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| Titel |
Effects of Neutral Collisions and Charge Exchange to Titan Plasma Interaction |
| VerfasserIn |
I. Sillanpää, R. E. Johnson |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250064463
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| Zusammenfassung |
| Our new hybrid simulations for Titan, which take into account the elastic collisions between
ions and the neutral gas at Titan, show that even above the exobase newly created (or
escaping ionospheric) ions transfer most of their energy to the neutrals via ion neutral
collisions. This is due to the extended nature of Titan’s exosphere.
We used SRIM [1] cross sections for hydrogen and oxygen ions in nitrogen gas to
calculate proper estimates for the cross sections for the five ions species used in the
HYB-Titan hybrid model [2, see also 3], namely H+, H2+, O+, CH4+, and N2+.
The N2 density profile used was from INMS measurements over a dozen or so
flybys.
The results indicate a decrease in both the ion energies and fluxes for the ambient flow
ions that reach Titan’s exobase often by about a third. Results from the simulations with
the elastic collisions will be described in detail as well as the implications of the
ion-neutral collisions for the heating of Titan’s neutral corona and atmospheric escape
[4].
In addition, we are studying the effect the charge exchange reactions for O+ has together
and without the neutral collision scheme. We model three reactions
A) O+ + N2 -> O + N2+ Charge Exchange or CT (O+ destroyed, N2+
created)
B) O+ + N2 -> O + N+ + N Dissociative CT (O+ destroyed, N+ created)
C) O+ + N2 -> O+ + N+ N+ Ionization (N+ created, no effect on direction or
energy of O+)
All reaction cross sections have energy dependence. Neutral particles are not created, but
the total ENA energy is recorded as well as the resulting reaction rates. We expect to present
first results of modeling these reactions.
References
[1] Stopping and Range of Ions in Matter (SRIM), Monte Carlo software by James F.
Ziegler (online at http://www.srim.org/ )
[2] Sillanpää, I., Hybrid Modelling of Titan’s Interaction with the Magnetosphere of
Saturn, Ph.D. dissertation, Finnish Meteorological Contributions, 68, Yliopistopaino,
Helsinki, 2008. (online at http://urn.fi/URN:ISBN:978-951-697-660-3)
[3] Sillanpää, I., D. Young, F. Crary, M. Thomsen, D. Reisenfeld, J-E. Wahlund, C.
Bertucci, E. Kallio, R. Jarvinen, and P. Janhunen, Cassini Plasma Spectro¬meter and
Hybrid Model Study on Titan’s Interaction: Effect of Oxygen Ions, J. Geophys. Res.,
doi:10.1029/2011JA016443, 2011.
[4] Johnson, R.E., O.J. Tucker, M. Michael, E.C. Sittler, H.T. Smith, D.T. Young, and J.H.
Waite, Mass Loss Processes in Titan’s Upper Atmosphere, Chap. 15 in "Titan from
Cassini-Huygens" (eds. R.H. Brown et al.) pp. 373-391, 2009. |
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