Changes in pedestal ballooning stability with 3D magnetic perturbation on DIII-D*

There is a significant need for understanding the physics of resonant magnetic perturbation (MP) ELM mitigation and suppression in order to understand how ELM control scenarios extrapolate to ITER. The 3D magnetic geometry associated with the kink response to MPs can change the local MHD stability boundary, with destabilized toroidally localized ballooning modes observed in AUG[1]. Evidence suggests that this mechanism also causes the ELM births to localize to the same toroidal position as the ballooning instabilities[2]. 

 

In this work, we extend the analysis of [1] to DIII-D discharges intended to mimic conditions in AUG by identifying cases with similar 3D ballooning structures using magnetic diagnostics. The pyBalloon code is used to study the 3D ballooning stability of these plasmas with respect to various 3D MP configurations. Localization of the 3D ballooning growth rates is observed in the DIII-D discharges when the kink response to the MPs is sufficiently strong, matching the observed behavior in AUG. Finally, initial analysis of the ELM birth localization is presented as well as a proposed mechanism connecting the ELM mitigation to the local 3D destabilization. 

 

[1] T.B. Cote et al., Nucl. Fusion. 59 (2019) 016015.

[2] M. Willensdorfer et al., Plasma Phys. Control. Fusion. 61 (2019) 014019.