Comparing Plasma Response to Magnetic Perturbations Applied to Limited and Diverted Discharges in HBT-EP

We report~experiments on and~ideal MHD models of the multi-mode plasma response to magnetic~perturbations applied to stable discharges that are limited with circular cross-section and diverted. We focus on the excitation of both ``stiff'' non-resonant perturbations with n $=$ 1 and 2 and on the resonant perturbations of marginally stable external kink modes. DCON is used to compute the multi-mode ideal plasma response. We find the ``stiff,'' non-resonant modes have low poloidal wavenumber - \textbar m\textbar $\approx $ 0. Consequently,~they have a ten-fold higher coupling coefficient to the HBT-EP magnetic control coils. ~For circular, limited plasmas, the mode is maximum at the high-field side of the~plasma; whereas in diverted geometry, the mode creates a highly localized perturbation near the x-point of the plasma. By driving this mode with external coils, it may be possible to actively control the heat deposited by a fusion plasma across a larger surface, relaxing the materials requirements of the~strike point. Additionally, the low level of spectral overlap between these modes and the edge-resonant kink in a typical tokamak (2/1 or greater) means that this mode can be strongly driven with minimal excitation of unstable edge modes.