Stabilization of Alfvén Eigenmodes in DIII-D via Controlled Energetic Ion Density Ramp and Validation of Theory and Simulations

Fast-ion driven Alfv\'en waves with frequency close to the ion cyclotron frequency ($f=0.58{f}_{ci}$) excited by energetic ions from a neutral beam are stabilized via a controlled energetic ion density ramp for the first time in a fusion research plasma. The scaling of wave amplitude with injection rate is consistent with theory for single mode collisional saturation near marginal stability. The wave is identified as a shear-polarized global Alfv\'en eigenmode excited by Doppler-shifted cyclotron resonance with fast ions with sub-Alfv\'enic energetic ions, a first in fusion research plasmas.