Dynamos and angular momentum transport in accretion disks

Journal Article · Thu Aug 01 00:00:00 EDT 1991 · Physics of Fluids B; (United States)

DOI:https://doi.org/10.1063/1.859606· OSTI ID:5597476

Vishniac, E T; Jin, L ^[1]; Diamond, P H ^[2]

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1. Department of Astronomy, The University of Texas at Austin, Austin, Texas 78712-1063 (USA)
2. Department of Physics, The University of California at San Diego, La Jolla, California 92093 (USA)

The transport of angular momentum in astrophysical disks is one of the major issues in modern astrophysics. Here, recent work (Astrophys. J. {bold 347}, 435 (1989); {bold 365}, 648 (1990)) will be reviewed that suggests that internal waves, analogous to deep ocean waves, play a critical role in transporting angular momentum in neutral disks and generating a magnetic dynamo in ionized disks. Previously, it was shown that low-frequency, slightly nonaxisymmetric ({vert bar}{ital m}{vert bar}=1) waves in thin accretion disks could penetrate to small radii with a unique amplitude because of nonlinear saturation. Here, the ability of these waves to drive an {alpha}-{Omega} dynamo in a disk of thickness {ital H} and radius {ital r} and keplerian rotational frequency {Omega}({ital r}){proportional to}{ital r}{sup {minus}3/2} is examined. The asymmetry in the wave distribution that creates a nonzero helicity follows from the fact that the fundamental waves all have a positive angular momentum flux. As a result, there will be a large-scale magnetic field driven by an {alpha}-{Omega} dynamo. It is also likely that small-scale fields, driven by higher-order wave modes, will contribute significantly to the local value of {ital B}{sub {ital r}}{ital B}{sub {phi}}. It is argued that the magnetic field saturates when its pressure is comparable to the thermal pressure and a crude model of the nonlinear transfer of power to small-scale turbulence is presented. The dynamo process creates a large-scale, axisymmetric toroidal field with {ital B}{sub {ital r}}{similar to}({ital H}/{ital r}){sup 3/2}{ital B}{sub {phi}}. Smaller-scale waves create small-scale fields with a maximum {ital b}{sub {ital r}}{ital b}{sub {phi}}{similar to}({ital H}/{ital r}){sup 6/5}{ital P}.

• DOE Contract Number: FG05-88ER53267
• OSTI ID: 5597476
• Journal Information: Physics of Fluids B; (United States), Vol. 3:8; ISSN 0899-8221
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ACCRETION DISKS
ANGULAR MOMENTUM
ASTROPHYSICS
ASYMMETRY
ENERGY TRANSFER
HELICITY
INSTABILITY
IONIZATION
MAGNETIC FIELDS
NONLINEAR PROBLEMS
RADIATION PRESSURE
REVIEWS
SATURATION
TEMPERATURE EFFECTS
THICKNESS
TOROIDAL CONFIGURATION
TURBULENCE
VISCOSITY
WAVE FORMS
ANNULAR SPACE
CLOSED CONFIGURATIONS
CONFIGURATION
DIMENSIONS
DOCUMENT TYPES
MAGNETIC FIELD CONFIGURATIONS
PARTICLE PROPERTIES
SPACE
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