2,602 research outputs found
Amplification of large-scale magnetic field in nonhelical magnetohydrodynamics
It is typically assumed that the kinetic and magnetic helicities play a
crucial role in the growth of large-scale dynamo. In this paper we demonstrate
that helicity is not essential for the amplification of large-scale magnetic
field. For this purpose, we perform nonhelical magnetohydrodynamic (MHD)
simulation, and show that the large-scale magnetic field can grow in nonhelical
MHD when random external forcing is employed at scale the box size. The
energy fluxes and shell-to-shell transfer rates computed using the numerical
data show that the large-scale magnetic energy grows due to the energy
transfers from the velocity field at the forcing scales.Comment: 8 pages, 13 figure
Energy transfers and magnetic energy growth in small-scale dynamo
In this letter we investigate the dynamics of magnetic energy growth in
small-scale dynamo by studying energy transfers, mainly energy fluxes and
shell-to-shell energy transfers. We perform dynamo simulations for magnetic
Prandtl number on grid using pseudospectral method.
We demonstrate that the magnetic energy growth is caused by nonlocal energy
transfers from the large-scale or forcing-scale velocity field to small-scale
magnetic field. The peak of these energy transfers move towards lower
wavenumbers as dynamo evolves, which is the reason why the integral scale of
the magnetic field increases with time. The energy transfers (velocity to
velocity) and (magnetic to magnetic) are forward and local.Comment: 6 pages, 8 figure
Dynamo in Protostar
In this paper, we estimate the magnetic Reynolds number of a typical
protostar before and after deuterium burning, and claim for the existence of
dynamo process in both the phases, because the magnetic Reynolds number of the
protostar far exceeds the critical magnetic Reynolds number for dynamo action.
Using the equipartition of kinetic and magnetic energies, we estimate the
steady-state magnetic field of the protostar to be of the order of kilo-gauss,
which is in good agreement with observations.Comment: 5 page
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