Dependence of Magnetic Perturbation Induced Fast Ion Losses on Perturbation Spectrum and Plasma Response in the ASDEX Upgrade and DIII-D Tokamaks

The impact of externally applied magnetic perturbations (MPs) on fast-ion losses has been investigated using the light ion beam probe (LIBP) technique[1] in the ASDEX Upgrade (AUG) and DIII-D tokamaks. This allows for experimental inference of the orbit displacement for first orbit losses. In AUG, the displacement against a series of applied spectra has been studied by varying the phase between the upper and lower MP coils. Experimentally, a minimum in the orbit displacement was found for a phase of 50\textdegree . This is offset from the minimum of the plasma boundary displacement, suggesting losses could be disentangled from ELM mitigation. Experiments at DIII-D focus on the impact of the plasma response over large number of shots, where the plasma response was varied by a scan in the plasma $\beta $. In this case, rigid rotation of the MPs was applied in an n$=$1 configuration. Measurements show an increase in displacement with the plasma response. [1] X.Chen \textit{et al}, Rev Sci Instrum \textbf{85}, 11E701 (2014)