Microphysics of magnetic reconnection in near-Earth space: spacecraft observations and numerical simulations

Magnetic reconnection is a fundamental energy conversion process occurring in space and laboratory plasmas. Reconnection takes place in thin current sheets leading to the reconfiguration of magnetic field topology and to conversion of magnetic energy into acceleration and heating of particles. Today reconnection is recognized to play a key role in the Earth-solar environment, from the solar corona to the solar wind, to magnetosheath, at the Earth’s magnetopause, and in the magnetotail. Reconnection is initiated in the Electron Diffusion Region (EDR), where electrons decouple from the magnetic field and are energized by electric fields. Despite the very significant advances that have been made in the understanding of the magnetic reconnection process by means of in-situ measurements (notably provided by the Cluster mission) and by numerical simulations, the small electron scale physics of the dissipation region remains basically unsolved. It is only the last years, with the launch of the Magnetospheric MultiScale mission (MMS) together with the recent impressive increasing of computational capabilities of supercomputers, that the dynamics of the Electron Diffusion Region has started to be enlightened. One of the key, yet still open questions, is whether the EDR has a preferred homogeneous or inhomogeneous structure at electron scales and below. The purpose of this Thesis is to advance in the understanding of the structure of the Electron Diffusion Region using two different approaches, notably MMS spacecraft observations and kinetic full Vlasov simulations.