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## Large scale dynamos with ambipolar diffusion nonlinearity
^{1} NORDITA, Blegdamsvej 17, 2100 Copenhagen O, Denmark^{2} Department of Mathematics, University of Newcastle upon Tyne, NE1 7RU, UK^{3} National Centre for Radio Astrophysics - TIFR, Poona University Campus, Ganeshkhind, Pune 411 007, India
It is shown that ambipolar diffusion as a useful model for nonlinearity leads to similar behaviour of large scale turbulent dynamos as full MHD. This is demonstrated using both direct simulations in a periodic box and a closure model for the magnetic correlation functions applicable to infinite space. Large scale fields develop via a nonlocal inverse cascade as described by the -effect. However, magnetic helicity can only change on a resistive timescale, so the time it takes to organize the field into large scales increases with magnetic Reynolds number.
Online publication: October 2, 2000 |