HPC Modelling of Turbulent Transport in Tokamak Plasmas: Recent Results regarding Critical Physical Issues

abstract: Turbulence governs heat confinement in tokamak fusion plasmas. In turn, turbulence properties explain why large machines, like ITER, are required so as to reach the desired performance in terms of energy gain. Understanding, predicting and possibly controlling turbulent transport is therefore of outermost importance in fusion research. In addition to experimental measurements, High Performance Computing (HPC) now allows one to gain much insight in these critical issues. The talk will first recall the basic principles of controlled fusion and of plasma confinement in tokamaks. The main features of turbulence and transport will be reviewed, with implications on the required modelling effort. The focus will be put on turbulence self-organization and on the multi-scale aspect of the problem, in particular regarding the interaction between electron and ion scales on the one hand, and ion and equilibrium scales on the other hand. The role of sheared flows will be shown to be critical. Finally, the route towards turbulence control will be discussed, emphasizing the modelling effort of the spontaneous bifurcation to transport barriers characterized by improved confinement regimes.