On the properties of spectral anisotropies and intermittency in ion-kinetic scale turbulence.

Simone Landi
University of Florence, Department of Physics and Astronomy, Largo E. Fermi 2, I-50125 Firenze, Italy
The spectral properties at ion kinetic scales are studied by means of high-resolution three-dimensional numerical simulations using a hybrid codes which integrates the Vlasov system equations for the ions while it treats the electron as a neutralising fluid. We show that the observed anisotropy is less than what expected by theories of plasma turbulence at such scales. More specifically, we observe that the spectral anisotropy is frozen once the magnetic energy cascade reaches the ion kinetic scales. However, the non-linear energy transfer is still in the perpendicular direction with respect to the magnetic field, only advected in the parallel direction as expected balancing the non-linear energy transfer time and the decorrelation time. Such result can be explained by a phenomenological model based on the formation of strong intermittent two-dimensional structures in the plane perpendicular to the local mean field that fulfill some prescribed aspect ratio eventually depending on the scale. This model supports the idea that small scales structures, such as reconnecting current sheets, contribute significantly to the formation of the turbulent cascade at kinetic scales.