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Flux-tube gyrokinetic codes are widely used to simulate drift-wave turbulencein magnetic confinement devices. While a large number of studies show thatflux-tube codes provide an excellent approximation for turbulent transport inmedium-large devices, it still needs to be determined whether they aresufficient for modeling supra-thermal particle effects on core turbulence. Thisis called into question given the large temperature of energetic particles(EPs), which makes them hardly confined on a single flux-surface, but also dueto the radially broad mode structure of energetic-particle-driven modes. Theprimary focus of this manuscript is to assess the range of validity offlux-tube codes in modeling fast ion effects by comparing radially globalturbulence simulations with flux-tube results at different radial locations forrealistic JET parameters using the gyrokinetic code GENE. To extend our studyto a broad range of different plasma scenarios, this comparison is made forfour different plasma regimes, which differ only by the profile of the ratiobetween the plasma kinetic and magnetic pressure. The latter is artificiallyrescaled to address the electrostatic limit and regimes with marginally stable,weakly unstable and strongly unstable fast ion modes. Theseenergetic-particle-driven modes is identified as an AITG/KBAE via linear ORB5and LIGKA simulations. It is found that the local flux-tube simulations canrecover well the global results only in the electrostatic and marginally stablecases. When the AITG/KBAE becomes linearly unstable, the local approximationfails to correctly model the radially broad fast ion mode structure and theconsequent global zonal patterns. According to this study, global turbulencesimulations are likely required in regimes with linearly unstable AITG/KBAEs.In conditions with different fast ion-driven modes, these results might change.

How accurate are flux-tube (local) gyrokinetic codes in modeling energetic particle effects on core turbulence?