Transition from Collisionless to Collisional MRI

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Recent calculations by Quataert et al. (2002) found that the growth rates of the magnetorotational instability (MRI) in a collisionless plasma can differ significantly from those calculated using MHD. This can be important in hot accretion flows around compact objects. In this paper, we study the transition from the collisionless kinetic regime to the collisional MHD regime, mapping out the dependence of the MRI growth rate on collisionality. A kinetic closure scheme for a magnetized plasma is used that includes the effect of collisions via a BGK operator. The transition to MHD occurs as the mean free path becomes short ... continued below

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844 Kilobytes pages

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Sharma, Prateek; Hammett, Gregory W. & Quataert, Eliot July 24, 2003.

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Description

Recent calculations by Quataert et al. (2002) found that the growth rates of the magnetorotational instability (MRI) in a collisionless plasma can differ significantly from those calculated using MHD. This can be important in hot accretion flows around compact objects. In this paper, we study the transition from the collisionless kinetic regime to the collisional MHD regime, mapping out the dependence of the MRI growth rate on collisionality. A kinetic closure scheme for a magnetized plasma is used that includes the effect of collisions via a BGK operator. The transition to MHD occurs as the mean free path becomes short compared to the parallel wavelength 2*/k(sub)||. In the weak magnetic field regime where the Alfven and MRI frequencies w are small compared to the sound wave frequency k(sub)||c(sub)0, the dynamics are still effectively collisionless even if omega << v, so long as the collision frequency v << k(sub)||c(sub)0; for an accretion flow this requires n less than or approximately equal to *(square root of b). The low collisionality regime not only modifies the MRI growth rate, but also introduces collisionless Landau or Barnes damping of long wavelength modes, which may be important for the nonlinear saturation of the MRI.

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844 Kilobytes pages

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INIS; OSTI as DE00814711

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  • Other Information: PBD: 24 Jul 2003

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  • Report No.: PPPL-3843
  • Grant Number: AC02-76CH03073
  • DOI: 10.2172/814711 | External Link
  • Office of Scientific & Technical Information Report Number: 814711
  • Archival Resource Key: ark:/67531/metadc738678

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  • July 24, 2003

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  • Oct. 18, 2015, 6:40 p.m.

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  • April 15, 2016, 9:56 p.m.

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Sharma, Prateek; Hammett, Gregory W. & Quataert, Eliot. Transition from Collisionless to Collisional MRI, report, July 24, 2003; Princeton, New Jersey. (digital.library.unt.edu/ark:/67531/metadc738678/: accessed June 18, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.