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Instrument: HEP : High Energy Particles (Geotail)
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There are three scientific objectives to be studied by the HEP investigation on
Geotail: (1) plasma dynamics in the geomagnetic tail, (2) solar flare particle
acceleration and propagation, and (3) the origin, lifetime and propagation of
cosmic ray particles. There are five instruments that make up this
investigation: Low-energy particle Detector (LD), Burst Detector (BD),
Medium-energy Isotope detectors (MI-1 and MI-2), and High energy Isotope
detector (HI).

LD and BD are mainly dedicated to magnetospheric studies.

MI and HI concentrate on solar flare and cosmic ray studies.

The LD sensor system consists of three identical Imaging Ion Mass spectrometers
which use time-of-flight/energy measurement, and covers 180 degrees in polar
angle over the energy range 20--300 keV for electrons, 2 keV--1.5 MeV for
protons, and 2 keV--1.5 MeV per charge for ions. LD provides distribution of
electrons and ions with complete coverage of the unit sphere in phase space,
and electron and proton flux in 4 azimuth sectors, helium and oxygen flux at an
azimuth of 0 degrees.

The BD sensor consists of three delta-E x E telescopes which identify particles
by their energy loss and residual energy over the energy range 0.12--2.5 MeV
for electrons, 0.7--35 MeV for protons, and 0.7--140 MeV for helium. The three
telescopes each have an opening angle of 30 degrees by 45 degrees with look
directions of 30, 90, and 150 degrees to the spin axis. BD provides count rates
for high energy electrons, protons and helium, as well as electron and proton
fluxes in four 90 degree azimuth bins.

The MI and HI instruments are all silicon semiconductor detector telescopes
utilizing the well-known dE/dx x E algorithm for isotope identification: mass
and nuclear charge. The MI instrument measures elemental and isotopic
compositions of solar energetic particles and energetic particles in the
heliosphere with 2<Z<28 in the 2.4--80 MeV/nucleon energy range , and
measures the elemental composition of solar energetic particles heavier than
iron. The HI instrument also measures elemental and isotopic compositions of
solar energetic particles and galactic cosmic rays with 2<Z<28 in the
10-210 MeV/nucleon energy range.

HEP operates continuously with no change in allocated bit rate. LD has two
operational modes: normal and burst. Burst mode is an internal high speed mode
which does not change the data output.

BD has four operational modes for calculating energy spectra for electrons,
protons, and helium: 16 sectors in 1 spin (time high resolution mode), 8
sectors in 32 spins (energy high resolution mode), 8 sectors in 2 spins, and 16
sectors in 4 spins. MI and HI have only one operational mode.

Principal Investigator:
Prof. Tadayoshi Doke
Waseda University


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Instrument Logistics
Data Rate: 1.664 kbps
Instrument Start Date: 1992-07-24
Instrument Owner: Waseda University, Japan