Legolas: magnetohydrodynamic spectroscopy with viscosity and Hall current

TL;DR

This paper extends the open-source MHD spectroscopy code Legolas to include viscosity and Hall current effects, enabling detailed stability analysis of plasmas with non-ideal effects relevant to various astrophysical and laboratory scenarios.

Contribution

The paper introduces and benchmarks viscosity and Hall current extensions in Legolas, demonstrating their impact on plasma stability analysis and eigenmode spectra.

Findings

Viscosity extension validated in Taylor-Couette flow and plasma slab.

Hall effect influences eigenmode spectrum and resistive tearing modes.

Legolas can simulate incompressible limit and assess compressibility effects.

Abstract

Many linear stability aspects in plasmas are heavily influenced by non-ideal effects beyond the basic ideal magnetohydrodynamics (MHD) description. Here, the extension of the modern open-source MHD spectroscopy code Legolas with viscosity and the Hall current is highlighted and benchmarked on a stringent set of historic and recent findings. The viscosity extension is demonstrated in a cylindrical setup featuring Taylor-Couette flow and in a viscoresistive plasma slab with a tearing mode. For the Hall extension, we show how the full eigenmode spectrum relates to the analytic dispersion relation in an infinite homogeneous medium. We quantify the Hall term influence on the resistive tearing mode in a Harris current sheet, including the effect of compressibility, which is absent in earlier studies. Furthermore, we illustrate how Legolas mimics the incompressible limit easily to compare to literature results. Going beyond published findings, we emphasise the importance of computing the full eigenmode spectrum, and how elements of the spectrum are modified by compressibility. These extensions allow for future stability studies with Legolas that are relevant to ongoing dynamo experiments, protoplanetary disks, or magnetic reconnection.