Journal Article

The dynamics of Rayleigh–Taylor stable and unstable contact discontinuities with anisotropic thermal conduction

Daniel Lecoanet, Ian J. Parrish and Eliot Quataert

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 423, issue 2, pages 1866-1882
Published in print June 2012 | ISSN: 0035-8711
Published online June 2012 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2012.21011.x
The dynamics of Rayleigh–Taylor stable and unstable contact discontinuities with anisotropic thermal conduction

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We study the effects of anisotropic thermal conduction along magnetic field lines on an accelerated contact discontinuity in a weakly collisional plasma. We first perform a linear stability analysis similar to that used to derive the Rayleigh–Taylor instability (RTI) dispersion relation. We find that anisotropic conduction is only important for compressible modes, as modes in the Boussinesq limit are isothermal. Modes grow faster in the presence of anisotropic conduction, but growth rates do not change by more than a factor of the order of unity. We next run fully non-linear numerical simulations of a contact discontinuity with anisotropic conduction. The non-linear evolution can be thought of as a superposition of three physical effects: temperature diffusion due to vertical conduction, the RTI and the heat flux driven buoyancy instability (HBI). We find that the presence of the magnetothermal instability (MTI) does not significantly affect the dynamics. In simulations with RTI-stable contact discontinuities, the temperature discontinuity spreads due to vertical heat conduction. This occurs even for initially horizontal magnetic fields due to the initial vertical velocity perturbation and numerical mixing across the interface. The HBI slows this temperature diffusion by reorienting initially vertical magnetic field lines to a more horizontal geometry. In simulations with RTI-unstable contact discontinuities, the dynamics are initially governed by temperature diffusion, but the RTI becomes increasingly important at late times. We discuss the possible application of these results to supernova remnants, solar prominences and cold fronts in galaxy clusters.

Keywords: conduction; instabilities; MHD; Sun: coronal mass ejections (CMEs); ISM: supernova remnants; galaxies: clusters: intracluster medium

Journal Article.  14629 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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