The turbulent dynamo as an instability in a noisy medium

Nicolas Leprovost (1) , Bérengère Dubrulle (1)

1 SPEC - UMR3680 - Service de physique de l'état condensé

We study an example of instability in presence of a multiplicative noise, namely the spontaneous generation of a magnetic field in a turbulent medium. This so-called turbulent dynamo problem remains challenging, experimentally and theoretically. In this field, the prevailing theory is the Mean-Field Dynamo (Krause and Rädler, 1980) where the dynamo effect is monitored by the mean magnetic field (other possible choices would be the energy, flux,...). In recent years, it has been shown on stochastic oscillators that this type of approach could be misleading. In this paper, we develop a stochastic description of the turbulent dynamo effect which permits us to define unambiguously a threshold for the dynamo effect, namely by globally analyzing the probability density function of the magnetic field instead of a given moment.

Mots clés: Turbulence; Effet dynamo; Processus stochastiques

Domaines: Cosmologie et astrophysique extra-galactique [astro-ph.CO]; Astrophysique [astro-ph]; Dynamique des Fluides [physics.flu-dyn]

Nicolas Leprovost, Bérengère Dubrulle. The turbulent dynamo as an instability in a noisy medium. The European Physical Journal B: Condensed Matter and Complex Systems, 2005, 44, pp.395. ⟨10.1140/epjb/e2005-00138-y⟩. ⟨hal-00001417v3⟩