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GLAST LAT Silicon Tracker
Marcus Ziegler APS April Meeting 2004 1
The GLAST Silicon TrackerThe GLAST Silicon Tracker
Marcus Ziegler
Santa Cruz Institute for Particle PhysicsUniversity of California at Santa Cruz
GLAST LAT Collaboration
Gamma-ray Large Gamma-ray Large Area Space Area Space TelescopeTelescope
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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
Routine Data
LAT
GBM
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OutlineOutline
Introduction Collaboration wide effort Italy/US/Japan
Tracker construction – fine SSD - fine MCM – fine Electronics Mounting -fine Tray ? READOUT scheme –fine
Mention zero suppression, binary readout and redunduncy EM Calibration results
Trigger rate per tray Charge injection for TOT linearity Efficiency vs DAC Efficiency vs TACK delay
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GLAST LAT Silicon Tracker
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GLAST LAT Silicon Tracker
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GLAST LAT Silicon Tracker
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Pair-Conversion TelescopePair-Conversion Telescope Heavy metal foils (e.g.
tungsten) convert high-energy gamma rays into electron-positron pairs.
Detectors interleaved with the converter foils track the charged particles. The gamma-ray direction is reconstructed from the tracks.
A calorimeter absorbs the electromagnetic shower and records the gamma-ray energy.
Veto counters reject background from the predominant charged cosmic rays (electrons, protons and heavy ions).
Multiple-scattering limits angular resolution
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GLAST LAT OverviewGLAST LAT Overview
e+ e–
Si Tracker8.8105 channels185 Watts
Grid (& Thermal Radiators)
3000 kg, 650 W (allocation)
1.8 m 1.8 m 1.0 m
Effective area ~1 m2
CsI Calorimeter8.4 radiation lengths 8 × 12 bars
ACD Veto CountersSegmented scintillator tiles
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Tracker Construction- OverviewTracker Construction- Overview
Kapton readout cables.
Tested SSDs procured from Hamamatsu Photonics
19 “trays” stack to form
one of 16 Tracker
modules.Electronics and
SSDs assembled on composite
panels.
4 SSDs bonded in series.
Composite panels, with tungsten foils bonded to
the bottom face.
2592
10,368
342
64834218
Carbon composite side panels
Chip-on-board readout electronics
modules.
Electronics mount on the tray edges.
“Tray”
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Silicon Strip DetectorSilicon Strip Detector
~80 m2 of PIN diodes, with P implants segmented into narrow strips.
Reliable, well-developed technology from particle-physics applications.
A/C coupling and strip bias circuitry built in.
>2000 detectors already procured from Hamamatsu Photonics. Very high quality: Leakage current < 2.5
nA/cm2
Bad channels < 1/10,000 Full depletion < 100 V.
8.95 cm square Hamamatsu-Photonics SSD before cutting from the 6-inch wafer. The thickness is 400 microns, and the strip pitch is 228 microns.
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Multi Chip Module (MCM)Multi Chip Module (MCM)
One of the challenges of this design in the Pitch-adapter flex circuit used to route the signals from the detectors to the front-end
electronics
Shown prior to wire-bond encapsulation and conformal coating.
The 24 readout chips (GTFE) of each MCMC are controlled by 2 controller chips (GTRC) at the edges
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Silicondetector
Cornerpost
connectorboss for attachment
GTFE
GTRC
•Binary readout•Redundancy scheme•Zero suppression
Hybrid Boards (MCM)
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Electronics PackagingElectronics Packaging
Dead area within the tracking volume must be minimized.
Hence the 16 modules must be closely packed.
This is achieved by attaching the electronics to the tray sides.
Flex circuits with 1552 fine traces are bonded to a radius on the PWB to interconnect the detectors and electronics.
Detector signals, 100 V bias, and ground reference are brought around the 90° corner by a Kapton circuit bonded to the PWB.
Composite Panel
High thermal conductivity transfer adhesive
PWB attached by screws
Detector
Readout IC
Machined corner radius with bonded flex circuit.
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Before bending kapton After bending
Attachmentfixture
Tray Tray
Electronics MountingSilicon ladder Readout
chipkapton
Hybridboard• gluing
• alignment• assembly time
main issues
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Readout ElectronicsReadout Electronics Based on 2 ASICs developed exclusively for this project:
64-channel amplifier-discriminator chip (GTFE); 24 per module. Readout controller chip (GTRC); 2 per module.
Two redundant readout and control paths for each GTFE chip (“left” or “right”) makes the system nearly immune to single-point failures.
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
Programmable channel masks and threshold DACs.
Internal, programmable charge-injection system.
Trigger implemented from OR of all channels/layer.
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GTFEGTFE
GTFC
Fast OR & Data
Fast ORData Token
Command
Clock
Trigger
. . .
Fast OR GTFE GTFC TEMTrigger TEM GTFC GTFE Read Event GTFE GTFC Data GTFE GTFC Token GTFC TEM
TEM
CommandClocktrigger
Readout SequenceGTFE – front end readout chip
GTFC – readout controller chip
TEM – tower electronics module
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Mechanical StructureMechanical Structure Carbon-fiber composite used for radiation transparency,
stiffness, thermal stability, and thermal conductivity. Honeycomb panels made from machined carbon-carbon
closeouts, graphite/cyanate-ester face sheets, and aluminum cores.
High-performance graphite/cyanate-ester sidewalls carry the electronics heat to the base of the module.
Titanium flexure mounts allow differential thermal expansion between the aluminum base grid and the carbon-fiber tracker.
SSDs Bias Circuits
Tungsten
Panel
MCMFlexure MountsThermal Gasket
Bottom Tray
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PerformancePerformance
The LAT silicon tracker performance has been studied in several ways: Detailed Monte Carlo simulation. Beam tests and cosmic-ray studies with
prototype detector assemblies. A high-altitude balloon flight.
Data from the prototypes have been used to tune and validate the simulation model.
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1997 Beam Test1997 Beam Test——Verify Simulation ModelVerify Simulation Model
Small-aperture first prototypeOperated in a tagged beam at Stanford
101 102 103 104
Energy (MeV)
0.1
1
10
Con
tain
men
t S
pace
Ang
le (
deg)
68% Containment95% Containment
Data
Monte Carlo
Published in NIM A446 (2000), 444.
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Beam Test of a Complete ModuleBeam Test of a Complete ModuleFull-scale Tracker module with 51,200 readout channels operated in
positron, photon, and hadron beams at Stanford Linear Accelerator Center.The Tracker power, noise, and efficiency requirements were met:
99% efficiency with <105 noise occupancy. Only 200 W of power consumed per channel.
Hit efficiency versus threshold for 5 GeV positrons.
Operating Point
NIM 457, 466, & 474
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Carbon-Composite Mechanical PrototypeCarbon-Composite Mechanical Prototype
First full-scale carbon-composite tracked module mechanical structure.
Thermal cycling, vacuum testing, and random vibration testing have been carried out at the tray and tower-module levels.
Results were satisfactory except that the joint between the corner flexures and the bottom tray failed at the highest vibration levels—work is in progress to reinforce the joint.
Full module instrumented for thrust-axis vibration
Bottom tray panel, electronics side
Bottom tray panel, orthogonal side
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LAT Tracker Status and ScheduleLAT Tracker Status and Schedule
January 2002: NASA PDR & DOE Baseline Review. Present: complete the Engineering-Model tracker
module: Complete mechanical-thermal module with dummy
silicon detectors. 4 fully instrumented and functional trays.
Winter 2003: Critical Design Review follows Engineering-Model testing.
First 2 of 18 tracker modules completed and ready for qualification testing by the end of 2003.
Final tracker modules completed by September 2004.
LAT Integration and Test until mid 2005. Launch in 3rd quarter of 2006.
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ConclusionsConclusions
Solid-state detector technology and modern electronics enable us to improve on the previous generation gamma-ray telescope by well more than an order of magnitude in sensitivity.
The LAT tracker design uses well-established detector technology but has solved a number of engineering problems related to putting a 900,000 channel silicon-strip system in orbit: Highly reliable SSD design for mass production Very low power fault-tolerant electronics readout Rigid, low-mass structure with passive cooling Compact electronics packaging with minimal dead area
We have validated the design concepts with several prototype cycles and are now approaching the manufacturing stage.
We’re looking forward to a 2006 launch and a decade of exciting GLAST science!
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SSD Testing or Ladder testingSSD Testing or Ladder testing
Get a plot with some stats Say how great the yield is and how important it is to have
alarge yield for space applications (can’t fix it up tehre). Has to be be good
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