Abstract of GRIMG Project

The recently developed code GRILLIX is aimed to investigate turbulent transport of particles and heat in the edge and scrape­off layer. Owing to a field line map approach, a distinguished feature of the code is its ability to perform simulations across the separatrix of diverted devices. Originally, GRILLIX was based on a simplified physical model (Hasegawa­-Wakatani), where the validity of the approach and its potential for an application to realistic models have been proven successfully. Currently, GRILLIX is being extended towards a more accurate model for the edge/SOL, i.e. full­f drift reduced Braginskii equations, which are based on valid assumptions. A major challenge arises thereby from the non­linear polarisation, i.e. an elliptic problem with varying coefficients that has to be solved in each timestep. Multigrid methods are usually the method of choice in order to solve such problems, and therefore a first prototypical solver has already been implemented in GRILLIX yielding promising results concerning accuracy and performance. However, in order to cope with problems of relevant sizes a performance tuning of this solver is still required. Secondly, the treatment of the boundary, which is not conforming with the computational grid, has to be improved within the multigrid solver. The result of this project, i.e. an efficient and versatile solver for elliptic problems, could be reused in many other codes and scientific fields.