Saturation of fishbone instability by self-generated zonal flows in tokamak plasmas

TL;DR

This study uses gyrokinetic simulations to show that self-generated zonal flows can saturate fishbone instabilities in tokamak plasmas, aligning with experimental data and suggesting benefits for ITER plasma performance.

Contribution

First quantitative simulation of fishbone saturation by zonal flows matching experimental measurements, highlighting their role in plasma confinement and stability.

Findings

Zonal flows dominate fishbone nonlinear saturation.

Simulation results agree with experimental saturation amplitudes.

Fishbone-induced zonal flows may help form internal transport barriers.

Abstract

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.