Abstract
After summarizing the variational approach to splitting mean flow and fluctuation kinetics in the standard Vlasov theory, the same method is applied to the drift-kinetic equation from Littlejohn’s theory of guiding-center motion. This process sheds a new light on drift-ordered fluid (drift-fluid) models, whose anisotropic pressure tensor is then considered in detail. In addition, current drift-fluid models are completed by the insertion of magnetization terms ensuring momentum conservation. Magnetization currents are also shown to lead to challenging aspects when drift-fluid models are coupled to Maxwell’s equations for the evolution of the electromagnetic field. In order to overcome these difficulties, a simplified guiding-center theory is proposed along with its possible applications to hybrid kinetic-fluid models.
Highlights
1.1 The mean-fluctuation splitting in Vlasov kinetic theoryWithin the Vlasov kinetic theory of charged particles, fluid models are usually obtained by wellestablished moment methods
This paper addresses the question of how the meanfluctuation splitting applies to Littlejohn’s kinetic equation for guiding-center motion [26] in order to shed a new light on the formulation of the so-called drift-ordered fluid models, or drift-fluids
This paper has exploited the variational structure of the mean-fluctuation splitting in kinetic theory to shed a new light on the formulation of drift-ordered fluid models for magnetized plasmas
Summary
Within the Vlasov kinetic theory of charged particles, fluid models are usually obtained by wellestablished moment methods In this process, it is convenient to split the dynamics of the mean flow velocity from the kinetics of velocity fluctuations. Are the zero-th and second kinetic moment, respectively, c = v − U is the fluctuation velocity coordinate, and F (x, c, t) = F (x, v, t) is the probability density in the Eulerian frame moving with the mean-flow velocity This system (1)-(2) is the most fundamental example of a hybrid kinetic-fluid model, a class of models widely studied in the computational physics of magnetized plasmas [29]. The variational structure of the mean-fluctuation splitting (1)-(2) was exploited in [40] to derive a class of kinetic models for the description of magnetic reconnection in space plasmas. In order to simplify the treatment, an alternative guiding-center model is proposed along with its possible applications in hybrid kinetic-fluid models
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