Amplification of large-scale magnetic field in nonhelical magnetohydrodynamics

TL;DR

This paper demonstrates through simulations that large-scale magnetic fields can be amplified in nonhelical magnetohydrodynamics without the need for helicity, challenging traditional assumptions about dynamo mechanisms.

Contribution

The study shows that nonhelical MHD can amplify large-scale magnetic fields via energy transfer from velocity fields, without relying on helicity.

Findings

Large-scale magnetic field growth observed in nonhelical MHD simulations.

Energy transfer from velocity to magnetic fields drives amplification.

Helicity is not necessary for large-scale dynamo action.

Abstract

It is typically assumed that the kinetic and magnetic helicities play a crucial role in the growth of large-scale dynamo. In this paper we demonstrate that helicity is not essential for the amplification of large-scale magnetic field. For this purpose, we perform nonhelical magnetohydrodynamic (MHD) simulation, and show that the large-scale magnetic field can grow in nonhelical MHD when random external forcing is employed at scale $1/10$ the box size. The energy fluxes and shell-to-shell transfer rates computed using the numerical data show that the large-scale magnetic energy grows due to the energy transfers from the velocity field at the forcing scales.