Pressure-Driven Instabilities in Astrophysical Jets

Longaretti, Pierre-Yves

doi:10.1007/978-3-540-76967-5_4

Cited by 8 publications

(7 citation statements)

References 24 publications

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“…The restoring force due to the magnetic tension is supposed to be minimum at these surfaces, which are hence more likely to trigger instabilities (see e.g. Longaretti 2008). By studying the global eigenfunctions of the most unstable modes, we shall test whether the above condition influences the instabilities in this work (see §5).…”

Section: Magnetic Resonance Conditionmentioning

confidence: 99%

“…The latter category is sub-classified as (see e.g. Longaretti 2008): (i) current-driven instabilities, which are driven by the current parallel (j ) to the total magnetic field B and are most easily studied in the context of cold, pressureless jets; and (ii) pressure-driven instabilities, which are driven by the gradient of the background plasma pressure and the electric current perpendicular (j ⊥ ) to B. The curvature of the magnetic field lines plays an important role in confining the plasma in this case, and instability occurs when the destabilizing plasma pressure gradient is strong enough to push the plasma out of this curvature.…”

Section: Introductionmentioning

confidence: 99%

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Internal instabilities in magnetized jets

Das

Begelman

2018

Monthly Notices of the Royal Astronomical Society

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We carry out an extensive linear stability analysis of magnetized cylindrical jets in a global framework. Foregoing the commonly invoked force-free limit, we focus on the small-scale, internal instabilities triggered in regions of the jet dominated by a toroidal magnetic field, with a weak vertical field and finite thermal pressure gradient. Such regions are likely to occur far from the jet source and boundaries, and are potential sites of magnetic energy dissipation that is essential to explain the particle acceleration and radiation observed from astrophysical jets. We validate the local stability analysis of Begelman by verifying that the eigenfunctions of the most unstable modes are radially localized. This finding allows us to propose a generic stability criterion in the presence of a weak vertical field. A stronger vertical field with a radial gradient complicates the stability criterion, due to the competition between the destabilizing thermal pressure gradient and stabilizing magnetic pressure gradients. Nevertheless, we argue that the jet interiors generically should be subject to rapidly growing, small-scale instabilities, capable of producing current sheets that lead to dissipation. We identify some new instabilities, not predicted by the local analysis, which are sensitive to the background radial profiles but have smaller growth rates than the local instabilities, and discuss the relevance of our work to the findings of recent numerical jet simulations.

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Section: Magnetic Resonance Conditionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Internal instabilities in magnetized jets

Das

Begelman

2018

Monthly Notices of the Royal Astronomical Society

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“…The growth rates of unstable modes are typically of the order of cs/R, where cs is the sound speed and R is the jet radius (Longaretti 2008).…”

Section: Pressure-balance (Pb) Equilibriummentioning

confidence: 99%

MHD simulations of three-dimensional resistive reconnection in a cylindrical plasma column

Striani

Mignone²,

Vaidya³

et al. 2016

Mon. Not. R. Astron. Soc.

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Magnetic reconnection is a plasma phenomenon where a topological rearrangement of magnetic field lines with opposite polarity results in dissipation of magnetic energy into heat, kinetic energy and particle acceleration. Such a phenomenon is considered as an efficient mechanism for energy release in laboratory and astrophysical plasmas. An important question is how to make the process fast enough to account for observed explosive energy releases. The classical model for steady state magnetic reconnection predicts reconnection times scaling as S 1/2 (where S is the Lundquist number) and yields times scales several order of magnitude larger than the observed ones. Earlier two-dimensional MHD simulations showed that for large Lundquist number the reconnection time becomes independent of S ("fast reconnection" regime) due to the presence of the secondary tearing instability that takes place for S 1 × 10 4 . We report on our 3D MHD simulations of magnetic reconnection in a magnetically confined cylindrical plasma column under either a pressure balanced or a force-free equilibrium and compare the results with 2D simulations of a circular current sheet. We find that the 3D instabilities acting on these configurations result in a fragmentation of the initial current sheet in small filaments, leading to enhanced dissipation rate that becomes independent of the Lundquist number already at S ≃ 1 × 10 3 .

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“…In the fusion confinement literature, Bondeson et al (1987) have extended the Suydam analysis to include velocity and have shown that the stability of localized pressure-driven modes depends on the quantity M = v z ρ 1/2 (Bzq /q) −1 , a form of Alfvénic Mach number. If M < β then velocity shear destabilizes local resonant modes; if M > β such modes are stabilized, though other global modes are excited with slow growth rates (for a discussion of pressure-driven modes in the context of jets, see Longaretti 2008). Thus, the apparent stability of the poloidal equilibrium in our jet propagation simulations may be due to high velocity shear, though Bondeson et al (1987)'s work would need to be extended to the relativistic regime for a more thorough understanding of how velocity shear affects pressure-driven instabilities in relativistic jets.…”

Section: Sim04 Sim05 Sim06 Sim07mentioning

confidence: 99%

Magnetic field structure of relativistic jets without current sheets

Gourgouliatos

Fendt

Clausen-Brown

et al. 2011

Monthly Notices of the Royal Astronomical Society

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We present an analytical class of equilibrium solutions for the structure of relativistic sheared and rotating magnetized jets that contain no boundary current sheets. We demonstrate the overall dynamical stability of these solutions and, most importantly, a better numerical resistive stability than the commonly employed force-free structures which inevitably require the presence of dissipative surface currents. The jet is volumetrically confined by the external pressure, with no pressure gradient on the surface. We calculate the expected observed properties of such jets. Given the simplicity of these solution we suggest them as useful initial conditions for relativistic jet simulations.Comment: 13 pages, 13 figures, Accepted by MNRA

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Pressure-Driven Instabilities in Astrophysical Jets

Cited by 8 publications

References 24 publications

Internal instabilities in magnetized jets

Internal instabilities in magnetized jets

MHD simulations of three-dimensional resistive reconnection in a cylindrical plasma column

Magnetic field structure of relativistic jets without current sheets

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