Nonhelical Inverse Transfer of a Decaying Turbulent Magnetic Field
Abstract
In the presence of magnetic helicity, inverse transfer from small to large scales is well known in magnetohydrodynamic (MHD) turbulence and has applications in astrophysics, cosmology, and fusion plasmas. Using high resolution direct numerical simulations of magnetically dominated selfsimilarly decaying MHD turbulence, we report a similar inverse transfer even in the absence of magnetic helicity. We compute for the first time spectral energy transfer rates to show that this inverse transfer is about half as strong as with helicity, but in both cases the magnetic gain at large scales results from velocity at similar scales interacting with smallerscale magnetic fields. This suggests that both inverse transfers are a consequence of universal mechanisms for magnetically dominated turbulence. Possible explanations include inverse cascading of the mean squared vector potential associated with local near two dimensionality and the shallower k^{2} subinertial range spectrum of kinetic energy forcing the magnetic field with a k^{4} subinertial range to attain largerscale coherence. The inertial range shows a clear k^{2} spectrum and is the first example of fully isotropic magnetically dominated MHD turbulence exhibiting weak turbulence scaling.
 Publication:

Physical Review Letters
 Pub Date:
 February 2015
 DOI:
 10.1103/PhysRevLett.114.075001
 arXiv:
 arXiv:1404.2238
 Bibcode:
 2015PhRvL.114g5001B
 Keywords:

 94.05.Lk;
 96.50.Tf;
 Turbulence;
 MHD waves;
 plasma waves turbulence;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Solar and Stellar Astrophysics;
 Physics  Plasma Physics
 EPrint:
 4 pages, 4 figures, submitted to PRL, plus 9 pages of supplemental material with 12 more figures