Saturation mechanism of the fluctuation dynamo at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">Pr</mml:mi><mml:mi>M</mml:mi></mml:msub><mml:mo> </mml:mo><mml:mo>≥</mml:mo><mml:mo> </mml:mo><mml:mn>1</mml:mn></mml:math>

Abstract

Exponential amplification of weak seed magnetic fields in a turbulent medium eventually slows and saturates due to back reaction by the Lorentz force. This is known as the fluctuation dynamo action. Using numerical simulations of driven turbulence, we show that the magnetic fields achieve a (statistically) more force-free state as they saturate. The spatially intermittent random magnetic field structures are also larger in the saturated stage than in the kinematic stage. The fluctuation dynamo saturation is explained by a decrease in amplification and an increase in magnetic field diffusion.

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