GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-11 GLAST...

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

[email protected]

Gamma-ray Large Gamma-ray Large Area Space Area Space TelescopeTelescope



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 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!



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)



33rdrd EGRET Source Catalog EGRET Source Catalog

271 sources 172 sources are unidentified



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.



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.



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 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 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



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



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.



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.



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



CalorimeterCalorimeter

CsI Crystals (Sweden)

Photo-Diodes (HPK)

Detector Assembly (NRL/Swales)

C-Composite Structure (France) Electronics & Assembly (NRL)

17283456 1728

18 18



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



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



Engineering Model HardwareEngineering Model Hardware

Prototypes completed this year, for functional and environmental testing.

Tracker (partial)

Calorimeter

TEM

Tracker



Example Engineering Model Cosmic-RayExample Engineering Model Cosmic-Ray

6 Tracker Layers Instrumented

Fully Instrumented Calorimeter



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-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.



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.

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GLAST Large Area Telescope (LAT) Science Instrument Robert P. JohnsonIEEE NSS 2003 N42-11 GLAST...

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