Near infrared spectral luminance deformation from carbonaceous plasma facing components in Tore-supra

This work concerns the understanding of a physical phenomenon which is important for the future course of magnetic confinement fusion research: namely the anomalous deformation in the near infrared of radiation from tokamak plasma facing components under plasma particle impact. The goal of this work was to reproduce this phenomenon in laboratory experiments, characterize it and explain it, so that the measurements of the temperature of plasma facing components can be made with confidence. Laboratory experiments have been performed using an ECR ions source and a helicon plasma source. The spectral luminance deformation has been observed on graphite surface under electrons and ions bombardment and the amplitude of this phenomenon was found to depend on the type of material used and the power density of the incident particles. A systematic consideration and evaluation of alternative explanations for the observed spectral deformation has been made. A number of plausible interpretations has been considered and discarded as e.g. Bremsstrahlung radiation, or assigned a low probability as the luminescence effect. The possible partial transparency of the material has also been considered at some length, but finally discarded because the low thermal conductivity of the graphite materials under consideration does not permit a strong enough temperature gradient to cause the observed deformation. The possible explanation is reduced to the non uniform surface temperature due to the presence of hot spots during particle bombardment. This hypothesis implies that the measured luminance is the contribution of several temperatures. The measured spectral luminance deformation, basing on hot spots hypothesis, is simulated. This hypothesis allows to asses the surface temperature, the hot spots temperature and the hot spots coverage on the surface. These results are validated using a thermal model of dust in radiate equilibrium. This model allows us to deduce an average size of the dust < 40 μm. These results are confirmed by the laser ablation experiment's on CFC of A. Hermann et al. in which it is inferred that the size of hot spots is less than the 30 μm spatial resolution of the IR camera which is used. Additional results are exhibited describing the micro-analysis of deposition samples removed from Tore Supra. The analyses have shown that the characteristics forms are due to deposition process and not to in situ surface alterations. The deposition is characterized and a ballistic model for the observed orientation and morphology is proposed and the global growth rate of these samples is evaluated. Correlations with the evolution of the infrared emission spectrum have been made, outlining the sequence of layer growth and the corresponding spectral deformation characteristics. (author)