Le séminaire a lieu le lundi
19 janvier 2005 de 11h00 à 12h00
dans la salle de réunion
du PHC (Observatoire de Nice).
Generation of magnetic fields in helical Hall-MHD turbulence
One-fluid magnetohydrodynamics, the standard framework for describing
dynamo activity in astrophysical environments, cannot be expected to
properly describe collisionless plasmas because it fails to distinguish
the relative motions between different species. A first step toward
creating a more appropriate theory for collisionless dynamics might be
to include the dominant two-fluid effects. Of all these effects, the
Hall effect is considered to be the most important in a wide range of
cases of interest.
In this talk, we will review recent advances in Hall-MHD dynamo theory.
An extension of mean field theory will be discussed, which shows that
the Hall current gives rise to a new contribution to helical dynamo
action. Direct numerical simulations will also be presented. The Hall
effect can have a profound effect on dynamo action; it can strongly
enhance or suppress the generation of the large-scale magnetic field
depending on the relative values of the length scales of the system.