Composés Carbone-Tungstène Ternaires et Hydrogène pour les parois des réacteurs à fusion – CRWTH

The CRWTH project (Carbon-Tungsten Ternary compounds with Hydrogen for fusion reactor walls) aims to provide certain answers related to mixed materials plasma-facing components (PFCs) issues, expected to arise in fusion reactors currently being designed (such as the new JET wall planned for 2011 and of course ITER). Indeed, we seek to determine the physico-chemical properties, structure and absorption capabilities of the hydrogen fuel (keeping in mind the strict safety controls imposed on fusion devices concerning radioactive tritium inventories) of the erosion products obtained from ablation and later re-deposition of PFC materials on the reactor walls, in the form of dust or flakes. These erosion products will unavoidably be mixtures, most often formed far from thermodynamic equilibrium, of the pure materials originally used to cover the PFC surfaces, namely carbon, tungsten and beryllium. Our project thus organizes itself in three main areas: 1) The manufacture, on the one hand, of multi-materials plasma targets in C-W or C'W'X (where X stands for an element similar either in atomic mass or in chemical behavior to Be, which we are not able to use in our facilities because of the associated health hazards), and, on the other hand, the production, by mechanical alloying of ternary C-W-X powder compounds in a planetary mill, including an ageing step in a dedicated oven under a hydrogen atmosphere. This synthesis method is very well suited to our purpose of creating out-of-chemical-equilibrium powders, akin to those likely to be formed under energetic plasma bombardment in fusion reactor environments. The powder fabrication step will be followed by a characterization step where their properties in terms of structure and hydrogen absorption capability, among others, will be ascertained. 2) The erosion by hydrogen or noble gases plasmas of the above prepared multi-materials targets and synthesized powders, the experimental and theoretical study of the sputtering of these samples, the transformation by the plasma of the erosion products, and the collection of the re-deposits. These will undergo the same material characterization analyses as the mecano-synthesized powders to evaluate any changes induced by plasma exposure. Moreover, chemical and surface analysis of the deposits and targets after exposure will give us information about preferential sputtering phenomena taking place between the various materials. 3) The implementation and publication of our obtained results in terms of ternary C-W-X compound properties and their measured preferential sputtering rates in databases accessible to the fusion materials research community and inside simulation models for edge plasma and plasma-wall interactions in fusion reactors. This project is a common endeavor of the 'High Pressure ' High Temperature Processes' and 'Polyphasic Media and Plasma Processes' research teams from LIMHP in Villetaneuse, in collaboration with the 'Dusty Plasmas' team from LPIIM in Marseille. The two laboratories have a several years history of working together on research contracts and the project proposed here builds on the existing collaboration dynamics between them as well as the synergy of joining expertise from LIMHP in materials synthesis and characterization on the one hand and the study of plasma-wall interactions on the other hand. In order to achieve the goals of this project, the ANR support is requested in order to finance a post-doctoral appointment of two (2) years at PIIM as well as the purchase of various critical equipment items for the attainment of our research goals above. These include a multi-dipolar plasma source to create a plasma energetic enough to yield appreciable tungsten sputtering rates, a mass spectrometer to identify the chemical species present in the erosion plasma, quartz microbalances to measure the erosion and deposition rates in our devices, a planetary mill, and an oven to prepare C-W-X ternary powder samples. Financial support is also sought to cover operating expenses for this equipment and the associated diagnostics as well as travel funding to ensure the proper dissemination and publication of the research results for sharing with the wider French, European and international fusion materials research community.