2003/05/31 by Prateek Sharma, Gregory W. Hammett, Eliot Quataert · 7 citations
Physics and Astronomy · #Astrophysics and Star Formation Studies #Dust and Plasma Wave Phenomena #Magnetic confinement fusion research #astro-ph #physics.plasm-ph
paper · pdf · doi:10.1086/378234
published as Astrophys.J. 596 (2003) 1121-1130 · 20 pages, 4 figures, submitted to ApJ with a clearer derivation of anisotropic pressure closure from drift kinetic equation
arxiv created 2003/06/13 · openalex publication_date 2003/10/13 · arxiv updated 2009/12/01 · openalex created_date 2017/04/07 · openalex updated_date 2026/08/01
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 ∥ c 0 , the dynamics are still effectively collisionless even if ω ≪ ν, so long as the collision frequency ν ≪ k ∥ c 0 ; for an accretion flow this requires ν ≲ Ω . 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.