Transition from collisionless to collisional magnetorotational instability

Prateek Sharma, Gregory W. Hammett, Eliot Quataert

Research output: Contribution to journalArticle

55 Scopus citations

Abstract

Recent calculations by Quataert and coworkers 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 2π/k∥. In the weak magnetic field regime where the Alfvén and MRI frequencies ω are small compared to the sound wave frequency k∥c0, the dynamics are still effectively collisionless even if ω ≫ ν, so long as the collision frequency ν ≫ k∥c0; for an accretion flow this requires ν ≲Ω√β. 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.

Original languageEnglish (US)
Pages (from-to)1121-1130
Number of pages10
JournalAstrophysical Journal
Volume596
Issue number2 I
DOIs
StatePublished - Oct 20 2003
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Accretion, accretion disks
  • MHD
  • Plasmas

Fingerprint Dive into the research topics of 'Transition from collisionless to collisional magnetorotational instability'. Together they form a unique fingerprint.

  • Cite this