Fluctuation dynamos at finite correlation times using renewing flows

Subcritical dynamos in shear flows

1 Laboratoire d’Astrophysique de Toulouse-Tarbes, Université de Toulouse, CNRS, 14 avenue Edouard Belin, F-31400 Toulouse, France 2 Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Centre for Mathematical Sciences, Wilberforce Road, Cambridge CB3 0WA, United Kingdom 3 Laboratoire d’hydrodynamique (LadHyX), CNRS – École polytechnique, 91128 Palaiseau cedex, France

Magnetic Dynamo Action in Random Flows with Zero and Finite Correlation Times

The spectrum of temporal fluctuations of total magnetic energy for several dynamo models is different from white noise at frequencies smaller than the inverse of the turnover time of the underlying turbulent velocity field. Examples of this phenomenon are known from previous work, and we add in this paper simulations of the G O Roberts dynamo and of convectively driven dynamos in rotating spher...

Efficiency statistics at all times: Carnot limit at finite power.

We derive the statistics of the efficiency under the assumption that thermodynamic fluxes fluctuate with normal law, parametrizing it in terms of time, macroscopic efficiency, and a coupling parameter ζ. It has a peculiar behavior: no moments, one sub-, and one super-Carnot maxima corresponding to reverse operating regimes (engine or pump), the most probable efficiency decreasing in time. The l...

Finite bath fluctuation theorem.

We demonstrate that a finite bath fluctuation theorem of the Crooks type holds for systems that have been thermalized via weakly coupling them to a bath with energy independent finite specific heat. We show that this theorem reduces to the known canonical and microcanonical fluctuation theorems in the two respective limiting cases of infinite and vanishing specific heat of the bath. The result ...

Optimized boundary driven flows for dynamos in a sphere