Magnetohydrodynamic Turbulence in the Plasmoid-Mediated Regime
26 Mar 2018
•
Comisso L.
•
Huang Y. -M.
•
Lingam M.
•
Hirvijoki E.
•
Bhattacharjee A.
Magnetohydrodynamic turbulence and magnetic reconnection are ubiquitous in
astrophysical environments. In most situations, these processes do not occur in
isolation, but interact with each other...This renders a comprehensive theory of
these processes highly challenging. Here, we propose a theory of
magnetohydrodynamic turbulence driven at large scale that self-consistently
accounts for the mutual interplay with magnetic reconnection occurring at
smaller scales. Magnetic reconnection produces plasmoids that grow from
turbulence-generated noise and eventually disrupt the sheet-like structures in
which they are born. The disruption of these structures leads to a modification
of the turbulent energy cascade, which, in turn, exerts a feedback effect on
the plasmoid formation via the turbulence-generated noise. The energy spectrum
in this plasmoid-mediated range steepens relative to the standard inertial
range and does not follow a simple power law. As a result of the complex
interplay between turbulence and reconnection, we also find that the length
scale which marks the beginning of the plasmoid-mediated range and the
dissipation length scale do not obey true power laws. The transitional magnetic
Reynolds number above which the plasmoid formation becomes statistically
significant enough to affect the turbulent cascade is fairly modest, implying
that plasmoids are expected to modify the turbulent path to dissipation in many
astrophysical systems.(read more)