Rayleigh-Taylor instabilities with sheared magnetic fields  in partially ionised plasmas

Ballai, I.; Khomenko, E.; Collados, M.

doi:10.1051/0004-6361/201731534

Cited by 13 publications

(10 citation statements)

References 22 publications

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“…It has been shown that ambipolar diffusion allows one to damp incompressible magnetic waves and currents as well as to convert magnetic perturbations into plasma thermal energy (this additional energy can be spent both in the ionization of the plasma and in the actual increase of the plasma temperature, see Khomenko et al 2018). Ambipolar diffusion also modifies the growth rates of instabilities (Soler et al 2012;Díaz et al 2014;Khomenko et al 2014b;Ballai et al 2017;Ruderman et al 2018), and it affects the amount of the emerged flux through the surface (Leake & Arber 2006;Arber et al 2007).…”

Section: Introductionmentioning

confidence: 99%

Joint action of Hall and ambipolar effects in 3D magneto-convection simulations of the quiet Sun

González-Morales

Khomenko

Vitas

et al. 2020

A&A

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The partial ionization of the solar plasma causes several nonideal effects such as the ambipolar diffusion, the Hall effect, and the Biermann battery effect. Here we report on the first three-dimensional realistic simulations of solar local dynamo where all three effects were taken into account. The simulations started with a snapshot of already saturated battery-seeded dynamo, where two new series were developed: one with solely ambipolar diffusion and another one also taking into account the Hall term in the generalized Ohm’s law. The simulations were then run for about 4 h of solar time to reach the stationary regime and improve the statistics. In parallel, a purely MHD dynamo simulation was also run for the same amount of time. The simulations are compared in a statistical way. We consider the average properties of simulation dynamics, the generation and dissipation of compressible and incompressible waves, and the magnetic Poynting flux. The results show that, with the inclusion of the ambipolar diffusion, the amplitudes of the incompressible perturbations related to Alfvén waves are reduced, and the Poynting flux is absorbed, with a frequency dependence. The Hall effect causes the opposite action: significant excess of incompressible perturbations is generated and an excess of the Poynting flux is observed in the chromospheric layers. The model with ambipolar diffusion shows, on average, sharper current sheets and slightly more abundant fast magneto-acoustic shocks in the chromosphere. The model with the Hall effect has higher temperatures at the lower chromosphere and stronger and more vertical magnetic field concentrations all over the chromosphere. The study of high-frequency waves reveals that significant power of incompressible perturbations is associated with areas with intense and more vertical magnetic fields and larger temperatures. This behavior explains the large Poynting fluxes in the simulations with the Hall effect and provides confirmation as to the role of Alfvén waves in chromospheric heating in internetwork regions, under the action of both Hall and ambipolar effects. We find a positive correlation between the magnitude of the ambipolar heating and the temperature increase at the same location after a characteristic time of 102 s.

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Section: Introductionmentioning

confidence: 99%

Joint action of Hall and ambipolar effects in 3D magneto-convection simulations of the quiet Sun

González-Morales

Khomenko

Vitas

et al. 2020

A&A

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“…Since solar prominences have often temperatures that are not high enough for a complete ionisation of the plasma, the effect of partial ionisation on the generation and evolution of MRT instabilities was also studied by (e.g. Diaz et al (2014), Ruderman et al (2017)). These investigations showed that the MRT instability becomes sensitive to the degree of plasma ionisation only for plasmas with small values of plasma beta and in a very weakly ionised state.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Rayleigh–Taylor instability at a contact discontinuity with an oblique magnetic field

Vickers

Ballai

Erdélyi

2020

A&A

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Aims. In the present work we investigate the nature of the magnetic Rayleigh-Taylor instability at a density interface permeated by an oblique, homogeneous magnetic field in an incompressible limit. Methods. Using the system of linearised ideal incompressible magnetohydrodynamics (MHD) equations we derive the dispersion relation for perturbations of the contact discontinuity by imposing the necessary continuity conditions at the interface. The imaginary part of the frequency describes the growth rate of waves due to instability. The growth rate of waves is studied by solving numerically the dispersion relation. Results. The critical wavenumber at which waves become unstable, present for a parallel magnetic field, disappears, due to the inclination of the magnetic field and instead waves are shown to be unstable for all wavenumbers. Theoretical results are applied to diagnose the structure of the magnetic field in prominence threads. When applying our theoretical results to observed waves in prominence plumes, we obtain a wide range of field inclination angle; from 0.5 • up to 30 • . These results highlight the diagnostic possibility of our study.

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“…They found that in the partially ionised case the plasma is always unstable and the growth rate for partially ionised plasmas is 50% larger than in the fully ionised case. The same problem of RTI was later analysed by Ruderman et al (2018), however they allowed the magnetic field to have a shear with respect to the direction of wave propagation. Their results show that the RTI becomes sensitive to the plasma ionisation degree only for plasmas corresponding to small values of plasma-beta and predominantly neutral plasma.…”

Section: Introductionmentioning

confidence: 99%

Dispersive shock waves in partially ionised plasmas

Ballai

Forgács‐Dajka

Marcu

2019

Advances in Space Research

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Compressional waves propagating in the partially ionised solar lower atmospheric plasmas can easily steepen into nonlinear waves, including shocks. Here we investigate the effect of weak dispersion generated by Hall currents perpendicular to the ambient magnetic field on the characteristics of shock waves. Our study will also focus on the interplay between weak dispersion and partial ionisation of the plasma. Using a multiple scale technique we derive the governing equation in the form of a Korteweg-de Vries-Burgers equation. The effect of weak dispersion on shock waves is obtained using a perturbation technique. The secular behaviour of second order terms is addressed with the help of a renormalisation technique. Our results show that dispersion modifies the characteristics of shock waves and this change is dependent also on the ionisation degree of the plasma. Dispersion can create short lived oscillations in the shocked plasma. The shock fronts become wider with the increase in the number of neutrals in the plasma.

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Rayleigh-Taylor instabilities with sheared magnetic fields in partially ionised plasmas

Cited by 13 publications

References 22 publications

Joint action of Hall and ambipolar effects in 3D magneto-convection simulations of the quiet Sun

Joint action of Hall and ambipolar effects in 3D magneto-convection simulations of the quiet Sun

Magnetic Rayleigh–Taylor instability at a contact discontinuity with an oblique magnetic field

Dispersive shock waves in partially ionised plasmas

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