Two-fluid MHD Regime of Resistive Drift-Wave Instability

TL;DR

This paper investigates the resistive drift wave instability using a 2-fluid MHD model, revealing a coupled macro-scale eigenmode with edge-localized features and complex dispersion relations relevant to tokamak edge turbulence.

Contribution

It provides a comprehensive framework combining micro-scale turbulence and large-scale MHD processes, including analytical and numerical analysis with the NIMROD code.

Findings

Identification of a macro-scale global drift wave eigenmode coupled with MHD dynamics.

Edge-localized radial mode structure influenced by azimuthal mode number.

Non-monotonic dispersion relation with respect to wavenumbers.

Abstract

Drift instabilities contribute to the formation of edge turbulence and zonal flows, and thus the anomalous transport in tokamaks. Experiments often found micro-scale tur- bulence strongly coupled with large-scale magnetohydrodynamic (MHD) processes, whereas a general framework has been lacking that can cover both regimes, in partic- ular, their coupling. In this paper, the linear resistive drift wave instability (DWI) is investigated using a full 2-fluid MHD model, as well as its numerical implementation in NIMROD code. Both analytical and numerical analyses reveal a macro-scale global drift wave eigenmode coupled with MHD dynamics and illustrate a non-monotonic dispersion relation with respect to both perpendicular and parallel wavenumbers. NIMROD results also reveal an edge-localized behavior in the radial mode structure as the azimuthal mode number increases, implying the dependence of the 2-fluid ef- fects due to the inhomogeneous density profile. The edge-localization introduces a non-trivial dependence of the effective perpendicular wavenumber to the perpendicular mode number, which may explain the quantitative difference between the global dispersion relation and its local approximation from the conventional local theory.