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Accueil > A propos du LPP > Communication > Actualités archivées > 2025 > Mohammed Baraka defended his PhD "Study of Dayside Magnetic Reconnection in the Presence of Cold Ions and Guide Field : A Focus on the Magnetospheric Separatrix"
Mohammed Baraka defended his PhD "Study of Dayside Magnetic Reconnection in the Presence of Cold Ions and Guide Field : A Focus on the Magnetospheric Separatrix"
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On February 10, 2025, Mohammed Baraka defended his PhD "Study of Dayside Magnetic Reconnection in the Presence of Cold Ions and Guide Field : A Focus on the Magnetospheric Separatrix".
Abstract :
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. The magnetic reconnection is called asymmetric as the plasma conditions on each side of
the magnetopause are different. 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 mod-
erate 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, and energy conversion
processes are investigated. From in-situ measurements at the separatrix, the current density is
dominated by the ion diamagnetic current, and the normal electric field in the magnetospheric
inflow region is 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. Using 2D kinetic simulations,
two sets of simulations were performed : one set with and without cold ions. And another set
with and without cold ions each conducted in the presence of a moderate guide field. The first
set allowed to validate the use of the new GPU version of the SMILEI code and confirmed the
role of magnetospheric cold ions for sustaining the earthward normal electric field, all along the
separatrix in the magnetospheric inflow region. Furthermore, cold ions produce a reduction of
the perpendicular current and the Hall electric field, and an increase of the parallel current on
either side of the separatrix. In their presence, the electron pressure term is increased, which
makes the electron decoupling from the magnetic field stronger. The second set confirmed these
effects of cold ions and notably showed that with a guide field, the presence of cold ions, which
reinforces the electron pressure gradient and reduces the normal electric field, increases the
motion of the reconnection region. All these effects modify the energy and plasma exchanges.
Jury :
Matteo Faganello Maître de Conférences (HDR) Rapporteur
Maria-Elena Innocenti Professeure Examinatrice
Karine Issautier Directrice de recherche Présidente
Aurélie Marchaudon Directrice de recherche Rapportrice
Thierry Passot Directeur de recherche Examinateur
Sergio Toledo-Redondo Professeur Examinateur
Olivier Le Contel Directeur de recherche Directeur de thèse
Patrick Canu Directeur de recherche émérite Co-Directeur de thèse
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