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Ann. Geophys., 21, 1159-1166, 2003
www.ann-geophys.net/21/1159/2003/
© European Geosciences Union 2003
Reconstruction of the ion plasma parameters from the current measurements: mathematical tool
E. Séran
CETP, Observatoire de Saint-Maur, 4, Avenue de Neptune, 94107 Saint-Maur-des-Fossés, Cedex, France
Abstract. Instrument d’Analyse du
Plasma (IAP) is one of the instruments of the newly prepared ionospheric
mission Demeter. This analyser was developed to measure flows of thermal ions
at the altitude of ~ 750 km and consists of two parts: (i) retarding potential
analyser (APR), which is utilised to measure the energy distribution of the ion
plasma along the sensor look direction, and (ii) velocity direction analyser
(ADV), which is used to measure the arrival angle of the ion flow with respect
to the analyser axis. The necessity to obtain quick and precise estimates of
the ion plasma parameters has prompted us to revise the existing mathematical
tool and to investigate different instrumental limitations, such as (i) finite
angular aperture, (ii) grid transparency, (iii) potential depression in the
space between the grid wires, (iv) losses of ions during their passage between
the entrance diaphragm and the collector. Simple analytical expressions are
found to fit the currents, which are measured by the APR and ADV collectors,
and show a very good agreement with the numerical solutions. It was proven that
the fitting of the current with the model functions gives a possibility to
properly resolve even minor ion concentrations and to find the arrival angles
of the ion flow in the multi-species plasma. The discussion is illustrated by
an analysis of the instrument response in the ionospheric conditions which are
predicted by the International Reference Ionosphere (IRI) model.
Key words. Ionosphere (plasma
convection; instruments and techniques) – Space plasma physics (experimental
and mathematical techniques)
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