The electron and ion spectrometer (EIS) is one of the fourteen instruments onboard the Nozomi spacecraft, a Mars orbiter, launched on July 4, 1998. EIS consists of two kinds of telescopes (TOF E and ΔE E telescopes) designed to measure the fluxes of electrons and ions in the energy range from ∼40 keV to a few MeV. The ΔE-E telescopes are used to measure electrons and protons, while the TOF-E telescope is mainly used to measure He, CNO-group, NeMgSi-group, and Fe-group. In this paper, (a) the objectives of this experiment, (b) the details of the instrument and (c) initial results of the observation in interplanetary space are described.
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