Strong and weak dynamo regimes in Taylor-Couette flows

TL;DR

This paper demonstrates the existence of a nonlinear magnetic dynamo in Taylor-Couette flows at small magnetic Prandtl numbers, revealing two distinct dynamo regimes and emphasizing the influence of initial conditions and domain geometry.

Contribution

It shows that dynamo action can occur at low magnetic Prandtl numbers in Taylor-Couette flows, contrary to previous beliefs, and identifies two main dynamo regimes.

Findings

Dynamo exists at small Pm (≤1) in Taylor-Couette flows.

Two dynamo regimes identified: weak large-scale and strong turbulent.

Initial perturbations and domain aspect ratio influence dynamo onset and evolution.

Abstract

We reveal a nonlinear magnetic dynamo in a Taylor-Couette flow at small magnetic Prandtl numbers $Pm\leq 1$, which has been previously believed to exist only at higher $Pm\gtrsim 10$ in this flow. The amplitude of initial perturbations, $Pm$ and domain aspect ratio play a key role in the onset and evolution of the dynamo. It exists in two main states -- a weak state dominated by large-scale modes and a strong, turbulent state with higher amplitude dominated by small-scale modes. These findings can be important for dynamo processes in various astrophysical objects with small $Pm$.