Search

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.

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.

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.

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; 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.

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; Directed self-assembly of block copolymers (BCP) is a very attractive technique for the realization of functional nanostructures at high resolution. In this work, we developed full dry-etching strategies for BCP nanolithography using an 18 nm pitch lamellar silicon-containing block copolymer. Both an oxidizing Ar/O2 plasma and a nonoxidizing H2/N2 plasma are used to remove the topcoat material of our BCP stack and reveal the perpendicular lamellae. Under Ar/O2 plasma, an interfacial layer stops the etch process at the topcoat/BCP interface, which provides an etch-stop but also requires an additional CF4-based breakthrough plasma for further etching. This interfacial layer is not present in H2/N2. Increasing the H2/N2 ratio leads to more profound modifications of the silicon-containing lamellae, for which a chemistry in He/N2/O2 rather than Ar/O2 plasma produces a smoother and more regular lithographic mask. Finally, these features are successfully transferred into silicon, silicon-on-insulator, and silicon nitride substrates. This work highlights the performance of a silicon-containing block copolymer at 18 nm pitch to pattern relevant hard-mask materials for various applications, including microelectronics.

The effect of a volumetric nanosecond discharge on detonation cell size was demonstrated experimentally in a detonation tube test rig. The experiments were performed in CH4:O2:Ar=1:2:2 and CH4:O2:Ar:H2=3:7:8:2 mixtures, at 180 mbar and 120 mbar respectively and ambient temperature. The plasma was generated by two consecutive pulses of − 50 and − 32 kV amplitude on the high-voltage electrode and 25 ns pulse duration. The analysis of the detonation cell size with and without plasma generation was performed via sooted-plate technique. The detonation cell size was reduced by a factor of 1.5–3, while passing through the region of the discharge.

This paper presents the results regarding the influence of cyclic growth of nanoparticles from the gas phase on the parameters of a low-temperature plasma. The measurements were carried out in an asymmetric RF (13.56 MHz) discharge in mixtures of argon and acetylene gases. The main plasma parameters such as the electron temperature, electron density and plasma potential were determined by a Langmuir probe and compared with the discharge self-bias voltage signal. The contamination problem of the electric probe tip in a reactive plasma due to the sticking of nanoparticles and radicals was minimized by applying a rapid “complex” sweep pattern of the probe voltage. The method based on the oscillation of the probe voltage with a frequency higher than the frequency of dust particles. The measurement results show a decrease in the electron density during the cyclic growth due to their absorption on the surface of the nanoparticles. On the contrary, the electron temperature and plasma potential increase. Additionally, a laser light scattering system was used to evidence the presence of the dust particle cloud in the vicinity of the probe position.

This paper presents and discusses the experimental data obtained in the investigation of a short-arc high-pressure xenon discharge in dc and pulse-periodic operation modes. In the case of the dc discharge, the main focus of attention is the cathode material (thorium) evaporation into the plasma. Spectroscopic measurements show that this process strongly influences the plasma characteristics and first of all the plasma optical emission. Due to low ionization energy, thorium atoms decrease the plasma temperature at the cathode, which is confirmed by experimentally obtained spectra with an unexpectedly low optical emission temperature. The fact cannot be interpreted without the assumption of cathode material evaporation: in a homogeneous short-arc gas discharge with a conical cathode, the emission temperature at the cathode should not be low because the strength of the electric field is obviously maximal near the cathode tip. The findings are important for modeling discharges of such kind. For the pulse-periodic discharge, two effects are described: a decrease in the anode temperature and an increase in the light efficiency of about 35% in some discharge conditions. These can be used for the development of more powerful and effective xenon light sources.

www.springerlink.com; International audience; We report a method to obtain biocompatible PEG copolymer coatings inside High Density Polyethylene (HDPE) and Pyrex tubes, which was successfully developed by using a transporting discharge. The latter being a dry process, it is easier to apply as compared to the conventional multistep wet chemical techniques. The results presented in this paper show that for a 70 cm tube good cell repellent properties as compared to the control was obtained for the entire length of the tube. The best nonfouling properties with respect to CT-26 (colon cancer) were obtained for coatings presenting the best retention of ether functionalities from the DEGME monomer i.e. between 5-25 cm downstream of the tube. These results are interesting for surface modification of biomaterial and biomedical devices which present hollow bodies.

International audience

A Faraday cup (FC) is an instrument dedicated to current measurement in beams, jets and plasmas. It consists of a set of polarized electrodes mounted in such a way plasma sheath effect can be neglected, yielding accurate and reliable results. A FC is composed of three main parts, namely a collector or cup, which collects the current, a collimator, which defines the collection area and can contribute to limit electrons from entering the cup and a housing which protects the instrument from perturbation caused by the surrounding medium. In this paper, we provide experimental results of the effect of the collimator upon the measured ion current within the beam of a low-power Hall thruster. Different collimator materials, aperture diameters and polarization voltages are studied to determine the optimum design. Minimum dimension as well as appropriate materials are given as a conclusion in the case of low-power Hall thruster beam investigation.

International audience; In DC plasma spray torches, anode erosion is a common concern. It mainly depends on the heat flux brought by the arc and on the dimensions and residence time of the arc attachment to a given location on the anode wall. The latter depend, to a great extent, on the attachment mode of the arc on the anode wall. This paper compares the anode arc attachment modes predicted by an LTE (Local Thermodynamic Equilibrium) and 2-T (two-temperature) arc models that include the electrodes in the computational domain. It deals with a commercial cascaded-anode plasma torch operated at high current (500 A) and low gas flow rate (60 NLPM of argon). It shows that the LTE model predicted a constricted anode arc attachment that moves on the anode ring, while the 2-T model predicted a diffuse and steady arc attachment. The comparison between the predicted and measured arc voltage showed that the 2-T prediction is closer to the actual voltage. Also, the postmortem observation of a new anode ring of the actual plasma torch operated under the same conditions for a short time confirmed a diffuse arc attachment on a new anode. Keywords atmospheric plasma spray (APS) Á torch modeling Á computational fluid dynamics Á electric arc model Á heat transfer This article is an invited paper selected from presentations at the 2021 International Thermal Spray Conference, ITSC2021, that was held virtually May 25-28, 2021 due to travel restrictions related to the coronavirus (COVID-19) pandemic. It has been expanded from the original presentation.

International audience; The energy of ions during plasma enhanced chemical vapor deposition (PECVD) is known to impact material quality, but isolating this effect from other process parameters (plasma density, pressure) in a capacitively coupled plasma (CCP) is not straightforward. In this work, we utilize a novel radio-frequency (RF) excitation technique-tailored voltage waveforms (TVW)-as a solution to achieve ion flux-energy decoupling through the electrical asymmetry effect. This makes it possible to independently study the impact of ion energy on material deposition. We study the impact of ion energy-more precisely the maximum ion bombardment energy (IBEmax) before collisions-on the PECVD of hydrogenated microcrystalline silicon (µc-Si:H) thin films from an SiF4/H2/Ar chemistry. Through structural and electronic analysis, we find that the variation of IBEmax directly translates into material quality, even at relatively high process pressure. Better material properties (crystalline grain features, material density and photoelectronic response) are obtained for films deposited with moderate values of IBEmax around 45-55 eV. Above this range, a deterioration in material quality is observed, presumably due to more effective bulk atomic displacements induced by the silicon-containing ions. These results are consistent with the performance of single-junction µc-Si:H solar cell devices using these materials as active layers. Optimum performance is obtained for devices with an absorber layer deposited using a plasma excitation resulting in IBEmax in the range of ~45-55 eV. The variation in device performance is mainly due to changes in the open circuit voltage.

This paper deals with a model that simulates an electrodeless lamp with argon/mercury chemistry. The plasma kinetics model equations were solved using COMSOL (multiphysics simulation software) with appropriate boundary conditions. The numerical modeling of inductively coupled plasma is of crucial importance to understand the behavior of different physical quantities that characterize the ionized gasses such as electrical parameters. The electric and magnetic fields were handled by the electromagnetic model using the multiturn coil method. Results are in fairly good agreement with the experimental data from the literature and fit well with the expected physics of the discharge plasma.

Introduction: Adenosquamous carcinoma (ASC) of the head and neck is a rare malignant tumor, with one hundred cases diagnosed so far in the literature. Observation: A 66 years old female patient had a ASC of the right posterior floor of the mouth with a classification T1N0M0. Treatment consisted of surgical management and active surveillance. Discussion: Through this case report, we present this type of tumor and we discuss the main differential diagnosis from a clinical and histological point of view. Conclusion: This entity was described for the first time in 1968 by Gerughty. The CAS is defined by the World Health Organization as “a tumor of the upper respiratory tract, with two distinct squamous and glandular components.” The CAS is considered as an aggressive tumor with a redoubtable prognosis should not be ignored.

This work deals with the formation kinetic of tungsten (W) blisters under smooth plasma conditions, i.e. low hydrogen flux and energy in order to analyze the first stages of their formation. In addition, we focus on determining the W grain orientation where blisters grow preferentially. For this purpose, mirror-polished polycrystalline tungsten samples were exposed to hydrogen plasma under fixed hydrogen flux of 2.2 × 1020 m−2 s−1, with a fluence in the range of ~ 1024 m−2, ion energy of ~ 20, 120 and 220 eV, and sample surface temperature of ~ 500 K. The formation of blisters at the surface was investigated using SEM, AFM and EBSD to determine the size, the distribution and the orientation of grain where blisters are formed, respectively. The critical fluence for initiating blisters was established around 2.3 × 1024 m−2. The evolution of blister size distribution and density is discussed as function of fluence and ion energy. At lower ion energy, i.e. 20 eV, only nanoblisters (less than 150 nm) are observed whatever the fluence value (1.5 and 2.3 × 1024 m−2). At higher ion energy i.e. 120 and 220 eV, micrometric (~ few to tens of µm) blisters are observed and their density highly depends on fluence. We show that blisters can also be formed on (001) oriented grains contrarily to previous results from the literature where the (111) orientation seemed more favorable. Such information is of importance for tungsten based fusion tokamak operation and design.

The ITER Ion Cyclotron Resonance Heating (ICRH) system is designed to couple to the plasma 20 MW of RF power from two antennas in the 40-55 MHz frequency range during long pulses of up to 3600 s and under various plasma conditions with Edge Localized Modes. Radio-Frequency (RF) contacts are integrated within the ITER ICRH launcher in order to ensure the RF current continuity and ease the mechanical assembly by allowing the free thermal expansion of the Removable Vacuum Transmission Line coaxial conductors during RF operations or during 250{\textdegree}C baking phases. A material study has been carried out to determine which materials and associated coatings are relevant for RF contacts application in ITER. In parallel, RF tests have been performed with a new prototype of Multi-Contact (r) LA-CUT/0,25/0 contacts made of silver-coated CuCrZr louvers. During these tests on a RF vacuum resonator, currents between 1.2 kA and 1.3 kA peak have been reached a few tens of times in steady-state conditions without any visible damage on the louvers. A final 62MHz pulse ending in a 300s flat top at 1.9kA resulted in severe damage to the contact. In addition, a test bed which performs sliding test cycles has been built in order to reproduce the wear of the contact prototype after 30 000 sliding cycles on a 3 mm stroke at 175{\textdegree}C under vacuum. The silver coating of the louvers is removed after approximately a hundred cycles whilst, to the contrary, damage to the CuCrZr louvers is relatively low., Fusion Engineering and Design, Elsevier, A Para{\^i}tre

The peculiar behaviour of zinc depending on whether it is used pure or alloyed in Cu63Zn37 wire electrodes leads either to nanosheets or to nanoparticles when it is processed by nanosecond pulsed discharges in liquid nitrogen. Using one electrode of copper and one electrode of zinc gives core-shell Cu@Zn nanoparticles but no alloy for the smallest nanoparticles (typically below 20 nm). Once nitrogen is evaporated, their oxidization in air produces Cu2O@ZnO nanoparticles. If both electrodes are made of Cu63Zn37, then the smallest nanoparticles are made of Cu and Zn and oxidized next in air to give Cu2O and ZnO nanoparticles. No alloy is formed either. Time-resolved optical emission spectroscopy gives clues on the origin of such behaviours, explaining why no alloy is formed when electrodes are made of different materials.

International audience; Nano crystalline diamond (NCD) films grown at a temperature below 400°C can open new applications on temperature sensitive substrates such as polymers or low-melting point alloys. One requirement for the applicative use of NCD is the ability of depositing on a structured substrate having high aspect ratio. This work presents a study on the three dimensional (3D) conformity of NCD deposition at low temperature (350°C) and low pressure (30 Pa). Silicon wafers have been structured using a mask-less photolithography and (hardmaskless) Deep Reactive Ion Etching (DRIE) process and seeded with nano-diamond particles. The NCD films were grown on these 3D patterned Si substrates with various trench geometries to provide means of determining the limiting geometries of this technique. By measuring the step coverage with changing trench width, a threshold for conformal NCD growth can be determined. The NCD films at the bottom of the 100 μm deep trenches were continuous down to an aspect ratio of 1:7.

Lightning strike damage on aircraft composite structure is very difficult to predict. The main source of this damage is the mechanical constraint generated by the lightning in interaction with the structure made of composite, protected with a metallic mesh and painted. The purpose of this paper is to propose a numerical model able to reproduce the surface overpressure generated by the explosion of the lightning strike protection (LSP) and its confinement with the paint. Comparisons of numerical displacements with lightning experimental ones are presented in order to analyse the predictability of the model. This is a first step in order to assess the damage in the composite structure depending on the design configurations (CFRP, LSP and Paint) when combined with a damage model.

In this paper, we examine the characteristics of the ISCT100 thruster, a miniature xenon-fueled 100-W permanent magnet Hall thruster (HT) suited for microspacecraft propulsion. The impact of the thruster design upon discharge behavior, ion beam properties, and performances is examined as for two discharge channel geometries as well as two values of the magnetic field strength. Thrust, specific impulse, and efficiency obtained between 50 and 200 W are compared with the ones of other low-power HTs.

Large amounts of antibiotics are produced and consumed worldwide, while wastewater treatment is still rather inefficient, leading to considerable water contamination. Concentrations of antibiotics in the environment are often sufficiently high to exert a selective pressure on bacteria of clinical importance that increases the prevalence of resistance. Since the drastic reduction in the use of antibiotics is not envisaged, efforts to reduce their input into the environment by improving treatment of contaminated wastewater is essential to limit uncontrollable spread of antibiotic resistance. This paper reviews recent progress on the use of non-thermal plasma for the degradation of antibiotics in water. The target compounds removal, the energy efficiency and the mineralization are analyzed as a function of discharge configuration and the most important experimental parameters. Various ways to improve the plasma process efficiency are addressed. Based on the identified reaction intermediates, degradation pathways are proposed for various classes of antibiotics and the degradation mechanisms of these chemicals under plasma conditions are discussed.

Acoustic resonance (AR) occurs in metal halide (MH) lamps and could cause light flicker, lamp arc bending and rotation, lamp extinction and arc tube explosion in the worst situations. This study takes place in the context of developing electronic ballasts with a low-cost and robust AR detection and avoidance mechanism. In this case, a lock-in amplifier is used to obtain the variations of lamp voltage envelope. A mathematical criterion is proposed to classify AR presence and severity. This criterion is based upon the short-term standard variation of voltage envelope and it was tested over a set of MH lamps with different powers and manufacturers. By varying the operation frequency of the high-frequency ballast, it was experimentally possible to control the average electrical power and the level of AR occurrence in the lamps. A data set consisting of healthy (without AR or AR-free) and faulty (with AR) cases was constructed by varying these parameters. The proposed criterion permitted to classify the observed waveforms in a two-dimensional (2D) plane. It was observed that AR-free and AR cases are separated. The results of this study show that the voltage envelope variations and the defined criterion are significantly correlated with AR presence whatever the lamp of the operation power.

International audience; RuO2 nanowires are synthesized by oxidation of ruthenium thanks to a micro-post-discharge at atmospheric pressure. However, RuO2 nanowires form islands. The growth mechanism depending on surface defects, the surface density of the nanowires is limited. We report on the influence of two alkali salts, NaCl and KCl, deposited as grains on ruthenium to act as defects and increase the nanowire density. These grains induce the growth of RuO2 nanowires all around them, creating a circular area where nanowires are found. Nanowires start growing at the triple point at the grain base where the alkali-salt grain, ruthenium from the substrate and oxidizing gaseous species coexist. When nanowires grow, the stress induced in the surrounding layer creates new cracks, making possible the radial propagation of the nanowires. The presence of nanowires on grains is due to the etching mechanism that converts the alkali salt into an oxide, enabling onward oxidation of ruthenium.

Mg-Ti-H films with a Ti content in the range 0 at.% Ti < 20 were obtained in a single-step process using the microwave reactive plasma-assisted co-sputtering technique. The morphology, crystal structure, chemical composition and spatial distribution of the elements were investigated by X-ray diffraction, scanning and transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy and precession electron diffraction. Our results show that the Ti-poor films (0 at.% Ti 0.45) exhibit mainly the tetragonal beMgH2 phase and have a dense microstructure with discontinuous columnar grains. For the films with a medium Ti content (2.7 at.% Ti 6.6), the beMgH2, metastable orthorhombic geMgH2 and Mg-Ti phases were found in different proportions, with a typical columnar growth. The abrupt microstructural changes of the films with a Ti content >10 at.% correlate with the change in crystallinity. These films exhibit a mainly amorphous/nanocrystalline structure with a granular morphology. We showed that the Ti content plays a significant role in the formation of structural and microstructural features of the Mg-Ti-H films, which might be a useful parameter in tuning the functional properties of magnesium hydride.

In this paper, we present the potentialities of the electro-optic technique for the radial electric field transient analysis of a three-phase power cable. A longitudinal electro-optic probe performing real time characterization of the field surrounding the cable has been developed. The measurement gives the transient evolution of the radial component of the field. The analysis provides information on amplitude, position, and phase of the conductors in the multicore cable. Theoretical analysis, simulations, and experimental measurements are in agreement and demonstrate the contactless voltage diagnostic of multicore cables.

We studied composite wires assembled from electric field-driven nanoparticles in a dielectric liquid (heptane) to elucidate the exact processes and controlling factors involved in the synthesis of the multi-phase nanocomposites. Filamentary wires are synthesized by a two-step process: (1) abundant nanoparticle production, mostly of carbonaceous types, from heptane decomposition by spark discharge and of metal nanoparticles by electrode erosion and (2) assembly of hydrogenated amorphous carbonaceous nano-clusters with incorporated metal nanoparticles forming wires by dielectrophoretic transport while maintaining a high electric field between electrodes kept sufficiently separated to avoid breakdown. Four types of nanocomposites products are identified to form at different steps in distinctive zones of the setup. The black carbonaceous agglomerates with metal spherules made by electrode erosion represent the pyrolytic residues of heptane decomposition by spark discharge during step 1. The filamentary wires grown in the interelectrode gap during step 2 get assembled by dielectrophoretic transport and chaining forces. Their great stability is shown to express the concurrent effect of polymerization favoured by the abundance of metal catalysts. The nature, abundance, and transformation of solid particles from the source materials versus discharge conditions control the morphological and compositional diversity of the wires. The production of mineral and metal nano-particles traces the efficiency of dielectrophoresis to separate compound particle mixtures by size and to co-synthesize nanostructured microcrystals and nanocomposites. The link between impurities and the variability from nano- to micro-scales of the synthesized products provides an innovative contribution to the knowledge of nanocomposite synthesis triggered by electric field.

International audience

International audience; In negative ion sources, a cusped magnetic field is generated by magnets placed around each aperture of the extraction grid in order to limit the co-extracted electron current. In spite of this suppression magnetic field, the co-extracted electron current is large, on the same order as the negative ion current extracted from the plasma. In this paper, we study the mechanisms of electron extraction from the plasma through a cusped aperture in a simplified situation, in the absence of negative ions, with the help of a three-dimensional Particle-In-Cell Monte Carlo Collisions model. The calculation results show that the electron current extracted from the plasma is small for an infinite slit aperture with a suppressed (cusped) magnetic field and significantly increases in the case of finite slit or circular grid apertures. We find that the E Â B electron drift plays an important role in the extraction of electrons through a finite slit grid aperture and that current driven micro instabilities are present in the aperture region. This work is relevant to negative ion sources and micro-ECR neutralizers designed for space propulsion.

International audience; There are a number of pressing problems mankind is facing today that could, at least in part, be resolved by space systems. These include capabilities for fast and far-reaching telecommunication, surveying of resources and climate, and sustaining global information networks, to name but a few. Not surprisingly, increasing efforts are now devoted to building a strong near-Earth satellite infrastructure, with plans to extend the sphere of active life to orbital space and, later, to the Moon and Mars if not further. The realization of these aspirations demands novel and more efficient means of propulsion. At present, it is not only the heavy launch systems that are fully reliant on thermodynamic principles for propulsion. Satellites and spacecraft still widely use gas-based thrusters or chemical engines as their primary means of propulsion. Nonetheless, similar to other transportation systems where the use of electrical platforms has expanded rapidly, space propulsion technologies are also experiencing a shift toward electric thrusters that do not feature the many limitations intrinsic to the thermodynamic systems. Most importantly, electric and plasma thrusters have a theoretical capacity to deliver virtually any impulse, the latter being ultimately limited by the speed of light. Rapid progress in the field driven by consolidated efforts from industry and academia has brought all-electric space systems closer to reality, yet there are still obstacles that need addressing before we can take full advantage of this promising family of propulsion technologies. In this paper, we briefly outline the most recent successes in the development of plasma-based space propulsion systems and present our view of future trends, opportunities, and challenges in this rapidly growing field.

International audience; Magnetic cusps have been used for more than 50 years to limit charged particle losses to the walls and confine the plasma in a large variety of plasma sources or ion sources. Quantification of the effective loss area has been the subject of many experimental as well as theoretical investigations in the 1970-1990's. In spite of these efforts there is no fully reliable expression of the effective wall loss as a function of cusp magnetic field, electron temperature, ion mass, gas pressure, etc… We describe in this paper a first attempt at obtaining scaling laws for the effective loss width of magnetic cusps, based on two-dimensional PIC MCC (Particle-In-Cell Monte Carlo Collisions) simulations. The results show that the calculated leak width follows a 1/B scaling in the collisionless low B limit, is approximately proportional to the hybrid gyroradius with an ion velocity equal to the Bohm velocity and is proportional to the square root of gas pressure in the collisional limit.

International audience; Travelling Wave Array (TWA) antennas distributed along the periphery of the tokamak are presently considered as Ion Cyclotron Resonance Frequencies (ICRF) heating solution for the DEMO reactor. Compared to the conventional ICRF antenna systems currently in use or designed for future machines like ITER, the TWA consists of antenna sections integrated in the breeding blanket scattered around the machine, each one fed through a variable coupler in a resonant ring configuration. Previous modelling of an antenna system for DEMO with 16 quadruple TWA sections of 8 straps shows that a power capability exceeding 50 MW can be obtained in the frequency band of interest using the reference low coupling plasma profile of ITER. The described system optimizes the coupling to the plasma by providing a large number of radiating elements, which results in enhanced antenna directivity hereby decreasing the antenna power density. This results in a maximum strap voltage amplitude of only 15 kV and maximum inter-strap voltage amplitude of 18 kV. The generators remain matched for all loading conditions: the system is totally load resilient. Following the recommendation of the work package heating and current drive (WPHCD) Review Panel, a TWA ICRH system consisting in fewer sections concentrated in front of the equatorial ports is analysed in this paper and compared to the previous design. Reducing the number of sections increases the power density and its associated voltages. To couple 50 MW on the ITER density profile, voltages up to 30 kV are now required. Some aspects like the coupling between sections and its repercussion on the feeding network are briefly discussed. To assess the feasibility of the TWA fed by a resonant ring as ICRH system for a DEMO reactor, a test on an existing medium size tokamak is under study.

Inconel samples with a surface oxide film composed of solely chromium oxide with a thickness of approximately 700 nm were exposed to low-pressure hydrogen plasma at elevated temperatures to determine the suitable parameters for reduction of the oxide film. The hydrogen pressure during treatment was set to 60 Pa. Plasma was created by a surfaguide microwave discharge in a quartz glass tube to allow for a high dissociation fraction of hydrogen molecules. Auger electron depth profiling (AES) was used to determine the decay of the oxygen in the surface film and X-ray diffraction (XRD) to measure structural modifications. During hydrogen plasma treatment, the oxidized Inconel samples were heated to elevated temperatures. The reduction of the oxide film started at temperatures of approximately 1300 K (considering the emissivity of 0.85) and the oxide was reduced in about 10 s of treatment as revealed by AES. The XRD showed sharper substrate peaks after the reduction. Samples treated in hydrogen atmosphere under the same conditions have not been reduced up to approximately 1500 K indicating usefulness of plasma treatment.

International audience; Oxidation of copper thin films was performed by means of a microwave micro-afterglow at atmospheric pressure to grow locally copper oxide nanowires with controlled morphologies. As for thermal oxidation, their growth follows a parabolic rate due to transport limitation by diffusion. TEM analyses indicate that most of the produced nanowires are single crystalline CuO with monoclinic structure and random axial crystallographic orientations. However, some nanowires exhibit a bi-crystalline structure with a twin-boundary along their growth direction. Residual stress was estimated by the curvature method and locally by the XRD sin 2 ψ method. Compressive (re-spectively tensile) stress is observed in the Cu 2 O (respectively CuO) layer. The grain size is larger close to the center than on the edges of the circular treated area, due to strong thermal gradients in the micro-afterglow. This ensures the growth of nanowires with large diameters close to the center and smaller diameters on the edges, although with higher surface density. As for thermal oxidation, the synthesis of CuO nanowires is driven by stress-induced grain boundary diffusion processes due to the development of stress gradients. However, the use of an afterglow increases the oxidation rate at low temperature with respect to thermal oxidation, enhancing the development of stress and thus enabling the synthesis of nanowalls.

International audience; This paper reports a rapid and simple method for the co-deposition of TiO2/SiO2 films, using a microwave plasma torch and organometallic precursors. Both structure and microstructure of the films have particularly been investigated. The results show that the characteristics of the deposits mainly depend on the torch to substrate distance (d). When this distance is short (d = 10 mm), the co-deposits are quite dense and exhibit crystalline TiO2 phases. By contrast, when d = 30 mm, the co-deposits are amorphous. At d = 30 mm, it was also shown that silica could act as an encapsulation matrix for titania particles in only one step. Moreover, for d = 30 mm, the adjunction of silica, about 40 mol% allows enhancing the adherence of the films, whereas pure titania deposits are not adherent at all.

International audience; Oxidation by a micro-post-discharge at atmospheric pressure of thin films of ruthenium deposited on fused silica by pressure-modulated magnetron sputtering is studied. Single-crystalline RuO 2 nanowires are obtained for the first time with a diffusion process over large areas. Nanowires grow typically at temperatures below 550-600 K, provided the level of stress is high enough to fragment grains in sub-grains with sizes between 30 and 50 nm. Because of the alternation of dense and porous layers forming the coating, inward diffusion of vacancies leads to no patent Kirkendall's effect, pores being distributed over the whole coating thickness and not mainly at the interface with the substrate. The centre of the treatment being heated at temperatures higher than 900 K, gaseous RuO 4 is formed, leading to an evaporated area. At its edge, a ring of microcrystals is formed, likely by a CVD mechanism.

International audience; Completely homogenous films formed via the layer-by-layer assembly of poly(diallyldimethylammonium chloride) (PDADMAC) and the poly(styrene sulfonate) were successfully obtained on plasma-treated poly(dimethylsiloxane) (PDMS) substrates. To modify the hydrophobicity of the PDMS surface, a cold plasma treatment was previously applied to the membrane, which led to the creation of hydrophilic groups on the surface of the membrane. PDMS wettability and surface morphology were successfully correlated with the plasma parameters. A combination of contact angle measurements, scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis was used to demonstrate that homogeneous and hydrophilic surfaces could be achieved on PDMS cold-plasma-treated membranes. The stability of the assembled PEL layer on the PDMS was evaluated using a combination of pull-off testing and X-ray photoelectron spectroscopy (XPS), which confirmed the relevance of a plasma pre-treatment as the adhesion of the polyelectrolyte multilayers was greatly enhanced when the deposition was completed on an activated PDMS surface at 80 W for 5 min.

The 100 W-class ISCT100-v2 Hall Thruster (HT) has been characterized in terms of far-field plume properties. By means of a Faraday Cup and a Retarding Potential Analyzer, both the ion current density and the ion energy distribution function have been measured over a 180 ∘ circular arc for different operating points. Measurements are compared to far-field plume characterizations performed with higher power Hall thrusters. The ion current density profiles remain unchanged whatever the HT input power, although an asymptotic limit is observed in the core of the plume at high discharge voltages and anode mass flow rates. In like manner, the ion energy distribution functions reveal that most of the beam energy is concentrated in the core of the plume [ &minus, 40 ∘, 40 ∘ ] . Moreover, the fraction of low energy ion populations increases at large angles, owing to charge exchange and elastic collisions. Distinct plume regions are identified, they remain similar to the one described for high-power HTs. An efficiency analysis is also performed in terms of current utilization, mass utilization, and voltage utilization. The anode efficiency appears to be essentially affected by a low voltage utilization, the latter originating from the large surface-to-volume ratio inherent to low-power HTs. Experimental results also show that the background pressure clearly affects the plume structure and content.

International audience; A control-oriented approach to the monitoring of wall power flux densities on ITER has been successfully developed. It is based on real-time equilibrium reconstruction in 2-D which is then used to describe the deposited heat flux as a poloidal flux function with user specified parameters for the power exhausted into the scrape-off layer (SOL) and the SOL heat flux width. To account for the real 3-D geometry of the plasma-facing components (PFC), appropriate weighting factors are derived from magnetic field line tracing in 3-D. Integration of the 3-D effect is performed with a new GUI-based software environment, SMITER, incorporating a field line tracer and permitting import and meshing of PFC CAD models. The paper discusses the experimental demonstration of the model-based wall heat flux algorithm on the TCV tokamak, reporting on the benchmarking of the new code package, SMITER against infra-red camera heat flux measurements and the derivation of the component shaping weighting factors. A comparison of the real-time estimation of the peak power flux and its spatial location against the off-line infra-red measurement for limiter plasma configurations is presented.

We consider the separation of motion related to internal gravity waves and eddy dynamics in stably stratified flows obtained by direct numerical simulations. The waves&rsquo, dispersion relation links their angle of propagation to the vertical &theta, to their frequency &omega, so that two methods are used for characterizing wave-related motion: (a) the concentration of kinetic energy density in the ( &theta, &omega, ) map along the dispersion relation curve, and (b) a direct computation of two-point two-time velocity correlations via a four-dimensional Fourier transform, permitting to extract wave-related space-time coherence. The second method is more computationally demanding than the first. In canonical flows with linear kinematics produced by space-localized harmonic forcing, we observe the pattern of the waves in physical space and the corresponding concentration curve of energy in the ( &theta, ) plane. We show from a simple laminar flow that the curve characterizing the presence of waves is distorted differently in the presence of a background convective mean velocity, either uniform or varying in space, and also when the forcing source is moving. By generalizing the observation from laminar flow to turbulent flow, this permits categorizing the energy concentration pattern of the waves in complex flows, thus enabling the identification of wave-related motion in a general turbulent flow with stable stratification. The advanced method (b) is finally used to compute the wave-eddy partition in the velocity&ndash, buoyancy fields of direct numerical simulations of stably stratified turbulence. In particular, we use this splitting in statistics as varied as horizontal and vertical kinetic energy, as well as two-point velocity and buoyancy spectra.

Introduction : La maladie de Wilson, ou degenerescence hepato-lenticulaire, est decrite pour la premiere fois en 1912 par le neurologue S.A.K. Wilson comme une affection genetique rare de transmission autosomique recessive, entrainant des anomalies du transporteur du cuivre : l’ATP7B. Elle se caracterise par une accumulation tissulaire de cuivre libre, essentiellement hepatique, cerebrale et pericorneenne. Des 1956, les patients beneficient d’un traitement efficace, la D-penicillamine, agent chelateur du cuivre limitant les consequences de la maladie. Observation : Il s’agissait d’un patient atteint de maladie de Wilson, porteur de valve mitrale mecanique necessitant la prise d’anticoagulant oral qui, suite a des avulsions dentaires, a presente plusieurs caillots exuberants. Discussion : Le nombre de cas de cette maladie est estime entre 700 et 1 800 en France. Les manifestations cliniques generales sont tres variees et le diagnostic est parfois difficile a etablir. Conclusion : Il est important de connaitre et d’anticiper les suites operatoires pathologiques potentielles chez ces patients, dont l’etat de sante necessite une prise en charge particuliere, pour les prevenir et les gerer au mieux.

This paper details a spray technique, named as “sparkjet”, which generates high-speed particles and a high temperature gas jet. It aims to demonstrate the feasibility of the process and the physical mechanisms, the influence of the process parameters on the characteristics of the flyer particles, and the quality of interfaces and coating structures. The coupling efficiency between the powder injector and the arc generator and the measurements of the process parameters were successively estimated. Tests proved the feasibility of this new process as well as its automated energy efficiency, which can offer a real potential application for developing metallic and ceramic coatings.

International audience; Molecular dynamics (MD) simulations are used to study AlCoCrCuFeNi high entropy alloy (HEA) thin film growth on a silicon (100) substrate. Effect of the atomic composition is studied on morphology and atomic scale structure. Input data are chosen to fit with experimental operating conditions of magnetron sputtering deposition process. It is observed that the different structures are determined by the chemical composition and atomic size mismatch. The simulated results are in good agreement with the solid-solution formation rules proposed by Zhang et al [1] for multi-principal component HEAs which based on the two parameters \omega and \delta , respectively describing describe the comprehensive effect of the atomic-size difference in the n-element alloy and the effects of enthalpy and entropy of mixing on formation of multi-component solid-solutions. When \omega>= 1.1 and \delta≤ 6.6%, the multi-component solid solution phase could form. In contrast, the multi-component alloys forming intermetallic compounds and bulk metallic glasses (BMG) have larger value of \delta and smaller value of \omega. The value of \omega for BMG is smaller than that of intermetallic compounds.

This paper reviews the electron- and heavy-particle impact processes governing the population/depletion of the states of N, O, N2, and N2+, which can be significantly affected by nonequilibrium conditions while strongly radiating in lunar-return shock layers. The collisional-radiative model developed in this work includes electron-impact excitation, ionization, heavy-particle impact excitation, vibration–electron, vibration–translation, dissociation and bound–bound radiative mechanisms. The available experimental and theoretical reaction rates governing these processes were critically reviewed to produce a reliable set of rate constants. The collisional-radiative model was then applied to typical nonequilibrium thermodynamic conditions encountered during lunar-return Earth reentry. The effect of heavy-particle impact processes is discussed.

International audience; Magnetron sputtering is a widely used physical vapor deposition technique for deposition and formation of nanocatalyst thin films and clusters. Nevertheless, so far only few studies investigated this formation process at the fundamental level. We here review atomic scale molecular dynamics simulations aimed at elucidating the nanocatalyst growth process through magnetron sputtering. We first introduce the basic magnetron sputtering background and machinery of molecular dynamics simulations, and then describe the studies conducted in this field so far. We also present a perspective view on how the field may be developed further.

Two low-temperature plasma jets using argon carrier gas at atmospheric pressure have been experimentally characterized using optical emission diagnostics. The first one is a double dielectric barrier discharge (DBD) plasma jet generated by a pulsed power supply (9 kV, 9.69 kHz, duty cycle: 1%) and the second one is a microwave (MW) induced plasma jet (2.45 GHz, 40 W ). The argon gas (4.5 purity) flowing through the quartz tube used to launch the plasma in open air is kept at 1 L/min for both plasma devices. Some thermodynamic parameters such as rotation ( $T_{\rm rot}$ ) and excitation ( $T_{\rm exc}$ ) temperatures have been determined as well as some plasma active species such as electron density, ultraviolet C (UVC) irradiance, and atomic oxygen concentrations. Most of these plasma parameters are spatially resolved along the plasma jet axis using the spectra of atomic lines (Ar and O) in the visible range and molecular bands (N2 and OH) in the UV range. At the tube outlet, the electron density and atomic oxygen concentration are one decade higher in the case of the dielectric barrier discharges (DBDs) plasma jet while $T_{\rm rot}$ is higher in the case of the MW plasma jet. These differences are mainly due to the way of plasma generation. Indeed, the guided-ionization waves generated by the DBD setup cause higher nonequilibrium phenomena since the difference between $T_{\rm rot}$ and $T_{\rm exc}$ is shown to be much larger in the DBD case. Furthermore, at the tube outlet, it is shown that UVC irradiance produced by the MW plasma jet is about twice as large as that of the DBD plasma jet. However, at 1.7 cm away from the tube outlet, the differences between the two plasma setups on temperatures and active species production become less significant. For instance, the plasma gas temperature measured with a thermocouple becomes the same (320 K) showing the ability of both plasma setups to be used in biomedical applications without inducing a significant thermal effect.