| definition |
- The Energetic Ion Spectrometer
also gathers all-sky measurements of
the energetic ions, gathering
information about their energy, their
arrival direction and their mass. EIS
can determine the mass of these
particles by measuring their velocity
and total energy. The mass information
helps determine how many protons,
helium and oxygen ions are present at
energies above those reachable by
HPCE.
To measure the energy, EIS uses a
solid state detector like the one on
FEEPS. Velocity is measured using
two very thin foils and a microchannel
plate sensor. When an ion travels
through the first foil it knocks a few
electrons off. These electrons are
deflected toward the microchannel
plate, which can amplify the signal,
sending 1 million electrons out the
other side -- just like the detectors
used in the plasma suite. The ion
continues traveling to the second foil,
where a similar process occurs. By
determining the time of flight between
electron detection at the first and
second foils, the instrument can
determine the velocity of the original
incoming particle.
Combining the comprehensive ion
measurements of EIS with the simpler
ion measurements on FEEPS allows
researchers to determine the ion
properties at a faster rate of 1/3 of a
spacecraft spin, a cadence that will
sometimes be needed in the vicinity of
fast changing reconnection sites.
EIS development was led by the Johns
Hopkins University Applied, Md.
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