Form and Substance: How plasma shaping and kinetic profile modifications change the MHD stability of DIII-D plasmas *

Plasma shape parameters such as elongation, triangularity and squareness have a strong impact on the ideal MHD stability of tokamak plasmas, due to changes in wall coupling and intrinsic MHD physics. Systematic scans of several shape parameters have been modeled on Negative Triangularity and Hybrid scenario equilibria, using the Corsica-DCON and GATO codes, to assess the variations in ideal MHD stability limits for the n=[1, 2, 3] global kink modes, and optimize upcoming DIII-D experiments. Trends in calculated pressure limits and mode structures for the marginal point identify optima attainable with DIII-D’s shaping capabilities. Scans in the core current and safety factor profiles (q_min = 1.06, 1.09, 1.12) yield differences in the n=1 external kink marginal β_N of nearly 50% in some cases. Modifications of the current density and pressure profiles as well as plasma volume have been performed, some of which were matched in experiments, to assess the changes in ideal and tearing MHD limits as a function of J, p and wall stabilization. Tearing mode onset and timing is shown to correlate with the changes in the ideal MHD limits as a function of wall distance and triangularity in the DIII-D experimental database.