Kinetic MHD Stability of Low-n Modes in Negative Triangularity Plasmas

Ideal MHD instabilities limiting high performance in tokamaks can be modified by kinetic stabilization effects, primarily due to anisotropy in the perturbed orbit trajectories of trapped particles. This study examines how these effects vary with magnetic configuration, focusing on the differences between positive and negative triangularity (PT and NT). A series of PT and NT equilibria is analyzed with GPEC, for ideal and kinetic stability as well as Kruskal–Oberman (KO) and Chew–Goldberger–Low (CGL) limits for comparison. NT plasmas are found to be less ideally stable as previously well known, but become as stable as PT when the full kinetic effects are accounted. This behavior is attributed to the increased population of deeply trapped particles and their strong bounce-harmonic resonances. As a result, it is shown that the kinetic effects can completely stabilize higher-n (n > 1) stability in NT, while the n = 1 remains as the primary β-limiting instability. Interestingly, strong NT shaping appears to enable a second stability regime even for n=1. The dominant (m,n) eigenfunctions are no longer unstable at higher beta, possibly due to increased shear in NT. In some cases, the gap between the first and second stability regimes can be substantially reduced by kinetic effects, highlighting the need for further investigation into kinetic stability in NT plasmas.