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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Instrument Performance
(Single Source F.o.M ~ Aeff /[(68%)]2)
FOV: 2.4 srSRD: 2.0 sr
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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.
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Cosmic Ray Rejection
Diffuse High Latitude gamma-ray flux
C.R. Rejection needed 105 : 1
segmented ACD segmented CAL Segmented TRK
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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)
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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.
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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.)
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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.
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Beam Test at SLAC 1999/2000: Electrons and Photons in BTEM
High efficiency (99.9%), low noise occupancy (10-5)
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Beam Test at SLAC 1999/2000: Hadrons in BTEM
Minimum Ionizing Hadron: easily rejected Interacting Hadron: generates background
Beam
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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
Hiroshima 2000 : GLAST Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
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