In this paper, the stability of and high-n quasi-interchange mode (QI mode) are numerically investigated in shaped tokamak plasmas under the weakly magnetic shear (both low magnetic shear and weakly reversed magnetic shear) configurations, where n is the toroidal mode number. The results reveal that the inverse aspect ratio (, where is the minor radius and is the large radius) generally destabilizes the QI mode but stabilizes high-n modes, irrespective of the shear configuration. This is attributed to the competition between the stabilization from the weakened ballooning drive the intrinsic destabilization from the more compact geometry. Elongation () and triangularity () individually destabilize QI mode regardless of magnetic shear configuration, whereas their combined effect can stabilize QI mode in positive triangularity side and destabilize QI mode in negative triangularity side. These complex dependencies highlight the critical need to incorporate realistic tokamak geometry when interpreting related experimental observations.
Toroidal mode structure in weak and reversed magnetic shear plasmas and its role in the internal transport barrier