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Optimization of Neutral Atom ImagersThe interactions between plasma structures and neutral atom populations in interplanetary space can be effectively studied with energetic neutral atom imagers. For neutral atoms with energies less than 1 keV, the most efficient detection method that preserves direction and energy information is conversion to negative ions on surfaces. We have examined a variety of surface materials and conversion geometries in order to identify the factors that determine conversion efficiency. For chemically and physically stable surfaces smoothness is of primary importance while properties such as work function have no obvious correlation to conversion efficiency. For the noble metals, tungsten, silicon, and graphite with comparable smoothness, conversion efficiency varies by a factor of two to three. We have also examined the way in which surface conversion efficiency varies with the angle of incidence of the neutral atom and have found that the highest efficiencies are obtained at angles of incidence greater then 80deg. The conversion efficiency of silicon, tungsten and graphite were examined most closely and the energy dependent variation of conversion efficiency measured over a range of incident angles. We have also developed methods for micromachining silicon in order to reduce the volume to surface area over that of a single flat surface and have been able to reduce volume to surface area ratios by up to a factor of 60. With smooth micro-machined surfaces of the optimum geometry, conversion efficiencies can be increased by an order of magnitude over instruments like LENA on the IMAGE spacecraft without increase the instruments mass or volume.
Document ID
20090006861
Acquisition Source
Goddard Space Flight Center
Document Type
Conference Paper
Authors
Shappirio, M.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Coplan, M.
(Maryland Univ. College Park, MD, United States)
Balsamo, E.
(McDaniel Coll. Westminster, MD, United States)
Chornay, D.
(Maryland Univ. College Park, MD, United States)
Collier, M.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Hughes, P.
(Maryland Univ. College Park, MD, United States)
Keller, J.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Ogilvie, K.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Williams, E.
(Maryland Univ. College Park, MD, United States)
Date Acquired
August 24, 2013
Publication Date
December 12, 2008
Subject Category
Astrophysics
Meeting Information
Meeting: American Geophysical Union Meeting
Location: San Francisco, CA
Country: United States
Start Date: December 12, 2008
End Date: December 19, 2008
Funding Number(s)
CONTRACT_GRANT: NASA ACT-05-40
Distribution Limits
Public
Copyright
Other

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