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SUMMARY:Transport of magnetic flux in astrophysical accretion discs - Phil
 ip K. C. Leung
DTSTART:20181120T130000Z
DTEND:20181120T140000Z
UID:TALK112096@talks.cam.ac.uk
CONTACT:Dr William Béthune
DESCRIPTION:The evolution of a large-scale poloidal magnetic field is in a
 n accretion disc is an important problem because it determines the launchi
 ng of winds and the feasibility of the magnetorotational instability to ge
 nerate turbulence or channel flows. Recent studies\, both semi-analytic an
 d numerical simulations\, have highlighted the crucial role non-ideal MHD 
 effects (Ohmic resistivity\, Hall drift and ambipolar diffusion)\, relevan
 t in the protoplanetary disc context\, might play in magnetic flux evoluti
 on in the disc. In some cases these magnetic effects led to the formation 
 of large scale structures (rings and gaps)\, which may be relevant for pla
 net formation theory. We investigated the flux transport in discs through 
 one-dimensional semi-analytic models in the vertical direction\, exploring
  regimes where different physical effects dominate. Flux transport rates a
 nd vertical structure profiles are calculated for a range of diffusivities
  and disc magnetisations. We found similar results to previous studies in 
 how Ohmic and ambipolar diffusivities drive radially outward flux transpor
 t with an inclined field\, while a wind would drive inward transport. The 
 Hall effect offers a correctional contribution to the flux transport given
  a background Ohmic and/or ambipolar diffusivity\, and drives no flux tran
 sport when it is the only non-ideal effect present. We report the surprise
  finding of a non-zero laminar $\\alpha$ in the vertical structures of our
  models in the absence of wind and viscosity\, suggesting that diffusiviti
 es have a role in disc accretion as well. Future plans for further semi-an
 alytic work and shearing box simulations will be presented. 
LOCATION:MR14\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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