Tungsten has been selected as the material of the divertor of the ITER fusion reactor. In operation, tungsten will be submitted to high alpha particles bombardment. The consequence of helium implantation is a major issue for the reliability of tungsten components. The aim of the study was to investigate the behavior of helium implanted in tungsten at low energy and low flux. 320eV Helium ions were introduced by plasma immersion at the flux of 2.5×1018ion/m−2/s−1. The helium behavior was investigated by Nuclear Reaction Analysis and the evolution of the tungsten lattice by Positron Annihilation Spectroscopy (PAS). Helium-implanted tungsten exhibits a low retention rate (13.6% at 9.4×1019Hem−2) which decreases with the implantation fluence. The desorption of helium starts at low temperature (<400K). SEM analysis after annealing over 973K shows sparse pores probably due to bubbles opening at the surface. The creation of helium-filled defects in the near surface layer (0.5 to ∼20nm) was followed by PAS. A low level of damages was introduced by 12MeV proton irradiation, prior to He introduction and allowed to examine the influence of pre-existing defects on the helium trapping. The PAS results suggest that the early stage of the formation of helium-filled vacancy clusters does not require the presence of pre-existing vacancy and thus proceed from the trap mutation phenomenon.

The behaviour of helium in polycrystalline 3He implanted tungsten at low energy (60 keV) and low fluence (2 × 1013 cm−2) has been studied as a function of post-implantation annealing temperature until 1873 K by means of Nuclear Reaction Analysis. Helium desorption has been observed only from ∼1500 K, suggesting a helium trapping at mono-vacancies. Only ∼75% of the implanted helium has been released after the annealing during 1 h at high temperature (1873 K); besides, the desorption rate decreased from 1673 K. The presence of a second type of helium trapping site is likely to explain this strong helium retention.

High entropy alloys (HEAs), containing five to thirteen metallic elements, with a concentration in the range of 5 to 35% for each element, exhibit very interesting properties (mechanical, tribological, formability, magnetism...). Their high mixing entropy promotes the formation of random solid solutions, amorphous alloys or nanocrystallized structures. Bulk pieces of these alloys are known to be stable at relatively high temperature (until 800 °C). We study the stability of AlCoCrCuFeNi thin film at temperatures in the range 110–810 °C. HEA thin films are deposited by magnetron sputtering from mosaic targets. In-situ X-ray diffraction (XRD) performed during annealing evidences damages of the film above 510 °C depending on the initial structure (or chemical composition) of the as-deposited HEA. Energy Dispersive Spectroscopy (EDS) and Scanning Electron Microscopy (SEM) analysis carried out before and after annealing show that partial evaporation of the thin film, crystalline phase transformation and chemical reaction with the substrate may take place during annealing.

Ni-YSZ films are deposited by reactive magnetron sputtering from a single Ni/Zr/Y metallic target at rates as high as 4 µm h− 1. Tailoring both DC pulsed power and oxygen partial pressure, a stable deposition process was obtained. Columnar morphology was observed in the as-deposited films. Annealing in air at 900 °C was conducted, after which a fully crystallized structure was achieved. Chemical composition has been measured by Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA). To find optimal conditions for reactive deposition of the films, effect of oxygen flow rate on the discharge parameters was studied. Film deposition onto glass substrates was carried out to measure electrical conductivity.

The behavior of tungsten under irradiation and helium implantation is a major stake of the material-related issues of fusion reactors. In this perspective the fate of helium in tungsten was studied by mean of several characterization techniques. The aim of this study is to highlight the trapping mechanisms of helium in tungsten and their correlation with implantation-induced defects. Helium was implanted into tungsten at two different energies, 0.32 and 60keV. The helium was studied as a function of temperature by using nuclear reaction analysis. The migration propensity of helium was correlated with the release rate of helium after annealing at a given temperature. In addition, the helium trapping sites and evolution with post-implantation annealing was investigated using Doppler-Broadening Positron Annihilation Spectroscopy. It has been shown that the release, and so the migration, of helium is guided by the concentration of implantation-induced defects and the nature of the helium traps created during the implantation.

Plasmas are energetic media that can give birth to dust particles due to the presence of reactive gases or plasma-surface interactions. Industrial plasmas are often concerned by these dust particles that can be either unwanted or useful for the process. For fusion plasmas, production of dust particles from wall erosion is a serious issue for performance and safety reasons. In this article, some aspects of dusty plasmas with potential implications for plasma experimenters will be discussed. Convenient ways for detecting the presence or the growth of dust particles will be presented. The spatial distribution of the dust cloud during the plasma phase determines the subsequent dust particle deposition. It will be shown that some reactor regions can attract or repeal these dust particles. Finally, the dust particle dynamics after the plasma extinction will be investigated. A special attention will be paid on the residual electric charge that can stay attached on the dust particle surface and on its implications for dust particle control or deposition.

La charge électrique résiduelle des poudres à l'extinction d'un plasma poussiéreux a été mesurée dans une décharge radio-fréquence. La force de gravité a été compensée par l'application d'une force de thermophorèse de même intensité et de direction opposée. Des poudres chargées positivement ou négativement ainsi que des poudres non chargées ont été observées. Ces charges résiduelles peuvent se maintenir pendant plus de 1minute après l'arrêt de la décharge. La charge électrique résiduelle moyenne pour des poudres d'environ 200nm de rayon a été mesurée à environ −5e pour une pression de 1,2mbar et −3e pour une pression de 0,4mbar. La charge électrique résiduelle sur les poudres étant reliée aux phénomènes de diffusion (ambipolaire et libre) des espèces chargées du plasma (ions et électrons), des mesures de densité électronique dans des plasmas post-décharges d'argon pur et d'argon/méthane (plasma poussiéreux) ont été effectuées afin de comprendre l'influence des poudres sur les mécanismes de perte des électrons. Cesmesures ont montré que la présence de poudres provoque d'abord une augmentation rapide de la densité électronique à l'arrêt du plasma suivie d'une décroissance accélérée.

We have studied the deposition of AlCoCrCuFeNi high entropy alloy (HEA) thin films on Si (1 0 0) substrates by DC magnetron sputtering process. Three mosaic targets have been used for easily tailoring the film composition. Energy dispersive X-ray spectrometry analysis has shown that chemical composition can be modified around the nominal value by tuning the ratio of the powers applied to the magnetron targets. The deposition rate is directly related to the power sum. Moreover, various surface morphologies have been evidenced by scanning electron microscopy and correlated to the crystalline phases present in the films. Morphology and crystalline structure have been found to depend on the chemical composition. Wetting contact angle has been measured with water droplets, showing that the hydrophobic properties of the thin films depend on their characteristics.

I - Physique et applications atmospheriques des filaments de plasma generes par des impulsions laser ultrabreves (Jerome Kasparian, Jean Pierre Wolf) Spectroscopie d'emission optique sur plasma induit par laser : Principe et applications (Patrick Mauchien, Catherine Gallou, Jean Luc Lacour, Laurent Salmon) II-2. Spectroscopie de fluorescence induite par diodes laser : Application au diagnostic des plasmas (Stephane Mazouffre) II-3. Un capteur de flux d'energie dans les plasmas (A.-L. Thomann, N. Semmar, R. Dussart, L. Bedra, J. Mathias, Y. Tessier et S. Mazouffre) III-1. Modelisation de la photoionisation dans les plasmas d'air non-thermiques a la pression atmospherique (Anne Bourdon, Sebastien Celestin, Julien Capeillere et Pierre Segur) III-2. Modelisation des plasmas produits par interaction laser-matiere (Tatiana E. Itina) IV-1. Proprietes et transferts radiatifs dans les plasmas (M.Y. Perrin, A. Soufiani, Ph. Riviere) IV-2. Modifications induites en surface de polymeres par traitement laser (Patricia Laurens, Sophie Petit) IV-3. Lampes fluorescentes sans mercure, a la recherche de l'efficacite energetique (Eric Robert, Sebastien Point, Sebastien Dozias, Christophe Cachoncinlle, Raymond Viladrosa et Jean Michel Pouvesle) IV-4. Sources plasmas de rayonnement X creees par laser (Fabien Dorchies) Importance du rayonnement dans les procedes thermiques industriels (Yann Cressault, Philippe Teulet, Jean-Jacques Gonzalez, Alain Gleizes) La spectroscopie optique appliquee a l'etude des disjoncteurs (Dunpin Hong, Jean-Marc Bauchire et Francois Gentils) Exemples de micro plasmas a haute densite : Electroerosion et ouverture de contacts electriques (Jean-Luc Dorier, Antoine Descoeudres, Christoph Hollenstein) Chauffage et generation de courant par ondes dans les tokamaks (Gerard Bonhomme)

Energy exchanges due to chemical reactions between a silicon surface and a SF6 plasma were directly measured using a heat flux microsensor (HFM). The energy flux evolution was compared with those obtained when only few reactions occur at the surface to show the part of chemical reactions. At 800 W, the measured energy flux due to chemical reactions is estimated at about 7 W cm−2 against 0.4 W cm−2 for ion bombardment and other contributions. Time evolution of the HFM signal is also studied. The molar enthalpy of the reaction giving SiF4 molecules was evaluated and is consistent with values given in literature.

We show that some experimentally observed instabilities, concerning the void region of a dust cloud, are similar to oscillations obtained in chemical systems or neuronal dynamics. The time evolution of these instabilities follows a well‐defined process particularly visible in the instability shape and frequency.

Dusty plasmas are complex systems where new phenomena arise from the presence of solid dust particles inside a plasma. Dust particles acquire a negative charge by attaching free electrons and are thus trapped in the plasma. This charge loss can be drastic for the plasma equilibrium and instabilities can appear due to the strong interdependence between the dust particle cloud and the plasma. In this paper, various types of self-excited instabilities consisting in regular or chaotic oscillations, are presented. They are obtained in low pressure radio-frequency discharges where dust particles are grown by using a reactive gas or by sputtering a surface exposed to the plasma. The complex evolution scheme of these instabilities is brought to the fore thanks to various diagnostics.

When a three-dimensional dust cloud is present in a plasma, a dust-free region, called a void, is usually obtained in the plasma centre. Under certain conditions, this region exhibits a self-excited unstable behaviour consisting of successive contractions and expansions of its size. In this paper, this low frequency instability ( few Hz), called a ` heartbeat', is characterised by various diagnostics. Electrical and optical measurements both correlated with high speed imaging brought to the fore the main features of this instability. Forces involved in the void existence are an inward electrostatic force and an outward ion drag one. The force balance ensures an open void but this equilibrium can be disturbed, leading to the observed instabilities. As these forces are strongly dependent on local ionisation conditions, correlations between physical processes in the plasma volume and the dust cloud motion are investigated through experimental results.

Dust particle growth instability and residual dust charges in a rf discharge have been studied. Dust particles were grown by sputtering of a polymer material previously deposited on the electrodes. We show that two regimes of the dust particle growth instability exist and are characterized by their frequencies. An empirical explanation based on the assumption of different dust particle growth rates is proposed for the existence of these regimes. We also show that dust particles do keep residual charges for a long time in afterglow plasma.

As part of the study on “Reference Asian Man” project, dried food from different Asian countries, in powdered form, was analyzed applying different techniques. Boron was determined by measuring prompt alphas in 11B(p,α)8Be reaction with 800 keV protons. Coulomb excitation was used for F and Na determination based on 19F(p,p'γ)19F (γ -rays: 110 and 197 keV) and 23Na(p,p'γ)23Na (γ -ray: 440 keV) reactions with 2.3 MeV protons. The elements Sc, Co, Zn, Rb, Ag and Ce were determined by neutron activation analysis. The elements Ca, Mn, Fe, Ni, Cu, Zn, Sr and Mo were determined by X-ray fluorescence technique.