# Simulating the Diverse Instabilities of Dust in Magnetized Gas

## TL;DR

This paper uses simulations to explore the complex instabilities of charged dust in magnetized gas, revealing diverse turbulence, structure formation, and magnetic field amplification across various parameter regimes.

## Contribution

It provides a comprehensive simulation study of dust-gas instabilities, characterizing their turbulence, structure, and magnetic effects under different conditions, extending prior theoretical work.

## Key findings

- Dust drives turbulence and magnetic field amplification.
- Dust forms extreme over-densities and complex structures.
- Different regimes produce diverse dust and gas behaviors.

## Abstract

Recently Squire & Hopkins showed that charged dust grains moving through magnetized gas under the influence of any external force (e.g. radiation pressure, gravity) are subject to a spectrum of instabilities. Qualitatively distinct instability families are associated with different Alfvenic or magnetosonic waves and drift or gyro motion. We present a suite of simulations exploring these instabilities, for grains in a homogeneous medium subject to an external acceleration. We vary parameters such as the ratio of Lorentz-to-drag forces on dust, plasma $\beta$, size scale, and acceleration. All regimes studied drive turbulent motions and dust-to-gas fluctuations in the saturated state, can rapidly amplify magnetic fields into equipartition with velocity fluctuations, and produce instabilities that persist indefinitely (despite random grain motions). Different parameters produce diverse morphologies and qualitatively different features in dust, but the saturated gas state can be broadly characterized as anisotropic magnetosonic or Alfvenic turbulence. Quasi-linear theory can qualitatively predict the gas turbulent properties. Turbulence grows from small to large scales, and larger-scale modes usually drive more vigorous gas turbulence, but dust velocity and density fluctuations are more complicated. In many regimes, dust forms structures (clumps, filaments, sheets) that reach extreme over-densities (up to $\gg 10^{9}$ times mean), and exhibit substantial sub-structure even in nearly-incompressible gas. These can be even more prominent at lower dust-to-gas ratios. In other regimes, dust self-excites scattering via magnetic fluctuations that isotropize and amplify dust velocities, producing fast, diffusive dust motions.