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Simulations of tokamak startup and control operations in realistic geometry enabled by EoCoE


The plasma-edge is the outer part of tokamak plasma, encompassing the outer core region until the plasma-facing components. Through its impact on the confinement of the plasma and on particles and heat flux exhaust, this part of the plasma is both determinant for the performances of a fusion reactor and for its durability. The physics at play is particularly complex, involving turbulence and plasma instabilities as well as plasma-neutral and plasma-wall interactions. Therefore, modelling the dynamics of the plasma-edge is crucial to enhance the performance of the tokamak, in terms of confinement and heat transfer to the walls, and also to design optimized operation scenarios. In the IRFM, the 3D turbulent code TOKAM3X is developed to analyze the turbulent heat and mass transfer in the plasma-edge. TOKAM3X is designed to run in a massively parallelized environment. One of the most important bottlenecks of the code is the inversion of the so-called 3D vorticity problem, which allows computing the electric potential in the machine. This problem takes the form of an implicit 3D linear system corresponding to an extremely anisotropic elliptic operator. The EoCoE collaboration network has allowed tackling this issue with new weapons, that is, the two iterative solvers AGMG and Maphys, that are now being tested in TOKAM3X. Preliminary results are very promising and now have to be confirmed in full scale simulations.

In parallel, other activities of improvement of the code have been undertaken, including the development of a new numerical scheme based on a high-order discontinuous Galerkin scheme. This new scheme is based on non-aligned computational grids, and will introduce new capabilities in the landscape of fluid solvers for the plasma-edge, such as for example, the possibility of computing the transport during a magnetic equilibrium evolution. This will allow performing simulations of tokamak startup and control operations in realistic geometry for both the plasma and the reactor’s wall (a world-wide unique capability), and it will also permit to enhance the consistency and flexibility of equilibrium-transport simulations.