About EPAM Data




Sensor Full Name Measured Species Measured Quantities Energy Range (MeV/nuc.) Measurement Technique

EPAM

Electron, Proton & Alpha Monitor Ions, e-, H, He, CNO, Fe Group Z, M, E 0.05 - 5.0 (ions)
0.04 - 0.31 (e-)
0.2 - 93 (atomic species)
dE/dx - E

The EPAM Instrument on ACE

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.

For more information about the EPAM instrument, visit the EPAM Home Page, at JHU/APL.


EPAM Data Description

Release notes for EPAM level 2 data - provided by the EPAM instrument team. All users of EPAM data should read these notes.

Note: The ACE Science Center provides spin-averaged EPAM fluxes (intensities) at 5-minute, hourly, and daily cadences as standard ACE EPAM Level 2 Data Products.
A more comprehensive set of EPAM data products is provided by Fundamental Technologies, LLC.

Time Data
All Level 2 data records for all ACE instruments contain timing information in the same format. The format of the timing information is described here.

Ion and Electron Fluxes
EPAM Level 2 data are organized into yearly data files. The Level 2 data contains time averages of energetic charged particle fluxes over the following time periods:

A flux value of -999.9 indicates bad or missing data.

Flux Uncertainties
Flux data uncertainties are derived from statistical (counting) errors only. The uncertainties are fractional uncertainties, and are given as 1/sqrt(N), where N is the number of events in the averaging period. For no events, an uncertainty value of -999.9 is given.

Quality Data
livetime - number of seconds of the averaging period during which the instrument was collecting data.

Download EPAM level 2 data

EPAM Energy passbands and geometric factors

LEMS30 Data

The LEMS30 telescope, (Low-Energy Magnetic Spectrometer), measures ions. The LEMS30 sensor is oriented at 30 degrees from the spin axis.

A rare-earth magnet in front of the LEMS30 detector sweeps out any electrons with energy below about 500 keV. These electrons are measured in the B detector which is located at the back of the CA60 telescope assembly and are referred to as DE30 electrons. The LEMS30 detector is a 200 micron, totally depleted, solid-state, silicon surface barrier detector. The geometrical factor for the LEMS30 ions is 0.428 (cm2*sr). The eight channels from the LEMS30 detector are P1, P2, P3, P4, P5, P6, P7, P8. Energy passbands and geometric factors

Note: After DOY 302, 2003, the P1-P6 channels contain fill data (-999.9). This is due to a sudden noise increase in the detector, which makes the output from these channels unreliable.

DE30 Data

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 four channels from the DE30 detector are DE1, DE2, DE3, DE4. Energy passbands and geometric factors

CA60 Data

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. Energy passbands and geometric factors

Channel

Species
Group

Z

W1

H

1

W2

H

1

W3

He

2

W4

He

2

W5

O

6-9

W6

O

6-9

W7

Fe

10-28

W8

Fe

10-28

Note: ACE Level 2 EPAM data only includes channels W3 - W8 at this time.

The above table lists the detailed information for each group. Defined for each energy channel W are the dominant species, and the atomic number response were appropriate. An example of the multiplicity of species for a given species group is given by the O-species group. This group is defined by the rate channels denoted W5 and W6 and is dominated by oxygen; however, there is also a significant contribution from Carbon and Nitrogen. This group is therefore also identified as the CNO group. Similarly, the Fe-group is made up of all species with (9 < Z < 29), but again iron is the dominant species.

LEFS60 Data

The LEFS60 detector, (Low Energy Foil Spectrometer), measures ions and electrons with a look angle of 60 degrees to the spin axis. An aluminized Parylene foil is used to absorb ions with energies below approximately 350 keV, while allowing electrons with energies above about 35 keV to pass through to the solid-state detector. The geometrical factor for the LEFS60 telescope is 0.397 (cm2*sr). The seven channels from the LEFS60 detector are E1', E2', E3', E4', FP5', FP6', FP7'. Energy passbands and geometric factors

WARTD60 Data

The WARTD60 is a special part of the CA60, (Composition Aperture) and measures ions above certain energy thresholds. These 4 channels measure integral flux, not differential flux as the other EPAM detectors. The four channels from the WARTD60 detector are Z2, Z2A, Z3, Z4.

LEMS120 Data

The LEMS120 detector, (Low-Energy Magnetic Spectrometer), measures ions at 120 degrees from the spacecraft spin axis. A rare-earth magnet in front of the detector sweeps out any electrons with energy below about 500 keV. The geometrical factor for the LEMS120 telescope is 0.428 (cm2*sr). The eight channels from the LEMS120 detector are P1', P2', P3', P4', P5', P6', P7', P8'. Energy passbands and geometric factors

LEFS150 Data

The LEFS150 detector, (Low Energy Foil Spectrometer), measures electrons with energies less than about 350 keV and ions with a look direction of 150 degrees from the spin axis. An aluminized Parylene foil is used to absorb ions with energies below approximately 350 keV, while allowing electrons with energies above about 35 keV to pass through to the solid-state detector. The geometrical factor for the LEFS150 telescope is 0.397 (cm2*sr). The seven channels from the LEFS150 detector are E1, E2, E3, E4, FP5, FP6, FP7. Energy passbands and geometric factors

Note: After DOY 78, 1998, the E1, E2 and E3 channels contain fill data (-999.9). This is due to a sudden noise increase in the detector, which makes the output from these channels unreliable.


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Last Updated: 14 August, 2007

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