Medium Energy Ion Mass and Neutral Atom Spectrometer

The primary objective of the medium energy ion mass spectrometer on the CRRES is to obtain the necessary data to construct models of the energetic ion and neutral atom (10-1500 keV) environment of the Earth's radiation belts. The spectrometer measures the energetic ion composition, energy spectrum, charge, and pitch angle distribution with good mass, temporal, and spatial resolution. The instrument principle of operation is based on ion momentum separation in a 7000-G magnetic field, followed by energy and mass defect analysis using an array of cooled silicon solid-state detectors. The architecture is parallel with simultaneous mass and energy analysis at relatively high sensitivity (100 percent duty cycle). The instrument performed as designed in orbit with the major groups of hydrogen, helium, oxygen, and neutrals clearly resolved. The energetic ion composition during the August 26, 1990, storm illustrates the instrument performance.