Comprehensive analysis of beam-driven ion cyclotron range instabilities in mixed species DIII-D plasmas

Dedicated DIII-D experiments were performed to investigate beam-driven instabilities in the ion cyclotron range of frequencies. Ion cyclotron emission (ICE) occurs at integer harmonics of f_ci, while global Alfvén eigenmodes (GAEs) occur at substantial fractions of f_ci. In fusion plasmas, these instabilities may provide valuable diagnostic information about fast ion confinement, once the physics basis is validated. Similar instabilities occur in space plasmas, where controlled parameter scans cannot be performed. In DIII-D, the fast ion distribution was varied by injecting beams with different energy, injection geometry, and species (D and H), while the thermal ion species mix was varied between D, H, and ³He. The instabilities are measured with magnetic loops with 100 MHz bandwidth, covering several f_ci harmonics. A comprehensive database is analyzed to understand the mode stability and time evolution [1]. Mode excitation is sensitive to the combination of beam and thermal ion species, in reasonable agreement with linear theory. A rich variety of time-dependent behavior is observed, including predator-prey cycles, response to sawtooth crashes, and nonlinear harmonic coupling. The observation of GAEs excited between f_cD < f < f_cH provides a novel stress test for linear theory, with mixed results.