Exact and locally implicit source term solvers for multifluidMaxwell systems
Abstract
Recently, a family of models that couple multifluid systems to the full Maxwell equations have been used in laboratory, space, and astrophysical plasma modeling. These models are more complete descriptions of the plasma than reduced models like magnetohydrodynamic (MHD) since they are derived more closely from the full kinetic VlasovMaxwell system, without assumptions like quasineutrality, negligible electron mass, etc. Thus these models naturally retain nonideal MHD effects like electron inertia, Hall term, pressure anisotropy/nongyrotropy, displacement current, among others. One obstacle to broader application of these models is that an explicit treatment of their source terms leads to the need to resolve rapid processes like plasma oscillation and electron cyclotron motion, even when these are not important. In this paper, we suggest two ways to address this issue. First, we derive the analytic solutions to the source update equations, which can be implemented as a practical, but less generic solver. We then develop a timecentered, locally implicit algorithm to update the source terms, allowing stepping over the fast kinetic timescales. For a plasma with S species, the locally implicit algorithm involves inverting a local (3 S + 3) × (3 S + 3) matrix only, thus is very efficient. The performance can be further increased by using the direct update formulas to skip null calculations. We present benchmarks illustrating the exact energyconservation of the locally implicit solver, as well as its efficiency and robustness for both smallscale, idealized problems and largescale, complex systems. The locally implicit algorithm can be also easily extended to include other local sources, like collisions and ionization, which are difficult to solve analytically.
 Publication:

Journal of Computational Physics
 Pub Date:
 August 2020
 DOI:
 10.1016/j.jcp.2020.109510
 arXiv:
 arXiv:1909.04125
 Bibcode:
 2020JCoPh.41509510W
 Keywords:

 Multifluid plasma model;
 Implicit source term;
 Fivemoment;
 Tenmoment;
 Physics  Computational Physics;
 Physics  Plasma Physics
 EPrint:
 doi:10.1016/j.jcp.2020.109510