Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsh13b..07h&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SH13B-07
Physics
7894 Instruments And Techniques
Scientific paper
The use of energetic neutral atoms to image plasma structures in interplanetary space has proved to be a very useful alternative to direct in situ measurements of the plasma ions*. In order for a neutral atom imager to be effective, it must have the capability of efficiently measuring both the angular and energy distributions of the detected neutral atoms. The critical element in neutral imagers is the surface that is used to convert neutral atoms to negative ions. We have examined in detail the conversion of hydrogen atoms to negatively charged hydrogen ions on tungsten and diamond-like carbon surfaces. The measurements covered a range of neutral atom kinetic energies from 20 eV to 925 eV and angles of incidence from 70° to 84°. The angular and energy distributions of the negative ions generated at the surfaces were measured both at room temperature and elevated temperatures. Total conversion efficiencies were calculated from the data. It was found that in general the angle of incidence and kinetic energy of the incident neutral atoms were accurately represented in the angular and energy distributions of the negative ions. Furthermore, conversion efficiency increased as the angle on incidence of the neutral atoms increased for a fixed incident kinetic energy. The conversion efficiency of heated surfaces was always less than that of room temperature surfaces leading to the conclusion that surface adsorbates have a large role in neutral to negative ion conversion. The application of the measurements to the design of neutral atoms imagers will be discussed. *T.E. Moore et al., Geophys. Res. Lett., 28:1143, 2001
Chornay Dennis
Collier Mark
Coplan Michael A.
Defazio J.
Hughes P. W.
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