Electron acceleration by Alfven waves in density cavities

A new electromagnetic two-dimensional guiding center particle in cell (PIC) code is used to investigate the propagation of an Alfven wave in the perpe ndicular density gradients that characterize the edges of the auroral densi ty cavities. It is shown that the wave planes are strongly distorted by the inhomogeneities of the plasma and that a significant electric field develo ps in the direction parallel to the background magnetic field during the pr opagation. This field efficiently accelerates the electrons in the parallel direction, and the incident wave is thus strongly absorbed. The associated dissipation rate is sufficiently strong to explain a complete wave absorpt ion on the density gradients over a fraction of wavelength. The electron pa rallel acceleration is also characterized. It corresponds to a global paral lel acceleration of the electron population. These PIC simulations suggest that the perpendicular density gradients corresponding to the auroral plasm a cavities play an important role in the auroral particle acceleration.