Effects of GAEs on the beam ions in NSTX-U

The 3D nonlinear simulations demonstrate that unstable global Alfven eigenmodes (GAEs) in the NSTX-U can very efficiently redistribute the beam ions, reducing the anisotropy in the pitch distribution in the resonant region of the phase space, and accelerate the fast ions to energies above the injection energy. It is shown that these effects are especially strong for super-Alfvénic injection velocities and more perpendicular injections. Significant modification of the distribution of the resonant particles occurs in case of the resonance overlap caused by the close spacing of the unstable mode frequencies with different toroidal mode numbers. Changes of the beam ion distribution correspond to a wider spread in the pitch parameter distribution, and reduction of the instability drive. The excited GAEs can very efficiently transfer energy from the perpendicular to the parallel component (for the particles driving the instability) or vice-versa (for the particles near the injection energy, which are taking energy from the mode). A small fraction of the energy goes into the excitation of the mode itself. In addition, the excitation of GAEs and low frequency instabilities in the TAE frequency range is studied including the fast ion sources and sinks.