Energy transfers and magnetic energy growth in small-scale dynamo

TL;DR

This study investigates magnetic energy growth in small-scale dynamo through detailed analysis of energy transfers, revealing nonlocal energy transfer from large-scale velocity to small-scale magnetic fields and the evolution of magnetic integral scale.

Contribution

It provides new insights into the mechanisms of magnetic energy growth by analyzing energy fluxes and shell-to-shell transfers in high-resolution dynamo simulations.

Findings

Magnetic energy growth is driven by nonlocal energy transfers from large-scale velocity to small-scale magnetic fields.

The peak of energy transfers shifts to lower wavenumbers as the dynamo evolves.

Velocity-to-velocity and magnetic-to-magnetic energy transfers are forward and local.

Abstract

In this letter we investigate the dynamics of magnetic energy growth in small-scale dynamo by studying energy transfers, mainly energy fluxes and shell-to-shell energy transfers. We perform dynamo simulations for magnetic Prandtl number $\mathrm{Pm}=20$ on $1024^3$ grid using pseudospectral method. We demonstrate that the magnetic energy growth is caused by nonlocal energy transfers from the large-scale or forcing-scale velocity field to small-scale magnetic field. The peak of these energy transfers move towards lower wavenumbers as dynamo evolves, which is the reason why the integral scale of the magnetic field increases with time. The energy transfers $U2U$ (velocity to velocity) and $B2B$ (magnetic to magnetic) are forward and local.