Electrostatic waves in the maximum-entropy fluid model: Longitudinal electron modes

Physics of Plasmas, vol. 32

Abstract

Traditional fluid models are unable to reproduce the kinetic dispersion relation of certain plasma waves and the onset of kinetic instabilities. Non-equilibrium fluid models (higher-order moment methods) permit to reproduce selected kinetic effects, but at a lower computational cost as compared to fully-kinetic models. In this work, we study the dispersion relation of longitudinal electrostatic electron modes. We show that the fourth-order maximum-entropy moment method is able to recover certain kinetic instabilities, although with a slightly increased region of stability if compared to the Vlasov equation. As in the kinetic-theory case, these instabilities appear when the gas is in a non-equilibrium state that is associated with a sufficiently bi-modal VDF. The maximum-entropy method is able to predict the classical two-stream instability within a single-fluid formulation, reproducing a reasonably accurate growth rate. The Vlasov-stability of maximum-entropy VDFs is also investigated via Nyquist diagrams and the Penrose criterion.

Authors 4

1. Stefano Boccelli

   Goddard Space Flight Center

   Affiliation as printed

   NASA Goddard Space Flight Center 1 , Greenbelt, Maryland 20771,

2. Rostislav‐Paul Wilhelm Aachen Applied and Computational Mathematics

   RWTH Aachen University · KU Leuven

   Affiliation as printed

   Applied and Computational Mathematics, RWTH Aachen University 2 , Aachen,

   Centre for Mathematical Plasma Astrophysics 3 , KU Leuven,

3. James G. McDonald

   University of Ottawa

   Affiliation as printed

   Department of Mechanical Engineering, University of Ottawa 4 , Ottawa, Ontario K1N 6N5,

4. Manuel Torrilhon Aachen Applied and Computational Mathematics

   RWTH Aachen University

   Affiliation as printed

   Applied and Computational Mathematics, RWTH Aachen University 2 , Aachen,