A similar time-of-flight plasma analyzer system will be flown as CODIF (COmposition and DIstribution Function analyzer) on the four CLUSTER spacecraft, as ESIC (Equator-S Ion Composition instrument) on Equator-S, and as TEAMS (Time-of-flight Energy Angle Mass Spectrograph) on FAST. These instruments will for the first time allow the 3-dimensional distribution functions of individual ion species to be determined within 1/2 or 1 spin period. This will be crucial for the study of selective energization processes in various regions of the magnetosphere. The design, test and calibration results for this instrumentation are presented. The sensor consists of a toroidal top-hat electrostatic analyzer with instantaneous acceptance of ions over 360 ^o in polar angle. For CLUSTER this range is subdivided into 2 halves with geometric factors different by a factor of 100 in order to cope with the wide dynamic range of the ion distributions throughout the magnetosphere. The measurement of the entire distribution function is completed within 1 spin. For FAST the time resolution is increased by a factor of 2 in order to focus on fast auroral phenomena by using both halves simultaneously. After post-acceleration of the incoming ions by up to 25 kV, a time-of-flight mass spectrograph discriminates the individual species. It has been demonstrated in calibration runs that the instruments can easily separate H ⁺ , He ²⁺ , He ⁺ , O ⁺ and for energies after post-acceleration of > 20 keV even O ²⁺ molecules. On board discrimination, accumulation, and moment computation allow efficient retrieval of the data stream.

Key Words Time-of-flight mass spectrometer, space instrumentation

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