F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Radiation
Issues in
GLAST Si
Science
Design of
Challenges
Radiation Issues
Hartmut F.-W. Sadrozinski
Santa Cruz Institute for Particle Physics (SCIPP)
F2k : 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 γ-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
4 x 4 Array
of Towers
Anticoincidence
Shield
Gamma
Ray
Tracker
Module
• Precision Si-strip Tracker (TKR)
• Hodoscopic CsI Calorimeter (CAL)
• Segmented Anticoincidence Detector (ACD)
• Advantages of modular design
Grid
Calorimeter
Module
• NASA, DoE, DoD, INFN/ASI, Japan, CEA, IN2P3, Sweden
Challenges of Science in Space
• Launch
• Limited Resources
• Space Environment
Resolving the γ-ray sky
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
GLAST Detector Concept: Pair Conversion Telescope
Photon attenuation in lead
photon attenuation length (cm)
1x101
1x100
1x10-1
photoelectric
Compton
pair-conversion
1x10-2
1x10-3
1x10-4
1x10-5
1x10-6
1x10-3
1x10-2
1x10-1
1x100
1x101
1x102
Energy (MeV)
1x103
charged particle
anticoincidence shield
1x104
γ
1x105
2
conversion
foils
1
particle tracking
detectors
e+
calorimeter
(energy measurement)
e-
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Science capabilities - sensitivity
100 s
large field-of-view
200 γ bursts per year
prompt emission sampled to > 20 µs
AGN flares > 2 mn
1 orbit
time profile +∆E/E ⇒ physics of jets and acceleration
γ bursts delayed emission
1 day
all 3EG sources + 80 new in 2 days
3EG 
limit
0.01 
1 yr
0.001
LAT 1 yr
2.3 10-9
cm-2s-1
⇒ 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 (γ + IR-opt)
⇒ new γ sources (µQSO, external galaxies, clusters)
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Science: High-Energy Behavior of GRBs
Important GLAST properties for
achieving science objectives:
Expected Numbers of GRBs and Delayed
Emission in GLAST
• Large area
• Low instrument deadtime (20 µs)
• Energy range to >300 GeV
• Large FOV
GLAST will probe the time structure
of GRB’s to the µs time scale
Spectral and temporal information might
allow observation of quantum gravity effects.
Time between detection of photons
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Science: 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
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Instrument Performance
(Single Source F.o.M ~ Aeff /[σ(68%)]2)
FOV: 2.4 sr
SRD: 2.0 sr
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Optimization of Converter Thickness t
Effective Area vs. Conversion Plane
2500
Graded Converter (2.5%, 25%)
Uniform Converter (3.5%)
2000
For Background limited Sources:
(Significance) = Aeff / PSF(68) 2
is independent of Converter Thickness
Aeff ~ t
1500
1000
For High Latitude Sources:
Number of detected gamma’s count.
500
0
0
5
10
15
x-y Plane
Gamma Angular Resolution PSF(68)
# of
Layers
X0 per
Layer
γ
Conversion
PSF(68)
@1GeV
[o]
Front
12
3.8%
38%
0.39
Back
4
26%
38%
0.90
68% Front
68% Back
10
1
0.1
PSF(68) ~ √t
0.01
0.01
0.1
1
10
Gamma Energy [GeV]
100
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Overview of TKR Baseline Design
• 16 towers, each with 37 cm × 37 cm of Si
(78m2 in all)
One Tracker Tower Module
• 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
Electronics flex
cables
Carbon
thermal
panel
F2k : GLAST
•
•
•
•
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Silicon-Strip Detectors
400 µm thick, single sided
8.95 cm × 8.95 cm (6” wafers)
Strip pitch: 228 µm
AC coupled with polysilicon bias
(~60MΩ)
• Qualify Prototypes from HPK
Guard Ring
Bias Ring
Pitch
194
Bias
Resistors
DC Pads
80 x 80
AC Pads
80 x 150
• GLAST Needs:
• ~10k detectors from 6” wafers
• ~ 1M readout channels
• > 5M bonds
Pads for
Bypass
Al Traces
80x150
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.
Tracker of the Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Beam Test Engineering Module
F2k : GLAST
The BTEM Tracker, (~1/16 of the flight instrument)
for the SLAC test beam (11/99 – 1/00)
- 2.7m2 silicon, ~500 detectors, 42k channels
- all detectors are in 32 cm long ladders.
BTEM
Tracker
Module with
side panels
removed.
Single BTEM Tray
Si Detectors
End of one readout
hybrid.
HPK 296 (4”), 251 (6”)
Micron 5 (6” )
Leakage I: 300 nA/detector (HPK)
Bad strips: about 1 in 5000
F2k : 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!
All done and all smiles.
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Challenge #1 : Space Environment and Launch
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.
Space Qualification:
Assembly Methods
Materials
Tests
Vibration Testing of a live tray up to 14g.
Leakage current before and after shaking identical
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Challenge #2: On Board Cosmic Ray Rejection
C.R. Rejection
needed 105 : 1
segmented ACD
segmented CAL
segmented TRK
Diffuse High Latitude gamma-ray flux
Radiation Levels: 1krad in a 5year mission
Issue: SEE from Heavy Ions (SEU & Latch-up)
See below
LVL1 : 5kHz
Downlink: 30Hz
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Challenge # 3: 1M channels, 250W Power
See Takanobu
Handa’s Poster
Redundant, ultra-low power, low-noise FEE
28 Amplifier
chips
Hybrid:
Electrical &
mechanical
Challenge
Boss for
mechanical and
thermal
attachment to the
wall.
Digital
readout
controller
chip at
each end
Kapton Cable
down the Tower
Walls
25-pin Nanonics
connector
needs shielding around cable.
Cross-over into the side arms
Bias + Analog 3.3V
Analog Ground
Analog 1.5V
Digital 3.3V
Digital Ground
LVDS Signals
TEM
Term
Resis
4 layers of 1/2 oz copp
Digital
Analog
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Challenge #4: Tracker Noise and Efficiency
1.1
1.0
Occupancy
Layer 6x
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.
0.9
Layer 10 x
Layer 10 y
Efficiency
0.8
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
Hit Efficiency
• Noise occupancy determines the noise rate of
the LVL1 trigger, a coincidence of 6 OR’d
layers.
• Noise RMS σ = 130 + 21*C/pF [e-] , τ =1.3µs
• Hit efficiency was measured using single
electron tracks and cosmic muons.
• The requirements were met: 99% efficiency
with <<10−4 noise occupancy.
99
98
Cosmic Rays
Electron Beam
97
Layer 6x
96
95
1
2
3
Detector Ladder
4
5
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Space Environment: Radiation
GLAST is in a Low-Earth Orbit (550km):
Shielding of Atmosphere and magnetic Field
Avoid (most!) of the radiation belts
Orbit co-determined by Re-entry > 10 Years, < 30years.
Radiation Belts:
- High Latitude
South Atlantic Anomaly (SAA)Trapped electrons and protons
USA on
ARGOS
responsible for Total Dose
cause huge trigger rate
(Detectors will be switched off)
Outside radiation Belts:
Charged Cosmic Ray Background (p, e, heavy ions)
Responsible for Single Event Effects (SEE)
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Radiation: Total Dose & Displacement
Long-term Radiation Damage:
Full dose - Spherical shield
550 km 28° circular orbit
5-year mission - Solar Minimum
100000
10000
Entirely given by electron and
proton flux trapped in the SAA
1000
Extremely soft spectrum:
Self shielding of Instrument:
Blanket, ACD, walls: 2.50g/cm2
Cut-off at 80MeV protons
GLAST Silicon Tracker
End-of-Mission Signal-to-Noise
100
Electrons
Bremsstrahlung
Protons
Total
10
1
0.01
0.1
1
10
Depth (g/cm2 Al)
30
25
Total Dose 1kRad (5 yrs) -NASA safety factor: 5xLeakage current increase 50% surface, 50% bulk
(same temperature dependence).
20
15
10
5
Increase in shot noise due to radiation constrains
operating temperature to below 25oC.
S/N E-o-M 1x
S/N E-o-M 5x
0
0
5
10
15
20
T emperature [deg C]
25
30
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Heavy Ion Radiation: Temporal Effects (SEE)
Linear Energy Transfer LET governs Single Event Effects: SEU, SEL, Punch Through
LET is dE/dx:
LET (Min ion) ≈ 1.3*10-3 MeV/(mg/cm2),
LET ~ Z2 :
LET (Fe) ≈ 1-2 MeV/(mg/cm2).
Update from AMS
Fe
GLAST IRD
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Heavy Ion Radiation: Single Event Upset
Credit: http://www.aero.org
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
Silicon Detectors in High Radiation Fields
Past Problems— beam loss
LEP (CERN)
ALEPH/Babar detector shorted out due
to beam loss; unexpected large voltage
across coupling capacitance
Future (?) Problems—High
Luminosity colliders
(BaBar, ATLAS)
prepare for large ionization in Silicon
microstrip detectors either from beam
loss or minimum bias particles
Detectors in Space(?)
(GLAST)
heavy ions (Fe) will have ionization
power of 1000’s of minimum ionizing
particles
• Beam loss is measured in fluence [MIPs / cm2] or total absorbed dose(Si) [Rad]
• In 300µm thickness 1 Rad = 106 MIPs/ cm2
• Detectors are designed for MIP signal: 1MIP = 4fC = 24,000 electron-holes pairs
• Detectors might not be optimized for high radiation field
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
GLAST Challenges from Radiation
Total Dose and Displacement requirements are modest,
but shot noise increase is noticeable due to detector length and long shaping time.
Limit on operating temperature.
SEE is more demanding and need careful testing.
Tests with lasers and heavy ion beams needed to make sure that SEE is not a problem.
Choice of CMOS technology helps: either SoI or HP 0.5um are attractive.
SEU hardened design and SEL resistant design are fallback.
SEU: Frequent refreshing of registers advisable.
Detectors are susceptible to breakdown for large LET.
Specify coupling capacitors for full operating voltage.
F2k : GLAST
Hartmut F.-W. Sadrozinski , SCIPP, UC Santa Cruz
GLAST Development Process and Status
Date
Activity
Program
93-98
Conceptual study
Detector R&D
98
DoE Review
98-00
Technology
Development
NASA SR&D
DoE R&D
(Beam Test 1998)
SAGENAP
Endorsement
NASA ATD
(BTEM
Full Size Modules
Manufact. Process
ASIC’s, DAQ)
Fall 99
What New Worlds are we going to see?
Instrument Proposal NASA AO
GLAST Base LIne
(Si TKR, CsI CAL, ACD)
Endorsements, MoA
Feb 25, 00 Decision on AO
GLAST-LAT selected
Sept 2005 Launch on Delta 2