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CATEGORIES:DAMTP Astrophysics Seminars
SUMMARY:Dynamo action\, magnetorotational instability\, Al
 fvén waves: Theory and experiments on astrophysica
 l magnetohydrodynamics - Frank Stefani (Helmholtz-
 Zentrum Dresden)
DTSTART;TZID=Europe/London:20240205T140000
DTEND;TZID=Europe/London:20240205T150000
UID:TALK209035AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/209035
DESCRIPTION:The homogeneous dynamo effect in moving electrical
 ly conducting fluids\, such as liquid metals or pl
 asmas\, is responsible for magnetic-field generati
 on in planets\, stars and galaxies. Magnetic field
 s\, in turn\, can promote cosmic structure formati
 on by destabilizing\, via the magnetorotational in
 stability (MRI)\, rotational flows in accretion di
 sks that otherwise would be hydrodynamically stabl
 e. \n\nFor a long time\, those topics have been th
 e subject of purely theoretical and numerical rese
 arch. This situation changed in 1999 when the thre
 shold of magnetic-field self-excitation was crosse
 d in two large-scale liquid-sodium experiments in 
 Riga and Karlsruhe. Later\, the VKS dynamo experim
 ent in Cadarache successfully reproduced field rev
 ersals and excursions that are of great geophysica
 l interest. Various types of the MRI were studied 
 in liquid metal experiments at the Princeton Plasm
 a Physics Laboratory and at Helmholtz-Zentrum Dres
 den-Rossendorf (HZDR). A liquid-rubidium experimen
 t at the Dresden High Magnetic Field Laboratory (H
 LD) reached the “magic point” of coinciding Alfvén
  and sound speeds\, which is thought to play a key
  role for the heating of the solar corona.\n\nAfte
 r a short introduction to the basic equations of m
 agnetohydrodynamics\, the lecture gives an overvie
 w about previous and future liquid metal experimen
 ts on dynamo action\, Alfvén waves\, and magnetica
 lly triggered flow instabilities such as the MRI. 
 Special focus lies on a precession driven dynamo e
 xperiment that is presently being constructed in f
 rame of the DRESDYN project at HZDR. Closely relat
 ed to this\, some emphasis is placed on the potent
 ial role of various astronomical forcings in trigg
 ering reversals of the geodynamo or even synchroni
 zing the solar\ndynamo.
LOCATION:MR14 DAMTP and online
CONTACT:Roger Dufresne
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