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Nonlinear force-free magnetic fields: Calculation and applicatin to astrophysicsThe problem concerned in this work is that of calculating magnetic field configurations in which the Lorentz force (vector)j x (vector)B is everywhere zero, subject to specified boundary conditions. The magnetic field is represented in terms of Clebsch variables in the form (vector)B = del alpha x del beta. These variables are constant on any field line. The most appropriate choice of boundary conditions is to specify the values of alpha and beta on the bounding surface. It is proposed that the field lines move in the direction of local Lorentz force and relax towards a force-free field configuration. This concept leads to an iteration procedure for modifying the variables alpha and beta that tends asymptotically towards the force-free state. This method is first applied to a simple problem in two rectangular dimensions; the calculation shows that the convergence of magnetic field energy to a minimum state (force-free) is close to exponential. This method is then applied to study some astrophysical force-free magnetic fields, such as the structures and evolution of magnetic fields of rotating sunspots and accretion disks. The implication of the results, as related to the mechanisms of solar flares, extragalactic radio sources and radio jets, are discussed.
Document ID
19870018134
Acquisition Source
Legacy CDMS
Document Type
Thesis/Dissertation
Authors
Yang, Wei-Hong
(Stanford Univ. CA, United States)
Date Acquired
September 5, 2013
Publication Date
March 1, 1987
Subject Category
Astronomy
Report/Patent Number
NASA-CR-181196
CSSA-ASTRO-87-11
NAS 1.26:181196
Accession Number
87N27567
Funding Number(s)
CONTRACT_GRANT: NGL-05-020-272
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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