Three-dimensional Hybrid Simulations of Decaying Plasma Turbulence from Fluid to Sub-ion Scales

We investigate properties of decaying plasma turbulence from fluid to sub-ion scales by means of three-dimensional high-resolution hybridparticle-in-cell simulations. Starting from a spectrum of Alfvénic-like fluctuations with an initial ambient magnetic field, a turbulent cascade develops in few non-linear times. The high resolution employed, in terms of both grid points and number of particles, allows us to observe a magnetohydrodynamic (MHD) inertial range where the magnetic field spectrum exhibits a clear Kolmogorov-like power-law scaling, followed by a transition near the ion kinetic scales and a second power-law interval at sub-ion scales, with a spectral index of about -3. We also observe an increase in the magnetic compressibility at kinetic scales. The two-dimensional (2D) spectrum of the magnetic fluctuations shows the sudden formation of a large spectral anisotropy, despite the initial isotropic condition, indicating that the cascade mainly develops in the direction perpendicular to the mean magnetic field. Finally, we discuss the effects of the plasma beta. Our results are in very good agreement with 2D hybrid simulations [1,2] and with solar wind in-situ observations.