Largescale nonlinear limiting of galactic alphasquaredomegadynamos
Abstract
Axisymmetric MHD simulations for galactic (thin disk) alphasquaredomegadynamos with independent alphafunctions are performed in order to elucidate the mechanisms of the nonlinear backreaction of largescale dynamics to the induction equation. The amplitudes of the magnetic field and the velocity field, after exponentional growth with time, attain steady values with nonnegligible oscillations. Estimates for the steady amplitudes are given, and they are in rough agreement with the simulation results. The steady amplitude of the velocity field is proportional to the linear growth rate multiplied by the disk thickness. The steady amplitudes take various values according to the parameters of the system. Consequently, if strict equality between the magnetic energy density and the kinetic energy density of smallscale chaotic motions holds for all galactic disks, smallscale nonlinear limiting must be operating.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 June 1993
 DOI:
 10.1093/mnras/262.4.970
 Bibcode:
 1993MNRAS.262..970N
 Keywords:

 Dynamo Theory;
 Galactic Structure;
 Interstellar Magnetic Fields;
 Magnetic Field Configurations;
 Eigenvalues;
 Plasma Dynamics;
 Velocity Distribution;
 Astrophysics