Tokamak edge-SOL turbulence in H-mode conditions simulated with a global, electromagnetic, transcollisional drift-fluid model

TL;DR

This paper presents the first global electromagnetic turbulence simulations of the tokamak edge and SOL in H-mode conditions, showing reasonable agreement with experiments and highlighting the importance of electromagnetic effects and specific turbulence modes.

Contribution

It introduces a comprehensive global drift-fluid model for simulating tokamak edge turbulence in H-mode, including electromagnetic effects and neoclassical corrections, advancing predictive capabilities.

Findings

Electromagnetic fluctuations are crucial in H-mode turbulence.

Zonal flows and neoclassical components influence flow shear.

Kinetic ballooning modes are prominent near the pedestal foot.

Abstract

The design of commercially feasible magnetic confinement fusion reactors strongly relies on the reduced turbulent transport in the plasma edge during operation in the high confinement mode (H-mode). We present first global turbulence simulations of the ASDEX Upgrade tokamak edge and scrape-off layer (SOL) in ITER baseline H-mode conditions. Reasonable agreement with the experiment is obtained for outboard mid-plane measurements of plasma density, electron and ion temperature, as well as the radial electric field. The radial heat transport is underpredicted by roughly 1/3. These results were obtained with the GRILLIX code implementing a transcollisional, electromagnetic, global drift-fluid plasma model, coupled to diffusive neutrals. The transcollisional extensions include neoclassical corrections for the ion viscosity, as well as either a Landau-fluid or free-streaming limited model for the parallel heat conduction. Electromagnetic fluctuations are found to play a critical role in H-mode conditions. We investigate the structure of the significant $E \times B$ flow shear, finding both neoclassical components as well as zonal flows. But unlike in L-mode, geodesic acoustic modes are not observed. The turbulence mode structure is mostly that of drift-Alfv\'en waves. However, in the upper part of the pedestal, it is very weak and overshadowed by neoclassical transport. At the pedestal foot, on the other hand, we find instead the (electromagnetic) kinetic ballooning mode (KBM), most clearly just inside the separatrix. Our results pave the way towards predictive simulations of fusion reactors.