The strahl as a source of electrostatic whistler waves in the solar wind turbulence

According to observations, the solar wind electron distribution consists of a dense core component (95{\%} of the total electron density) and the suprathermal population (5{\%}) that consists of halo with Maxwellian distribution with hotter temperature and of so-called strahl with a narrow pitch angle distribution directed along the magnetic field. This distribution can be unstable with regards to excitation of lower hybrid waves at anomalous Doppler resonance when the energy source of instability is parallel motion of electrons.\footnote{Shevchenko V., and V. Galinsky, Nonlinear Processes in Geophysics (submitted) (2010).} We investigated the nonlinear dynamics of instability in local approximation by using a hybrid method on resonant numeric simulations. The dynamics of wave power spectrum as well as the strahl distribution function were studied for different distribution function over parallel velocities of strahl electrons. The halo formation is discussed.