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Session 66 - Galaxies.
Display session, Thursday, June 11
In turbulent plasmas, velocities at scales smaller than a scale l_d are strongly damped by viscosity, and magnetic fields below a scale l_R are strongly dissipated by resistivity. In galaxies and protogalaxies, l_d\gg l_R. i.e., the magnetic Prandtl number is very large. A weak seed magnetic field will initially be amplified at scales smaller than l_d. We present 2D numerical simulations of such amplification based upon a numerical algorithm that is designed to take advantage of the large separation of scales between the magnetic and velocity fields. When magnetic forces are negligible, we compare numerical and analytic results for the evolving magnetic spectrum and the scaling of the magnetic-energy growth rate with the correlation time of the driving velocity field. When magnetic forces are appreciable, the velocity is determined by a balance between viscous and magnetic forces. We compare the subsequent magnetic evolution with that in the weak-field case. Even in two dimensions, the nonlinear effect of the magnetic field can halt the transfer of magnetic energy to the resistive scale. We discuss the the extension of this behavior to 3D and the effects of small-scale magnetic fields on thermal conduction and viscosity.
Program listing for Thursday