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CO2 impact ionization-driven plasma instability observed by Pioneer Venus Orbiter at PeriapsisObservations of enhanced ac electric field noise about Pioneer Venus periapsis are shown to be related to spacecraft-generated impact ionization of the ambient CO2. The frequency of the electric field noise is found to peak in the vicinity of the CO2(+) ion plasma frequency and to closely follow the form of the neutral CO2 density profile. When the electric field noise in all channels is normalized by the square root of the CO2 number density, the ratio is constant. Since the impact electron density measured by the Pioneer Venus Langmuir probe, is observed to scale directly with the neutral CO2, the growth of the electric field amplitude is found to be linear in time with a growth rate proportional to the CO2(+) ion plasma frequency. On the basis of these results the impact ionization-driven instability is shown to be the ion acoustic instability. Implications for the lack of observations by Pioneer Venus of reflected-O(+)-driven instabilities, as have been proposed for the space shuttle, are discussed.
Document ID
19850058064
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Curtis, S. A.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Brace, L. H.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Niemann, H. B.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Scarf, F. L.
(TRW, Inc. Applied Technology Div., Redondo Beach, CA, United States)
Date Acquired
August 12, 2013
Publication Date
July 1, 1985
Publication Information
Publication: Journal of Geophysical Research
Volume: 90
ISSN: 0148-0227
Subject Category
Lunar And Planetary Exploration
Accession Number
85A40215
Distribution Limits
Public
Copyright
Other

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