GAE-induced energetic particle transport in NSTX-U

A set of nonlinear simulations has been performed to study the effects of unstable global Alfvén eigenmodes (GAEs) on the energetic particle transport in the NSTX-U. Experimentally, the indirect evidence of significant redistribution of fast ions by the GAEs was found, for example, in NSTX, where the GAE bursts were followed by lower frequency TAE avalanches or EPMs [E. D. Fredrickson, et al., Nucl. Fusion 52, 043001 (2012)]. Analysis of the simulation results shows that for resonant particles redistribution occurs mainly in the velocity space. Significant radial displacements occur mostly near orbit boundaries, but there is a net radial redistribution of passing particles close to resonant region for energies near the injection energy. Simulations also show an increase in the beam ion losses due to GAEs, with the majority of the lost orbits being of the trapped orbit type. The total number of the GAE-related losses is about 0.45% of the total beam ion inventory on the simulation time 0.1 msec. The simulations, therefore, suggest that multiple GAE bursts of a sufficiently large amplitude, persisting for 100s msec, can lead to a noticeable net beam ion loss.