New Ion-Wave Path in the Energy Cascade

We present the results of kinetic numerical simulations that demonstrate the existence of a novel branch of electrostatic nonlinear waves driven by particle trapping processes. These waves have an acoustic-type dispersion with phase speed comparable to the ion thermal speed and would thus be heavily Landau damped in the linear regime. At variance with the ion-acoustic waves, this novel electrostatic branch can exist at a small but finite amplitude even for low values of the electron to ion temperature ratio. Our results provide a new interpretation of observations in space plasmas, where a significant level of electrostatic activity is observed in the high frequency region of the solar-wind turbulent spectra.