Closure of the single fluid magnetohydrodynamic equations in presence of electron cyclotron current drive

TL;DR

This paper introduces a new closure relation for electron cyclotron current drive (ECCD) in single fluid MHD equations, capturing its nonlocal nature and validating it through analytical and numerical simulations.

Contribution

It presents a novel closure relation for ECCD in MHD that accounts for nonlocal effects and is validated against analytical and simulation data.

Findings

The new closure accurately models the nonlocal ECCD current.

Validation against Fokker-Planck solutions confirms the model's reliability.

The model generalizes previous approaches by Giruzzi et al.

Abstract

In the presence of electron cyclotron current drive (ECCD), the Ohm's law of single fluid magnetohydrodynamics (MHD) is modified as ${\bf E} + {\bf v} \times {\bf B} = \eta( {\bf J} - {\bf J}_{\rm EC} )$. This paper presents a new closure relation for the EC driven current density appearing in this modified Ohm's law. The new relation faithfully represents the nonlocal character of the EC driven current and its main origin in the Fisch-Boozer effect. The closure relation is validated on both an analytical solution of an approximated Fokker-Planck equation as well as on full bounce-averaged, quasi-linear Fokker-Planck code simulations of ECCD inside rotating magnetic islands. The new model contains the model put forward by Giruzzi et al., Nucl. Fusion 39 (1999) 107, in one of its limits.