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Multi-fluid approach to high-frequency waves in plasmas. III. Nonlinear regime and plasma heating  

David Martínez-Gómez   Submitted: 2018-02-26 04:54

The multi-fluid modelling of high-frequency waves in partially ionized plasmas has shown that the behavior of magnetohydrodynamics waves in the linear regime is heavily influenced by the collisional interaction between the different species that form the plasma. Here, we go beyond linear theory and study large-amplitude waves in partially ionized plasmas using a nonlinear multi-fluid code. It is known that in fully ionized plasmas, nonlinear Alfvén waves generate density and pressure perturbations. Those nonlinear effects are more pronounced for standing oscillations than for propagating waves. By means of numerical simulations and analytical approximations, we examine how the collisional interaction between ions and neutrals affects the nonlinear evolution. The friction due to collisions dissipates a fraction of the wave energy, which is transformed into heat and consequently rises the temperature of the plasma. As an application, we investigate frictional heating in a plasma with physical conditions akin to those in a solar quiescent prominence.

Authors: David Martínez-Gómez, Roberto Soler and Jaume Terradas
Projects: None

Publication Status: Accepted for publication in The Astrophysical Journal
Last Modified: 2018-02-28 13:58
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Multi-fluid Approach to High-frequency Waves in Plasmas: I. Small-amplitude Regime in Fully Ionized Medium  

David Martínez-Gómez   Submitted: 2016-09-26 04:07

Ideal MHD provides an accurate description of low-frequency Alfvén waves in fully ionized plasmas. However, higher frequency waves in many plasmas of the solar atmosphere cannot be correctly described by ideal MHD and a more accurate model is required. Here, we study the properties of small-amplitude incompressible perturbations in both the low and the high frequency ranges in plasmas composed of several ionized species. We use a multi-fluid approach and take into account the effects of collisions between ions and the inclusion of Hall's term in the induction equation. Through the analysis of the corresponding dispersion relations and numerical simulations we check that at high frequencies ions of different species are not as strongly coupled as in the low frequency limit. Hence, they cannot be treated as a single fluid. In addition, elastic collisions between the distinct ionized species are not negligible for high frequency waves since an appreciable damping is obtained. Furthermore, Coulomb collisions between ions remove the cyclotron resonances and the strict cut-off regions that are present when collisions are not taken into account. The implications of these results for the modelling of high-frequency waves in solar plasmas are discussed.

Authors: David Martínez-Gómez, Roberto Soler and Jaume Terradas
Projects: None

Publication Status: Accepted for publication in The Astrophysical Journal
Last Modified: 2016-09-26 09:54
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Onset of the Kelvin-Helmholtz instability in partially ionized magnetic flux tubes  

David Martínez-Gómez   Submitted: 2015-04-22 02:14

Context: Recent observations of solar prominences show the presence of turbulent flows that may be caused by Kelvin-Helmholtz instabilites (KHI). However, the observed flow velocities are below the classical threshold for the onset of KHI in fully ionized plasmas. Aims: We investigate the effect of partial ionization on the onset of KHI in dense and cool cylindrical magnetic flux tubes surrounded by a hotter and lighter environment. Methods: The linearized governing equations of a partially ionized two-fluid plasma are used to describe the behavior of small-amplitude perturbations superimposed on a magnetic tube with longitudinal mass flow. A normal mode analysis is performed to obtain the dispersion relation for linear incompressible waves. We focus on the appearance of unstable solutions and study the dependence of their growth rates on various physical parameters. An analytical approximation of the KHI linear growth rate for slow flows and strong ion-neutral coupling is obtained. An application to solar prominence threads is given. Results: The presence of a neutral component in a plasma may contribute to the onset of the KHI even for sub-Alfvénic longitudinal shear flows. Collisions between ions and neutrals reduce the growth rates of the unstable perturbations but cannot completely suppress the instability. Conclusions: Turbulent flows in solar prominences with sub-Alfvénic flow velocities may be interpreted as consequences of KHI in partially ionized plasmas.

Authors: David Martínez-Gómez, Roberto Soler and Jaume Terradas
Projects: None

Publication Status: Accepted for publication in A&A
Last Modified: 2015-04-22 12:12
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Abstracts by Author
Multi-fluid approach to high-frequency waves in plasmas. III. Nonlinear regime and plasma heating
Multi-fluid Approach to High-frequency Waves in Plasmas: I. Small-amplitude Regime in Fully Ionized Medium
Onset of the Kelvin-Helmholtz instability in partially ionized magnetic flux tubes

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