Abstract:
Magnetically confined plasmas, such as tokamaks, require a number of different heating schemes in order to reach a temperature for fusion reactions to occur. One of the primary forms of heating in current fusion research plasmas and in future burning plasmas such as ITER is neutral beam injection (NBI). NBI, along with fusion reactions, can excite a variety of instabilities known as Alfvén waves that can enhance scattering and loss of energetic ions. An experiment was performed at the DIII-D National Fusion Facility to investigate Alfvén waves with frequencies at a large fraction of the ion cyclotron frequency. For the first time in a fusion research plasma, the controlled stabilization of a fast-ion driven Alfvén wave was demonstrated via an energetic ion density ramp. Furthermore, this wave was identified as a shear-polarized global Alfvén eigenmode (GAE) excited by Doppler-shifted cyclotron resonance with fast-ions with sub-Alfvénic energetic ions, a first in fusion research plasmas.