The effect of plasma triangularity on turbulent transport: modelling TCV experiments by linear and non linear gyrokinetic simulations

Experimental evidence in the TCV tokamak revealed that the core electron heat transport is significantly reduced by a negative triangularity ($\delta$) configuration. This variation in heat transport cannot be explained by the flux surfaces compression; rather, it must be due to a (partial) stabilization of the microinstabilities at play in a positive d configuration. The present work is a theoretical investigation of the effect exerted by triangularity on plasma turbulence of actual TCV shots, using the gyrokinetic code GS2. A complex interplay of deeply and barely trapped particles, which react in opposite ways to triangularity, results in a stabilizing effect of negative $\delta$ on Trapped Electron Modes both in the linear and non-linear phases. The non-linear simulations are in qualitative agreement with the experimental results.