The Influence of Rotation and SOL Drifts on Poloidal Asymmetries of Pedestal Fueling

SOLPS-ITER simulations of DIII-D H-mode plasmas show that plasma rotation coupled with drift effects near the plasma edge plays a significant role in the poloidal distribution of neutrals. It is observed in SOLPS that including drift and rotation effects greatly enhance particle flux and recycling at the inner target. This allows a reproduction of the strong in-out asymmetry of the Lyman-𝛼 signal experimentally measured by the LLAMA diagnostic [1] in this scenario. Additionally, these simulations show that the poloidal location of the SOL flow stagnation point moves closer to the LFS target when the parallel rotation matches the experimentally measured C⁶⁺ rotation. The mechanism by which the SOL flow stagnation point changes in the code is found to be closely related to the radial transport of parallel momentum, enhanced by plasma rotation. The SOLPS results are corroborated by comparisons with an extended dataset including bolometry, Thomson scattering and Charge-Exchange Recombination measurements, as well as previous work employing the gyrokinetic XGC code. This work indicates that by including rotation coupling, existing models (SOLPS) can achieve qualitative reproduction of experimental neutral asymmetries, suggesting that this effect, typically neglected, should be taken into account.

[1] A.M Rosenthal et al Rev. Sci. Instrum. 92, 033523 (2021)