The Role of Helical and Non-Helical Drives on the evolution of Self-Consistent Dynamos

TL;DR

This paper investigates how helical and non-helical drives influence the initiation and saturation of self-consistent dynamos, revealing that both can trigger small-scale dynamo activity and follow established spectral scalings.

Contribution

It demonstrates the role of different forcing mechanisms in dynamo saturation and confirms spectral scalings across various magnetic Prandtl numbers through numerical analysis.

Findings

Both helical and non-helical drives induce small-scale dynamo activity.

Kinetic energy follows Kolmogorov's $k^{-5/3}$ law.

Magnetic energy follows Kazantsev's $k^{3/2}$ scaling.

Abstract

In the self-consistent dynamo limit, the magnetic feedback on the velocity field is sufficiently strong to induce a change in the topology of the magnetic field. Consequently, the magnetic energy reaches a state of non-linear saturation. Here, we investigate the role played by helical and non-helical drives in the triggering and the eventual saturation of a self-consistent dynamo. Evidence of small-scale dynamo (SSD) activity is found for both helical and non-helical forcing, driven at the largest possible scale. Based on the spectrum analysis, we find that the evolution of kinetic energy follows Kolmogorov's $k^-{\frac{5}{3}}$ law while that of magnetic energy follows Kazantsev's $k^{\frac{3}{2}}$ scaling. Also, we have verified that the aforementioned scalings remain valid for various magnetic Prandtl numbers (Pm). Statistical analysis is found to support our numerical finds.