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GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 1
GLAST Large Area Telescope:GLAST Large Area Telescope:
Project Overview
Robert P. JohnsonSanta Cruz Institute for Particle PhysicsPhysics DepartmentUniversity of California at Santa Cruz
LAT Tracker Subsystem ManagerRepresenting the LAT Collaboration
Gamma-ray Large Gamma-ray Large Area Space Area Space TelescopeTelescope
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 2
Gamma-ray Large Area Space TelescopeGamma-ray Large Area Space Telescope
GLAST Mission High-energy gamma-ray
observatory with 2 instruments:
Large Area Telescope (LAT)
Gamma-ray Burst Monitor (GBM)
Launch vehicle: Delta-2 class
Orbit: 550 km, 28.5o inclination
Lifetime: 5 years (minimum)
GLAST Gamma-Ray Observatory:• LAT ~20 MeV and up• GBM 20 keV to 20 MeV• Spacecraft bus (Spectrum Astro)
LAT
GBM
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 3
GLAST Science OpportunitiesGLAST Science Opportunities
Active Galactic Nuclei Isotropic Diffuse Background
Radiation Endpoints of Stellar Evolution
Neutron Stars/Pulsars Black Holes
Cosmic Ray Production: Identify sites and mechanisms
Unidentified Gamma-ray Sources Gamma-Ray Bursts Dark Matter Solar Physics DISCOVERY!
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 4
Scientific Heritage: CGRO-EGRETScientific Heritage: CGRO-EGRET
CygnusRegion
3C279
Geminga
Vela
Cosmic RayInteractions
With ISM
LMC
PKS 0528+134
PKS 0208-512
Crab
PSR B1706-44
EGRET All-Sky Map (E> 100MeV)
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 5
33rdrd EGRET Source Catalog EGRET Source Catalog
271 sources 172 sources are unidentified
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 6
LAT Source CatalogsLAT Source Catalogs
M31 > 1 GeV
GRB, AGN, 3EG + Gal. plane & halo sources
LAT Catalog: ~10,000 sources expected.
5 sources from a simulated 1-year all-sky survey.
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 7
LAT Science Capabilities - ResolutionLAT Science Capabilities - Resolution
Source localization (68% radius):Source localization (68% radius): bursts 1 to tens of arcmin
Unidentified EGRET sources 0.3’ to 1’
> 1 GeV M31 > 1 GeV
Unidentified EGRET Sources
Cygnus region (150 x 150), E > 1 GeV
Greatly improved source localization, continuous monitoring of transient behavior, and rapid GRB notification will aid the search for counterparts and the identification of sources and bursts.
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 8
Pair-Conversion Telescope PrinciplePair-Conversion Telescope Principle
• Veto counters: a signal indicates presence of a charge cosmic ray, instead of a photon.
• Tracker/Converter: heavy metal converts the photon to a positron-electron pair. The measured tracks point back to the astronomical source.
• Calorimeter: measures the photon energy
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 9
GLAST LAT Overview: DesignGLAST LAT Overview: Design
e+ e–
Si Tracker8.8105 channels<160 Watts16 tungsten layers36 SSD layersStrip pitch = 228 µmSelf triggering
Grid (& Thermal Radiators)
Data acquisition
3000 kg, 650 W (allocation)
1.8 m 1.8 m 1.0 m
20 MeV – 300 GeV
CsI CalorimeterHodoscopic array8.4 X0 8 × 12 bars
2.0 × 2.7 × 33.6 cm cosmic-ray rejection shower leakage correction
ACDSegmented scintillator tiles0.9997 efficiencyMinimal self veto
Mega-channel particle-physics detector in orbit: Low power (<650 W)! Extensive data reduction on orbit! No maintenance!
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 10
GLAST LAT Overview: PerformanceGLAST LAT Overview: Performance
e+ e–
Point Source Sensitivity:< 6 x 10-9 ph cm-2s-1
(est. performance: < 3 x 10-9 ph cm-2s-1)
~40 times EGRET’s sensitivity
Single Photon Angular Resolution:3.5o @ 100 MeV0.15o @ 10 GeV
Large Effective Area(Aeff)peak > 8,000 cm2
Wide Field of View (> 2 sr)
Good Energy ResolutionE/E ~ 10%; 100 MeV – 10 GeV ~ < 20%; 10 GeV – 300 GeV
Low dead time:< 100 s/event
Wide Energy Range: 20 MeV - >300 GeV
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 11
Anti-Coincidence Detector (NASA GSFC)Anti-Coincidence Detector (NASA GSFC)
Scintillator & Wave-Shifting Fibers
Readout Electronics
Scintillator Tiles
FibersComposite Shell
Photomultiplier Tubes & Electronics
LAT Mechanical Structure (SLAC)
Fermilab
Tile detector assembly
2 PMTs
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 12
ACD PerformanceACD Performance
Charged Particles
(MIP)
Backsplash + noise
Requirement
Measurement
Threshold setting of 0.3 MIP achieves the required efficiency (>0.9997) with low noise.
Backsplash self-veto measurements (made at CERN) indicate good margin with respect to requirements.
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 13
Silicon-Strip Tracker/ConverterSilicon-Strip Tracker/Converter
Flex-Circuit Readout Cables
36 Multi-Chip Electronics Modules (MCM)
2 mm gap between x,y SSD layers
19 Carbon-Fiber Tray Panels
Titanium Flexure Mounts
Carbon-Fiber Sidewalls (Aluminum covered)
Cu Thermal Strap
M55J/CC Closeouts
Ti Reinforced Corners
19 stiff composite panels support 18 x and 18 y layers of silicon-strip detectors and 16 layers of tungsten converter foils.
36 custom readout electronics boards, each with 1536 amplifier channels, mount on the sides of the panels to minimize inter-tower dead space.
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 14
Tracker Production OverviewTracker Production Overview
Readout CablesUCSC, SLAC (Parlex)
SSD Procurement, TestingJapan, Italy (HPK)
Electronics Fabrication, burn-in, & TestUCSC, SLAC (Teledyne)
Tracker Module Assembly and Test Italy (Alenia Spazio)
Tray Assembly and TestItaly (G&A)
SSD Ladder AssemblyItaly (G&A, Mipot)
Composite Panel, Converters, and Bias CircuitsItaly (Plyform): fabricationSLAC: CC, bias circuits, thick W, Al cores
2592
10,368
342
648
18
Module Structure ComponentsSLAC: Ti parts, thermal straps, fasteners.Italy (Plyform): Sidewalls
342
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 15
CalorimeterCalorimeter
CsI Crystals (Sweden)
Photo-Diodes (HPK)
Detector Assembly (NRL/Swales)
C-Composite Structure (France) Electronics & Assembly (NRL)
17283456 1728
18 18
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 16
Data Acquisition Electronics (SLAC)Data Acquisition Electronics (SLAC)
ACD
spare
EPU-3
EPU-2EPU-1
spare spare
Pwr Dist. Box
GASU
spare
spare
SIU-P SIU-R
LAT Mockup (upside down)
Power Supply (PS)
Tower Electronics Module (TEM)
16 PS
16 TEM
Power
Spacecraft Interface
Event Processors
Detector Systems
Thermal Radiator
Global Trigger & Signal Distribution
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 17
LAT Structural/Thermal DesignLAT Structural/Thermal Design
Aluminum Grid
Grooves for heat pipes
Radiator
Variable conductance heat pipes
Spacecraft
Rocket Shroud
More heat pipes on bottom plate directly connect the 2 radiators
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 18
Engineering Model HardwareEngineering Model Hardware
Prototypes completed this year, for functional and environmental testing.
Tracker (partial)
Calorimeter
TEM
Tracker
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 19
Example Engineering Model Cosmic-RayExample Engineering Model Cosmic-Ray
6 Tracker Layers Instrumented
Fully Instrumented Calorimeter
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 20
Sample Engineering Model ResultsSample Engineering Model Results
CalorimeterMuon EnergyDeposition
CalorimeterMuon PositionResolution0.4 cm rms
Track Polar Angle, cosmic rays
Tracker Ionization Measurement (TOT), cosmic rays (From a
single crystal)
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 21
GLAST-LAT ScheduleGLAST-LAT Schedule
2000 2001 2002 2003 2004 2005
Formulation Implementation
PDR
CDR (Joint DOE/NASA Review)
Begin LAT-S/CIntegration Launch
Build & TestFlight Units
Inst.I&T
ScheduleReserve
ObservatoryI&T
1st JointDOE/NASA Review
of GLAST LAT
2006
Build & TestEngineering Models
• LAT integration and functional test at SLAC.
• LAT environmental test at NRL (Washington).
• Spacecraft vendor: Spectrum Astro (Arizona).
• LAT-Spacecraft integration & test in Arizona.
• Launch at Cape Canaveral, Florida.
GLAST Large Area Telescope (LAT) Science Instrument
Robert P. Johnson IEEE NSS 2003 N42-1 22
ConclusionsConclusions
The LAT is presently wrapping up engineering model work and design engineering and is starting into flight-hardware production.
The LAT is a large detector array with unprecedented channel count and computing power for a space-based experiment.
The LAT will be our eye into the gamma-ray sky in the energy range from about 50 MeV to 50 GeV and will complement and work together with new ground based detectors sensitive only to higher energies (HESS, Magic, Veritas, etc.).
Working together with telescopes for all other wavelengths, GLAST will help to answer many puzzling questions in astrophysics and related particle physics by observing many of the most energetic and enigmatic objects in the universe.
By using modern detector and computing technology, GLAST will By using modern detector and computing technology, GLAST will greatly surpass the sensitivity of previous high-energy gamma-ray greatly surpass the sensitivity of previous high-energy gamma-ray telescopes, providing us with exciting discovery potential.telescopes, providing us with exciting discovery potential.