Effects of negative triangularity on plasma scrape-off layer turbulence in gyrokinetic simulations*

Gyrokinetic edge simulations of inner-wall limited discharges on DIII-D have been completed to isolate the effects of triangularity on plasma profiles and turbulence. Negative triangularity plasmas are potentially attractive scenarios for future fusion reactors because they have confinement and pressure levels that approach standard H-mode plasmas, while maintaining an L-mode edge that is free from edge localized modes (ELMs). Initial simulations include only the open field line region and neutral interactions are neglected. A Miller approximation is used for the magnetic equilibria to model DIII-D inner-wall limited discharges with positive and negative triangularity, based on pure electron cyclotron heated discharges. Compared to positive triangularity, the negative triangularity simulation had lower values of plasma density, electron temperature, ion temperature, and parallel heat flux magnitude but higher density fluctuation levels. In the Gkeyll code, the open and closed field line regions can now be simulated simultaneously for inner-wall limited scenarios [1]. Thus, the same discharges were modelled, including part of the edge region inside the last closed flux surface. This results in more self-consistent sources of heat and particles into the scrape-off layer (SOL). These simulations were compared to the SOL-only simulations to demonstrate how including the edge region affects plasma profiles and blob formation.

[1] Francisquez et al. arXiv:2110.02249 (2021).