Dynamo Action in a Quasi-Keplerian Taylor-Couette Flow

TL;DR

This study demonstrates a finite-amplitude dynamo in a quasi-Keplerian Taylor-Couette flow, showing that turbulence and magnetic fields can mutually sustain each other, leading to enhanced angular momentum transport.

Contribution

First numerical demonstration of a finite-amplitude dynamo in a quasi-Keplerian Taylor-Couette flow with implications for astrophysical disk dynamics.

Findings

Existence of a finite-amplitude dynamo at Re=10^4 and Rm=10^5.

Dynamo leads to increased angular momentum transport.

Maxwell stresses dominate over Reynolds stresses in transport.

Abstract

We numerically compute the flow of an electrically conducting fluid in a Taylor-Couette geometry where the rotation rates of the inner and outer cylinders satisfy $\Omega_o/\Omega_i=(r_o/r_i)^{-3/2}$. In this quasi-Keplerian regime a non-magnetic system would be Rayleigh-stable for all Reynolds numbers $Re$, and the resulting purely azimuthal flow incapable of kinematic dynamo action for all magnetic Reynolds numbers $Rm$. For $Re=10^4$ and $Rm=10^5$ we demonstrate the existence of a finite-amplitude dynamo, whereby a suitable initial condition yields mutually sustaining turbulence and magnetic fields, even though neither could exist without the other. This dynamo solution results in significantly increased outward angular momentum transport, with the bulk of the transport being by Maxwell rather than Reynolds stresses.