Physically part of the Three dimensional plasma analyzer (3DA) instrument, EPI consists of an array of
solid-state telescopes measuring electrons and ions in the energy range 20 - 226 keV and 20 - 400 keV, respectively,
in 6 energy channels and 4 angle channels at a time. During each spacecraft spin the telescopes trace out a large
fraction (70%) of the solid-angle sphere. The EPI instrument (together with the 3DA instrument) is a derivative of
the 3D Plasma and Energetic Particle Instrument on the WIND spacecraft.