. The performance of this solver is assessed by simulating buoyancy-driven flows in a closed deferentially heated cavity with large temperature differences (non-Boussinesq) at Rayleigh numbers ranging from 103 to 107. Simulations show that mass leakage at solid walls in such configurations is a critical issue to obtain reliable solutions, and it eventually leads to simulations overflow when the cavity is inclined. The proposed mass correction scheme is, however, shown to be effective to control the mass leakage and get accurate solutions. Thus, associated with the proposed mass conservation scheme, the pressure-based LB method becomes reliable to study natural convection dominated flows at large temperature differences in closed geometries with mesh aligned boundaries or not

International audience; This work presents an analysis of the full-bridge voltage inverter widely used to supply dielectric barrier discharges. The main contribution of this work is the deduction of the analytical equations for the delivered power, peak voltage and duration of the discharge as a function of the DC input voltage and of the switching frequency, but also, as a function of the parasitic elements of the transformer and the parameters of the DBD load. To date, these equations are not found in the literature and are useful to design a power converter complying with specifications derived from plasma process requirements. The state plane is used to understand the different sub-intervals taking place in an entire switching period. The equations are verified using a simple example of design, which implementation accurately obeys the sizing equations, and provide the expected performances.

International audience

National audience; La Dynamique Moléculaire est une méthode de simulation bien adaptée pour décrire les réactions chimiques aux échelles moléculaires. Elle consiste en la résolution des équations du mouvement de newton, et donc du calcul des trajectoires d’un ensemble de particules.m_i d^2/〖dt〗^2 r ⃗_i (t)= -∇ ⃗_(r_i ) V(r ⃗_1 (t),⋯,r ⃗_N (t))=F ⃗_i (t), i=1,⋯,N (1)avec r ⃗_i (t) la position des espèces i au temps t, V est la fonction potentiel d’interaction total et F ⃗_i (t) est le champ de force agissant sur les espèces i au temps t. Cette technique nécessite donc de connaître les positions et vitesses initiales, que l’on peut déduire relativement facilement des expériences que l’on souhaite décrire. L’ingrédient majeur pour résoudre ces équations est donc la connaissance des potentiels d’interaction (ou des champs de force) entre ces particules. A ce jour, d’énormes progrès ont été obtenus pour produire des champs de force semi-empiriques adaptés aux réactions chimiques : il s’agit, en plus de décrire la formation/brisure de liaisons, de tenir compte du maximum de liaisons possible pour un atome donné et des charges partielles. Un tel champ de force est appelé réactif à charge variable : les plus utilisés actuellement sont ReaxFF et COMB3 [1].Quand ces potentiels ne sont pas connus, on peut les calculer à chaque pas de temps ou bien tous les quelques pas de temps par des méthodes quantiques comme la DFT. Cependant cela conduit à un accroissement considérable du temps de calcul. La Dynamique Moléculaire n’est pas capable actuellement de traiter complètement la dynamique réactive dans un plasma puisque les électrons ne sont pas explicitement pris en compte. Des champs de forces peuvent les inclure comme eFF et eReaxFF, mais la masse de l’électron est égale à 1 pour permettre des temps de calculs raisonnables. Néanmoins, les interactions neutres-neutres et ions-neutres peuvent être abordées de façon très précise et donc moyennant une connaissance « correcte » d’une composition initiale, il devient possible de mener des calculs de réactivité qui peuvent se comparer aux expériences plasma (il est également possible d’inclure un champ électrique). Il est également possible de faire des études paramétriques afin de mieux comprendre le rôle d’espèces particulières dans la réactivité.Afin d’illustrer cette méthodologie et les capacités de la Dynamique Moléculaire, l’exposé donnera des résultats portant la réactivité de molécules organiques polluantes telles que le paracétamol (anti-douleur) [2] et la sulfaméthoxazole (antibiotique) vis-à-vis du radical hydroxyl (par exemple issu de l’interaction avec un plasma en interaction avec l’eau), dans l’eau. Dans le premier cas, les calculs sont menés avec un potentiel ReaxFF et dans le second avec un couplage chimie quantique (DFTB), pour calculer le potentiel, et Dynamique Moléculaire.Références[1] T. Liang, Y. K. Shin, D. E. Yilmaz, K. G. Vishnu, O. Verners, C. Zou, S. R. Phillpot, S. B. Sinnot, A. C. T. van Duin, Reactive potentials for advanced atomistic potentials, Ann. Review of Materials Research 43, 109 (2013)[2] P. Brault, M. Abraham, A. Bensebaa, O. Aubry, D. Hong, H. Rabat, M. Magureanu, Insight into plasma degradation of paracetamol in water using a reactive molecular dynamics approach, J. Appl. Phys 129 (2021) 183304