Physics of drift Alfvén instabilities and energetic particles in fusion plasmas

Abstract

Abstract Shear Alfvén wave (SAW)/drift Alfvén wave (DAW) fluctuations can be destabilized by energetic particles (EPs) as well as thermal plasma components, which play a key role in the EP energy and momentum transport processes in burning fusion plasmas. The drift Alfvén energetic particle stability (DAEPS) code, which is an eigenvalue code using the finite element method, was developed to analyze Alfvén instabilities excited by EPs. The model equations, consisting of the quasineutrality condition and the Schrödinger-like form of the vorticity equation, are derived within the general fishbone-like dispersion relation theoretical framework, which is widely used to analyze SAW/DAW physics. The mode structure decomposition approach and asymptotic matching between the inertial/singular layer and ideal regions are adopted. Therefore, the DAEPS code can provide not only frequency and growth/damping rate but also the parallel mode structure as well as the asymptotic behavior corresponding to the singular-layer contribution. Thus, it fully describes fluid and kinetic continuous spectra as well as unstable and damped modes. The model equations have been extended to include general axisymmetric geometry and to solve for the response of circulating and trapped particles by means of the action-angle approach. In this work, we discuss linear dispersion relation and parallel mode structure of drift Alfvén instabilities excited by EPs, computed with the DAEPS code with realistic experimental plasma profile and magnetic configuration. We compare DAEPS results with FALCON/LIGKA to provide a verification of the code. We then adopt the Dyson–Schrödinger model (DSM) to further analyze the EP energy and momentum flux. We will briefly discuss how the parallel mode structure of the drift Alfvén instabilities can be used in the DSM to calculate the nonlinear radial envelope evolution and the EP transport.