Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
GLAST
Gamma Ray
Large Area
Space
Telescope
Hartmut F.-W. Sadrozinski
Santa Cruz Institute for Particle Physics (SCIPP)
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 g-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 experience in high-energy astrophysics and
particle physics (science + instrumentation)
• Resources identified, commitments made by partners
• Management structure in place
Broad E/PO program
Resolving the g-ray sky
Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
GLAST Detector Concept: Pair Conversion Telescope
Photon attenuation in lead
charged particle
anticoincidence shield
g
conversion
foils
particle tracking
detectors
e+
calorimeter
(energy measurement)
e-
Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Detector Design
Instrument
16 towers  modularity
height/width = 0.4  large field-of-view
TKR
Si-strips: fine pitch 201 µm & high efficiency
TKR+CAL:
prototypes + 1engineering model
16 flight +1(qualspare) +1(spare)
ACD:
1(qual) +1 flight
0.44 X0 front-end  reduce multiple scattering
1.05 X0 back-end  increase sensitivity > 1 GeV
CAL
CsI: E/E <10 %
hodoscopic
0.1-100 GeV
 cosmic-ray rejection
 shower leakage correction
XTOT = 10.1 X0  shower max contained < 100 GeV
ADC
segmented plastic scintillator
 minimize self-veto
> 0.9997 efficiency & redundant readout
Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Science capabilities - sensitivity
100 s
large field-of-view
200 g bursts per year
prompt emission sampled to > 20 µs
AGN flares > 2 mn
1 orbit
time profile +E/E  physics of jets and acceleration
g bursts delayed emission
1 day
all 3EG sources + 80 new in 2 days
3EG 
limit
0.01 
1 yr
 periodicity searches (pulsars & X-ray binaries)
 pulsar beam & emission vs. luminosity, age, B
104 sources in 1-yr survey
 AGN: logN-logS, duty cycle,
0.001
LAT 1 yr
2.3 10-9
cm-2s-1
emission vs. type, redshift, aspect angle
 extragalactic background light (g + IR-opt)
 new g sources (µQSO, external galaxies, clusters)
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 ms)
• 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 ms time scale
Spectral 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
2 days of the survey: 344 sources
GRB, AGN, 3EG + Gal. plane & halo sources
Catalog strategy
precise interstellar emission model
new statistical analyses including
variability and spectral signatures
> 1 GeV
Transients or Flares
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
 distinguish unresolved gas
clumps
 flux histories
cross references
astronomical
M31 with
> 1 GeV
catalogs
Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
GLAST Source Localization Capability
10900 sources
~4500 sources
Expected number of AGN
detected with LAT at |b| >
30o for 2 year survey
Spectral cutoff
above 3 GeV
1 year, all-sky survey source
localization capability
1
s/c systematics will limit
source localization capability
to > 0.3`
spectral
index -2
-
-
-
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.
Mk 501
Flares
Crab
Synchrotron Radiation
Inverse Compton
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 % range
is needed..
X
q
X
q
or gg or Zg
Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Instrument Performance
(Single Source F.o.M ~ Aeff /[s(68%)]2)
FOV: 2.4 sr
SRD: 2.0 sr
Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Importance of Energy Reach
• At low energy, angular resolution is
determined by multiple scattering
qrms ~ 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.
qrms ~ smeas/d, detector resolution
limit
Maximum Likelihood test statistic for detection of point
sources. For typical spectral indices, the sensitivity is
maximum in the GeV energy domain.
• Large field of view demands small
aspect ratio which means small smeas
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
C.R. Rejection needed 105 : 1
segmented ACD
segmented CAL
Segmented TRK
Diffuse High Latitude gamma-ray flux
Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Optimization of Converter Thickness
Effective area Aeff
~ 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.
Angular Resolution PSF(68)
~ (Converter Thickness)
# of
Layers
X0 per
Layer
g
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
Trade: Performance vs. Resources (Power)
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 %.
Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Beam Test Engineering Module (BTEM) Tracker
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.
BTEM
Tracker
Module with
side panels
removed.
Single BTEM Tray
End of one readout
hybrid.
• 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
Aluminum and carbonfiber mechanical model
of 10 stacked tracker
trays, used by Hytec,
Inc. to validate the
design in vibration tests.
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.
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)
Beam Test in SLAC’s Endstation A ( Dec 1999/Jan 2000)
CsI Calorimeter
•Test Fabrication Methods
•Verify Performance
Resolutions
Trigger
•Investigate Hadron Rejection
Silicon Tracker
ACD
Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Assembly of BTEM Tracker at SCIPP
4 trays, 10 eyes & 10 hands
2 trays and 2 observers
2 delicate hands
17 trays!
See
Eduardo de Couto e Silva’s talk
All done and all smiles.
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 beam test
tracker. For
configuration on left,
the converter/detector
planes are 3 cm apart;
on the right the
separation is 6 cm.
Layout of
hodoscopic
CsI beam test
calorimeter
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
Calendar Years
2000
SRR
2001
I-PDR
NAR
2003
2002
M-PDR
I-CDR
M-CDR
2005
2004
Inst. Delivery
Launch
Implementation
Formulation
Build & Test
Engineering Models
Build & Test
Flight Units
Procurement of ~10k Si Detectors
2010
Ops.
Inst.
I&T
Inst.-S/C
I&T
Schedule
Reserve
Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
GLAST Development Process and Status
Date
Activity
Program
93-98
Conceptual study
Detector R&D
NASA SR&T Funds Beam Test 1998:
DoE R&D Funds
Verification of Simulations
98
DoE Review
SAGENAP
Endorsement
98-00
Technology Development
NASA ATD
BTEM
Full Size Modules
Manufacturing Process
ASIC’s, DAQ
Fall 99
GLAST Instrument Proposal
NASA AO
GLAST Base Line Instr.
(Si Tracker, CsI Calorimeter, ACD)
Budget, Schedule, WBS
Endorsements, MoA
Feb 25, 00 Decision on AO
Sept 2005 Launch on Delta 2
Result
Si-GLAST selected
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 grid
One Tracker Tower Module
Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Tracker Module Mechanical Design
• 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.
Vectran cables
run through the
corner posts to
compress the
stack.
44 array of Si sensors
arranged in 4 “ladders”
Kapton bias circuit
C-fiber face sheet
Hex cell core
Al closeout
C-fiber face sheet
44 array of Pb foils
Kapton bias circuit
Electronics board
44 array of Si sensors
arranged in 4 “ladders”
Electronics flex
cables
Carbon
thermal
panel
Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Silicon-Strip Detectors
• 400 mm thick, single sided
• 9.2 cm  9.2 cm (still to be reviewed)
• Strip pitch is not finalized:
– 194 mm pitch in beam test module
– 201 mm in the NASA proposal
– May have to increase to 235 mm or 282
mm, 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
Bypass
strip
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.
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 mm 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?
Schematic of the gluing jig
Edge joint and wire bonds before encapsulation
Encapsulated wire bonds
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 mm 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.
Alignment jig
Handle attached to the closeout
for handling during assembly.
Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Tracker Electronics System
See Takanobu
Handa’s Poster!
Redundant, ultra-low power, low-noise
Hybrid:
28 Amplifier
chips
Electrical &
mechanical
Challenge
Boss for
mechanical and
thermal
attachment to the
wall.
2 Digital
readout
controller
chip
Kapton Cable
down the Tower
Walls
25-pin Nanonics
connector
Lengthy run past the Calorimeter,
needs shielding around cable.
TEM
4 layers of 1/2 oz copper traces and power/ground planes
Termination
Hiroshima 2000 : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Tracker Noise and Efficiency
1.0
0.9
Layer 10 x
Layer 10 y
0.8
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 <<104 noise occupancy.
• However, this was with no live trigger during
the readout. We are now measuring occupancy
during digital activity.
1.1
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
200
400
600
800
1000
1200
1400
Threshold (mV)
Hit efficiency versus threshold for
5 GeV positrons.
101
100,000
triggers
-5
10
0
200
400
600
800 1000 1200 1400
Strip Number
Noise occupancy
and hit efficiency
for Layer 6x,
using in both
cases a threshold
of 170 mV. No
channels were
masked.
100
Hit Efficiency
Occupancy
Layer 6x
99
98
Cosmic Rays
Electron Beam
97
Layer 6x
96
95
1
2
3
Detector Ladder
4
5