gamma-ray large area space telescope 15th international workshop on vertex detectors september 25 -...

Gamma-ray Large Area Gamma-ray Large Area Space TelescopeSpace Telescope

15th INTERNATIONAL WORKSHOP ON VERTEX DETECTORS

September 25 - 29, 2006Perugia, Italy

GLAST GLAST Silicon Tracker Silicon Tracker

beam test resultsbeam test results

Stefano GermaniINFN Perugia

September 25-29 2006 Perugia, Italy S. Germani - INFN Perugia

OutlineOutline

• GLAST: mission and science• The LAT instrument• The LAT Tracker• Beam test motivations• The LAT Calibration Unit• Beam test description

– Preliminary results

• Conclusions


The GLAST mission

•High energy Gamma Ray observatory 2 instruments: --Large Area Telescope (LAT) --Gamma Ray Burst Monitor (GBM)

GBM:GBM: ~10 keV – 30 MeV LAT:LAT: ~20 MeV - >300 GeV

Observe γ ray sky (10 keV –300 GeV)

All sky survay

Pointed observations Answer to important question in high energy astrophysics raised by results from EGRETLifetime 5 years (minimum)

•LAT assembly completed•Environmental tests completed•LAT is being integrated on spacecraft•Tests will continue (termal, vibrational …)•Launch end 2007


LAT science and performancesLAT science and performances

AGN spectrum

GRB emission time structure

All sky survey with large field of vew (2.4 sr)

Large energy range (20 MeV – 300 GeV) 30-100 GeV: unexplored energy window

Small dead time ~ 25 μs


The Large Area Telescope (LAT)The Large Area Telescope (LAT)

γ

e+ e-

ACD

ThermalBlanket

CalorimeterDAQ

Electronics

Tracker4x4 Towers Array

ACD (Aanti Coincidence Detector) : segmented plastic scintillator surrounding the 4x4 Traker Towers array

Tracker: silicon microstrip 18 XY layers interleaved with W converters ~ 1.5 X0

Calorimeter: 8 CsI(Tl) hodoscopic array layers ~ 8.5 X0


Space Environment Limitations and Space Environment Limitations and RequirementsRequirements

• Total mass budget: 3000 Kg• Total power budget 650 W

– Tracker 160 W

• Temperature Range +45 -15 °C• Vibrations at Launch• No consumables• Limited Data Flow (8-10 min contact/day @ 40 Mbps )

– Trigger rate: ~ 4 kHz– Downlink rate: ~ 370 Hz– Photon rate : few Hz


Tracker Design OverviewTracker Design Overview

• 16 tower modules 37 37cm2 active cross section/layer • 83m2 of Si 11500 SSD, ~ 1M channels strip pitch: 228 μm• 18 xy layers per tower

– 19 “tray” structures• 12 with 3% X0 W on top

• 4 with 18% X0 W on bottom • 3 with no converter foils

– every tray is rotated by 90° wrt the previous one: W foils followed by x,y plane of detectors

• 2mm gap between x and y oriented detectors

• Trays stack and align at their corners• Electronics on sides of trays:

– Minimize gap between towers

xx

xx

y

y

y

y

xy plane

Tkr Tower

Tray


Tracker Readout ElectronicsTracker Readout Electronics

24 64-channel amplifier-discriminator chips for each detector layer

2 readoutcontroller chipsfor each layer

Con

trol

sig

nal f

low

Control signal flow

Data flow to FPGAon DAQ TEM board.

Data flow to FPGAon DAQ TEM board.

Control signal flow

Data flow

Nine detector layers are read out on each side of each tower.

GTRC

GTFEGTFE

GTRC

GTRC

GTRC

GTRC

GTRC

9-998509A22

24 GLAST Tracker Fornt End (GTFE) chips mounted on Multi-Chip Module (MCM) on tray side 9 GLAST Tracker Readout Controllers (GTRC) per cable Time Over Threshold (TOT) from layer-OR trigger signal

Any single component (GTFE, GTRC, cable)

can fail without affecting the other


Tracker HighlightsTracker Highlights

10368 Wafers

Yeld ~ 99.5%

Tray Structure

SSD

MCM

MCM-SSD right-angle interconenction

Kapton cables 4 layers flexible circuiteach cable in the tower module is different 84-98 cm long

Each Layer passed several Electrical Tests

Each Tray passedthermal-cycle tests

Each Tower passedvibrational teststhermal vacuum tests

Difficult work but now the Tracker is complete and working well


Why Beamtest ?Why Beamtest ?

LAT performances have been studied with MC (GEANT4)

and cosmic muons

The whole energy, angle, position phase space will be available

only in orbit

Need to verify MC with real data

Sample critical/typical points for detector performances and

background rejection with particle Beam

Check basic quantities (energy deposit, hit multiplicities)

Check high level quantities(energy and direction reconstruction)

Eventually tune MC


Photons: what to check ?Photons: what to check ?

γ Energy Spectrum

γ Angular Distribution wrt LAT axis Most of γwill cross 2 Towers

Most of γ will have very low Energy

Energy and Direction reconstructionperformances scale with energy

Check absolute values and scaling especially in the low energy region

Direction reconstruction performances scales with angle

Check absolute values and scaling especially in the most probable region

Check two towers effects

Check passive material description


Background: what to check ?Background: what to check ?

Photons

Photons coming backword and hitting the CAL

can mimic a track

Protons

ACD can miss some p

Check efficiency

Protons hitting the CAL side can mimic a track

Check hadron reactions

Check efficiencies

MMS

e+

γ γ

Positrons

e+ can annihilate in MicroMeteorite Shild

Check efficiency


Check BackSplashCheck BackSplash

High energy γ/electrons produce backsplash from calorimeter

Can affect direction reconstruction

High multiplicity can saturate cables FIFO

Check hit multiplicity

Most backsplash hits in bottom layers

Direction informations in firsts track hits

Study optimal FIFO configurations(Max allowed hits/layer) and dead time

Tracker Towers readout by flex cables

Max read hits (strips) / Cable = 128

Layer read from bottom to top (FIFO)

Flex Cable


The Calibration UnitThe Calibration Unit

The LAT could not be tested on beam (environmental tests at NRL during beam time)

anyway:

Use Calibration Unit (2 complete Towers + 2 CAL)

To scan and test each single Tower for all configuartions is not feasible

Most of of the events are contained in 2 towers

Calibration Unit allows to test all the geometry related configurations

Impact position and angle

2 Towers crossing

The aim of the Beamtest is to check and eventually tune MC response


The Calibration UnitThe Calibration Unit

tower 3 tower 2 tower 1 bay 0

~ 8

20 m

m

~ 1500 mm


Where ?Where ?

Need wide energy range (50 MeV – 300 GeV)

Need several particle types( γ e± protons)

CERN

T9 line – extracted from PS

e±, p, π 0.5 – 10 GeV

H4 line – extracted from SPS

e-, p, π 10 – 280 GeV

Beam time: 24/7 – 22/8

Beam time: 4–15/9


Analysis StatusAnalysis Status

Beamtest is finished 10 days ago data analysis started but

ALL PLOTS shown in the following slides are

PRELIMINARY


Setup at T9 (CERN - PS)Setup at T9 (CERN - PS)

GLAST CU

C1 C2

S0

Sh

S1

S2

DumpMagnet

S4

SSDs

SSDsPhotons (Magnet ON) andCharged Particles (Magnet OFF)

S4

GLAST CU

C1 C2

S0

Sh

S1

S2

DumpMagnet

SSDs

SSDs

Positrons


Setup at T9 PictureSetup at T9 Picture

Magnet ScintillatorsSSDs

Dump

CU


T9 data - PhotonsT9 data - Photons

Tagged γ

Full bremsstrahlung

Use tagger to measure photon direction and energy Small momentum range and limited rate

Fixed tagger positionuse different beam energies(and Magnet B) to coverthe needed energy spectrum

Ebeam: 0.5, 1 1.5 2.5 GeV

No momentum or rate limitations Assume gamma direction from beam

PRELIMIN

ARY

For both cases measurementsat several angles (0, 30, 50 deg)


Tagged PhotonsTagged Photons

Photon Energy measured by Tagger e- beam energy:• 0.5 GeV• 1 GeV• 1.5 GeV• 2.5 GeV

Electron Energy measured by Tagger+CU

Full range covered:50 MeV 1.4 GeV

PRELIMINARY

PR

EL

IMIN

AR

Y


First look at Beam Data vs MC First look at Beam Data vs MC II

Full bremsstrahlung Beam DataMC

Conversion Point PRELIMINARY


First look at Beam Data vs MC First look at Beam Data vs MC IIII

Full bremsstrahlung Beam Data MC

CAL Energy vs Layer Direction Error

PRELIMINARY

PRELIMINARY


Event DisplayEvent Display

γ


T9 data – charged particlesT9 data – charged particles

Electrons:All the γ configurations for comparisonSeveral other positions energies and angles

Protons:E = 10, 6 GeVSmall angles on MMS

Angle 30, 60, 90 deg

CU

Positrons:Only a small angle on MMS

CU


Setup at H4 (CERN – SPS)Setup at H4 (CERN – SPS)

GLAST CU

C1 C2

S1

S2

CU

CherenkovupstreamGOLIATH BEAM

Scintillators


H4 dataH4 data

Electrons:E 10 280 GeV (10, 20, 50, 100, 200, 280 GeV)

Angle 0 90 deg (0, 10, 20, 30, 45, 60 90 deg)

Several impact pointsSeveral FIFO configurations

Protons:E 10 150 GeV (10, 20, 100, 150 GeV)

Angle 0 90 deg (0, 30, 45, 60, 90 deg)

Number of Hits in thick W converterlayers

Number of reconstructed tracks

PRELIMINARY

PRELIMINARY


First look at Beam Data vs MCFirst look at Beam Data vs MC

20 GeV electrons Beam DataMC

Number of Tracker Hits

PRELIMINARY


ConclusionsConclusions

• Program completed both at T9 and H4• We have a lot of data

– CU configurations– Energies– Particles

• Data analysis is started – Tagger performances – Beam systematics– Hit multiplicity– FIFO configurations– Direction reconstruction– Efficiency– Background– …

under study • First look analysis show reasonable agreement with MC• Heavy Ions test beam scheduled for November at GSI


Backup SlidesBackup Slides


Italian contribution to the TrackerItalian contribution to the Tracker

INFN/ASI responsabilities for the LAT-TKR INFN/ASI responsabilities for the LAT-TKR constructionconstruction

ASI

Tracker Tower built and tested in Italy


LAT Science Requiremnts LAT Science Requiremnts

Large Energy Range: 20 MeV -300 GeV

Large Effective Area: > 8000 cm2 10000 cm2 (at 10 GeV)Wide Field of View: > 2 sr 2.4 sr

Dead Time: < 100 μs/event 25 μs/event

Energy Resolution : < 10 % 9 % (at 100 MeV)Point Source Sensitivity: < 6x10-9 cm-2s-1 3x10-9 cm-2s-1

(>100 MeV)(on axis 100 MeV - 10 GeV)

Angular Resolution – 68%: < 0.15° 0.086° (thin)(on axis E>10 GeV) 0.115° (total)

Spectral coverage and ground based observations overlap

Bright sources variability andGRBs monitor

Transient sources emission time structures

Spectral studies

Good Source localization and minimize sources confusion

Requirement - Present Value


EGRET – LAT propertiesEGRET – LAT properties

EGRET LAT

Energy range 20 Mev – 30 GeV 20 Mev – 300 GeV

Energy resolution 10 % 9 %

Effective Area 1500 cm2 10000 cm2

Angular resolution5.80 - 0.30 3.40 - 0.090

Field of View 0.5 sr 2.4 sr

Flux sensitivity (E>100 MeV)

10-7 cm-2 s-1 3 · 10-9 cm-2 s-1

Dead Time 100 ms 25 s


LAT PerformancesLAT Performances


Data Downlink and CommandsData Downlink and Commands

White Sands Complex/GFEP

TDRS

Ground Stations

USN: Hawaii;Australia

GPS GPS Timing & Position Data

TLM: Ku-band SA @ 40 Mbps S-band SA @ 1,2,4,8 kbps MA@ 1 kbpsCMD: S-band SA @ 4 kbps MA @ 0.25 kbps

TLM: S-band @ 2.5 MbpsCMD: S-band @ 2 kbps

GLAST


Tracker FeaturesTracker Features

• Conversion Efficiency > 58%• Aspect (H/W) ratio < 0.45 (wide field of view)• Active area > 19,000 cm2 (Fraction > 88%)• 6-in-a-row tracker trigger

– Efficiency > 90%– Single layer trigger rate < 50 kHz

• Average Noise occupancy < 5x10-5 • Hit efficiency > 98%


Layer assemblyLayer assembly


Silicon Sensor Devices Specifications

Wafer size 6”

Sensor size (cmXcm)

8.95X8.95

Thickness (mm) 400

Doping n-type

Implant p+

Read-out Single-sided

Coupling AC

Bias Poly-Si

Strips 384

Strip pitch (mm) 228

Implant width (mm) 56

Bias voltage < 120V

Breakdown < 175V

Current(@150V) <500nA AND <200nA (averaged any 100 SSD)

Bad strips rate 0.2 %

Hamamatsu Photonics

gamma-ray large area space telescope 15th international workshop on vertex detectors september 25 -...

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