Impact of fast ions and fishbones on core turbulence at rational surfaces via global gyrokinetic GENE simulations

Abstract In this work, the interplay between fast ions (FIs) and safety factor rational surfaces is studied in a turbulent plasma via global nonlinear gyrokinetic simulations. The fast particle-induced enhancement of shearing structures from turbulence self-interaction is analyzed. Our study takes into account the competition between this mechanism and other FIs effects, i.e. thermal profiles dilution and quasi-resonant interaction. We find the reduction of the zonal modes destabilization threshold caused by FIs (Hahm et al 2023 Phys. Plasmas 30 072501) to be a very effective method to suppress turbulence. Indeed, it leads to the formation of regions where turbulent transport is reduced by 90% of its original value. Furthermore, an n = m = 1 fishbone is driven unstable inside the plasma and its interaction with turbulence is studied. We find the beat-driven zonal structure generated by this mode to further reduce turbulence when its presence does not drastically flatten the thermal profiles.