Kelvin-Helmholtz Instability in Partially Ionized Compressible Plasmas

Soler, Roberto; Díaz, Antonio; Ballester, J. L.; Goossens, Marcel

doi:10.1088/0004-637x/749/2/163

Cited by 55 publications

(78 citation statements)

References 54 publications

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“…The peculiar behaviour of neutrals under prominence conditions was discussed earlier (see, e.g. Soler et al 2012) and the unstable behaviour corresponds to the standard hydrodynamic KH instability. Another important result of this limit is that a two-fluid approach allows the propagation of two pairs of waves, one due to charged particles, and the other one for neutrals.…”

Section: Two-fluid Approximationmentioning

confidence: 51%

Dissipative instability in a partially ionised prominence plasma slab

Ballai

Pintér

Oliver

et al. 2017

A&A

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Aims. We aim to investigate the nature of dissipative instability appearing in a prominence planar thread filled with partially ionised plasma in the incompressible limit. The importance of partial ionisation is investigated in terms of the ionisation factor and the wavelength of sausage and kink waves propagating in the slab. Methods. In order to highlight the role of partial ionisation, we have constructed models describing various situations we can meet in solar prominence fine structure. Matching the solutions for the transversal component of the velocity and total pressure at the interfaces between the prominence slab and surrounding plasmas, we derived a dispersion relation whose imaginary part describes the evolution of the instability. Results were obtained in the limit of weak dissipation. We have investigated the appearance of instabilities in prominence dark plumes using single and two-fluid approximations .Results. Using simple analytical methods, we show that dissipative instabilities appear for flow speeds that are less than the Kelvin-Helmholtz instability threshold. The onset of instability is determined by the equilibrium flow strength, the ionisation factor of the plasma, the wavelength of waves and the ion-neutral collisional rate. For a given wavelength and for ionisation degrees closer to a neutral gas, the propagating waves become unstable for a narrow band of flow speeds, meaning that neutrals have a stabilising effect. Our results show that the partially ionised plasma describing prominence dark plumes becomes unstable only in a two-fluid (charged particles-neutrals) model, that is for periods that are smaller than the ion-neutral collision time.Conclusions. The present study improves our understanding of the complexity of dynamical processes and stability of solar prominences and the role partial ionisation in destabilising the plasma. We showed the necessity of two-fluid approximation when discussing the nature of instabilities: waves in a single fluid approximation show a great deal of stability. Our results clearly show that the problem of partial ionisation introduces new aspects of plasma stability with consequences on the evolution of partially ionised plasmas and solar prominences, in particular.

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Section: Two-fluid Approximationmentioning

confidence: 51%

Dissipative instability in a partially ionised prominence plasma slab

Ballai

Pintér

Oliver

et al. 2017

A&A

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“…Considering the same prominence/plume parameters as in Soler et al (2012), we obtain that the interface between these two partially ionised media becomes unstable for almost all values of flows (below the KH threshold) for an ionisation degree of the prominence larger than the ionisation degree of the plume, but the growth rate of this instability is very low, meaning that the dissipative instability (at least in this simplified framework) cannot explain the generation of upflows in plumes by instability.…”

Section: Instability Conditionsmentioning

confidence: 68%

Dissipative instability in partially ionised prominence plasmas

Ballai

Oliver

Alexandrou

2015

A&A

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Aims. We investigate the nature of dissipative instability at the boundary (seen here as tangential discontinuity) between the viscous corona and the partially ionised prominence plasma in the incompressible limit. The importance of the partial ionisation is investigated in terms of the ionisation fraction. Methods. Matching the solutions for the transversal component of the velocity and total pressure at the interface between the prominence and coronal plasmas, we derive a dispersion relation whose imaginary part describes the evolution of the instability. Results are obtained in the limit of weak dissipation. Results. Using simple analytical methods, we show that dissipative instabilities appear for flow speeds that are lower than the Kelvin-Helmholtz instability threshold. While viscosity tends to destabilise the plasma, the effect of partial ionisation (through the Cowling resistivity) will act towards stabilising the interface. For ionisation degrees closer to a neutral gas the interface will be unstable for larger values of equilibrium flow. The same principle is assumed when studying the appearance of instability at the interface between prominences and dark plumes. The unstable mode appearing in this case has a very small growth rate and dissipative instability cannot explain the appearance of flows in plumes.Conclusions. The present study improves our understanding of the complexity of dynamical processes at the interface of solar prominences and solar corona, and the role partial ionisation can have on the stability of the plasma. Our results clearly show that the problem of partial ionisation introduces new aspects of plasma stability with consequences on the evolution of solar prominences.

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“…The KHI has been studied in the presence of kink oscillations in coronal loops (Terradas et al 2008;Soler et al 2010), in twisted magnetic flux tubes with nonmagnetic environment , magnetic tubes with partially ionized plasmas (Soler et al 2012), in spicules (Zhelyazkov 2012a) and soft X-ray jets (Zhelyazkov 2012b), as well as in photospheric tubes (Zhelyazkov & Zaqarashvili 2012). Kelvin-Helmholtz vortices can be considered one of the important sources for MHD turbulence in the solar wind.…”

Section: Discussionmentioning

confidence: 99%

Kelvin-Helmholtz instability of twisted magnetic flux tubes in the solar wind

Zaqarashvili

Vörös

Zhelyazkov

2013

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Context. Tangential velocity discontinuity near the boundaries of solar wind magnetic flux tubes results in Kelvin-Helmholtz instability, which might contribute to solar wind turbulence. While the axial magnetic field stabilizes the instability, a small twist in the magnetic field may allow sub-Alfvénic motions to be unstable. Aims. We aim to study the Kelvin-Helmholtz instability of twisted magnetic flux tubes in the solar wind with different configurations of the external magnetic field. Methods. We use magnetohydrodynamic equations in cylindrical geometry and derive the dispersion equations governing the dynamics of twisted magnetic flux tubes moving along its axis in the cases of untwisted and twisted external fields. Then, we solve the dispersion equations analytically and numerically and find thresholds for Kelvin-Helmholtz instability in both cases of the external field.Results. Both analytical and numerical solutions show that the Kelvin-Helmholtz instability is suppressed in the twisted tube by the external axial magnetic field for sub-Alfvénic motions. However, even a small twist in the external magnetic field allows the Kelvin-Helmholtz instability to be developed for any sub-Alfvénic motion. The unstable harmonics correspond to vortices with high azimuthal mode numbers that are carried by the flow. Conclusions. Twisted magnetic flux tubes can be unstable to Kelvin-Helmholtz instability when they move with small speed relative to the main solar wind stream, then the Kelvin-Helmholtz vortices may significantly contribute to the solar wind turbulence.

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Kelvin-Helmholtz Instability in Partially Ionized Compressible Plasmas

Cited by 55 publications

References 54 publications

Dissipative instability in a partially ionised prominence plasma slab

Dissipative instability in a partially ionised prominence plasma slab

Dissipative instability in partially ionised prominence plasmas

Kelvin-Helmholtz instability of twisted magnetic flux tubes in the solar wind

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