Hybrid MHD/particle simulation study of sub-cyclotron Alfv\'{e}n Eigenmodes in NSTX

Low toroidal mode number, high frequency compressional (CAE) and global (GAE) Alfv\'{e}n Eigenmodes are often driven unstable by super-Alfv\'{e}nic beam ions in NSTX. These modes have been identified as part of an energy channeling mechanism that may explain observed anomalous electron temperature profile flattening in beam-heated NSTX discharges [1]. 3D hybrid simulations using the HYM code are conducted to study the excitation and stability properties of such CAE and GAE modes in NSTX and NSTX-like plasmas. HYM allows for the self-consistent simulation of these modes with a delta-f particle treatment of the energetic beam ions coupled to a single fluid resistive MHD model of the thermal plasma. Particular attention is paid to the sensitivity of CAE/GAE excitation on parametric changes in the equilibrium beam ion distribution function, among other factors.\\[4pt] [1] E.V. Belova, et al., Phys. Rev. Lett. \textbf{115}, 015001 (2015).