Turbulence is ubiquitous in space and astrophysical plasmas where it plays a key role in all physical phenomena such as mass transport, energy dissipation and particle heating. Unlike neutral fluids, where energy dissipation occurs via viscous effects originating from particle collisions at the microscopic level, most of space plasmas are collisionless (or weakly collisional). Most of the relevant interactions are therefore in the form of field-particle interactions between the charged particles and the electromagnetic fields. Among the near-Earth space plasmas the solar wind (SW) is certainly the most accessible astrophysical plasma to in-situ measurements. Observations of SW turbulence have usually emphasized magnetohydrodynamic (MHD) scales where the Kolmogorov scaling f^-5/3 of the magnetic spectra is frequently observed. These spectra are thought to result from strongly nonlinear interacting Alfvén waves. However, the question as to how turbulence of the MHD scales terminates its cascade at smaller (kinetic) scales is still hotly debated. Answering this question is indeed fundamental to understanding the processes of particle acceleration and plasma heating in the SW and in other astrophysical plasmas. Two possible channels of energy dissipation are currently subject to intensive research work. The first channel is dissipation via collisionless kinetic effects such as resonant field-particle interactions (e.g. cyclotron and/or Landau resonances) or non-resonant effects such as Finite Larmor Radius effects (FLRs). The second channel is dissipation through magnetic reconnection occurring within current sheets that form naturally in turbulent plasmas.
This project aims at studying each of these mechanisms of energy dissipation. We will use a multiple approach that combines in-situ fields and particles data available from the multispacecraft missions, and numerical simulations to model the complex behavior of turbulence cascade at kinetic scales where it is dissipated. The observations will be made using mainly data from the Cluster and Themis satellites, which offer a unique chance to identify and to characterize three-dimensional (3D) spatial plasma structures. Moreover, their high time resolution E and B measurements makes it possible to probe into the smallest scales ever explored in the SW. The simulation work will be done using different codes, Hall-MHD, PIC and Vlasov, available in the group.