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PhD Thesis defense of William Bethune
Large-scale dynamics of protoplanetary disks
William Bethune (IPAG)
Monday, July 3rd, 2pm ;
Salle Forestini (bât. OSUG-A)
Accretion on young stars requires a transport of angular momentum within protoplanetary disks. Angular momentum can be transported via turbulence, and the magnetorotational instability (MRI) provides a favored route to turbulence in accretion disks. However, the low ionization degree expected in protoplanetary disks could prevent the development of the MRI. By considering a weakly ionized plasma, local studies (of a small portion of the disk) have shown that not only turbulence could be quenched, but also that the flow could spontaneously organize itself, leading to the formation of axisymmetric structures. I realized global simulations of weakly ionized disks to study the transport of mass, angular momentum and magnetic flux through protoplanetary disks. These simulations show the predominant role played by magneto-thermal winds on the extraction of angular momentum, thereby allowing accretion. They also reveal the importance of non-ideal plasma effects in the formation of large-scale structures.
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