Raman micro-spectroscopy as a tool to measure the absorption coefficient and the erosion rate of hydrogenated amorphous carbon films heat-treated under hydrogen bombardment

We present a fast and simple way to determine the erosion rate and absorption coefficient of hydrogenated amorphous carbon films exposed to a hydrogen atomic source based on ex-situ Raman micro-spectroscopy. Results are compared to ellipsometry measurement. The method is applied to films eroded at different temperatures. A maximum of the erosion rate is found at ~ 450 {\degree}C in agreement with previous results. This technique is suitable for future quantitative studies on the erosion of thin carbonaceous films, especially of interest for plasma wall interactions occurring in thermonuclear fusion devices

Raman study of CFC tiles extracted from the toroidal pump limiter of Tore Supra

International audienceThe structure of six tiles extracted from the erosion and deposition zones (thin and thick deposition) of the Tore Supra toroidal pump limiter (TPL) have been analysed in the framework of the DITS campaign using micro-Raman spectroscopy. This post-mortem analysis gives information on both carbon structure and D content. We have found that the carbon structure is most often similar to that of plasma-deposited hard amorphous carbon layers. The role of the surface temperature during the discharge in the D content is investigated: in all locations where the temperature does not reach more than 500°C the D content seems to be roughly uniform with D/D+C ≈ 20%

Plasma growth processes inside gaps of the castellated limiter of the Tore Supra tokamak

We performed electron microscopy analysis of carbon tiles dismantled from the toroidal limiter of the Tore Supra tokamak. The tile top surfaces are either eroded, or covered with deposits, depending on ion flux. On the contrary, the tile gap surfaces are covered with deposits whatever the region of the limiter. We analyzed both the topography and the microstructure of gap deposits. Deposits are tip-shaped and deposition is significant only down to ~1 mm, due to the limited penetration of ions. The direction of tips results from the combination of the ion speed along the magnetic lines and the drift associated to the local electric fields. The microstructure of deposits reveals the presence of graphitic species, such as onion-like nanoparticles, and our results therefore show that deposition results from local plasma chemistry similar to what is observed for cold plasmas

Post-mortem analyses of the Tore Supra toroidal limiter: experimental evidence of ion transport in a magnetized sheath

Abstract The topography of tiles dismantled from the main plasma-facing component of Tore Supra has been analyzed by scanning electron microscopy. Erosion zones show striation corresponding to a surface ripple. Deposition zones show well-oriented deposits with tip shapes. We show that these features are footprints of ion flow at the component surface. They are in good agreement with what is expected by modeling of ion trajectories in the case of grazing incidence in a strongly magnetized sheath