ON THE FORMATION OF WAVE-PACKETS IN PLANETARY FORESHOCKS

Kinetic localization of beam-driven Langmuir waves is studied for para meters relevant to the electron foreshock environment. Particle-in-cel l simulations of the interaction occurring between energetic electrons and Langmuir waves are performed. It is shown that the nonlinearities in the resonant electrons lead to the formation of packets growing ou t of the noise. The characteristic spatial scale depends upon the beam velocity and has a weak dependence on the wave amplitude. The mechani sm takes place within shorter timescales and for smaller amplitudes th an the classic nonlinearities due to bulk electrons and ions. As an ex ample, we apply the results to observations made in the Earth and Jovi an foreshocks.