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A limitation of the generation of magnetic fieldsSimple arguments are put forward to show that the currents produced in disks by radiative or other types of drag forces on electrons must give rise to extraordinarily small magnetic fields. The field strengths are consistent with earlier (more complex) treatments of this class of problem, but inconsistent with the claims of recent papers in the literature. The discrepancies involve the treatment of self-induction. Ion-electron inductive coupling limits the generated magnetic field to have an associated ion Larmor radius greater than or of order of the radius of the disk, a result which follows most directly from conservation of canonical ion momentum, p + eA/c. An explicit time-dependent model for the buildup of the field leads to the same conclusion. If internal velocity gradient scales are smaller than the ion Larmor radius, and the plasma is not collision dominated, standard dynamo amplification within the disk is hardly likely to be effective. But to explain the Galactic field, dynamo amplification in a collisional plasma is also likely to be problematic. The difficulties posed by the existence of ordered Galactic-scale magnetic fields are made all the more acute by the simplicity and the scope of the discussed field limitation.
Document ID
19930071110
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Balbus, Steven A.
(Virginia Univ. Charlottesville, United States)
Date Acquired
August 16, 2013
Publication Date
August 20, 1993
Publication Information
Publication: Astrophysical Journal, Part 2 - Letters
Volume: 413
Issue: 2
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
93A55107
Funding Number(s)
CONTRACT_GRANT: NSF AST-90-21348
CONTRACT_GRANT: NAGW-2376
CONTRACT_GRANT: NAGW-1510
Distribution Limits
Public
Copyright
Other

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