Nonlinear interaction of Alfv\'enic instabilities and turbulence via the modification of the equilibrium profiles

TL;DR

This paper investigates how Alfvénic instabilities driven by energetic particles can nonlinearly modify plasma temperature profiles, which in turn affects turbulence levels, demonstrating an indirect interaction between energetic particles and turbulence.

Contribution

The study combines gyrokinetic simulations and analytical models to reveal the nonlinear feedback of Alfvén modes on turbulence, including application to experimental conditions.

Findings

Turbulence is reduced when profiles are relaxed by Alfvén modes.

Alfvén modes carry heat flux and modify temperature profiles.

Indirect interaction between energetic particles and turbulence is demonstrated.

Abstract

Nonlinear simulations of Alfv\'en modes (AM) driven by energetic particles (EP) in the presence of turbulence are performed with the gyrokinetic particle-in-cell code ORB5. The AMs carry a heat flux, and consequently they nonlinearly modify the plasma temperature profiles. The isolated effect of this modification on the dynamics of turbulence is studied, by means of electrostatic simulations. We find that turbulence is reduced when the profiles relaxed by the AM are used, with respect to the simulation where the unperturbed profiles are used. This is an example of indirect interaction of EPs and turbulence. First, an analytic magnetic equilibrium with circular concentric flux surfaces is considered as a simplified example for this study. Then, an application to an experimentally relevant case of ASDEX Upgrade is discussed.