Advanced Composition Explorer (ACE) Electron, Proton, and Alpha Monitor (EPAM) Level 2 Data

The Electron, Proton, and Alpha Monitor (EPAM) is composed of five telescope apertures of three different types. Two Low Energy Foil Spectrometers (LEFS) measure the flux and direction of electrons above 30 keV (geometry factor = 0.397 cm2*sr), two Low Energy Magnetic Spectrometers (LEMS) measure the flux and direction of ions greater than 50 keV (geometry factor = 0.48 cm2*sr), and the Composition Aperture (CA) measures the elemental composition of the ions (geometry factor = 0.24 cm2*sr). The telescopes use the spin of the spacecraft to sweep the full sky. Solid-state detectors are used to measure the energy and composition of the incoming particles. EPAM Level 2 data is organized into 27-day time periods (Bartels Rotations - roughly one solar rotation period). For each Bartels Rotation, the Level 2 data contains time averages of energetic charged particle fluxes over the following time periods: - hourly - daily - 27 days (1 Bartels rotation) The DE30 detector, (Deflected Electrons), measures electrons at 30 degrees from the spacecraft spin axis. Electrons entering the LEMS30 detector are swept out by a rare-earth magnet and are deflected into the B detector. The 4 DE channels are pure electron channels. The geometrical factor for the DE30 channels is 0.14 (cm2*sr). The CA60 telescope, (Composition Aperture) measures ion composition. It's look-direction is oriented 60 degrees from the spacecraft spin-axis. The CA telescope is capable of determining ion composition using a dE X E detection scheme. Although the principal responsibility of EPAM is to monitor electrons, protons, and alphas, the CA provides an unambiguous determination of ion composition, unlike the LEMS detectors. The CA60 telescope is comprised of three solid state detectors, a thin, ~5 micron epitaxial silicon detector referred to as the D detector, and two thick (200 micron) totally depleted surface barrier silicon detectors known as C and B. The B detector, as measures deflected electrons from the LEMS30 head, but also acts as the anti-coincidence detector for the CA. The CA system uses log amplifiers to extend the dynamic range of the detector. These amplifiers are extremely temperature sensitive, and therefore are thermally regulated with heaters to maintain calibration. The logic used in the CA depends on slanted discriminators to define each species group. The eight Ca rate channels, denoted by the symbols W1 - W8, count all particles in a given energy/nucleon range. Multiple species may therefore be associated with a single Ca rate channel. As a result, a species group is identified by the dominant species in that group. See: http://www.srl.caltech.edu/ACE/ASC/level2/epam_l2desc.html