Electron, Proton, and Alpha Monitor on the advanced composition explorer spacecraft

The Electron, Proton, and Alpha Monitor (EPAM) is designed to make measurem ents of ions and electrons over a broad range of energy and intensity. Thro ugh five separate solid-state detector telescopes oriented so as to provide nearly full coverage of the unit-sphere, EPAM can uniquely distinguish ion s (E(i)greater than or similar to 50 keV) and electrons (E(e)greater than o r similar to 40 keV) providing the context for the measurements of the high sensitivity instruments on ACE. Using a Delta E x E telescope, the instrum ent can determine ion elemental abundances (E greater than or similar to 0. 5 MeV nucl(-1)). The large angular coverage and high time resolution will s erve to alert the other instruments on ACE of interesting anisotropic event s. The experiment is controlled by a microprocessor-based data system, and the entire instrument has been reconfigured from the HI-SCALE instrument on the Ulysses spacecraft. Inflight calibration is achieved using a variety o f radioactive sources mounted on the reclosable telescope covers. Besides t he coarse (8 channel) ion and (4 channel) electron energy spectra, the inst rument is also capable of providing energy spectra with 32 logarithmically spaced channels using a pulse-height-analyzer. The instrument, along with i ts mounting bracket and radiators weighs 11.8 kg and uses about 4.0 W of po wer. To demonstrate some of the capabilities of the instrument, some initia l performance data are included from a solar energetic particle event in No vember 1997.