# Magneto-Rayleigh-Taylor instability in an elastic finite-width medium overlying an ideal fluid

## TL;DR

This paper develops a linear theory for magneto-Rayleigh-Taylor instability in an elastic layer over an ideal fluid, revealing complex interactions between magnetic and elastic effects that influence stability.

## Contribution

It introduces a novel analysis of the combined effects of elasticity and magnetic fields on instability, highlighting unexpected destabilization in thin layers.

## Key findings

- Magnetic and elastic effects generally enhance stability in thick layers.
- In thin layers, magnetic effects can counteract elasticity, leading to increased instability.
- Implications for magnetically driven experiments and neutron star crust-quakes are discussed.

## Abstract

We present the linear theory of two-dimensional incompressible magneto-Rayleigh-Taylor instability in a system composed of a linear elastic (Hookean) layer above a lighter semi-infinite ideal fluid with magnetic fields present, above and below the layer. As expected, magnetic field effects and elasticity effects together enhance the stability of thick layers. However, the situation becomes more complicated for relatively thin slabs, and a number of new and unexpected phenomena are observed. In particular, when the magnetic field beneath the layer dominates, its effects compete with effects due to elasticity, and counteract the elasticity stabilising effects. As a consequence, the layer can become more unstable than when only one of these stabilising mechanism is acting. This somewhat unexpected result is explained by the different physical mechanisms for which elasticity and magnetic fields stabilise the system. Implications for experiments on magnetically driven accelerated plates and implosions are discussed. Moreover, the relevance for triggering of crust-quakes in strongly magnetised neutron stars is also pointed out.