Characterization of Deposited Carbon Layers in Tore Supra

M. Richou, C. Martin, University of Provence, Marseille (France); C. Brosset, B. Pegourie, Association EURATOM-CEA, Saint-Paul-lez-Durance (France); P. Roubin (Sp), University of Provence, Marseille (France) 
The estimated amount of deuterium (D) implanted in the bulk of carbon Plasma Facing Components (PFC) in direct interaction with plasma is much more lower than the retention capacity observed during long discharges performed in Tore Supra (TS) in the CIEL toroidal pumped limiter configuration. Diffusion in the bulk of carbon PFC as well as carbon deposited layers are therefore expected to play an important role in D trapping phenomena.
We compare here the original PFC which is a Carbon Fiber Composite (CFC) to samples scraped off from TS PFC, as for example carbon deposited layers coming from the target plates of the neutralizers of TS (thickness up to 800 mm). We use various techniques: Scanning Electronic Microscopy, X-Ray diffraction, Fourier Transform InfraRed spectroscopy, Raman spectroscopy, Nuclear Magnetic Resonance, X-Ray Absorption Near Edge Spectroscopy and adsorption isotherm volumetry. The aim is to characterize physical and/or chemical D retention and D diffusion parameters in carbon PFC.
All the spectroscopic diagnostics consistently show that the deposited layers contain a low amount of deuterium and that they are disorded-graphite like, i.e. distinct from soft or hard layers.
On the other hand, adsorption isotherm volumetry allows the measurement of the surface available for diffusion and adsorption inside the material and gives information on the pore network nature and on the retention capacity. This only concerns physical adsorption on the walls or in the pores and competes with chemical processes where D is bonded to C. We have measured a large enhancement of the specific surface area (~ x 80) for the deposited layer compared to CFC, indicating a large enhancement of the retention capacity. A detailed study of the pore network, especially for determining the pore size distribution function, is currently on progress.

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