Satellite borne energetic ion mass spectrometer for three-dimensional measurement of velocity distribution.

For research of the magnetospheric plasma, we have developed a new type of energetic ion energy-mass spectrometer on board a spinning spacecraft, which is capable of measuring three-dimensional velocity distributions of different ion species simultaneously with a wide angular coverage and high time resolution. It can cover the energy-mass range of 5–400 amu keV/e, while lower-energy ions can also be measured by using preacceleration. The fan-shaped field of view is 130°×10°, with the longer dimension being divided into five sectors. The instrument consists of three major elements with axially symmetric configuration in order to cover the wide angular acceptance. The first stage is a tandem energy analyzer which consists of a spherical analyzer and a saddle-type poloidal analyzer. The second is an orange-type mass spectrometer with multiple sector fields. The third is an array of microchannel plate detectors with one-dimensional position sensitive anodes for snapshot measurement of mass distributions in different incident angles. Nearly optimum design parameters of each element are determined by means of a numerical ray-tracing simulation of ions trajectories. The instrumental characteristics are also investigated experimentally by using a calibration facility. The experimental results are generally in good agreement with those obtained by the numerical method. The present instrument can resolve the dominant ion species (H+,He2+,He+,O2+,O+) in the Earth’s magnetosphere, which play a crucial role as tracers to study the origin of plasmas. Finally, future possible improvements are also discussed. [ABSTRACT FROM AUTHOR]