Speaker
Description
Simulations and experiments have shown that zonal flows can play a crucial role in the regulation of turbulence. In the context of energetic particles physics for magnetic confinement devices, it is then interesting to study how the interplay of energetic particles and Alfvén eigenmodes can affect the dynamics of zonal flows, and more in general zonal structures, and potentially impact the confinement and self-organization of a burning plasma. In particular, the present work focuses on further theoretically understanding how Alfvén eigenmodes destabilized by energetic particles can generate zonal fields via non-linear mode-mode coupling. After showing that previous literature can be considered satisfying only for the case of single dominant poloidal harmonic eigenmodes (e.g., reversed shear Alfvén eigenmodes), for which the zonal flow generation is mediated exclusively by the thermal plasma, we explore the role of energetic particles in the mediation of the non-linear interaction for a generic Alfvén eigenmode (e.g., toroidal Alfén eigenmodes with two dominant poloidal harmonics). In the framework of non-linear gyrokinetic theory, the investigation is divided into two parts. On the one hand we refine previous analytical treatments in the simplified case of well-passing particles in circular cross section geometry, on the other hand we formulate a semi-analytical approach valid in general tokamak geometry for both passing and trapped particles. Comparisons with the gyrokinetic code ORB5 are also carried out. While the current work still focuses on the linear growth stage of the Alfén eigenmodes, corresponding to the beat-driven growth phase of the zonal fields, future work including the non-linear saturation regime and the impact of the investigated zonal fields on plasma confinement is foreseen.
This work has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No 101052200 — EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them.