The role of zonal structures as mediators of energetic particles and turbulence

Spatial gradients of density and temperature are present in tokamak plasmas. Microinstabilities grow due to these gradients, and nonlinearly interact, forming turbulence. Zonal (i.e. axisymmetric) structures (ZS) take an important role in the nonlinear saturation of turbulence. Energetic particle populations are also present in tokamak plasmas due to fusion reactions, and in part due to external heating mechanisms. In the recent years, the interaction of EPs and turbulence has taken a particular attention of the magnetic-confinement fusion community. A global gyrokinetic model is necessary, if one wants to address such an intrinsically multiscale kinetic problem. In this work, we investigate the nonlinear dynamics of ZS as mediators of turbulence and EPs. The main theoretical tool is the global particle-in-cell code ORB5, originally developed for electrostatic turbulence studies, and later on extended to its multispecies electromagnetic version. The effect of the EPs on the ZS will be shown, and the role of macroscopic instabilities as mediators will be considered.