Numerical study of the ITER divertor plasma with the B2-EIRENE code package

The problem of plasma-wall interaction and impurity control is one of the remaining critical issues for development of an industrial energy source based on nuclear fusion of light isotopes. In this field sophisticated integrated numerical tools are widely used both forthe analysis of current experiments and for predictions guiding future device design. The present work is dedicated to the numerical modelling of the edge plasma region in divertor configurations of large-scale tokamak fusion devices. A well established software tool for this kind of modelling is the B2-EIRENE code. It was originally developed for a relatively hot ($\geq$ 10 eV) “high recycling divertor”. It did not take into account a number of physical effects which can be potentially important for “detached conditions” (cold, - several eV,- high density, - $\approx 10^{21} m^{-3}$, - plasma) typical for large tokamak devices. This is especially critical for the modelling of the divertor plasma of ITER: an international project of an experimental tokamak fusion reactor to be built in Cadarache, France by 2016. This present work is devoted to a major upgrade of the B2-EIRENE package, which is routinely used for ITER modelling, essentially with a significantly revised version of EIRENE: the Monte-Carlo neutral transport code. The main part of the thesis address three major groups of the new physical effects which have been added to the model in frame of this work: the neutral-neutral collisions, the up-to date hydrogen molecular reaction kinetics and the line radiation transport. The impact of the each stage of the upgrade on the self-consistent (between plasma, the neutral gas and the radiation field) solution for the reference ITER case is analysed. The strongest effect is found to be due to the revised molecular collision kinetics, in particular due to hitherto neglected elastic collisions of hydrogen molecules with ions. The newly added non-linear effects (neutral-neutral collisions, radiation opacity) are found to be quite significant for ITER conditions (large size and density) as well, despite the fact that their experimental identification in the presently available smaller devices (including JET) is very difficult. An experimental validation of this particular package which is used for the ITER design has been carried out for a series of discharges at the Joint European Torus (JET) tokamak (UK, Culham). A relatively good (within a factor 2) agreement for the outer divertor has been found. At the same time, a significant discrepancy between the modelling and the experiment is seen in the inner divertor. As in the case of ITER the model for molecular kinetics has a significant impact on the solution. The new version of the coupled code (SOLPS4.2) has been made available to the ITER International Team and is now extensively used there. It has already provided significant revisions of currently predicted divertor operational scenarios