An electron spectrograph is described that covers electron energies from 400 eV to 200 keV with an energy resolution of 10percnt;. This overlaps the range of electrostatic deflection devices at low energy and solid state detectors at high energy. The spectrograph uses magnetic deflection of the electrons to achieve energy separation and images the full range of energies on a single plane. The magnetic circuit uses the fringing field of two axially located magnets to attain the large energy range. Six separate electron beams can be dispersed in the field, each entering the circuit from a different angle. This is a particular advantage when measuring plasma electron threehyphen;dimensional velocity distributions. The angular response of the instrument is particularly favorable and the stray magnetic field is sufficiently low to meet spacecraft requirements. Compared with electrostatic deflection devices, the spectrograph is particularly advantageous for measuring high energy electron plasma velocity distribution functions with fast time resolution at modest energy resolution.
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