Nov. 9, 2018, 3:30 p.m. - 5 p.m.
Room 6704 Geology

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A semi-implicit Particle-In-Cell Expanding-Box-Model code for fully kinetic simulations of the expanding solar wind plasma - M.E. Innocenti, JPL

The solar wind is far from thermodynamical equilibrium. Both protons and electrons display highly anisotropic velocity distribution functions (VDF) that evolve with radial distance possibly due to a combination of expansion effects and kinetic instabilities [Maksimovic 2005, Matteini 2013]. Fully kinetic Particle In Cell (PIC) simulations can help achieving a better understanding of electron and ion VDF evolution in the solar wind. In this talk, we present a new tool to simulate large and small scale kinetic instabilities in the solar wind and the effects of solar wind expansion: the fully kinetic, semi-implicit Expanding Box Model (EBM) code EB-iPic3D [Innocenti, Tenerani, Velli, under review]. The main ingredients of our code are its semi-implicit temporal discretisation (the Implicit Moment Method, IMM [Brackbill 1982, Lapenta 2006], implemented in the code iPic3D [Markidis 2010]) and the Expanding Box Model [Velli 1992, Grappin 1996, Liewer 2001]. The IMM formulation allows the freedom to choose to resolve either the small-scale, fast, electron dynamics or the larger-scale, slower ion dynamics. Spatial and temporal resolution and domain of the simulation in space and time can be adjusted according to the process of interest, rather than to the strict stability constraints of explicit discretisation. The EBM describes the dynamics of a parcel of plasma while it is advected away from the Sun at constant radial speed. The radial expansion is mimicked within a locally cartesian geometry where the radial (x) direction stays unaltered while the perpendicular directions (y and z) expands at a rate proportional to the distance from the Sun. The EBM variable change allows to follow the propagation of a parcel of solar wind over times and distances that would soon become prohibitive for a non EBM simulation. The IMM EBM method has the potential of comprehensively simulating solar wind expansion, accounting for both ion and electron dynamics, over scales unreachable with explicit formulations. Here we present the constitutive equations of the model, the results of our validation activity and preliminary results.