RAPID - THE IMAGING ENERGETIC PARTICLE SPECTROMETER ON CLUSTER

The RAPID spectrometer (Research with Adaptive Particle Imaging Detect ors) for the Cluster mission is an advanced particle detector for the analysis of suprathermal plasma distributions in the energy range from 20-400 keV for electrons, 40 keV-1500 keV (4000 keV) for hydrogen, an d 10 keV nucl(-1)-1500 keV (4000 keV) for heavier ions. Novel detector concepts in combination with pin-hole acceptance allow the measuremen t of angular distributions over a range of 180 degrees in polar angle for either species. Identification of the ionic component (particle ma ss A) is based on a two-dimensional analysis of the particle's velocit y and energy. Electrons are identified by the well-known energy-range relationship. Details of the detection techniques and in-orbit operati ons are described. Scientific objectives of this investigation are hig hlighted the discussion of selected critical issues in geospace.