Abstract Details
Abstracts
Author: Tyler B Cote
Requested Type: Poster
Submitted: 2017-03-17 12:52:23
Co-authors: C.C. Hegna, M. Willensdorfer, E. Strumberger, W. Suttrop, H. Zohm, ASDEX Upgrade Team
Contact Info:
University of Wisconsin-Madison
6237 Pheasant Lane, Apt. 41
Middleton, WI 53562
United States
Abstract Text:
Applied 3D magnetic perturbations can destabilize ideal MHD ballooning modes in tokamak pedestals[1]. In this work, we implement techniques for studying infinite-n ballooning stability of 3D equilibria deduced from VMEC calculations. Full magnetic profiles from VMEC are used to construct local equilibria for a given flux surface and magnetic field-line in and around the edge pedestal region. These local equilibrium calculations are coupled with ideal ballooning stability analysis to determine stability of the 3D shaped system to edge ballooning modes. Analysis shows localization of the ballooning mode to specific field-lines corresponding to minima in the local magnetic shear. 3D distortion of the flux surfaces cause significant change in the normal torsion, a key component of the local shear, and act as the primary mechanism for ballooning destabilization on certain field-lines.
This theoretical development is motivated by recent ASDEX-U experiments, where toroidally localized high-n MHD activity is observed in the presence of applied 3D fields. Our analysis agrees well with the experimentally observed localization of the ballooning modes in regions of small local shear.
[1] T.M. Bird and C.C. Hegna, Nucl. Fusion, 53 (2013)
Comments:
T.B. Cote and C.C. Hegna: Affiliation is University of Wisconsin-Madison. M. Willensdorfer, E. Strumberger, W. Suttrop, H. Zohm, AUX Team: Affiliation is Max-Planck-Institute fur Plasmaphysic