Face-to-Face IDT Meeting Session 3 Characterization of the South Atlantic Anomaly for the LAT S. W. Digel

1
Face-to-Face IDT Meeting Session
3Characterization of the South Atlantic Anomaly
for the LAT S. W. Digel

• March 19, 2002
• SLAC

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Origin of the South Atlantic Anomaly

• Offset and tilt of the magnetic axis with respect
  to the rotation axis permits the intense trapped
  radiation (circulating on magnetic field lines)
  to reach relatively low altitudes in a large
  region more or less centered on the south Atlantic

http//www.estec.esa.nl/wmwww/wma/rad_env.html
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General Issues for Operation in the SAA

• Radiation damage to detectors, SEUs, latchups
• Charging of spacecraft, instruments arcing,
  overcurrent damage to high-voltage devices
• For LAT The high rate of triggers on charged
  particles within the SAA is likely to saturate
  the data acquisition system (large deadtime), and
  extracting useful celestial photons may be
  problematic anyway.

4
Options for Coping with the SAA

• SAA task force met last May
• Options defined
• GPS and a map of boundary to have LAT turn itself
  (i.e., ACD high voltage) off and on
• Stored (uploaded) commands to turn off and on
• ACD rate (possibly in a time) to define turn
  off/on times
• Dedicated SAA detector to do the same thing
• Self-protect the components
• Option 2 is a given 1 more for desired
  reliability may not be clear what the impact on
  the instrument would be of being on during SAA
  passage

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More Options

• Fly under (or around) the SAA

Inclination of orbit
30
Nominal altitude, inclination of GLAST
18
6
Representative
AP8MIN, gt1 proton cm-2 s-1 (gt1 MeV)
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Radiation Environment of the SAA
Differential Intensities at Peak

• Modeling the SAA AP8 AE8 models
• Fluxes are really anisotropic
• SAA changes size and is moving (0.3/yr to the
  west)

Trapped Electrons
Trapped Protons