Comparison of DIII-D and AUG pedestal ballooning stability during 3D magnetic perturbations

Recent work has shown the importance of local 3D magnetic geometry on the stability of localized MHD ballooning instabilities in the presence of applied 3D magnetic perturbations in ASDEX Upgrade plasmas[1]. In this work, we extend this analysis to DIII-D discharges with ASDEX-like plasma shaping. While the 3D localized instabilities of [1] have been observed in the ECE signals for these DIII-D discharges, the instabilities appear to be less prevalent than expected when comparing to the similar AUG discharges. To better understand this discrepancy, we utilize VMEC to construct 3D MHD equilibria associated with comparable DIII-D and AUG discharges with applied 3D magnetic perturbations, and analyze the infinite-n ballooning stability of these equilibrium using the PYBALLOON code. We compare both the ballooning stability and local 3D magnetic geometry of the two experiments, considering the strength of the magnetic perturbations and plasma response, 2D plasma shaping, and error field effects. Additionally, benchmarking results between the PYBALLOON and COBRA codes are presented. [1] T.B. Cote et al., Nucl. Fusion. 59 (2019) 016015.