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Combined energy and pitch angle diffusion of pickup ions at Comet HalleyIt is well known that cometary pickup ions, e.g., H2O(+), OH(+), O(+), CO(+), H(+), initially form a ring-beam distribution in the solar wind reference frame, which is highly unstable to the growth of MHD waves (such as ion-cyclotron waves). The low-frequency magnetic fluctuations (or waves), which were observed upstream of Comet Halley, cannot only pitch-angle-scatter the pickup ions so that the distribution becomes at least partially isotropized, but also stochastically accelerate the ions, resulting in the energetic ion populations observed in the vicinity of Comet Halley. Here, numerical solutions of the quasi-linear diffusion equation were used to investigate the cometary ion pickup process at Comet Halley. Both pitch angle and energy diffusion are taken into account. Many quasi-linear models of cometary pickup ions exist which involve one type of diffusion or the other but not both types at once. It is found that the pitch angle scattering occurs faster than the energy diffusion, as expected. Moreover, the results demonstrate that the distribution of accelerated energetic ions is more isotropic than that of ions which have just been picked up. In fact, the ion distribution function on the initial pickup shell is quite anisotropic, even close to the Comet-Halley bow shock.
Document ID
19910048786
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Ye, Gang
(Kansas Univ. Lawrence, KS, United States)
Cravens, T. E.
(Kansas, University Lawrence, United States)
Date Acquired
August 14, 2013
Publication Date
April 1, 1991
Publication Information
Publication: Journal of Geophysical Research
Volume: 96
ISSN: 0148-0227
Subject Category
Astrophysics
Accession Number
91A33409
Funding Number(s)
CONTRACT_GRANT: NAGW-1559
CONTRACT_GRANT: NSF ATM-89-96116
Distribution Limits
Public
Copyright
Other

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