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The importance of plasma-wall interaction processes for the edge plasma is well known: creation of impurities by different sputtering mechanisms or recycling properties of the walls are examples of processes determining the divertor characteristics and the edge plasma profiles. To be able to have a better understanding of the plasma-wall interaction process itself, a multi-scale procedure is followed: molecular dynamics calculations resolve the microscopic length scale and deliver quite precise input data for kinetic Monte Carlo calculations (jump frequencies, migration energies, jump step-sizes) used for meso-scale up to the macroscopic system length. To cover the whole length scale involved -from microscopic up to macroscopic -several subsequent levels of kinetic Monte Carlo are needed, each providing the necessary input data for the next level. With this procedure the corresponding time scales spanning from picoseconds atomic interaction times to wall equilibration times of at least milliseconds will be spanned. Inclusion of a realistic structure model is also important, like for porous graphite where the void structure and orientation of the microcrystallites have to be included. First results of such a multi-scale calculation are presented studying the diffusion of hydrogen isotopes in porous graphite and are compared with experimental results from the literature.

Numerical and analytical study of a detached divertor equilibrium is presented. The model uses one-dimensional equations for continuity, momentum and energy balance with radiation, ionization, charge-exchange, and recombination processes. A reasonably simple neutral model is also employed. Analytical calculation, using a simple five-region model for a case with negligible convective heat flux and constant sources/sinks, captures the essence of detailed numerical calculation for the same case. More general cases are handled numerically. The detachment is studied as a function of the ratio Q⊥/S⊥ [the ratio of power and particle volume source, coming from the core to the scrape-off layer (SOL) region]. For low values of Q⊥/S⊥ (detached state), at the midplane and at the target, the ion temperature (Ti) is almost equal to the electron temperature (Te). As this ratio increases (attached state), Ti is larger than Te at the midplane. However at the target, Te is found to be slightly larger than Ti. It is also observed that as Q⊥/S⊥ increases, the region of most intense radiation shifts progressively from closer to the X-point towards the target plate.

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