Topic/Type: 1. Plasma Simulation, Oral

Particle in cell (PIC) simulations: applications to collisionless shocks

B. Lemb?ge

LATMOS-UVSQ-IPSL-CNRS, 10-12 avenue de l'Europe, Velizy, France

Full particle-in-cell (PIC) simulations reveal to be very powerful tools to analyze the dynamics of collisionless shocks. Such shocks are commonly found in space plasma around the cometary and planetary environments (in front of the terrestrial magnetosphere for instance), in solar physics (during Coronal Mass Ejection), in interplanetary space, in heliospheric physics and astrophysics as well as in fusion plasmas. These shocks allow a transition between an (upstream) supersonic flow to a subsonic (downstream) flow. The huge amount of data collected by various space missions have clearly evidenced that kinetic effects play a dominant role in the dynamics of collisionless shocks via important wave-particle interactions which take place at the shock front. These in-situ measurements indicate that magnetohydrodynamic simulations are not appropriate to describe in details the intrinsic shock structure and that Hybrid and full PIC simulations are necessary.

More recently, the success of the 4-satelites CLUSTER mission has clearly evidenced the nonstationarity of the terrestrial collisionless shock. On the other hand, different mechanisms of shock nonstationarity have been identified with the help of mono- and multi-dimensional full PIC simulations. These simulations have shown that the dynamics of shocks can strongly vary in time with two main consequences: (i) the spatial scale of the shock front and the amplitude of the associated macroscopic magnetic and electric fields drastically vary on large (ion) scale, and (ii) microstructures (with scales of a few tens of Debye lengths) may also appear within the shock front itself. Herein, (a) we will summarize the advantages of PIC simulations for analysing shocks but also the limitations imposed at present time, and (b) we will show the main guidelines recently followed to compare space experimental and numerical results, in particular concerning the so called self-reformation process.