Linear Stability of an Impulsively Accelerated Density Interface in an Ideal Two-Fluid Plasma

TL;DR

This paper analyzes the linear evolution of Richtmyer-Meshkov instability in a two-fluid plasma, exploring how coupling strength and magnetic fields influence instability growth and suppression.

Contribution

It introduces a detailed two-fluid plasma model for RM instability, examining the effects of coupling regimes and magnetic fields on instability dynamics.

Findings

Weak coupling leads to separate ion-electron evolution.

Strong coupling results in ions and electrons behaving as one fluid.

Magnetic fields suppress the instability over time.

Abstract

We investigate the linear evolution of Richtmyer-Meshkov (RM) instability in the framework of an ideal two-fluid plasma model. The two-fluid plasma equations of motion are separated into a base state and a set of linearized equations governing the evolution of the perturbations. Different coupling regimes between the charged species are distinguished based on a non-dimensional Debye length parameter $d_{D,0}$. When $d_{D,0}$ is large, the coupling between ions and electrons is sufficiently small that the induced Lorentz force is very weak and the two species evolve as two separate fluids. When $d_{D,0}$ is small, the coupling is strong and the induced Lorentz force is strong enough that the difference between state of ions and electrons is rapidly decreased by the force. As a consequence, the ions and electrons are tightly coupled and evolve like one fluid. The temporal dynamics is divided into two phases: an early phase wherein electron precursor waves are prevalent, and a post ion shock-interface interaction phase during which the RM instability manifests itself. We also examine the effect of an initially applied magnetic field in the streamwise direction characterized by the non-dimensional parameter $\beta_0$. For a short duration after the ion shock-interface interaction, the growth rate is similar for different initial magnetic field strengths. As time progresses the suppression of the instability due to the magnetic field is observed. The growth rate shows oscillations with a frequency that is related to the ion or electron cyclotron frequency. The instability is suppressed due to the vorticity being transported away from the interface.