Gyrokinetic investigation of the damping channels of Alfv\'en modes in ASDEX Upgrade

TL;DR

This paper investigates the collisionless damping mechanisms of Alfvénic modes in tokamaks using gyrokinetic simulations, highlighting the dominance of electron Landau damping and applying findings to ASDEX Upgrade experiments.

Contribution

It provides a comprehensive gyrokinetic analysis of damping channels of Alfvén modes, comparing simulation tools and applying results to experimental tokamak data.

Findings

Electron Landau damping dominates ion Landau damping in relevant cases.

Gyrokinetic simulations align with eigenvalue code results.

Application to ASDEX Upgrade shows consistency with experimental observations.

Abstract

The linear destabilization and nonlinear saturation of energetic-particle driven Alfv\'enic instabilities in tokamaks strongly depend on the damping channels. In this work, the collisionless damping mechanisms of Alfv\'enic modes are investigated within a gyrokinetic framework, by means of global simulations with the particle-in-cell code ORB5, and compared with the eigenvalue code LIGKA and reduced models. In particular, the continuum damping and the Landau damping (of ions and electrons) are considered. The electron Landau damping is found to be dominant on the ion Landau damping for experimentally relevant cases. As an application, the linear and nonlinear dynamics of toroidicity induced Alfv\'en eigenmodes and energetic-particle driven modes in ASDEX Upgrade is investigated theoretically and compared with experimental measurements.