7 research outputs found
Magnetized Turbulent Dynamo in Protogalaxies
The prevailing theory for the origin of cosmic magnetic fields is that they
have been amplified to their present values by the turbulent dynamo inductive
action in the protogalactic and galactic medium. Up to now, in calculation of
the turbulent dynamo, it has been customary to assume that there is no back
reaction of the magnetic field on the turbulence, as long as the magnetic
energy is less than the turbulent kinetic energy. This assumption leads to the
kinematic dynamo theory. However, the applicability of this theory to
protogalaxies is rather limited. The reason is that in protogalaxies the
temperature is very high, and the viscosity is dominated by magnetized ions. As
the magnetic field strength grows in time, the ion cyclotron time becomes
shorter than the ion collision time, and the plasma becomes strongly
magnetized. As a result, the ion viscosity becomes the Braginskii viscosity.
Thus, in protogalaxies the back reaction sets in much earlier, at field
strengths much lower than those which correspond to field-turbulence energy
equipartition, and the turbulent dynamo becomes what we call the magnetized
turbulent dynamo. In this paper we lay the theoretical groundwork for the
magnetized turbulent dynamo. In particular, we predict that the magnetic energy
growth rate in the magnetized dynamo theory is up to ten time larger than that
in the kinematic dynamo theory. We also briefly discuss how the Braginskii
viscosity can aid the development of the inverse cascade of magnetic energy
after the energy equipartition is reached.Comment: accepted to ApJ, 35 pages, 3 figure
Magnetic dynamo action in astrophysical turbulence
We investigate the structure of magnetic field amplified by turbulent
velocity fluctuations, in the framework of the kinematic Kazantsev-Kraichnan
model. We consider Kolmogorov distribution of velocity fluctuations, and assume
that both Reynolds number and magnetic Reynolds number are very large. We
present the full numerical solution of the model for the spectra and the growth
rates of magnetic fluctuations. We consider astrophysically relevant limits of
large and small magnetic Prandtl numbers, and address both helical and
nonhelical cases.Comment: 13 pages, 3 figures, minor changes are made to match the published
versio
Amplification of magnetic fields by dynamo action in Gaussian-correlated helical turbulence
We investigate the growth and structure of magnetic fields amplified by
kinematic dynamo action in turbulence with non-zero kinetic helicity. We assume
a simple Gaussian velocity correlation tensor, which allows us to consider very
large magnetic Reynolds numbers, up to one trillion. We use the kinematic
Kazantsev-Kraichnan model of dynamo and find a complete numerical solution for
the correlation functions of growing magnetic fields.Comment: 7 pages, 3 figure
Atomic data and collisional-radiative model for beryllium and its ions
In this work we present a collisional–radiative model constructed for all ionization stages of beryllium. Convergent close-coupling, K-matrix and Coulomb–Born-exchange methods were applied to calculate the necessary atomic data. For the neutral beryllium atom a comparison of all methods is given. Fractional ion abundances, radiative power losses and electron cooling rates were calculated as functions of electron temperature. The comparison with other available data shows a rather good agreement