Solar Wind Electron, Proton, and Alpha Monitor

for the Advanced Composition Explorer (ACE)


Los Alamos National Laboratory
Sandia National Laboratory

The purpose of the Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) is to provide detailed knowledge of solar wind conditions to aid in the interpretation of data measured by the ion and the electron composition monitors of the ACE mission payload. This purpose is achieved by modifying the spare Ulysses BAM-E and BAM-I instruments to provide high quality measurements of electron and ion fluxes in the low-energy solar wind range (electrons: 1 to 1240 eV; ions: 0.26 to 35 keV).

Simultaneous electron and ion measurements are made using two separate instruments. Each instrument consists of a curved plate, >90 bending angle electrostatic analyzer (ESA) followed by biased channel electron multipliers (CEMs) spaced along the exit apertures of the ESAs. Different CEMs sample different portions of the fan shaped fields of view (FOV), allowing measurement of particle arrival directions relative to a spacecraft coordinate system of azimuthal and polar angle. Polar angle from the sun-pointing spin axis is given by the CEM number, while azimuthal angle is given by phase of spacecraft spin. Later, this local coordinate system is converted to a standard solar ecliptic frame of reference for data analysis.

Each instrument is powered by its own low-voltage converter, sweeping ESA high-voltage power supply, and fixed level CEM high-voltage supply. Each instrument is operated with an independent microprocessor based electronics control and data handling system.

SWEPAM is one of the four instruments that supplies data for the NOAA Real Time Solar Wind 24-hour monitoring of Space Weather.

SWEPAM is a joint project of the Space and Atmospheric Sciences Group at the Los Alamos National Laboratory (LANL) and the Center for Monitoring Systems and Technology at the Sandia National Laboratory (SNL).

For further SWEPAM information contact Phil Barker at
Los Alamos National Laboratory ACE/SWEPAM web page

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Author and Curator: Eric R. Christian (
Responsible NASA Official: Tycho von Rosenvinge (
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    This file was last modified on Thursday, 15-Feb-2001 11:50:24 EST