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Title: Definition of a Twelve-Point Polygonal SAA Boundaryfor the GLAST Mission

Abstract

The Gamma-Ray Large Area Space Telescope (GLAST), set to launch in early 2008, detects gamma rays within a huge energy range of 100 MeV - 300 GeV. Background cosmic radiation interferes with such detection resulting in confusion over distinguishing cosmic from gamma rays encountered. This quandary is resolved by encasing GLAST's Large Area Telescope (LAT) with an Anti-Coincidence Detector (ACD), a device which identifies and vetoes charged particles. The ACD accomplishes this through plastic scintillator tiles; when cosmic rays strike, photons produced induce currents in Photomultiplier Tubes (PMTs) attached to these tiles. However, as GLAST orbits Earth at altitudes {approx}550km and latitudes between -26 degree and 26 degree, it will confront the South Atlantic Anomaly (SAA), a region of high particle flux caused by trapped radiation in the geomagnetic field. Since the SAA flux would degrade the sensitivity of the ACD's PMTs over time, a determined boundary enclosing this region need be attained, signaling when to lower the voltage on the PMTs as a protective measure. The operational constraints on such a boundary require a convex SAA polygon with twelve edges, whose area is minimal ensuring GLAST has maximum observation time. The AP8 and PSB97 models describing the behavior ofmore » trapped radiation were used in analyzing the SAA and defining a convex SAA boundary of twelve sides. The smallest possible boundary was found to cover 14.58% of GLAST's observation time. Further analysis of defining a boundary safety margin to account for inaccuracies in the models reveals if the total SAA hull area is increased by {approx}20%, the loss of total observational area is < 5%. These twelve coordinates defining the SAA flux region are ready for implementation by the GLAST satellite.« less

Authors:
;
Publication Date:
Research Org.:
Stanford Linear Accelerator Center (SLAC)
Sponsoring Org.:
USDOE
OSTI Identifier:
915382
Report Number(s):
SLAC-TN-07-015
TRN: US0804971
DOE Contract Number:  
AC02-76SF00515
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 58 GEOSCIENCES; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; CHARGED PARTICLES; COSMIC RADIATION; DETECTION; ENERGY RANGE; GEOMAGNETIC FIELD; IMPLEMENTATION; PHOTOMULTIPLIERS; PHOTONS; PLASTIC SCINTILLATORS; RADIATIONS; SAFETY MARGINS; SENSITIVITY; TELESCOPES; Astrophysics,ASTRO

Citation Formats

Djomehri, Sabra I., and /UC, Santa Cruz /SLAC. Definition of a Twelve-Point Polygonal SAA Boundaryfor the GLAST Mission. United States: N. p., 2007. Web. doi:10.2172/915382.
Djomehri, Sabra I., & /UC, Santa Cruz /SLAC. Definition of a Twelve-Point Polygonal SAA Boundaryfor the GLAST Mission. United States. doi:10.2172/915382.
Djomehri, Sabra I., and /UC, Santa Cruz /SLAC. Wed . "Definition of a Twelve-Point Polygonal SAA Boundaryfor the GLAST Mission". United States. doi:10.2172/915382. https://www.osti.gov/servlets/purl/915382.
@article{osti_915382,
title = {Definition of a Twelve-Point Polygonal SAA Boundaryfor the GLAST Mission},
author = {Djomehri, Sabra I. and /UC, Santa Cruz /SLAC},
abstractNote = {The Gamma-Ray Large Area Space Telescope (GLAST), set to launch in early 2008, detects gamma rays within a huge energy range of 100 MeV - 300 GeV. Background cosmic radiation interferes with such detection resulting in confusion over distinguishing cosmic from gamma rays encountered. This quandary is resolved by encasing GLAST's Large Area Telescope (LAT) with an Anti-Coincidence Detector (ACD), a device which identifies and vetoes charged particles. The ACD accomplishes this through plastic scintillator tiles; when cosmic rays strike, photons produced induce currents in Photomultiplier Tubes (PMTs) attached to these tiles. However, as GLAST orbits Earth at altitudes {approx}550km and latitudes between -26 degree and 26 degree, it will confront the South Atlantic Anomaly (SAA), a region of high particle flux caused by trapped radiation in the geomagnetic field. Since the SAA flux would degrade the sensitivity of the ACD's PMTs over time, a determined boundary enclosing this region need be attained, signaling when to lower the voltage on the PMTs as a protective measure. The operational constraints on such a boundary require a convex SAA polygon with twelve edges, whose area is minimal ensuring GLAST has maximum observation time. The AP8 and PSB97 models describing the behavior of trapped radiation were used in analyzing the SAA and defining a convex SAA boundary of twelve sides. The smallest possible boundary was found to cover 14.58% of GLAST's observation time. Further analysis of defining a boundary safety margin to account for inaccuracies in the models reveals if the total SAA hull area is increased by {approx}20%, the loss of total observational area is < 5%. These twelve coordinates defining the SAA flux region are ready for implementation by the GLAST satellite.},
doi = {10.2172/915382},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed Aug 29 00:00:00 EDT 2007},
month = {Wed Aug 29 00:00:00 EDT 2007}
}

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