Abstract
In hybrid-Vlasov plasma modeling, the ion velocity distribution function is propagated using the Vlasov equation while electrons are considered a charge-neutralizing fluid. It is an alternative to particle-in-cell methods, one advantage being the absence of sampling noise in the moments of the distribution. However, the discretization requirements in up to six dimensions (3D position, 3V velocity) make the computational cost of hybrid-Vlasov models higher. This is why hybrid-Vlasov modeling has only recently become more popular and available to model large-scale systems. The hybrid-Vlasov model Vlasiator is the first to have been successfully applied to model the solar-terrestrial interaction. It includes in particular the bow shock and magnetosheath regions, albeit in 2D-3V configurations so far. The purpose of this study is to investigate how Vlasiator parameters affect the modeling of a plasma shock in a 1D-3V simulation. The setup is similar to the Earth's bow shock in previous simulations, so that the present results can be related to existing and future magnetospheric simulations. The parameters investigated are the spatial and velocity resolution, as well as the phase space density threshold, which is the key parameter of the so-called sparse velocity space. The role of the Hall term in Ohm's law is also studied. The evaluation metrics used are the convergence of the final state, the complexity of spatial profiles and ion distributions as well as the position of the shock front. In agreement with previous Vlasiator studies it is not necessary to resolve the ion inertial length and gyroradius in order to obtain kinetic phenomena. While the code remains numerically stable with all combinations of resolutions, it is shown that significantly increasing the resolution in one space but not the other leads to unphysical results. Past a certain level, decreasing the phase space density threshold bears a large computational weight without clear physical improvement in the setup used here. Finally, the inclusion of the Hall term shows only minor effects in this study, mostly because of the 1D configuration and the scales studied, at which the Hall term is not expected to play a major role.
Highlights
Direct numerical simulation is a cornerstone of modern plasma physics
The comparison of the occurrence of steepened foreshock waves impinging on the shock front reveals that they reach similar amplitudes both
In order to reduce the parameter space to be covered, the physical system chosen for this study is relatively simple, in particular with respect to global magnetospheric simulations which are the primary target in the development of Vlasiator
Summary
Direct numerical simulation is a cornerstone of modern plasma physics. It is crucial in the study of laboratory plasmas [e.g., 1], in the design of fusion devices [e.g., 2] and spacecraft [e.g., 3] or to provide context to and interpretations of observations in space, helio- and astrophysics [e.g., 4– 6]. Describing systems at large scales while retaining a certain level of kinetic physics, hybrid algorithms model ions kinetically while approximating electron dynamics with a fluid description. They follow the temporal and spatial scales of ion dynamics instead of the much shorter electron scales, a major gain in computations. This by definition excludes electron kinetic phenomena from the model
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