Composition measurements of energetic neutral atoms using the IMAGE/HENA sensor

D. G. Mitchell, D. C. Hamilton, K. Retterer, and P. Brandt

The High Energy Neutral Atom instrument (HENA; see Mitchell et al.,
2000) on the IMAGE spacecraft has, for more than a year, returned
energetic neutral atom images of the Earthıs ring current during
magnetic storms. Recent analysis of the pulse-height data has indicated
that hydrogen ENA may be separated from oxygen ENA on the basis of their
microchannel plate pulse-height, combined with the measured particle
velocity.  Taking advantage of this analysis, the HENA team generated a
new version of the HENA flight software, which now enables the
instrument to form ENA images separately for hydrogen and for oxygen. We
will show first results from HENA demonstrating this new capability,
which should permit us to follow the global dynamics of hydrogen and
oxygen independently throughout a storm.