Global simulations of kinetic-magnetohydrodynamic processes with energetic electrons in tokamak plasmas

Abstract

The energetic electrons (EEs) produced from auxiliary heatings have been found to destabilize various Alfven eigenmodes (AEs) in recent experiments. To investigate EE relevant kinetic-magnetohydrodynamic (MHD) processes, a global fluid-kinetic hybrid model is formulated and verified in this work, which consists of Landau-fluid bulk plasmas and drift-kinetic EEs that incorporates the dominant damping and drive mechanisms, respectively. The numerical capability of Landau-fluid bulk plasmas is obtained based on a well-benchmarked eigenvalue code multiscale analysis for plasma stability (MAS) using general geometry (Bao et al 2023 Nucl. Fusion 63 076021), and the comprehensive EE responses to the low frequency ( $\omega\ll\Omega_{ci}$ ) MHD fluctuations are analytically derived and implemented in MAS, which not only cover contributions from trapped and passing particles, but also take into account the effects of adiabatic fluid convection and non-adiabatic kinetic compression. The linear properties of EE-driven beta-induced AEs (e-BAEs) are systematically studied using both MAS model and gyrokinetic toroidal code (GTC) particle-in-cell simulations. Building on the good agreements on the mode structure and dispersion relation, several key issues of e-BAE physics are analyzed and discussed, including the parametric dependences of e-BAE stability on EE mass, temperature and density with corresponding phase space dynamics, EE non-perturbative effects on the symmetry breaking of mode structure, and the EE density and temperature thresholds for e-BAE excitation that overcome bulk plasma damping. With these efforts, the upgraded MAS model is superior than initial-value simulations restricted by stringent electron Courant condition for fast linear analyses of most EE-AE problems with $\omega\ll\Omega_{ci}$ , of which wave–particle resonance can be used to analyze the analogous effect of alpha particle driven AEs in future fusion reactor.

Keywords

• kinetic-magnetohydrodynamic
• energetic electrons
• Alfvén eigenmodes
• non-perturbative
• global eigenvalue approach