Test of Plasma Equilibrium Response against MHD Models Using Slowly Rotating 3D Magnetic Perturbations in \hbox{DIII-D} RMP Experiments

Slowly rotating non-axisymmetric magnetic perturbations provide a convenient means to study plasma response to perturbation fields in \hbox{H-mode} discharges using \hbox{DIII-D} diagnostics such as the edge Thomson scattering measurements of electron temperature. Magnetic perturbations with $n=1$$-$3 have been routinely used to investigate plasma response in DIII-D RMP experiments. For $n=1$, a 0.1$-$0.3\% perturbation of the poloidal equilibrium magnetic field can result in a large 2$-$4\% change in the edge magnetic topology. Perturbations from higher $n=2$ and 3 typically result in smaller flux-surface distortions. In this study, the effects of 3D perturbation fields on plasma equilibria from these experiments are tested against theoretical predictions using 3D linear and non-linear MHD codes \hbox{MARS-F}, \hbox{M3D-C1}, and VMEC. First comparative results indicate that the response from stable helical kink modes contribute significantly to the observed plasma equilibrium responses. Details will be presented.