Bi-Directional Energy Cascades and the Origin of Kinetic Turbulence in the Solar Wind

The kinetic turbulence of solar wind originates in the solar corona. The solar wind carries the fluctuations and escapes from the corona along the open magnetic field lines, and enters into the interplanetary space. The energy exchange among waves and particles reaches a balance, and the decay rate is very small and able to travel to 1 AU and beyond. The magnitude of the magnetic turbulence is about 20% of the solar wind background magnetic field, consistent with the observations. The observation-motivated model not only provides a viable solution to both long-standing puzzles of electron halo formation and the origin of solar wind turbulence on kinetic scale, but also establishes a possible link between the solar wind turbulence and the acceleration of electrons by nanoflares in solar corona.