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EDI (Electron Drift Instrument) measures the displacement of a weak (<1 ľA) beam of test electrons after one gyration in the ambient magnetic field. This displacement (the drift step), that is induced by electric fields or magnetic gradients, causes the beam to return to a detector on the spacecraft only when emitted in one of two precisely determined directions. By employing two beams and two detectors, these directions can be monitored continuously and the displacement obtained by triangulation.
For small magnetic fields the triangulation degenerates and the displacement is obtained instead from the difference in the travel times of the electrons in the two beams. As a by-product, the measured times-of-flight provide a precise measurement of the magnetic field magnitude. Furthermore, EDI measurements can be used at a high-time resolution monitor of the ambient electrons.
In Graz, the physical interpretation of the EDI data focuses on the dynamics of the Earth's magnetotail.
EDI was built by an international consortium under the leadership of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany. More information is found at the University of New Hampshire.
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