Damping and drive of low-frequency modes in tokamak plasmas

Abstract

The ability to predict the stability of fast-particle-driven Alfvén eigenmodes in burning fusion plasmas requires a detailed understanding of the dissipative mechanisms that damp these modes. In order to address this question, the linear gyro-kinetic, electromagnetic code LIGKA (Lauber 2003 Linear gyrokinetic description of fast particle effects on the MHD stability in tokamaks PhD Thesis Technical University München, Lauber et al 2007 J. Comp. Phys. 226 447) is employed to investigate their behaviour in realistic tokamak geometry.Recently, the model and the implementation of LIGKA were extended in order to capture rigorously the coupling of the shear Alfvén wave to the drift and sound waves. This coupling becomes important for the investigation of low-frequency modes such as the Alfvén cascade modes (AC), the beta-induced Alfvén eigenmodes (BAEs), the geodesic acoustic modes (GAMs), the energetic particle modes (EPMs) and—at even lower frequencies—the resistive wall modes (RWMs).The authors report on an effort to close the gap between high-n micro-scale turbulence codes (in their linear phase) and low-n global MHD codes. More precisely, the aim is to describe both regimes within the same framework of equations and with the same numerical implementation by improving the range of applicability and validity of LIGKA: an eigenvalue code allows one to explore both the local complex dispersion relations, e.g. kinetic Alfvén waves (electromagnetic), ion acoustic waves (electrostatic) or drift waves in realistic geometry and also their global eigenfunctions.As an application of this extension, an investigation of the kinetic RWM damping mechanisms is carried out.