Ion-scale current sheet instabilities in kinetic plasma turbulence

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A key unsolved problem of the physics of collisionless plasmas, e.g., solar wind and solar corona, is the irreversible dissipation of macroscopic energy without collisional viscosity and electrical resistivity. It is enabled by turbulent transfer of energy from macroscopic to kinetic scales where the energy is finally dissipated. In-situ multi-spacecraft (Cluster, MMS) space observations and numerical simulations of collisionless plasma turbulence show evidences of intermittent dissipation localized in and around kinetic scale current sheets self-consistently formed in the turbulence. Plasma instabilities in these current sheets can provide the collisionless dissipation and determine the associated properties of kinetic plasma turbulence, e.g., the ion-scale break in magnetic field spectra and non-monotonous scale dependence of wave-vector anisotropy. Role of kinetic scale current sheet instabilities in determining the dissipation and the turbulence properties is, however, not clear yet. Goal of this proposal is to investigate the role of ion-scale plasma instabilities, which are likely to grow in current sheets formed in ion kinetic plasma turbulence, in determining the ion-scale properties of the turbulence, in particular, location of the ion-scale break and non-monotonous scale dependence of wave-vector anisotropy. First, we will carry out 3-D hybrid simulations (ions as particles and electrons as inertia-less fluid) of ion-kinetic plasma turbulence using the A.I.K.E.F. code of the TU Braunschweig to characterize (1) the fully developed 3-D turbulence by power spectra of variables, location of the break and wave-vector anisotropy, (2) the current sheets formed thereof by their peak current density, thicknesses, widths, heights and fractions of electron and ion currents and (3) free energy sources in these current sheets by gradient scale lengths of density and ions and electrons bulk velocities and ion temperature anisotropy. Next, nonlinear evolution of plasma instabilities in individual laminar current sheets with free energy sources and parameters typical of the current sheets of the turbulence will be studied by the hybrid code simulations initialized with appropriate one dimensional current sheet equilibria. Links, if any, between the turbulence and plasma instabilities in individual current sheets will be explored by comparing the properties of the turbulence with the corresponding properties of the nonlinear state of the evolution of individual current sheets. Our studies for eight values of ion plasma beta in the range 0.1-10 will be compared with MMS/CLUSTER observations of current sheets and turbulence in collaboration with the group of Z. Vörös and Y. Narita at Graz. Our studies are just timely since dedicated kinetic scale measurements of magnetic reconnection, current sheets and turbulence will be carried out by the MMS space mission and by laboratory experiments VINETA-II at Greifswald and FLARE at Princeton starting 2018.