A Parametric Study of Extended-MHD Drift Tearing

TL;DR

This paper investigates the linear drift-tearing mode across different plasma-$eta$ regimes using an extended-MHD model, deriving new dispersion relations at moderate $eta$ and verifying the NIMROD code's implementation.

Contribution

It introduces new dispersion relations for the drift-tearing mode at moderate plasma-$eta$ and classifies previous results as applicable only at small $eta$, enhancing understanding of mode stabilization.

Findings

New dispersion relations at moderate plasma-$eta$

Verification of NIMROD code's extended-MHD implementation

Discussion on the validity of finite-Larmor-radius models

Abstract

The linear drift-tearing mode is analyzed for different regimes of the plasma-$\beta$, ion-skin-depth parameter space with an unreduced, extended-MHD model. New dispersion relations are found at moderate plasma $\beta$ and previous drift-tearing results are classified as applicable at small plasma $\beta$. The drift stabilization of the mode in the regimes varies from non-existent/weak to complete. As the diamagnetic-drift frequency is proportional to the plasma $\beta$, verification exercises with unreduced, extended-MHD models in the small plasma-$\beta$ regimes are impractical. The new dispersion relations in the moderate plasma-$\beta$ regimes are used to verify the extended-MHD implementation of the NIMROD code [C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004)]. Given the small boundary-layer skin depth, discussion of the validity of the first-order finite-Larmour-radius model is presented.