Multi-Fluid Simulations of Upper Chromospheric Magnetic Reconnection with Helium-Hydrogen mixture (Q.M. Wargnier, Lockheed Martin Solar and Astrophysics Laboratory and Baeri)

11.11.2022 10:30

Magnetic reconnection (MR) with multicomponent plasmas under chromospheric conditions remains poorly understood. Recent observations have demonstrated the important role of ion-neutral interactions in the dynamics of the chromosphere. However, the comparison between spectral profiles and synthetic observations of reconnection events suggests that current MHD approaches fail to be consistent with observations. First, collisions and multi-thermal aspects of the plasma play a role in these regions. Then, helium ionization effects appear to be relevant to the energy balance of the chromosphere.

This work investigates multifluid multi-species (MFMS) effects on MR in conditions representative of the upper chromosphere using the multifluid Ebysus code. Ebysus is an extension of the state-of-the-art radiative MHD code Bifrost (Gudiksen et al. 2011), which can solve any MFMS or two-fluid model for any species and/or ionized/excited level as desired separately. A specific numerical strategy has been established and implemented in order to cope with the full spectrum of temporal and spatial scales of these models while guaranteeing a high level of accuracy and reasonable computational costs.

We compare an MFMS approach based on a helium-hydrogen mixture with a classical two-fluid MHD model based on hydrogen only. The simulations of MRs are performed in a high Lundquist number regime subject to plasmoids production and instabilities. We study the evolution of the MR and compare the two approaches at different levels, including the composition, the structure of the current sheet and plasmoids, the decoupling of the particles, and the evolution of the heating mechanisms.

We will show how the presence of helium species leads to more efficient heating mechanisms than the two-fluid case. On top of that, thermodynamic conditions in the upper chromosphere give rise to the ionization of helium species leading to large heating inside the current sheet and plasmoids. This scenario, out of reach by the classical two-fluid or single-fluid models, could reach characteristic transition region temperatures from upper chromospheric conditions.

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Bâtiment: Conseil Général 7-9

Conference room, 8th floor, Séminaire d'analyse numérique

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