J/A+A/600/A3 Comet ion acoustic waves code (Gunell+, 2017)
Ion acoustic waves at comet 67P/Churyumov-Gerasimenko.
Observations and computations.
Gunell H., Nilsson H., Hamrin M., Eriksson A., Odelstad E., Maggiolo R.,
Henri P., Vallieres X., Altwegg K., Tzou C.-Y., Rubin M., Glassmeier K.-H.,
Stenberg Wieser G., Simon Wedlund C., De Keyser J., Dhooghe F.,
Cessateur G., Gibbons A.
<Astron. Astrophys. 600, A3 (2017)>
=2017A&A...600A...3G 2017A&A...600A...3G (SIMBAD/NED BibCode)
ADC_Keywords: Comets ; Models
Keywords: comets: general - comets: individual: 67P/Churyumov-Gerasimenko -
instrumentation: detectors - methods: analytical - plasmas - waves
Abstract:
On 20 January 2015 the Rosetta spacecraft was at a heliocentric
distance of 2.5AU, accompanying comet 67P/Churyumov-Gerasimenko on
its journey toward the sun. The Ion Composition Analyser (RPC-ICA),
other instruments of the Rosetta Plasma Consortium, and the ROSINA
instrument made observations relevant to the generation of plasma
waves in the cometary environment.
Observations of plasma waves by the Rosetta Plasma Consortium Langmuir
probe (RPC-LAP) can be explained by dispersion relations calculated
based on measurements of ions by the Rosetta Plasma Consortium Ion
Composition Analyser (RPC-ICA), and this gives insight into the
relationship between plasma phenomena and the neutral coma, which is
observed by the Comet Pressure Sensor of the Rosetta Orbiter
Spectrometer for Ion and Neutral Analysis instrument (ROSINA-COPS).
We use the simple pole expansion technique to compute dispersion
relations for waves on ion timescales based on the observed ion
distribution functions. These dispersion relations are then compared
to the waves that are observed. Data from the instruments RPC-LAP,
RPC-ICA and the mutual impedance probe (RPC-MIP) are compared to find
the best estimate of the plasma density.
We find that ion acoustic waves are present in the plasma at comet
67P/Churyumov-Gerasimenko, where the major ion species is H2O+.
The bulk of the ion distribution is cold, kBTi=0.01eV when the ion
acoustic waves are observed. At times when the neutral density is
high, ions are heated through acceleration by the solar wind electric
field and scattered in collisions with the neutrals. This process
heats the ions to about 1eV, which leads to significant damping of
the ion acoustic waves.
In conclusion, we show that ion acoustic waves appear in the H2O+
plasmas at comet 67P/Churyumov-Gerasimenko and how the interaction
between the neutral and ion populations affects the wave properties.
Description:
The general package for dispersion relations and fluctuation
calculations using simple pole expansions is in the directory named
simple. The directory ThisPaper contains files that are specific to
the present paper.
ThisPaper/startup.m sets up paths and physical constants.
ThisPaper/aa16appendix.m plots the figure in the appendix.
ThisPaper/aa16figs7to9.m performs the computations behind Figs. 7-9
and plots those figures.
ThisPaper/aa16fig6.m performs the computations behind Fig. 6
and plots it.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
ThisPaper/* . 5 Files specific to the present paper
simple/* . 20 General package for dispersion relations and
fluctuation calculations using simple pole
expansions
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Acknowledgements:
Herbert Gunell, herbert.gunell(at)physics.org
(End) Patricia Vannier [CDS] 23-Jan-2017