FOXTAIL: Modeling the nonlinear interaction between Alfv\'en eigenmodes and energetic particles in tokamaks

TL;DR

FOXTAIL is a hybrid code that models nonlinear interactions between energetic particles and Alfvén eigenmodes in tokamaks, enabling realistic geometry simulations and analysis of mode-particle dynamics.

Contribution

The paper introduces FOXTAIL, a novel hybrid MHD-kinetic code that efficiently simulates nonlinear wave-particle interactions in tokamaks with realistic geometries.

Findings

Validated the code against the bump-on-tail approximation.

Verified effects of the Chirikov criterion in two-mode scenarios.

Demonstrated the code's application to realistic tokamak geometries.

Abstract

FOXTAIL is a new hybrid magnetohydrodynamic-kinetic code used to describe interactions between energetic particles and Alfv\'en eigenmodes in tokamaks with realistic geometries. The code simulates the nonlinear dynamics of the amplitudes of individual eigenmodes and of a set of discrete markers in five-dimensional phase space representing the energetic particle distribution. Action-angle coordinates of the equilibrium system are used for efficient tracing of energetic particles, and the particle acceleration by the wave fields of the eigenmodes is Fourier decomposed in the same angles. The eigenmodes are described using temporally constant eigenfunctions with dynamic complex amplitudes. Possible applications of the code are presented, e.g., making a quantitative validity evaluation of the one-dimensional bump-on-tail approximation of the system. Expected effects of the fulfillment of the Chirikov criterion in two-mode scenarios have also been verified.