Étude de la reconnexion magnétique du côté jour en présence d'ions froids et de champ guide

Depending on the orientation of the interplanetary magnetic field (IMF) transported by the solar wind, the magnetic field lines of the Earth's magnetic field can reconnect with those of the IMF at the dayside magnetopause, the boundary between the solar wind and the Earth's magnetic field. As the plasma conditions on each side of the magnetopause are different, the magnetic reconnection is called asymmetric. The reconnection process starts in a diffusion region at electron scales and generates fast diverging electron and ion jets. The boundaries separating the plasma flowing into the reconnection region from the outflow plasma are called the separatrices. This PhD thesis investigates in detail the structure of the magnetospheric separatrix far from the diffusion region in the presence of magnetospheric cold ions, a high density gradient and a moderate guide field. Using in-situ measurements of the NASA Magnetospheric Multiscale(MMS) mission and fully kinetic 2D Particle-In-Cell (PIC) simulations obtained from the open source SMILEI code, the current densities, electric and magnetic signatures as well as energy conversion processes are investigated. From in-situ measurements at the separatrix, the current density is found dominated by the ion diamagnetic current and the normal electric field sustained by the drift of the cold ions in agreement with the simulations. The energy conversion in the fluid frame is ensured by the parallel current and the electric field produced by the parallel electron pressure term. The partitioning of the energy between ions and electrons is discussed based on the pressure strain calculations. From the kinetic simulations performed with and without cold ions, and with and without guide field, it is found that with a guide field, the presence of cold ions reinforces the electron pressure gradient reducing the normal electric field and increasing the motion of the reconnection region. All these effects modify the energy and plasma exchanges between the solar wind and the Earth's magnetosphere.