GEOTAIL ENERGETIC PARTICLES AND ION COMPOSITION INSTRUMENT

The Energetic Particles and Ion Composition (EPIC) instrument, flown onboard the GEOTAIL satellite, is designed to measure the characteristics of particle populations important to understanding the make-up and dynamics of the earth's geomagnetic tail. To do this, EPIC, a joint endeavor between the Technical University of Braunschweig (TUB), the University of Maryland (UM), and The Johns Hopkins University Applied Physics Laboratory (JHU/APL), is made up of five subassemblies: the Supra-Thermal Ion Composition Spectrometer (STICS) sensor, the STICS analog electronics, the Ion Composition System (ICS) sensor, the ICS analog electronics, and the Data Processing Unit (DPU). The STICS sensor provides approximately 4pi angular coverage, composition and spectral observations, with charge state determination for all ions from 30 keV to 230 keV/e, and mass per charge measurements greater-than-or-equal-to 7.5 keV/e. The ICS sensor provides flux, composition, spectra, and angular distributions over two polar angles of the elemental species protons through iron from greater-than-or-equal-to 50 keV to 3 MeV along with angular distributions in one plane of electron fluxes >32 keV and >1 10 keV. The DPU provides the capability of numerous operating modes from which a small number will be selected to optimize data collection throughout the many phases of the GEOTAIL mission. To date the EPIC instrument performance has been very successful. In this paper we describe the instrument, its operation, and show some of our early results.