Astrophysical magnetic fields and non-Linear Dynamo theory

Brandenburg, Axel ; Subramanian, Kandaswamy (2005) Astrophysical magnetic fields and non-Linear Dynamo theory Physics Reports, 417 (1-4). pp. 1-209. ISSN 0370-1573

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The current understanding of astrophysical magnetic fields is reviewed, focusing on their generation and maintenance by turbulence. In the astrophysical context this generation is usually explained by a self-excited dynamo, which involves flows that can amplify a weak 'seed' magnetic field exponentially fast. Particular emphasis is placed on the nonlinear saturation of the dynamo. Analytic and numerical results are discussed both for small scale dynamos, which are completely isotropic, and for large scale dynamos, where some form of parity breaking is crucial. Central to the discussion of large scale dynamos is the so-called alpha effect which explains the generation of a mean field if the turbulence lacks mirror symmetry, i.e. if the flow has kinetic helicity. Large scale dynamos produce small scale helical fields as a waste product that quench the large scale dynamo and hence the alpha effect. With this in mind, the microscopic theory of the alpha effect is revisited in full detail and recent results for the loss of helical magnetic fields are reviewed.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Magnetohydrodynamics; Dynamos; Turbulence; Mean Field Theory
ID Code:68029
Deposited On:02 Nov 2011 03:15
Last Modified:02 Nov 2011 03:15

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