Multi-Scale Physics in Velocity Shear Driven Vortices in Space Plasmas
Résumé
Velocity shear driven vortices associated to the Kelvin-Helmholtz instability (KHI) have been detected by in-situ observations at the Earth[1], Saturn[2] and Mercury[3] magnetospheres' boundary due to the interaction with the solar wind[4]. KHI in magnetized plasmas have been widely studied numerically in the framework of a fluid and hybrid descriptions, while only very few studies have focused on the physics of electrons[5,6] because of computational constraints. In this work we present a full kinetic particle in cell study of the KHI spanning a range of scales going from fluid to electron scales. The simulation is initialized with an extended fluid equilibrium[7] including finite ion Larmor radius effects. Our large-scale configuration includes two-possible alignment of the vorticity with the background magnetic field each one corresponding to the interaction of the solar wind with the dawn and dusk side of a planet. We discuss electron heating and acceleration by the wave and turbulent activity as well as magnetic reconnection induced by vortex dynamics. Two-fluid simulations have suggested that KHI instability can lead to the formation of coherent structures resulting from the saturation of the mirror instability[8]. Our full kinetic approach confirms such hypothesis. We investigate the formation, the properties and the electron distribution functions of the mirror modes in our simulations and in complementary dedicated ones. [1] J. E. Stawarz, S. Eriksson, et al., Journal of Geophysical Research: Space Physics, 121, 2016, 11,021-11,034 [2] A. Masters, N. Achilleos, et al., Journal of Geophysical Research: Space Physics, 115, 2010, 7225 [3] T. Sundberg, S. A. Boardsen, et al., Planetary and Space Sciences, 59, 2011, 2051-2057 [4] M. Faganello, F. Califano, Journal of Plasma Physics, 83, 2017, 535830601 [5] P. Henri, S. S. Cerri, F. Califano, F. Pegorago, et al., Physics of Plasmas, 20, 2013, 102118 [6] W. Daughton, T. K. M. Nakamura, et al., Physics of Plasmas, 21, 2014, 252307. [7] S. S. Cerri, P. Henri, F. Califano, et al., Physics of Plasmas, 20, 2013, 112112 [8] S. De Camillis, S. S. Cerri, F. Califano, and F. Pegoraro, Plasma Physics and Controlled Fusion, 28, 2016, 045007