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SUMMARY:Characterizing emergent phenomena in MRI turbulence\, using the (s
 pectral harmonic) test-field method - Oliver Gressel (Leibniz-Institut fü
 r Astrophysik Potsdam)
DTSTART:20231106T140000Z
DTEND:20231106T150000Z
UID:TALK206404@talks.cam.ac.uk
CONTACT:Roger Dufresne
DESCRIPTION:Astrophysical outflows are seen in objects ranging from compac
 t binaries up to active galactic nuclei\, and magnetized accretion disks a
 re the central engines behind these phenomena. Disk turbulence has a profo
 und effect on the evolution of the large-scale magnetic field and hence on
  the ability of the system to power its outflows. We aim to characterize t
 he turbulence coefficients emerging in local simulations of magnetorotatio
 nal (MRI) turbulence. We have generalized our diagnostics to the case of n
 ovel non-local and non-instantaneous closure relations\, accounting for an
 d extended “domain of dependence” in space\, and “memory effects” 
 in time. In concrete terms\, we obtain Fourier spectra of the effective tu
 rbulent transport coefficients as a function of oscillation frequency. The
 se are well approximated by a simple response function\, describing a fini
 te-time build-up of the electromotive force (EMF) as a result of a time-va
 riable mean magnetic field. For intermediate timescales\, we observe a sig
 nificant phase lag of the EMF compared to the causing field.
LOCATION:Streaming in MR14 and online
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