Two-fluid implementation in MPI-AMRVAC, with applications in the solar chromosphere

Abstract

The chromosphere is a partially ionized layer of the solar atmosphere, the transition between the photosphere where the gas is almost neutral and the fully ionized corona. As the collisional coupling between neutral and charged particles decreases in the upper part of the chromosphere, the hydrodynamical timescales may become comparable to the collisional timescale, and a two-fluid model is needed. In this paper we describe the implementation and validation of a two-fluid model which simultaneously evolves charges and neutrals, coupled by collisions. The two-fluid equations are implemented in the fully open-source MPI-AMRVAC code. In the photosphere and the lower part of the solar atmosphere, where collisions between charged and neutral particles are very frequent, an explicit time-marching would be too restrictive, since for stability the timestep needs to be proportional to the inverse of the collision frequency. This is overcome by evaluating the collisional terms implicitly using an explicit-implicit (IMEX) scheme. The cases presented cover very different collisional regimes and our results are fully consistent with related literature findings. If collisional time and length scales are smaller than the hydrodynamical scales usually considered in the solar chromosphere, density structures seen in the neutral and charged fluids are similar, with the effect of elastic collisions between charges and neutrals being similar to diffusivity. Otherwise, density structures are different and the decoupling in velocity between the two species increases. The use of IMEX schemes efficiently avoids the small timestep constraints of fully explicit implementations in strongly collisional regimes. Adaptive Mesh Refinement (AMR) greatly decreases the computational cost, compared to uniform grid runs at the same effective resolution.

accepted for publication in A&A

References in corpus (14)

• Fluid description of multi-component solar partially ionized plasma
• Global Three-Dimensional Simulations of Outer Protoplanetary Disks with Ambipolar Diffusion
• Rayleigh-Taylor instability in prominences from numerical simulations including partial ionization effects
• Chromospheric magnetic reconnection: Two-fluid simulations of coalescing current loops
• Multi-fluid Approach to High-frequency Waves in Plasmas. II. Small-amplitude Regime in Partially Ionized Media
• Two-fluid numerical simulations of solar spicules
• Multi-fluid approach to high-frequency waves in plasmas: I. Small-amplitude regime in fully ionized medium
• Intermediate shock substructures within a slow-mode shock occurring in partially ionised plasma
• Two-fluid simulations of Rayleigh-Taylor instability in a magnetized solar prominence thread II. Effects of collisionality
• Three-dimensional MHD wave propagation near a coronal null point: a new wave mode decomposition approach
• On the origin of magnetic fields in stars II: The effect of numerical resolution
• Evidence for the two fluid scenario in solar prominences
• Magnetohydrodynamics of protoplanetary discs
• Stability of two-fluid partially-ionised slow-mode shock fronts

Cited by in corpus (5)

• MPI-AMRVAC 3.0: updates to an open-source simulation framework
• Two-fluid reconnection jets in a gravitationally stratified atmosphere
• Coronal rain formation in a two-fluid approximation
• Influence of the magnetic field topology in the evolution of small-scale two-fluid jets in the solar atmosphere
• The Rayleigh Taylor instability in partially ionized plasmas: ambipolar diffusion effects in the non linear phase