Turbulence Suppression in Negative Triangularity and Negative Central Shear Toroids

Plasma transport in tokamaks and optimized stellarators is dominated by turbulence. It has been shown both experimentally and numerically that negative triangularity shaping and negative central shear in toroidal plasmas produces a stabilizing effect, likely due to the suppression ion-scale modes, which leads to lower levels of turbulent transport and thus improved confinement. We present the results of global gyrokinetic simulations directly comparing turbulent instability growth rates of equivalent low-beta positive- and negative-triangularity geometries, with both positive and negative central shear. The effects of various temperature, density, and safety factor profiles are explored. We also examine the effectiveness and viability of this turbulence suppression mechanism when moving to reactor-relevant parameters such as high beta.