Kelvin-Helmholtz instability and collapse of a twisted magnetic null point with anisotropic viscosity

Quinn, James; MacTaggart, David; Simitev, Radostin D.

doi:10.1051/0004-6361/202140460

Cited by 4 publications

(8 citation statements)

References 37 publications

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“…For brevity, we will refer to this model of viscosity as 'the switching model '. In Quinn et al ( 2020c ) andSimitev ( 2021 ), we implemented the switching model as a module for the widely used general MHD code Lare3d (Arber et al 2001 ), and demonstrated significant effects of anisotropic viscosity on the development of the non-linear MHD kink instability and the Kelvin-Helmholtz instability . More generally , the interest in anisotropic viscosity stems from the open question of which heating mechanism (viscous or Ohmic) is dominant in the solar corona (Klimchuk 2006 ), an important facet of solving the coronal heating problem.…”

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confidence: 99%

Flute and kink instabilities in a dynamically twisted flux tube with anisotropic plasma viscosity

Quinn,

Simitev

2022

Monthly Notices of the Royal Astronomical Society

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Magnetic flux tubes such as those in the solar corona are subject to a number of instabilities. Important among them is the kink instability which plays a central part in the nanoflare theory of coronal heating, and for this reason in numerical simulations it is usually induced by tightly-controlled perturbations and studied in isolation. In contrast, we find that fluting modes of instability are readily excited when disturbances are introduced in our magnetohydrodynamic flux tube simulations by dynamic twisting of the flow at the boundaries. We also find that the flute instability, which has been theorised but rarely observed in the coronal context, is strongly enhanced when plasma viscosity is assumed anisotropic. We proceed to investigate the co-existence and competition between flute and kink instabilities for a range of values of the resistivity and of the parameters of the anisotropic and isotropic models of viscosity. We conclude that while the flute instability cannot prevent the kink from ultimately dominating, it can significantly delay its development especially at strong viscous anisotropy induced by intense magnetic fields.

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Flute and kink instabilities in a dynamically twisted flux tube with anisotropic plasma viscosity

Quinn,

Simitev

2022

Monthly Notices of the Royal Astronomical Society

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“…Expression ( 11) is identical to the strong field approximation of the general anisotropic viscosity tensor derived by Braginskii (Braginskii 1965). Expressions ( 9) and ( 11) arise as asymptotic limits of the more general switching model used in our earlier works (MacTaggart et al 2017;Quinn et al 2020cQuinn et al , 2021 which, includes both isotropic and anisotropic contributions and can switch gradually between them depending on the strength of the magnetic field at a given spaciotemporal location. For example, in the vicinity of a null point where the magnetic field becomes weak the isotropic viscosity contribution becomes dominant in the switching model.…”

Section: Mathematical Formulation and Numerical Setupmentioning

confidence: 99%

“…The non-dimensionalisation of equations ( 7) is identical to that used in our earlier works (Quinn et al 2020c(Quinn et al , 2021 and in reference (Arber et al 2001) that describes the code Lare3d we use for numerical solution, see further below. A typical magnetic field strength 𝐵 0 , density 𝜌 0 and length scale 𝐿 0 are chosen and the other variables non-dimensionalised appropriately.…”

Section: Mathematical Formulation and Numerical Setupmentioning

confidence: 99%

“…The problem formulated above is solved numerically using the staggered-grid, Lagrangian-Eulerian remap code for 3D MHD simulations Lare3D of Arber et al (2001) where a new module for anisotropic viscosity has been included as detailed in (Quinn et al 2021). The resolution used in the current work is 512 grid points per dimension, comparable to the highest resolution kink instability studies of Hood et al (2009) or medium resolution studies of Bareford & Hood (2015).…”

Section: Mathematical Formulation and Numerical Setupmentioning

confidence: 99%

“…For brevity, we will refer to this model of viscosity as "the switching model". In (Quinn et al 2020c(Quinn et al , 2021 we implemented the switching model as a module for the widely-used general MHD code Lare3d (Arber et al 2001), and demonstrated significant effects of anisotropic viscosity on the development of the nonlinear MHD kink instability and the Kelvin-Helmholtz instability. More generally, the interest in anisotropic viscosity stems from the open question of which heating mechanism (viscous or Ohmic) is dominant in the solar corona (Klimchuk 2006), an important facet of solving the coronal heating problem.…”

Section: Introductionmentioning

confidence: 99%

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Flute and kink instabilities in a dynamically twisted flux tube with anisotropic plasma viscosity

Quinn,

Simitev

2021

Preprint

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Magnetic flux tubes such as those in the solar corona are subject to a number of instabilities. Important among them is the kink instability which plays a central part in the nanoflare theory of coronal heating, and for this reason in numerical simulations it is usually induced by tightly-controlled perturbations and studied in isolation. In contrast, we find that when disturbances are introduced in our magnetohydrodynamic flux tube simulations by dynamic twisting of the flow at the boundaries fluting modes of instability are readily excited. We also find that the flute instability, which has been theorised but rarely observed in the coronal context, is strongly enhanced when plasma viscosity is assumed anisotropic. We proceed to investigate the co-existence and competition between flute and kink instabilities for a range of values of the resistivity and of the parameters of the anisotropic and isotropic models of viscosity. We conclude that while the flute instability cannot prevent the kink from ultimately dominating, it can significantly delay its development especially at strong viscous anisotropy induced by intense magnetic fields.

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Magnetic reconnection: MHD theory and modelling

Pontin

Priest

2022

Living Rev Sol Phys

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In this review we focus on the fundamental theory of magnetohydrodynamic reconnection, together with applications to understanding a wide range of dynamic processes in the solar corona, such as flares, jets, coronal mass ejections, the solar wind and coronal heating. We summarise only briefly the related topics of collisionless reconnection, non-thermal particle acceleration, and reconnection in systems other than the corona. We introduce several preliminary topics that are necessary before the subtleties of reconnection can be fully described: these include null points (Sects. 2.1–2.2), other topological and geometrical features such as separatrices, separators and quasi-separatrix layers (Sects. 2.3, 2.6), the conservation of magnetic flux and field lines (Sect. 3), and magnetic helicity (Sect. 4.6). Formation of current sheets in two- and three-dimensional fields is reviewed in Sect. 5. These set the scene for a discussion of the definition and properties of reconnection in three dimensions that covers the conditions for reconnection, the failure of the concept of a flux velocity, the nature of diffusion, and the differences between two-dimensional and three-dimensional reconnection (Sect. 4). Classical 2D models are briefly presented, including magnetic annihilation (Sect. 6), slow and fast regimes of steady reconnection (Sect. 7), and non-steady reconnection such as the tearing mode (Sect. 8). Then three routes to fast reconnection in a collisional or collisionless medium are described (Sect. 9). The remainder of the review is dedicated to our current understanding of how magnetic reconnection operates in three dimensions and in complex magnetic fields such as that of the Sun’s corona. In Sects. 10–12, 14.1 the different regimes of reconnection that are possible in three dimensions are summarised, including at a null point, separator, quasi-separator or a braid. The role of 3D reconnection in solar flares (Sect. 13) is reviewed, as well as in coronal heating (Sect. 14), and the release of the solar wind (Sect. 15.2). Extensions including the role of reconnection in the magnetosphere (Sect. 15.3), the link between reconnection and turbulence (Sect. 16), and the role of reconnection in particle acceleration (Sect. 17) are briefly mentioned.

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Kelvin-Helmholtz instability and collapse of a twisted magnetic null point with anisotropic viscosity

Cited by 4 publications

References 37 publications

Flute and kink instabilities in a dynamically twisted flux tube with anisotropic plasma viscosity

Flute and kink instabilities in a dynamically twisted flux tube with anisotropic plasma viscosity

Flute and kink instabilities in a dynamically twisted flux tube with anisotropic plasma viscosity

Magnetic reconnection: MHD theory and modelling

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