Computational modeling of a purely neoclassical scrape-off layer

The influence of neoclassical drifts on the structure of a tokamak Scrape-off Layer (SOL) is at present the subject of massive research efforts. In fact, neoclassical effects are always present in tokamaks, not only as background processes. For example, drifts are thought to be responsible for the inboard-outboard asymmetries of the target loads. For such reasons, increasing attention is currently paid also to the problem of including neoclassical terms in fluid edge modelling. Moreover, transport in the improved-confinement regimes may drop down to values comparable with the neoclassical predictions at least in some localised regions. It is then clear that neoclassical transport is expected to play a relevant role in a future tokamak reactor. In the recent past we have presented a computational fluid study of the SOL dominated by classical transport terms. The simulations were performed with the recently developed B2-Solps5.0 code. That initial work was limited to a simplified rectangular geometry; here we extend the model to a realistic tokamak configuration, taking as reference parameters typical of Asdex-Upgrade. In particular, we aim at pointing out the different structures of the Scrape-off layer when neoclassical transport is dominating versus the usually modeled case, where transport is largely determined by anomalous contributions. (orig.)