Astrophysical Dynamos
Eric Blackman
University of Rochester
September 25, 2006, 4PM, Steward N210
Dynamo theory describes the amplification and sustenance of magnetic
fields in turbulent plasmas and magneto-fluids and has been an topic of
active research for over 50 years. I will distinguish and compare
different types of dynamos and identify some long standing research
directions. One class of dynamos focuses on understanding the origin and
saturation of large scale magnetic fields such as those observed in the
Sun and Galaxy, and those likely present in jet-mediating accretion disks.
Recent progress in large scale dynamo theory has benefitted from focusing
on a conserved quantity called "magnetic helicity." I will discuss its
meaning and role and how it leads to thinking about the origin of large
scale magnetic fields as two coupled but distinct processes: velocity
driven field amplification of magnetic fields inside the rotators,
followed by magnetically dominated relaxation in their coronae. The
concepts have broad applicability to stellar and accretion disk engines,
the solar cycle, and share unifying principles with dynamos in laboratory
plasmas.
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