Gyrokinetic study of neoclassical and turbulence properties in the negative triangularity edge

Tokamak discharges with negative triangularity show promising characteristics, including good energy confinement, no impurity accumulation, and the absence of detrimental edge localized modes [1]. In addition, it is reported that the H-mode transition is difficult with sufficiently strong negative triangularity. To investigate the impact of triangularity on edge plasma properties, we performed gyrokinetic simulations using the total-f, edge specialized gyrokinetic code XGC. We simulate two DIII-D-like geometries based on DIII-D negative triangularity discharge #193802 with adjustments of far scrap-off layer and private flux region: one with negative triangularity and the other with a “manufactured” positive triangularity with the separatrix and limiter/divertor shapes mirrored. Flux-surface-averaged plasma profiles are kept the same between the two shapes. The simulations show that negative triangularity gives a deeper Er well and higher ExB shearing rate than positive triangularity, and that the parallel flow direction is opposite from each other. The observed edge Er and toroidal flow from the negative triangularity simulation agree qualitatively with experimental measurements. Differences in turbulence properties will also be discussed.