Hall effect on the joint cascades of magnetic energy and helicity in helical magnetohydrodynamic turbulence

TL;DR

This paper investigates how Hall effects influence the transfer of magnetic energy and helicity in helical magnetohydrodynamic turbulence, revealing a new mechanism affecting large-scale magnetic fields.

Contribution

It demonstrates that Hall effects induce cross helicity and suppress inverse cascades, affecting large-scale magnetic energy and helicity accumulation, supported by simulations and Ulysses data.

Findings

Hall effects induce cross helicity in turbulence.

Suppression of inverse cascade leads to large-scale magnetic energy buildup.

Confirmation of results using Ulysses spacecraft data.

Abstract

Helical magnetohydrodynamic turbulence with Hall effects is ubiquitous in heliophysics and plasma physics, such as star formation and solar activities, and its intrinsic mechanisms are still not clearly explained. Direct numerical simulations reveal that when the forcing scale is comparable to the ion inertial scale, Hall effects induce remarkable cross helicity. It then suppresses the inverse cascade efficiency, leading to the accumulation of large-scale magnetic energy and helicity. The process is accompanied by the breaking of current sheets via filaments along magnetic fields. Using the Ulysses data, the numerical findings are separately confirmed. These results suggest a novel mechanism wherein small-scale Hall effects could strongly affect large-scale magnetic fields through cross helicity.