41 research outputs found
Collisionless magnetic reconnection in a plasmoid chain
The kinetic features of plasmoid chain formation and evolution are
investigated by two dimensional Particle-in-Cell simulations. Magnetic
reconnection is initiated in multiple X points by the tearing instability.
Plasmoids form and grow in size by continuously coalescing. Each chain plasmoid
exhibits a strong out-of plane core magnetic field and an out-of-plane electron
current that drives the coalescing process. The disappearance of the X points
in the coalescence process are due to anti-reconnection, a magnetic
reconnection where the plasma inflow and outflow are reversed with respect to
the original reconnection flow pattern. Anti-reconnection is characterized by
the Hall magnetic field quadrupole signature. Two new kinetic features, not
reported by previous studies of plasmoid chain evolution, are here revealed.
First, intense electric fields develop in-plane normally to the separatrices
and drive the ion dynamics in the plasmoids. Second, several bipolar electric
field structures are localized in proximity of the plasmoid chain. The analysis
of the electron distribution function and phase space reveals the presence of
counter-streaming electron beams, unstable to the two stream instability, and
phase space electron holes along the reconnection separatrices.Comment: accepted for publication in special issue "Magnetic reconnection and
turbulence in space, laboratory and astrophysical systems" of Nonlinear
Processes in Geophysic
3D implicit PIC simulations of solar wind - moon interactions
We present three-dimensional Particle-in-Cell simulations of an unmagnetized insulating Moon-sized body immersed in the solar wind. The simulations are performed using the implicit electromagnetic Particle-in-Cell code iPIC3D [Markidis, 2009]. Multiscale kinetic physics is resolved for all plasma components (heavy ions, protons and electrons) in the code, recently updated with a set of open boundary conditions designed for solar wind - body interaction studies. Particles are injected at the inflow side of the computational domain and absorbed at all others. A bow shock is not formed upstream of the body, but the obstacle generates faint dispersive waves propagating parallel to the magnetic field lines, in agreement with numerical simulations done in MHD approach. Polarization electric field is generated in the wake. In addition, plasma flows filling the wake tend to excite streaming instabilities, which lead to bipolar signatures in the parallel electric field. Our future work includes updating the physical model to include photoionization and re-emission at the object's surface.status: publishe
A Fully Kinetic Perspective on Weakly Active Comets: Asymmetric Outgassing
International audienceFor more than two years, ESA's Rosetta mission measured the complex and ever-evolving plasma environment surrounding comet 67P/Churyumov-Gerasimenko. In this work, we explore the structure and dynamics of the near-comet plasma environment at steady state of a weakly active comet like 67P at 4 AU from the Sun. We directly compare the results of a spherically symmetric Haser model and an asymmetric outgassing profile that is inspired by the measurements from the ROSINA instrument onboard Rosetta during 67P's weakly outgassing stages. We analyse the effects of the asymmetric profile for different rotation phases of nucleus with respect to the solar wind and interplanetary magnetic field direction. Using a fully kinetic semi-implicit particle-in-cell code, we characterise (1) the various ion and electron populations and their interactions, and (2) the implications to the mass-loading process caused by asymmetric outgassing. Our model complements observations by providing a full 3D picture that is directly relevant to help interpret the measurements made by the Rosetta Plasma Consortium instruments. In addition, understanding such details better is key to help disentangle the physical drivers active in the plasma environment of comets visited by future exploration missions