Fast growth of magnetic fields in galaxy clusters: a self‐accelerating dynamo

Schekochihin, A. A.; Cowley, S. C.

doi:10.1002/asna.200610600

Cited by 14 publications

(16 citation statements)

References 39 publications

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“…As is generally the case in high-β collisionless plasma dynamics (e.g. Schekochihin & Cowley 2006;Squire et al 2016), nonlinearity can be important for perturbation amplitudes far below what one might naively expect. For the MRI in the collisionless regime, this occurs a factor of ∼β 0 (or ∼β 7/6 0 for δB y with B 0y = 0) below where nonlinear effects become important in standard MHD.…”

Section: General Discussion Of 1-d Nonlinearitiesmentioning

confidence: 92%

Pressure-anisotropy-induced nonlinearities in the kinetic magnetorotational instability

2017

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In collisionless and weakly collisional plasmas, such as hot accretion flows onto compact objects, the magnetorotational instability (MRI) can differ significantly from the standard (collisional) MRI. In particular, pressure anisotropy with respect to the local magnetic-field direction can both change the linear MRI dispersion relation and cause nonlinear modifications to the mode structure and growth rate, even when the field and flow perturbations are very small. This work studies these pressure-anisotropy-induced nonlinearities in the weakly nonlinear, high-ion-beta regime, before the MRI saturates into strong turbulence. Our goal is to better understand how the saturation of the MRI in a low collisionality plasma might differ from that in the collisional regime. We focus on two key effects: (i) the direct impact of self-induced pressure-anisotropy nonlinearities on the evolution of an MRI mode, and (ii) the influence of pressure anisotropy on the "parasitic instabilities" that are suspected to cause the mode to break up into turbulence. Our main conclusions are: (i) The mirror instability regulates the pressure anisotropy in such a way that the linear MRI in a collisionless plasma is an approximate nonlinear solution once the mode amplitude becomes larger than the background field (just as in MHD). This implies that differences between the collisionless and collisional MRI become unimportant at large amplitudes. (ii) The break up of large amplitude MRI modes into turbulence via parasitic instabilities is similar in collisionless and collisional plasmas. Together, these conclusions suggest that the route to magnetorotational turbulence in a collisionless plasma may well be similar to that in a collisional plasma, as suggested by recent kinetic simulations. As a supplement to these findings, we offer guidance for the design of future kinetic simulations of magnetorotational turbulence.

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Section: General Discussion Of 1-d Nonlinearitiesmentioning

confidence: 92%

Pressure-anisotropy-induced nonlinearities in the kinetic magnetorotational instability

2017

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“…Certainly, much of the increase comes from flux-freezing during gravitational collapse, which is not included here. In addition, smaller scale field increases could come from purely kinetic processes such as the Alfvén wave cascade or other kinetic process (e.g., Schekochihin & Cowley 2006a, 2006b. The largescale turbulence can serve as energy input for this process.…”

Section: Fixed Anisotropic Thermal Conductionmentioning

confidence: 99%

The Magnetothermal Instability in the Intracluster Medium

Parrish

Stone

Lemaster

2008

Astrophysical Journal

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The electron mean free path in the intracluster medium (ICM) of galaxy clusters is much larger than the gyroradius; thus, heat is transported anisotropically along magnetic field lines. We show that the intracluster medium is unstable to the magnetothermal instability (MTI ) where the temperature declines with radius using MHD simulations with anisotropic thermal conduction. As a result of the MTI, we find that the temperature profile of the ICM can be substantially modified on timescales of several billion years, while the magnetic field is amplified by dynamo action up to more than 50 times the original energy. We also show that the instability drives field lines to become preferentially radial, leading to conduction that is a highly efficient fraction of the Spitzer conductivity.

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“…It is a plausible mechanism by which cosmic magnetic fields were created (e.g., [1][2][3][4][5][6][7][8][9]). Dynamo action has also been studied in laboratory experiments [10][11][12].…”

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confidence: 99%

“…Here v 0 and l 0 are the velocity and the scale associated with the largest eddies. The final equation (8) in the Kazantsev-Kraichnan model involves only the integral of the velocity correlation function over time, that is, the turbulent diffusivity, which in Kolmogorov turbulence scales as hjvðk; tÞj 2 iðkÞ $ v 0 l À1=3 0 k À13=3 . By requiring that the Kazantsev-Kraichnan model have the same scaling of turbulent diffusivity, we obtain R hv iÃ ðk; tÞv i ðk; t 0 Þidt 1 ii ðkÞ $ v 0 l À1=3 0 k À13=3 , and, therefore,…”

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confidence: 99%

Magnetic Dynamo action at Low Magnetic Prandtl Numbers

Malyshkin

Boldyrev

2010

Phys. Rev. Lett.

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Amplification of magnetic field due to kinematic turbulent dynamo action is studied in the regime of small magnetic Prandtl numbers. Such a regime is relevant for planets and stars interiors, as well as for liquid-metal laboratory experiments. A comprehensive analysis based on the Kazantsev-Kraichnan model is reported, which establishes the dynamo threshold and the dynamo growth rates for varying kinetic helicity of turbulent fluctuations. It is proposed that in contrast with the case of large magnetic Prandtl numbers, the kinematic dynamo action at small magnetic Prandtl numbers is significantly affected by kinetic helicity, and it can be made quite efficient with an appropriate choice of the helicity spectrum.

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Fast growth of magnetic fields in galaxy clusters: a self‐accelerating dynamo

Cited by 14 publications

References 39 publications

Pressure-anisotropy-induced nonlinearities in the kinetic magnetorotational instability

Pressure-anisotropy-induced nonlinearities in the kinetic magnetorotational instability

The Magnetothermal Instability in the Intracluster Medium

Magnetic Dynamo action at Low Magnetic Prandtl Numbers

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