Validation of gyrokinetic edge and scrape-off layer turbulence simulations vs TCV experiments

Turbulence in the edge and scrape-off layer (SOL) of magnetic confinement fusion devices is of upmost importance for the feasibility of fusion energy. Two major aspects of a future fusion reactor, confinement and heat exhaust, are predominantly affected by turbulence, requiring the development of predictive edge turbulence codes.

In this work, we present the latest improvements to the grid-based "continuum" gyrokinetic turbulence code, GENE-X [1], with applications to TCV. GENE-X is specifically targeted for edge and SOL simulations, since it can perform simulations in diverted geometries by using the flux-coordinate independent approach [2]. From the start, it features a full-f, gyrokinetic turbulence model and it was recently improved to include electromagnetic effects [3]. Here, we introduce further improvements to the physics model, by including the effect of collisions via either a basic Bhatnagar-Gross-Krook or a more sophisticated Lenard-Bernstein/Dougherty collision operator [4].

We present the results of a series of GENE-X simulations for the diverted L-mode validation case "TCV-X21" [5]. The simulations presented use different collision models, which vary in their physics fidelity. We analyze the resulting plasma profiles, power balance, and SOL heat flux and compare against experimental measurements in the openly available TCV-X21 dataset [5]. The result of the code validation generally improves with the fidelity of the collision model chosen. Based on these results, we assess and discuss the effect of collisions on gyrokinetic edge and SOL turbulence.

[1] D. Michels et al., Comput. Phys. Commun. 264 (2021) 107986

[2] F. Hariri et al., Comput. Phys. Commun. 184 (2013) 2419

[3] D. Michels et al., Phys. Plasma 29 (2022) 032307

[4] P. Ulbl et al., Contrib. Plasma Phys., e202100180 (2021)

[5] S. Oliveira et. al., Nucl. Fusion, (2022), in press