Linear and nonlinear excitation of TAE modes by external electromagnetic perturbations using ORB5

TL;DR

This paper investigates the excitation and nonlinear interactions of TAE modes in toroidal plasmas using external electromagnetic perturbations, employing advanced simulation techniques to analyze mode stability, coupling, and particle interactions.

Contribution

It introduces a novel simulation framework for long-time stable excitation of TAE modes with external antennas and explores their nonlinear couplings and stability margins.

Findings

Successful long-time linear simulations of TAE excitation.

Identification of mode interactions with fast particles.

First nonlinear simulations showing mode coupling and excitation of GAE.

Abstract

The excitation of toroidicity induced Alfv{\'e}n eigenmodes (TAEs) using prescribed external electromagnetic perturbations (hereafter ``antenna") acting on a confined toroidal plasma as well as its nonlinear couplings to other modes in the system is studied. The antenna is described by an electrostatic potential resembling the target TAE mode structure along with its corresponding parallel electromagnetic potential computed from Ohm's law. Numerically stable long-time linear simulations are achieved by integrating the antenna within the framework of a mixed representation and pullback scheme [A. Mishchenko, et al., Comput. Phys. Commun. \textbf{238} (2019) 194]. By decomposing the plasma electromagnetic potential into symplectic and Hamiltonian parts and using Ohm's law, the destabilizing contribution of the potential gradient parallel to the magnetic field is canceled in the equations of motion. Besides evaluating the frequencies as well as growth/damping rates of excited modes compared to referenced TAEs, we study the interaction of antenna-driven modes with fast particles and indicate their margins of instability. Furthermore, we show first nonlinear simulations in the presence of a TAE-like antenna exciting other TAE modes, as well as Global Alfv\'en Eigenmodes (GAE) having different toroidal wave numbers from that of the antenna.