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Multi-fluid modeling of magnetic reconnection in solar partially ionized and laboratory plasmas - Alejandro Alvarez Laguna - Ph.D. Thesis - Free download

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VKI PHDT 2018-03, Alejandro Alvarez Laguna, Multi-fluid modeling of magnetic reconnection in solar partially ionized and laboratory plasmas, ISBN 978-2-87516-130-7, 203 pgs


https://doi.org/10.35294/phdt201803

Multi-fluid modeling of magnetic reconnection in solar partially ionized and laboratory plasmas  - Alejandro Alvarez Laguna - Ph.D. Thesis - Free download

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Multi-fluid modeling of magnetic reconnection in solar partially ionized and laboratory plasmas
By Alejandro Alvarez Laguna

PhD Thesis from the von Karman Institute / KU Leuven, December 2017, ISBN 978-2-87516-130-7, 203 pgs

https://doi.org/10.35294/phdt201803


Abstract

Astrophysical and laboratory plasmas host a wide variety of complex phenomena that are caused by the interaction between plasmas and electromagnetic fields. The magnetic field can store large amounts of energy that may be transferred to the plasma by magnetic reconnection. This exchange of energy is responsible for massive eruptions in the solar atmosphere as well as disruptions in magnetic confinement devices for controlled nuclear fusion. Nevertheless, this process is not fully understood as magnetohydrodynamic (MHD) models are not able to completely capture the small-scale phenomena responsible for reconnecting the field lines. Alternatively, kinetic codes represent very accurately the small-scales but are computationally very costly and cannot afford full-domain simulations.

We propose multi-fluid plasma models as a sound alternative to the kinetic and MHD approaches. The multi-fluid plasma model represents the species within the plasma as different interpenetrating fluids that interact among each other by exchanging momentum and energy through elastic collisions, and mass through chemical reactions. Additionally, the charged species interact with the electromagnetic fields. This allows to capture important small-scale phenomena that results from the interplay of the species among themselves and with the electromagnetic fields, while representing the fullscale dynamics.

A novel numerical method that solves for the multi-fluid plasma equations coupled to full Maxwell's equations is developed and implemented into a high performance computing platform. The disparity of time scales contained in the set of equations is a great challenge from the numerical point of view. In order to tackle this problem, we propose an innovative numerical scheme based on the finite volume method on unstructured meshes with implicit time integration. The numerical method proves its versatility in a wide range of plasma conditions - from low-subsonic to supersonic, from reactive partially to fully-ionized, and from collisionally dominated to collisionless and magnetically dominated.

In this dissertation, we focus on the study of two long-standing problems in plasma physics: the role of neutrals in the dynamics of the partially-ionized solar atmosphere and the plasma instabilities inside nuclear fusion devices.

First, we study the complex interaction of the chemical non-equilbrium, ambipolar diffusion, and radiation in magnetic reconnection events under partially-ionized chromospheric conditions. The study shows that the results accounting for radiation show time scales and out flows comparable to these observed in spicules and chromospheric jets. Second, we simulate the propagation of magnetosonic waves across the photosphere and the chromosphere. For the first time, a global multi-fluid simulation of the solar lower atmosphere is performed.

Finally, we analyze the dynamics of a magnetic flux tube under realistic conditions of the DIII-D nuclear fusion reactor. The evolution of the kink instability and the drift-wave instability in a full-scale 3D simulation is studied. Multi-fluid models allow for capturing the influence of the small-scale processes that results of the separation of the motions of the fluids on the macroscopic dynamics.

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Manufacturer von Karman Institute for Fluid Dynamics

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