hiroshima 2000 : glast hartmut f.-w. sadrozinski, scipp, uc santa cruz glast hartmut f.-w....

Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz

GLAST

Hartmut F.-W. SadrozinskiSanta Cruz Institute for Particle Physics (SCIPP)

Gamma RayLarge AreaSpaceTelescope


GLAST Gamma-Ray Large Area Space Telescope

An Astro-Particle Physics Partnership Exploring the High-Energy Universe

Design Optimized for Key Science Objectives

• Understand particle acceleration in AGN, Pulsars, & SNRs• Resolve the -ray sky: unidentified sources & diffuse emission

• Determine the high-energy behavior of GRBs & Transients

Proven technologies and 7 years of design, development and demonstration efforts

• Precision Si-strip Tracker (TKR)

• Hodoscopic CsI Calorimeter (CAL)

• Segmented Anticoincidence Detector (ACD)

• Advantages of modular design

International and experienced team

Broad E/PO program

• Broad experience in high-energy astrophysics and

particle physics (science + instrumentation)

• Resources identified, commitments made by partners

• Management structure in place

Resolving the -ray sky


e+ e- calorimeter (energy measurement)

particle tracking detectors

conversion foils

charged particle anticoincidence shield

GLAST Detector Concept: Pair Conversion Telescope

1x10-6

1x10-5

1x10-4

1x10-3

1x10-2

1x10-1

1x100

1x101

1x10-3 1x10-2 1x10-1 1x100 1x101 1x102 1x103 1x104 1x105

Energy (MeV)

photoelectric Compton pair-conversion

Photon attenuation in lead


Detector Design

16 towers modularity

height/width = 0.4 large field-of-view

Si-strips: fine pitch 201 µm & high efficiency

0.44 X0 front-end reduce multiple scattering

1.05 X0 back-end increase sensitivity > 1 GeV

CsI: E/E <10 % 0.1-100 GeV

hodoscopic cosmic-ray rejection

shower leakage correction

XTOT = 10.1 X0 shower max contained < 100 GeV

segmented plastic scintillator

minimize self-veto

> 0.9997 efficiency & redundant readout

TKR+CAL: prototypes + 1engineering model 16 flight +1(qualspare) +1(spare)ACD: 1(qual) +1 flight

TKR+CAL: prototypes + 1engineering model 16 flight +1(qualspare) +1(spare)ACD: 1(qual) +1 flight

InstrumentInstrument

TKRTKR

CALCAL

ADCADC


Science capabilities - sensitivity

200 bursts per year prompt emission sampled to > 20 µs

AGN flares > 2 mntime profile +E/E physics of jets and acceleration

bursts delayed emission

all 3EG sources + 80 new in 2 days

periodicity searches (pulsars & X-ray binaries)

pulsar beam & emission vs. luminosity, age, B

104 sources in 1-yr survey AGN: logN-logS, duty cycle,

emission vs. type, redshift, aspect angle

extragalactic background light ( + IR-opt)

new sources (µQSO, external galaxies, clusters)

1 yr

100 s

1 orbit

1 day

3EG limit

0.01

0.001

LAT 1 yr2.3 10-9 cm-2s-1

large field-of-view


Key Science Objective: Determine the High-Energy Behavior of GRBs

Important GLAST properties for achieving science objectives:

• Large area• Low instrument deadtime (20 s)• Energy range to >300 GeV• Large FOV

Expected Numbers of GRBs and Delayed Emission in GLAST

GLAST will probe the time structure of GRB’s to the s time scaleSpectral and temporal information might allow observation of quantum gravity effects.

Time between detection of photons


Source Catalogs

> 1 GeV

M31 > 1 GeV

2 days of the survey: 344 sources

GRB, AGN, 3EG + Gal. plane & halo sources

rapid alert for GRBs (15 s to the ground)

sky survey data analyzed on a daily basis

timely IAU circulars and WWW announcements

GRB catalog

Transients or FlaresTransients or Flares

precise interstellar emission model

new statistical analyses including variability and spectral signatures

distinguish unresolved gas clumps flux histories

cross references with astronomical catalogs

Catalog strategyCatalog strategy


GLAST Source Localization Capability

~4500 sources

10900 sources

spectral index -2

Spectral cutoff above 3 GeV

s/c systematics will limit source localization capability to > 0.3`

1

- - -

Expected number of AGN detected with LAT at |b| > 30o for 2 year survey

1 year, all-sky survey source localization capability


Key Science Objective: Understand Mechanisms of Particle Acceleration in AGN, Pulsars, & SNRs

Multi-wavelength Observations are crucial for the understanding of Pulsars and AGN’s. Flares are largest at high energy.

Overlap of GLAST with ACT’s provides Needed energy calibration.

Crab

Mk 501

Synchrotron Radiation Inverse Compton

Flares


Key Science Objective: Probe dark matter

Dark Matter Candidates (e.g. SUSY particles) would lead to mono-energetic gamma lines through the annihilation process.

GLAST has good sensitivity for a variety of MSSModels in the 10-100GeV range,

Good energy resolution in the few % rangeis needed..

X

X

q

qor or Z


Instrument Performance

(Single Source F.o.M ~ Aeff /[(68%)]2)

FOV: 2.4 srSRD: 2.0 sr


Importance of Energy Reach

Maximum Likelihood test statistic for detection of point sources. For typical spectral indices, the sensitivity is maximum in the GeV energy domain.

• At low energy, angular resolution is determined by multiple scattering

rms ~ 1/E, multiple scattering • At high energy, resolution is determined by detector resolution and lever arm over which measurement is made. Lever arm restricted by fact that direction measurement must be made before 1st bremsstrahlung photon is emitted.

rms ~ meas/d, detector resolution limit

• Large field of view demands small aspect ratio which means small meas

hence silicon detectors.

• Steeply falling spectra require large effective area to reach the detector limit.


Cosmic Ray Rejection

Diffuse High Latitude gamma-ray flux

C.R. Rejection needed 105 : 1

segmented ACD segmented CAL Segmented TRK


0

500

1000

1500

2000

2500

0 5 10 15

Effective Area vs. Conversion Plane

Graded Converter (2.5%, 25%)Uniform Converter (3.5%)

x-y Plane

0.01

0.1

1

10

0.01 0.1 1 10 100

Gamma Angular Resolution PSF(68)

68% Front

68% Back

Gamma Energy [GeV]

Effective area Aeff

~ Converter Thickness

Optimization of Converter Thickness

Angular Resolution PSF(68)~ (Converter Thickness)

For Background limited Sources: (Significance) = Aeff / PSF(68) 2 is independent of Converter Thickness

For High Latitude Sources: Number of detected gamma’s count.

# of Layers

X0 per

Layer

Conversion

PSF(68)

@1GeV

[o]

Front

12

3.8%

38%

0.39

Back

4 26%

38% 0.90


Optimization of Pitch

Angular resolution is multiple scattering dominated at low energy (<1GeV).

At High Energy, measuring precision is dominant, but lever arm of measurement still limited by accumulated multiple scattering in transversed planes.

At 10GeV:Changing pitch from 201 to 282 micron, increases the PSF(68) by 12%, decreases the power by 25%, increases the noise (from Leakage currents) by few %.

0.01

0.1

1

10

100 1000

GLAST LAT Front 68% Containment vs. Pitch

0.1GeV1GeV10GeV

y = 3.1609 + 0.0003327x R= 0.68731

y = 0.34298 + 0.00027954x R= 0.99286

y = 0.057264 + 0.00011859x R= 0.99527

Pitch [micron]

Trade: Performance vs. Resources (Power)


Beam Test Engineering Module (BTEM) Tracker

End of one readout hybrid.

BTEM Tracker Module with side panels removed.

Single BTEM Tray

The BTEM Tracker, with 16 x,y planes, undergoing tests in the SLAC test beam (11/99 – 12/99).

- partially (81%) instrumented with detectors

- all detectors are in 32 cm long ladders.

• 51,200 amp/discriminator channels.

• 130 detector ladders.

• 41,600 instrumented strips.

• Working VME-based TEM DAQ system.


FEM Modeling and Vibration Testing

FEM analysis of (a) TKR tray deflections and (b) of a complete TKR module. Fundamental frequencies are above 550 Hz for the tray and 300 Hz for the module, clamped only at its base.

Aluminum and carbon-fiber mechanical model

of 10 stacked tracker trays, used by Hytec,

Inc. to validate the design in vibration tests.

BTEM TKR tray undergoing random vibration testing at GSFC.

Lowest global support mode of the LAT is the lowest bending mode of the Grid structure at 139 Hz. (Only half of the modules are shown.)


Beam Test Engineering Module (BTEM)

Silicon Tracker

CsI Calorimeter

ACD

Beam Test in SLAC’s Endstation A ( Dec 1999/Jan 2000)

•Test Fabrication Methods•Verify Performance

ResolutionsTrigger

•Investigate Hadron Rejection


Assembly of BTEM Tracker at SCIPP

4 trays, 10 eyes & 10 hands

17 trays!

2 delicate hands

2 trays and 2 observers

All done and all smiles.

See Eduardo de Couto e Silva’s talk


1997 Beam Test of Prototypes

Results of 1997 beam test of instrument components: Atwood, W.B. et al. 1999, NIM A (in press)

Layout of hodoscopic

CsI beam test calorimeter

Layout of beam test tracker. For

configuration on left, the converter/detector planes are 3 cm apart;

on the right the

separation is 6 cm.


Beam Test at SLAC 1999/2000: Electrons and Photons in BTEM

High efficiency (99.9%), low noise occupancy (10-5)


Beam Test at SLAC 1999/2000: Hadrons in BTEM

Minimum Ionizing Hadron: easily rejected Interacting Hadron: generates background

Beam


GLAST Schedule

2000 2001 2002 2003 2004 2005 2010

Formulation Implementation

SRR NAR M-PDR M-CDRI-PDR I-CDR Inst. Delivery Launch

Build & TestEngineering Models

Build & TestFlight Units

Inst.I&T

ScheduleReserve

Inst.-S/CI&T

Ops.

Calendar Years

Procurement of ~10k Si Detectors


GLAST Development Process and Status

Date Activity Program Result

93-98 Conceptual study NASA SR&T Funds Beam Test 1998:Detector R&D DoE R&D Funds Verification of Simulations

98 DoE Review SAGENAP Endorsement

98-00 Technology Development NASA ATD BTEMFull Size ModulesManufacturing ProcessASIC’s, DAQ

Fall 99 GLAST Instrument Proposal NASA AO GLAST Base Line Instr.(Si Tracker, CsI Calorimeter, ACD)Budget, Schedule, WBSEndorsements, MoA

Feb 25, 00 Decision on AO Si-GLAST selected

Sept 2005 Launch on Delta 2


Overview of the Baseline Design• 16 towers, each with 37 cm 37 cm of Si• 18 x,y planes per tower

– 19 “tray” structures• 12 with 2.5% Pb on bottom• 4 with 25% Pb on bottom• 2 with no converter

– Every other tray rotated by 90°, so each Pb foil is followed immediately by an x,y plane

• 2mm gap between x and y• Electronics on the sides of trays

– Minimize gap between towers– 9 readout modules on each of 4 sides

• Trays stack and align at their corners• The bottom tray has a flange to mount on

the grid• Carbon-fiber walls provide stiffness and

the thermal pathway to the gridOne Tracker Tower Module


Tracker Module Mechanical Design

Electronics flex cables

Carbon thermal

panel

Vectran cables run through the corner posts to compress the stack.

• The tray must be very stiff to avoid collisions (f0>500 Hz).• All prototypes to date have been made with machined aluminum

closeouts—high multiple scattering and poor thermal matching.• A development effort is in progress at Hytec Inc. (Los Alamos, NM) to

make tray structures entirely from carbon fiber.• Hytec is also developing the carbon-fiber walls, hex-cell cores, and face

sheets.

44 array of Si sensors arranged in 4 “ladders”

Kapton bias circuit

C-fiber face sheet

Hex cell core

Al closeout

C-fiber face sheet

44 array of Pb foils

Kapton bias circuit

44 array of Si sensors arranged in 4 “ladders”

Electronics board


Silicon-Strip Detectors• 400 m thick, single sided• 9.2 cm 9.2 cm (still to be reviewed)• Strip pitch is not finalized:

– 194 m pitch in beam test module– 201 m in the NASA proposal– May have to increase to 235 m or 282

m, depending on power allocation

• AC coupled with polysilicon bias (~60M)

• Beamtest module: 296 detectors from 4” wafers and 251 from 6” wafers from HPK, plus 5 of the large size from Micron.

– Typical leakage: 300 nA/detector (HPK)– Bad strips: about 1 in 5000

• 35 9.5-cm square detectors from HPK• Prototypes on order from STM

Schematic layout of the detector. • Bypass strips will not be used.• DC pads will increase in size.• A second AC pad will be added on

each strip, for probing and for a second chance at wire bonding.

Bypass strip


Si Detector Ladders• Detectors were edge bonded at SLAC by

hand, using a simple alignment jig.– Some problems with vertical steps on

the larger detectors.– Not ideal control of the amount of

epoxy in the joint (a few joints failed during later handling).

– Bond-line thickness set by hand and amount of adhesive.

– Alignment in the plane: ~30 m rms.• Wire bonding is straightforward.• Wire bonds were encapsulated with a

hard curing epoxy.– Epoxy was sprayed onto the bonds

through a slit.– Control was by hand and eye

(tedious).– There was some overspray.– More efficient methods need to be

investigated. Or is it even needed?

Edge joint and wire bonds before encapsulation

Encapsulated wire bonds

Schematic of the gluing jig


Ladder Placement on Trays• Ladders were aligned with

respect to the holes in the corner posts, by pressing against a straight edge.

• Shims set the spacing between ladders.

• Silver-loaded epoxy was used to bond detectors to the bias circuit.

• 50 m thick tape set the adhesive bond thickness.

• This procedure relies upon accurate dicing of the detector wafers.

• Lots of issues with adhesives still need to be worked out.

Handle attached to the closeout for handling during assembly.

Alignment jig


Tracker Electronics System See Takanobu Handa’s Poster!

Boss for mechanical and thermal attachment to the wall.

28 Amplifier chips

2 Digital readout controller chip

25-pin Nanonics connector

TerminationResistors4 layers of 1/2 oz copper traces and power/ground planesTEM

Lengthy run past the Calorimeter,needs shielding around cable.

Power filtering, and connection of digitaland analog grounds to the shield here.

Kapton Cable down the Tower Walls

Hybrid:

Electrical & mechanical Challenge

Redundant, ultra-low power, low-noise


0 200 400 600 800 100012001400

10-5

Strip Number

Layer 6x

Occ

up

an

cyTracker Noise and Efficiency

• Noise occupancy was obtained by inducing triggers, followed by readout, at random times.

• Hit efficiency was measured using single electron tracks and cosmic muons.

• The requirements were met: 99% efficiency with <<104 noise occupancy.

• However, this was with no live trigger during the readout. We are now measuring occupancy during digital activity.

0 200 400 600 800 1000 1200 1400

Threshold (mV)

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

Eff

icie

ncy

Layer 10 xLayer 10 y

1 2 3 4 5Detector Ladder

95

96

97

98

99

100

101

Hit

Eff

icie

ncy

Layer 6xCosmic RaysElectron Beam

Noise occupancy and hit efficiency for Layer 6x, using in both cases a threshold of 170 mV. No channels were masked.

Hit efficiency versus threshold for 5 GeV positrons.

100,000 triggers

hiroshima 2000 : glast hartmut f.-w. sadrozinski, scipp, uc santa cruz glast hartmut f.-w....

Documents