Laser Raman microprobe analysis of graphite exposed to edge plasma in the TEXTOR tokamak

An isotropic fine grain graphite (EK98) block has been exposed to the edge plasma in the TEXTOR tokamak and studied by Raman spectroscopy. Spectra from the net erosion area and deposition area where co-deposits (hard layer) were created by the tokamak discharges, are remarkably different. The spectra at the net erosion areas consist of two sharp peaks: the D-peak (≈1355 cm−1) and the G-peak (≈1580 cm−1). The spectra at the net deposition areas were very broad, which are similar to the Raman spectra of amorphous carbon. Fitting analyses of the Raman spectra for the net erosion area exhibit a linear relationship between the G-peak width (FWHMG) and the peak intensity ratio (ID/IG). Comparison with the diagram derived for ion-irradiated graphite revealed that thermally unstable defects of single vacancies scarcely remained due to the power loading in this plasma exposure condition but thermally stable defects such as the dislocation dipoles could be accumulated.