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Particle chaos and pitch angle scatteringPitch angle scattering is a factor that helps determine the dawn-to-dusk current, controls particle energization, and it has also been used as a remote probe of the current sheet structure. Previous studies have interpreted their results under the exception that randomization will be greatest when the ratio of the two timescales of motion (gyration parallel to and perpendicular to the current sheet) is closet to one. Recently, the average expotential divergence rate (AEDR) has been calculated for particle motion in a hyperbolic current sheet (Chen, 1992). It is claimed that this AEDR measures the degree of chaos and therefore may be thought to measure the randomization. In contrast to previous expectations, the AEDR is not maximized when Kappa is approximately equal to 1 but instead increases with decreasing Kappa. Also contrary to previous expectations, the AEDR is dependent upon the parameter b(sub z). In response to the challenge to previous expectations that has been raised by this calculation of the AEDR, we have investigated the dependence of a measure of particle pitch angle scattering on both the parameters Kappa and b(sub z). We find that, as was previously expected, particle pitch angle scattering is maximized near Kappa = 1 provided that Kappa/b(sub z) greater than 1. In the opposite regime, Kappa/b(sub z) less than 1, we find that particle pitch angle scattering is still largest when the two timescales are equal, but the ratio of the timescales is proportional to b(sub z). In this second regime, particle pitch angle scattering is not due to randomization, but is instead due to a systematic pitch angle change. This result shows that particle pitch angle scattering need not be due to randomization and indicates how a measure of pitch angle scattering can exhibit a different behavior than a measure of chaos.
Document ID
19950053473
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Burkhart, G. R.
(Univ. of Colorado, Boulder, CO United States)
Dusenbery, P. B.
(Univ. of Colorado, Boulder, CO United States)
Speiser, T. W.
(Univ. of Colorado, Boulder, CO United States)
Date Acquired
August 16, 2013
Publication Date
January 1, 1995
Publication Information
Publication: Journal of Geophysical Research
Volume: 100
Issue: A1
ISSN: 0148-0227
Subject Category
Physics (General)
Accession Number
95A85072
Funding Number(s)
CONTRACT_GRANT: NSF ATM-90-02447
CONTRACT_GRANT: NAGW-1176
Distribution Limits
Public
Copyright
Other

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