On the Saturation of the Magnetorotational Instability via Parasitic Modes
by
Martin Pessah(Niels Bohr Institute, Copenhagen)
→
Europe/Stockholm
122:026
122:026
Description
The magnetorotational instability (MRI) is considered a key process for
driving efficient angular momentum transport in astrophysical disks.
Understanding its non-linear saturation constitutes a fundamental problem
in modern accretion disk theory. The large dynamical range in physical
conditions in accretion disks makes it challenging to address this problem
only with numerical simulations. I will discuss the results of recent work
analyzing the idea that (secondary) parasitic instabilities are
responsible for the saturation of the MRI. This approach enables us to
explore dissipative regimes that are relevant to astrophysical and
laboratory conditions that lie beyond the regime accessible to current
numerical simulations. I will argue that the ``saturation'' amplitude
obtained within this framework provides an estimate of the magnetic field
that can be generated by the MRI before the secondary instabilities
suppress its growth significantly. I will show that Kelvin-Helmholtz and
tearing modes are responsible for saturation at high and low Elsasser
numbers, respectively. Several features of numerical simulations designed
to address the saturation of the MRI in accretion disks surrounding young
stars and compact objects can be interpreted in terms of these findings.
