Evidence of ion Foreshock in Full-particle 2-D Simulations of a Supercritical Curved Collisionless Shock
Résumé
Ion foreshock filled in with energized particles backstreaming from a curved shock is analyzed with the help of a 2-D full particle simulations (PIC). Full curvature and time of flight effects, and both electrons and ions dynamics are fully described by a self consistent approach. The analysis is restricted within a quasi-perpendidular shock with 90° ≥ θBn 45°, where θBn is the angle between the shock normal and the upstream magnetostatic field. It is for the first time to our knowledge, that the formation of both electron and ion foreshock is evidenced within a full self-consistent approach. Herein, we focuss only on the ion foreshock and more particularly, on the different populations of backstreaming ions observed in the upstream region. Present preliminary results show that, in agreement with experimental data, two distinct ion populations are observed : (i) the field-aligned beams (FAB) which consist of ions collimated along the IMF and (ii) the gyro-phase bunch ions (hereafter named GPB) characterized by a non-vanishing perpendicular bulk velocity and a global gyration around the magnetic field. More precisely, (a) the FAB population is observed at the edge of the foreshock and near the shock front, while GPB population is observed deeper in the foreshock and further from the shock shock; (b) both backstreaming populations can be identified versus their individual interaction time τ int with the shock front. In particular, GBP population shows a short interaction time (τ int ≈ 1-2 τci) while the FAB population evidences a larger time range (from 1 τci to 10 τci); (iv) FAB population may have different origins, and is composed with ions coming from the shock front itself but also from "leaked" ions (issued from the downstream region)