Chapter

Dynamo processes in stars

Leon Mestel

in Stellar Magnetism

Published in print February 2012 | ISBN: 9780199641741
Published online May 2012 | e-ISBN: 9780191738609 | DOI: http://dx.doi.org/10.1093/acprof:oso/9780199641741.003.0006

Series: International Series of Monographs on Physics

                   Dynamo processes in stars

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The term ‘dynamo action’ appears in the literature describing two related but distinct processes. When the velocity v of a conducting fluid is driven by the non-magnetic forces in the direction opposite to that of the Lorentz force, the rate of working (j × B/c) · v is negative, implying an input of energy into the magnetic field; and in the high magnetic Reynolds number domain, the input on balance exceeds the Ohmic dissipation, so that an already existing field is amplified. This chapter discusses the ‘self-exciting dynamo’ problem, which demands that there be no sources of the magnetic field B other than the currents generated by fluid motions in the presence of B. It covers laminar kinematic dynamos; the Parker model; turbulent dynamos; kinematic models of the turbulent dynamo; non-linear dynamical feedback; fundamental problems; the role of magnetic helicity in the dynamo problem; numerical simulations; and dynamo action guided by a strong pre-existing field.

Keywords: self-exciting dynamo problem; magnetic field; laminar kinematic dynamos; Parker model; turbulent dynamos; non-linear dynamical feedback; magnetic helicity

Chapter.  25939 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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