The effect of triangularity on predicted pedestals for the CFETR

In this work, the dominant unstable magnetohydrodynamic mode and its stable region in the pedestal of the China Fusion Engineering Test Reactor are studied by numerical modeling with the peeling-ballooning theory over a wide range of triangularities (delta) and collisionalities (v*). A new accessible stable region is found at delta < -0:1 for large beta(N; ped) and v*. This new stable region expands toward lower beta(N; ped) and v* with decreasing d and is totally covered by the peeling unstable region with delta = -0:5 because of the increasing trapped particle fraction (f (t;eff)). The sensitivity of this new stable region to the kinetic ballooning mode constraint and elongation is studied. For negative and low d < 0:1, the boundary of the first stable region is determined from the ballooning mode. For delta> 0:1, the peeling mode becomes dominant as the boundary approaches low s with low v*, while the ballooning mode is still dominant at the boundary with high v*. When delta increases beyond 0.46, the first stable region is expanded, and access to the second stable region of the ballooning mode opens up. The entire newly connected region of the first and second stable regions keeps expanding with further increases in d until delta = 0:6. Beyond this value, the ballooning mode becomes more unstable with increasing delta, while the peeling mode is approximately unchanged with increasing d in this range. The change in the dominant mode and the stable region with increasing delta can be explained by the trade-off between the stabilization effect from the deeper poloidal magnetic well and destabilization due to the enlarged drive term.