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Instrument: LEP : Low Energy Particles (Geotail)
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The objective of the LEP experiment on Geotail is to observe plasma and
energetic electrons and ions in the terrestrial magnetosphere and in the
interplanetary medium.

The LEP consists of three sensors: LEP-EA, LEP-SW, and LEP-MS, with common
electronics (LEP-E).

LEP-EA measures three-dimensional velocity distributions of hot plasma in the
magnetosphere. EA consists of two nested sets of quadrispherical electrostatic
analyzers. The inner analyzer measures electrons in the energy range from 6--36
eV, and the outer one measures positive ions from 7 eV/Q to 42 keV/Q. The field
of view for each quadrispherical analyzer covers 10 degrees by 145 degrees,
where the longer dimension is parallel to the satellite spin axis.

LEP-SW measures three-dimensional velocity distributions of solar wind ions in
the energy range from 0.1--8 keV/Q with a 270 degree spherical electrostatic
analyzer with a field of view of 5 degrees by 60 degrees.

LEP-MS is an energetic ion mass spectrometer, which provides three-dimensional
determinations of the ion composition in 32 steps over the energy range of
0--25 keV/Q. All sensors operate continuously as long as the spacecraft power
budget can allow, except for the orbit/attitude maneuvering operation.

When spacecraft power budget is not sufficient to fully operate the
instruments, priority is given to LEP-EA and LEP-E.

Although this experiment ceased operation shortly after launch, the LEP-EA and
LEP-SW portions of the experiment resumed operation in late 1993 and have
worked well ever since.

Principal Investigator:
Dr. Tsugunobu Nagai
Tokyo Institue of Technology
Earth and Planetary Sciences
Tokyo 152-8551 Japan


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Instrument Logistics
Instrument Start Date: 1992-07-24
Instrument Owner: ISAS, Japan