KINETIC LOCALIZATION OF BEAM-DRIVEN LANGMUIR-WAVES

The bursts of Langmuir waves observed in the auroral ionosphere are in terpreted as localized wave packets of tens to a hundred wavelengths a long the geomagnetic field, which interact with streaming, energetic e lectrons. We investigate the interaction at a kinetic level and show b y means of self-consistent, particle-in-cell simulations with open bou ndary conditions that the interaction itself can lead to wave localiza tion. Ballistic perturbations of the distribution function and nonline ar orbit corrections combine to modulate the perturbed density that dr ives the waves. The resulting kinetic localization takes place within shorter timescales and for smaller wave amplitudes than the focusing v ia ponderomotive force.