# Magnetic Helicities and Dynamo Action in Magneto-rotationally Driven Turbulence

## TL;DR

This study investigates the relationship between magnetic helicity and flux in magneto-rotational turbulence-driven dynamos, finding no direct correlation and highlighting the nonlinear nature of the dynamo process.

## Contribution

It introduces a gauge-invariant method to measure magnetic helicity and flux in open domains within MRI-driven dynamo simulations, revealing their complex relationship.

## Key findings

- Total helicity remains small despite magnetic flux generation.
- No direct link between magnetic flux and helicity flux.
- Helicity measurements are clarified using a new gauge approach.

## Abstract

We examine the relationship between magnetic flux generation, taken as an indicator of large-scale dynamo action, and magnetic helicity, computed as an integral over the dynamo volume, in a simple dynamo. We consider dynamo action driven by Magneto-Rotational Turbulence (MRT) within the shearing-box approximation. We consider magnetically open boundary conditions that allow a flux of helicity in or out of the computational domain. We circumvent the problem of the lack of gauge invariance in open domains by choosing a particular gauge -- the winding gauge -- that provides a natural interpretation in terms of average winding number of pairwise field lines. We use this gauge precisely to define and measure the helicity and helicity flux for several realizations of dynamo action. We find in these cases, that the system as a whole does not break reflectional symmetry and the total helicity remains small even in cases when substantial magnetic flux is generated. We find no particular connection between the generation of magnetic flux and the helicity or the helicity flux through the boundaries. We suggest that this result may be due to the essentially nonlinear nature of the dynamo processes in MRT.