Global Three-Dimensional Simulations of Outer Protoplanetary Disks with Ambipolar Diffusion

TL;DR

This study uses 3D non-ideal MHD simulations to explore how ambipolar diffusion influences magnetic flux concentration, turbulence, and substructure formation in outer protoplanetary disks, revealing the coexistence of disk winds and MRI-driven turbulence.

Contribution

First global 3D non-ideal MHD simulations with ambipolar diffusion showing magnetic flux concentration and annular substructure formation in outer PPDs.

Findings

Magnetized disk wind dominates angular momentum transport.

Magnetic flux spontaneously concentrates into axisymmetric flux sheets.

Disk exhibits natural formation of annular substructures due to flux concentration.

Abstract

The structure and evolution of protoplanetary disks (PPDs) are largely governed by disk angular momentum transport, mediated by magnetic fields. In the most observable outer disk, PPD gas dynamics is primarily controlled by ambipolar diffusion as the dominant non-ideal magnetohydrodynamic (MHD) effect. In this work, we study the gas dynamics in outer PPDs by conducting a set of global 3D non-ideal MHD simulations with ambipolar diffusion and net poloidal magnetic flux, using the Athena++ MHD code, with resolution comparable to local simulations. Our simulations demonstrate the co-existence of magnetized disk wind and turbulence driven by the magneto-rotational instability (MRI). While MHD wind dominates disk angular momentum transport, the MRI turbulence also contributes significantly. We observe that magnetic flux spontaneously concentrate into axisymmetric flux sheets, leading to radial variations in turbulence levels, stresses, and accretion rates. Annular substructures arise as a natural consequence of magnetic flux concentration. The flux concentration phenomena show diverse properties with different levels of disk magnetization and ambipolar diffusion. The disk generally loses magnetic flux over time, though flux sheets could prevent the leak of magnetic flux in some cases. Our results demonstrate the ubiquity of disk annular substructures in weakly MRI turbulent outer PPDs, and imply a stochastic nature of disk evolution.