Physics of drift Alfvén instabilities and energetic particles in fusion plasmas

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 (FEM), was developed to analyze Alfvén
instabilities excited by EPs. The model equations, consisting of
quasi-neutrality condition and Schrödinger-like form of vorticity
equation, are derived within the general fishbone-like dispersion
relation (GFLDR) theoretical framework, which is widely used to analyze
SAW/DAW physics. The mode structure decomposition (MSD) 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 by the `DAEPS` code with realistic experimental plasma profile
and magnetic configuration. Based on this information, we adopt the
Dyson-Schrödinger Model (DSM) to further analyze EP energy and momentum
flux. We will also 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.

ATEP: an advanced transport model for energetic particles

“…To that end, comparisons with other reduced models will be carried out, e.g. with an ongoing extension of the DAEPS code [12,43] that uses explicit analytical expressions for calculating the phase space fluxes. Also, a 1d reduced model based on the beam-plasma bump-on-tail paradigm that is designed to go beyond the quasi-linear approximation and thus forecast possible EP transport transitions such as avalanching [36] will be used to determine the limits of the ATEP model.…”

Nonlinear equilibria and transport processes in burning plasmas

“…Notably, a recent advancement in this field is the proposed Dyson-Schrödinger transport Model (DSM) [8]. PSZS fluxes, computed using the DAEPS-FALCON suite of codes [49,50], have been calculated within the LIGKA EP workflow [51,52] considering realistic Tokamak configurations. This is a crucial step towards the practical implementation of the PSZS transport theory in realistic geometry.…”