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| Titel |
Revisiting the theory of the evolution of pick-up ion distributions: magnetic or adiabatic cooling? |
| VerfasserIn |
H. J. Fahr  |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 25, no. 12 ; Nr. 25, no. 12 (2008-01-02), S.2649-2659 |
| Datensatznummer |
250015971
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| Publikation (Nr.) |
 copernicus.org/angeo-25-2649-2007.pdf |
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| Zusammenfassung |
| We study the phasespace behaviour of heliospheric pick-up
ions after the time of their injection as newly created ions into the solar
wind bulk flow from either charge exchange or photoionization of
interplanetary neutral atoms. As interaction with the ambient MHD wave fields
we allow for rapid pitch angle diffusion, but for the beginning of this paper
we shall neglect the effect of quasilinear or nonlinear energy diffusion
(Fermi-2 acceleration) induced by counterflowing ambient waves. In the
up-to-now literature connected with the convection of pick-up ions by the
solar wind only adiabatic cooling of these ions is considered which in the
solar wind frame takes care of filling the gap between the injection energy
and energies of the thermal bulk of solar wind ions. Here we reinvestigate the
basics of the theory behind this assumption of adiabatic pick-up ion reactions
and correlated predictions derived from it. We then compare it with the new
assumption of a pure magnetic cooling of pick-up ions simply resulting from
their being convected in an interplanetary magnetic field which decreases in
magnitude with increase of solar distance. We compare the results for pick-up
ion distribution functions derived along both ways and can point out essential
differences of observational and diagnostic relevance. Furthermore we then
include stochastic acceleration processes by wave-particle interactions. As we
can show, magnetic cooling in conjunction with diffusive acceleration by
wave-particle interaction allows for an unbroken power law with the unique
power index γ=−5 beginning from lowest velocities up to highest energy
particles of about 100 KeV which just marginally can be in resonance with
magnetoacoustic turbulences. Consequences for the resulting pick-up ion
pressures are also analysed. |
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