Kinetic Alfvén wave turbulence and intermittent current sheets at sub-ion scales in the solar wind

The solar wind is an ideal laboratory of plasma turbulence with an energy cascade over a wide range of scales from the solar system size down to electron scales. At scales comparable or smaller than the ion skin-depth, kinetic physics plays an important role. We perform particle-in-cell simulations of turbulence initialized by an ensemble of either kinetic Alfvén waves (KAWs) or whistler waves at supra-ion scales. Two-fluid polarization ratios of KAWs and whistlers are used for the initialization and identification of the wave-modes excited non-linearly. We show that KAWs are the dominant waves at sub-ion scales over whistler waves, even in simulations initialized with whistlers. We also find strong intermittency at sub-ion scales manifested in the form of thin current sheets. We use clustering techniques to identify these current sheets in our simulations and measure their thickness. The most intense current sheets have a thickness that scales with the electron skin depth. Our results compare favorably with observations of magnetosheath turbulence. We also measure intermittency in solar wind data obtained from the NASA - Magnetosphere Multiscale Mission (MMS) magnetometer. Current sheet structures are identified with three different techniques and cross-verified. We show that the current sheets are thinner than the ion scale, matching with the results obtained from our simulations. These results provide insights into the properties of sub-ion scale plasma turbulence.