Dynamo action by turbulence in absolute equilibrium
Laboratoire de Physique Statistique, Ecole Normale Supérieure, CNRS, Université P. et M. Curie, Université Paris Diderot - Paris, France
Received: 17 January 2014
Accepted: 11 April 2014
We consider the generation of a large-scale magnetic field by a turbulent flow driven by a small-scale helical forcing in a low magnetic Prandtl number fluid. We provide an estimate of the dynamo threshold that takes into account the presence of large-scale turbulent fluctuations by considering that the scales of the flow that mostly contribute to the dynamo process are roughly in absolute equilibrium. We show that turbulent flows in absolute equilibrium do generate dynamos and we compare their growth rates to their laminar counterparts. Finally, we show that the back reaction of the growing magnetic field modifies the statistical properties of turbulent flow by suppressing its kinetic helicity at large magnetic Reynolds number.
PACS: 91.25.Cw – Origins and models of the magnetic field; dynamo theories / 47.65.-d – Magnetohydrodynamics and electrohydrodynamics
© EPLA, 2014