Modeling Heliospheric Plasma Turbulence: A Critique of the Effects of Completeness, Realism and Size

Abstract:

With the Solar Probe and Solar Orbiter missions approaching, and the highly capable instruments of MMS already in orbit, there is an upwelling of interest in understanding plasma turbulence and related effects at kinetic scales. Accordingly a variety of methods have been employed to study kinetic turbulence and in particular dissipation and cascade processes and their effects on protons, electrons and minor ions. Here we discuss the influence of system size, and the completeness and realism of the several kinetic physics models that are employed. One important issue is whether coherent structures such as current sheets can be properly represented and evolved in smaller systems; this is particular important when turbulence is intermittent and non-self similar, so that couplings become nonlocal in scale. Another factor is resolution, both spatial and statistical – what are the effects of counting statistics in PIC and velocity filamentation in Vlasov models? Also discussed is the efficacy and strategic use of models with reduced physics and/or dimensionality – hybrid, Reduced MHD and gyrokinetics, for example. It is suggested, using several example problems, how the cross comparison of models in the context of a framework such as Turbochallenge may have wide ranging conceptual impact.