Small-scale dynamo action in multi-scale magnetohydrodynamic and micro-turbulence

Nonlinear interplay between resistive magnetohydrodynamic (MHD) magnetic island and drift wave micro-turbulence is investigated using direct Landau-fluid simulations. A twisting oscillation of magnetic island associated with the driving force of micro-turbulence is observed, which is referred to as magnetic island seesaw. In the initiating phase of the seesaw oscillation, small-scale current and magnetic field fluctuations increase dramatically while the magnetic induction grows exponentially at small-scales corresponding to the spatial scale of micro-turbulence, showing a small-scale dynamo action. A minimal model consisting of reduced MHD turbulence and a micro-instability is proposed to elucidate the underlying mechanism. It is identified that the island seesaw is driven by a net oscillatory electromagnetic torque, which results from small-scale dynamo-generated current and magnetic field. The dynamo mechanism may offer an important energy exchange channel between MHD and micro-turbulence in magnetic fusion plasmas. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3698111]