Christoph Wersal

The GBS code for tokamak scrape-off layer simulations

We describe a new version of GBS, a 3D global, flux-driven plasma turbulence code to simulate the turbulent dynamics in the tokamak scrape-off layer (SOL), superseding the code presented by Ricci et al. (2012) 14. The present work is driven by the objective of studying SOL turbulent dynamics in medium size tokamaks and beyond with a high-fidelity physics model. We emphasize an intertwining framework of improved physics models and the computational improvements that allow them. The model extensions include neutral atom physics, finite ion temperature, the addition of a closed field line region, and a non-Boussinesq treatment of the polarization drift. GBS has been completely refactored with the introduction of a 3-D Cartesian communicator and a scalable parallel multigrid solver. We report dramatically enhanced parallel scalability, with the possibility of treating electromagnetic fluctuations very efficiently. The method of manufactured solutions as a verification process has been carried out for this new code version, demonstrating the correct implementation of the physical model.

A first-principles self-consistent model of plasma turbulence and kinetic neutral dynamics in the tokamak scrape-off layer

A first-principles self-consistent model that couples plasma and neutral physics suitable for the simulation of turbulent plasma behavior in the tokamak SOL is presented. While the plasma is modeled by the drift-reduced two fluid Braginskii equations, a kinetic model for the neutrals is developed, valid in short and in long mean free path scenarios. The model includes ionization, charge-exchange, recombination, and elastic collisional processes. The solution of the neutral kinetic equation is implemented within the GBS plasma turbulence code (Ricci et al 2012 Plasma Phys. Control. Fusion 54 124047) and it is performed by using the method of characteristics. The details of the numerical implementation are discussed. Finally, we show initial results of the first self-consistent simulations of plasma turbulence and neutral dynamics.