  Gyrokinetic simulations of the fishbone instability in DIII-D tokamak plasmas
find that self-generated zonal flows can dominate the nonlinear saturation by
preventing coherent structures from persisting or drifting in the energetic
particle phase space when the mode frequency down-chirps. Results from the
simulation with zonal flows agree quantitatively, for the first time, with
experimental measurements of the fishbone saturation amplitude and energetic
particle transport. Moreover, the fishbone-induced zonal flows are likely
responsible for the formation of an internal transport barrier that was
observed after fishbone bursts in this DIII-D experiment. Finally, gyrokinetic
simulations of a related ITER baseline scenario show that the fishbone induces
insignificant energetic particle redistribution and may enable high performance
scenarios in ITER burning plasma experiments.
