title: Magnetorotational Turbulence and Dynamo in a Collisionless Plasma.
abstract: We present results from the first 3D kinetic numerical simulation of magnetorotational turbulence and dynamo, using the local shearing-box model of a collisionless accretion disk. The kinetic magnetorotational instability grows from a subthermal magnetic field having zero net flux over the computational domain to generate self-sustained turbulence and outward angular-momentum transport. Significant Maxwell and Reynolds stresses are accompanied by comparable viscous stresses produced by field-aligned ion pressure anisotropy, which is regulated primarily by the mirror and ion-cyclotron instabilities through particle trapping and pitch-angle scattering. The latter endow the plasma with an effective viscosity that is biased with respect to the magnetic-field direction and spatiotemporally variable. Energy spectra suggest an Alfvén-wave cascade at large scales and a kinetic-Alfvén-wave cascade at small scales, with strong small-scale density fluctuations and weak nonaxisymmetric density waves. Ions undergo nonthermal particle acceleration, their distribution accurately described by a κ distribution. These results have implications for the properties of low-collisionality accretion flows, such as that near the black hole at the Galactic center.
authors.affiliation: Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, New Jersey 08544, USA.|Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543, USA.
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Kunz
authors.affiliation: Department of Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, New Jersey 08544, USA.
authors.forename: James M
authors.initials: JM
authors.lastname: Stone
authors.affiliation: Department of Astronomy and Theoretical Astrophysics Center, University of California, 501 Campbell Hall #3411, Berkeley, California 94720-3411, USA.
authors.forename: Eliot
authors.initials: E
authors.lastname: Quataert