Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Global Evolution of an Accretion Disk with Net Vertical Field: Coronal
  Accretion, Flux Transport, and Disk Winds   We report new global ideal MHD simulations for thin accretion disks (with
thermal scale height H/R=0.1 and 0.05) threaded by net vertical magnetic
fields. Our computations span three orders of magnitude in radius, extend all
the way to the pole, and are evolved for more than one viscous time over the
inner decade in radius. Static mesh refinement is used to properly resolve MRI.
We find that:(1) inward accretion occurs mostly in the upper magnetically
dominated regions of the disk, similar to the predictions from some previous
analytical work and the "coronal accretion" in previous GRMHD simulations.
Rapid inflow in the upper layers combined with slow outflow at the midplane
creates strong $R\phi$ and $z\phi$ stresses in the mean field; the vertically
integrated $\alpha\sim 0.5-1$ when the initial field has $\beta_{0}=10^3$ at
the midplane. (2) A quasi-static global field geometry is established in which
flux transport by inflows at the surface is balanced by turbulent diffusion.
The field is strongly pinched inwards at the surface. A steady-state
advection-diffusion model, with turbulent magnetic Prandtl number of order
unity, reproduces this geometry well. (3) Weak unsteady disk winds are launched
at $z/R\sim1$ with the Alfven radius $R_{A}/R_{0}\sim3$. Although the wind is
episodic, the time averaged properties are well described by steady wind
theory. Wind is not efficient at transporting angular momentum. Even with
$\beta_{0}=10^3$, only 5% of the angular momentum transport is driven by torque
from the wind, and the wind mass flux from the inner decade of radius is only
$\sim$ 0.4% of the mass accretion rate. With weaker fields or thinner disks,
the wind contributes even less. (4) Most of the disk accretion is driven by the
$R\phi$ stress from the MRI and global magnetic fields. Our simulations have
many applications to astrophysical accretion disk systems.

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The categories of this paper are: adap-org
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The categories of this paper are: hep-th
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The categories of this paper are: cond-mat
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: gr-qc
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The categories of this paper are: comp-gas
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The categories of this paper are: econ
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The categories of this paper are: chao-dyn
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The categories of this paper are: acc-phys
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The categories of this paper are: bayes-an
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The categories of this paper are: plasm-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-lat
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The categories of this paper are: physics
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The categories of this paper are: nlin