Abstract
Abstract. Modern investigations of dynamical space plasma systems such as magnetically complicated topologies within the Earth's magnetosphere make great use of supercomputer models as well as spacecraft observations. Space plasma simulations can be used to investigate energy transfer, acceleration, and plasma flows on both global and local scales. Simulation of global magnetospheric dynamics requires spatial and temporal scales currently achievable through magnetohydrodynamics or hybrid-kinetic simulations, which approximate electron dynamics as a charge-neutralizing fluid. We introduce a novel method for Vlasov-simulating electrons in the context of a hybrid-kinetic framework in order to examine the energization processes of magnetospheric electrons. Our extension of the Vlasiator hybrid-Vlasov code utilizes the global simulation dynamics of the hybrid method whilst modelling snapshots of electron dynamics on global spatial scales and temporal scales suitable for electron physics. Our eVlasiator model is shown to be stable both for single-cell and small-scale domains, and the solver successfully models Langmuir waves and Bernstein modes. We simulate a small test-case section of the near-Earth magnetotail plasma sheet region, reproducing a number of electron distribution function features found in spacecraft measurements.
Highlights
Physical processes in near-Earth space are dominated by plasma effects such as non-thermal particle distributions, instabilities, plasma waves, shocks, and reconnection
Heating is found in particular near the X-line configuration and where the plasma sheet boundary layer (PSBL) meets the magnetosphere, with parallel heating more localized than perpendicular heating
In most of the simulation domain, the value is very small, but enhanced agyrotropy are found in the PSBL regions and at the magnetic field X line. Some of this agyrotropy may be due to spatial sampling of electron gyromotion with a magnetic field gradient leading to larger gyroradii further away from the plasma sheet
Summary
Physical processes in near-Earth space are dominated by plasma effects such as non-thermal particle distributions, instabilities, plasma waves, shocks, and reconnection. Using explicit solvers, resolving waves and kinetic electron instabilities to prevent simulation self-heating requires the spatial resolution to encompass the Debye length λD (Birdsall and Langdon, 2005) and the time stepping must resolve the electron plasma oscillation ωpe This can, be bypassed via semi-implicit or implicit solver methods. Lapenta et al (2010) discusses modifications to electron microphysics at reconnection sites in more detail in relation to proton–electron mass ratios of 64, 256, and 1836 using an implicit PIC model Another approach compared to PIC simulations is to represent particle velocity distributions with moments beyond the MHD approach (Wang et al, 2015). The aim is to investigate how much of the global electron physics and distribution functions can be understood by utilizing ion-generated field as modelled by hybrid-kinetic codes, as opposed to a numerically unfeasible global full-kinetic approach.
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