Astronomy and Astrophysics – Astrophysics
Scientific paper
2002-09-16
Phys.Rev. E68 (2003) 036301
Astronomy and Astrophysics
Astrophysics
12 pages, REVTEX4, submitted to Phys. Rev. E
Scientific paper
10.1103/PhysRevE.68.036301
An effect of sheared large-scale motions on a mean electromotive force in a nonrotating turbulent flow of a conducting fluid is studied. It is demonstrated that in a homogeneous divergence-free turbulent flow the alpha-effect does not exist, however a mean magnetic field can be generated even in a nonrotating turbulence with an imposed mean velocity shear due to a new ''shear-current" effect. A contribution to the electromotive force related with the symmetric parts of the gradient tensor of the mean magnetic field (the kappa-effect) is found in a nonrotating turbulent flows with a mean shear. The kappa-effect and turbulent magnetic diffusion reduce the growth rate of the mean magnetic field. It is shown that a mean magnetic field can be generated when the exponent of the energy spectrum of the background turbulence (without the mean velocity shear) is less than 2. The ''shear-current" effect was studied using two different methods: the Orszag third-order closure procedure and the stochastic calculus. Astrophysical applications of the obtained results are discussed.
Kleeorin Nathan
Rogachevskii Igor
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