Solar Wind Electron Proton Alpha Monitor (SWEPAM) for the Advanced Composition Explorer

The Solar Wind Electron Proton Alpha Monitor (SWEPAM) experiment provides t he bulk solar wind observations for the Advanced Composition Explorer (ACE) . These observations provide the context for elemental and isotopic composi tion measurements made on ACE as well as allowing the direct examination of numerous solar wind phenomena such as coronal mass ejections, interplaneta ry shocks, and solar wind fine structure, with advanced, 3-D plasma instrum entation. They also provide an ideal data set for both heliospheric and mag netospheric multi-spacecraft studies where they can be used in conjunction with other, simultaneous observations from spacecraft such as Ulysses. The SWEPAM observations are made simultaneously with independent electron and i on instruments. In order to save costs for the ACE project, we recycled the flight spares from the joint NASA/ESA Ulysses mission. Both instruments ha ve undergone selective refurbishment as well as modernization and modificat ions required to meet the ACE mission and spacecraft accommodation requirem ents. Both incorporate electrostatic analyzers whose fan-shaped fields of v iew sweep out all pertinent look directions as the spacecraft spins. Enhanc ements in the SWEPAM instruments from their original forms as Ulysses spare instruments include (1) a factor of 16 increase in the accumulation interv al (and hence sensitivity) for high energy, halo electrons; (2) halving of the effective ion-detecting CEM spacing from similar to 5 degrees on Ulysse s to similar to 2.5 degrees for ACE; and (3) the inclusion of a 20 degrees conical swath of enhanced sensitivity coverage in order to measure suprathe rmal ions outside of the solar wind beam. New control electronics and progr amming provide for 64-s resolution of the full electron and ion distributio n functions and cull out a subset of these observations for continuous real -time telemetry for space weather purposes.