Comparison of global gyrokinetic simulations of turbulent transport in DIII-D tokamak with negative and positive triangularity

Two DIII-D shots with different triangularities were studied to understand the effects of triangularity on the turbulent transport using a global gyrokinetic code, GTC. Given different plasma profiles and magnetic field geometries, multiple factors, such as the pressure gradient, the magnetic shear and the triangularity, could affect the turbulence simultaneously. GTC simulations find that the linear growth rates of the most unstable mode in the inner core region were mainly influenced by the pressure profiles. For the outer core region, the dominant factor for the mode growth is the safety factor q-profile. In the nonlinear simulations, the ion heat transport shows a consistent trend for both the inner core and the outer core regions. The pressure and the q profiles from the negative triangularity case seem to be associated with higher transport levels in simulations, while the negative triangularity itself can reduce the transport levels. Furthermore, lower linear growth rates are not necessarily associated with lower transport levels, since the modes with lower growth rates could saturate at higher levels and eventually lead to larger ion heat conductivities. The overall ion heat conductivity from the turbulence transport is larger in the negative triangularity case, but this is a combined result based on all three factors, triangularity, pressure, and q-profiles. These results suggest that when interpreting the experimental measurements with different triangularities, one should isolate various contributors to the observed transport levels.