  In low-collisionality scenarios exhibiting mitigation of edge localized modes
(ELMs), stable ideal kink modes at the edge are excited by externally applied
magnetic perturbation (MP)-fields. In ASDEX Upgrade these modes can cause
three-dimensional (3D) boundary displacements up to the centimeter range. These
displacements have been measured using toroidally localized high resolution
diagnostics and rigidly rotating n = 2 MP-fields with various applied poloidal
mode spectra. These measurements are compared to non-linear 3D ideal
magnetohydrodynamics (MHD) equilibria calculated by VMEC. Comprehensive
comparisons have been conducted, which consider for instance plasma movements
due to the position control system, attenuation due to internal conductors and
changes in the edge pressure profiles. VMEC accurately reproduces the amplitude
of the displacement and its dependencies on the applied poloidal mode spectra.
Quantitative agreement is found around the low field side (LFS) midplane. The
response at the plasma top is qualitatively compared. The measured and
predicted displacements at the plasma top maximize when the applied spectra is
optimized for ELM-mitigation. The predictions from the vacuum modeling
generally fails to describe the displacement at the LFS midplane as well as at
the plasma top. When the applied mode spectra is set to maximize the
displacement, VMEC and the measurements clearly surpass the predictions from
the vacuum modeling by a factor of four. Minor disagreements between VMEC and
the measurements are discussed. This study underlines the importance of the
stable ideal kink modes at the edge for the 3D boundary displacement in
scenarios relevant for ELM-mitigation.
