Impact of triangularity on edge peeling–ballooning modes in H-mode plasmas

Triangularity is an important shaping parameter in tokamak plasmas that affects the edge plasma state. In this work, we utilize the BOUT++ code to study the effect of positive and negative triangularity on the peeling–ballooning modes with H-mode profiles. The model equilibria with a JET-like geometry are self-consistently generated by the CORSICA equilibrium code, with a fixed pressure profile when varying triangularity. The linear simulations reveal that increasing positive triangularity results in the increase in magnetic shear and decrease in radial electric field (Er) curvature, leading to the stabilization of the peeling–ballooning modes. On the contrary, the increase in negative triangularity results in a destabilizing effect due to the decrease in magnetic shear and increase in Er curvature. It is found that the modification of Er shear due to triangularity variation cannot impact edge stability significantly. The nonlinear simulations further demonstrate that more positive triangularity results in reduced nonlinear energy loss fraction or pedestal collapse, while more negative triangularity results in increased nonlinear energy loss fraction or pedestal collapse. These results provide qualitative insights into experimental observations of the high pedestal pressure profiles with positive triangularity configuration and restricted low pedestal pressure profiles with negative triangularity configuration.