Fully Kinetic Simulation of 3D Kinetic Alfven Turbulence

We present results from a three-dimensional particle-in-cell simulation of plasma turbulence, resembling the plasma conditions found at kinetic scales of the solar wind. The spectral properties of the turbulence in the subion range are consistent with theoretical expectations for kinetic Alfv\' en waves. Furthermore, we calculate the local anisotropy, defined by the relation $k_{\parallel}(k_{\perp})$, where $k_{\parallel}$ is a characteristic wave number along the local mean magnetic field at perpendicular scale $l_{\perp}\sim 1/k_{\perp}$. The subion range anisotropy is scale dependent with $k_{\parallel}<k_{\perp}$ and the ratio of linear to nonlinear time scales is of order unity, suggesting that the kinetic cascade is close to a state of critical balance. Our results compare favorably against a number of \emph{in situ} solar wind observations and demonstrate---from first principles---the feasibility of plasma turbulence models based on a critically balanced cascade of kinetic Alfv\' en waves.