The PAMELA Silicon Tracker
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Transcript of The PAMELA Silicon Tracker
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Firenze, 06 October 2005 - RD05 Lorenzo Bonechi
TheThe PAMELAPAMELA Silicon TrackerSilicon Tracker
Lorenzo Bonechi - PAMELA collaborationLorenzo Bonechi - PAMELA collaborationINFN Sezione di Firenze - Dipartimento di Fisica dell’Universita’ di FirenzeINFN Sezione di Firenze - Dipartimento di Fisica dell’Universita’ di Firenze
INTRODUCTIONINTRODUCTION MAGNETIC SPECTROMETERMAGNETIC SPECTROMETER
PERMANENT MAGNETPERMANENT MAGNET SILICON TRACKING SYSTEMSILICON TRACKING SYSTEM ((MECHANICSMECHANICS))
PERFORMANCES of the tracking PERFORMANCES of the tracking systemsystem
CONCLUSIONSCONCLUSIONS
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Firenze, 06 October 2005 - RD05 Lorenzo Bonechi
The PAMELA experiment
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Firenze, 06 October 2005 - RD05 Lorenzo Bonechi
Earth observation 350 / 610 km Inclination = 70.4o
Soyuz 2 launcher Baikonur Cosmodrome Launch date = end 2005 3 year mission
350 - 610 km
Pamela operationalDuring launch / orbital manoeuvres
Housed in an atmospheric pressure vessel Temperature = 5oC ÷ 35oC All subsystems must withstand launch vibrations! Electronics must withstand up to ~3 krad
Resurs DK1Resurs DK1
Total mass ~ 470kg / 345W power budget
Satellite and orbit
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The PAMELA subdetectors
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–
The permanent magnet
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• Double Sided (x & y view)• Double Metal on the n side (No Kapton
Fanout)• AC Coupled (No external chips)• Produced by HamamatsuGeometrical Dimensions 70.0 x 53.3 mm2
Thickness 300 mLeakage Current < 3 ADecoupling Capacitance > 20 pF/cmTotal Defects < 2%
p sideImplant Pitch 25.5 mReadout Pitch 51 mBiasing Resistance (FOXFET) > 50 MInterstrip Capacitance < 10 pF
n sideImplant Pitch 67 mReadout Pitch 50 mBiasing Resistance (PolySilicon) > 10 MInterstrip Capacitance < 20 pF
DESCRIPTION of the SILICON SENSORS
The silicon tracking system
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“ ”
“ ”
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Request to Hamamatsu: Defects < 2%Defects: Short Circuit of AC coupling (Most common, not destructive)
Short between adjacent stripsOpen circuit on metal lines
0
2
4
6
8
10
12
0
0.2
0.4
0.6
0.8 1
1.2
1.4
1.6
1.8 2
Mor
e
# total defects
It seems to be ‘ perfect ’
BUT…The first batch was OK (Prototype ladders were ‘perfect’, bad strip <
2%)We started the mass production… Huge number of bad strips
(>10%)!!!!!After a big ‘fight’ we discovered in many sensors short circuits
between adjacent strips at the level of implantation (p side).Hamamatsu replaced all the bad sensors (few months of delay)
Silicon sensors defects
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Implantation procedure problems!
Transverse ‘cuts’ on the junction sidereduce the interstrip resistance
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Requirements:Requirements:• 1 plane made by 3 ladders• no material above/below the plane (1 plane = 0.3% X0!!!)• survive to the launch phase (7.4 grms, 50 g shocks!!!)• good alignment precision• thermal stresses (5-35 0C)
Solution:Solution: Carbon fibers stiffeners glued laterally to the sensors• very high Young module carbon fiber (300 Gpa)• pultrusion technology
Elastic + Rigid gluing
A very thin (2.5 m) Mylar foil is glued on the plane to increasethe safety of the whole spectrometer during integration and flight phases
No coating on the bonding
The mechanical assembly
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The first silicon plane
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Mylar film protecting the plane
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Test plane lodging on the magnet
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The flight model of the magnetic
spectrometer
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Detector performances (1)
<SIG>GOOD = 9.2 <SIG>GOOD = 4.4
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x = (2.77 ± 0.04) m
y = (13.1 ± 0.2) m
Detector performances (2)
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Momentum resolution
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On-ground muon results
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Conclusions
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Firenze, 06 October 2005 - RD05 Lorenzo Bonechi
The The PAMELAPAMELA experiment experiment
• fluxes measurement• Search for light Antinuclei
• Modulation of GCR’s in the Heliosphere• Solar Energetic Particles (SEP)• Earth Magnetosphere• …
spectra 80spectra 80 MeV/c … 190MeV/c … 190 GeV/cGeV/cee++ spectra 50 spectra 50 MeV/c … 270MeV/c … 270
GeV/cGeV/c
MAIN TOPICSMAIN TOPICS::
SECONDARY TOPICSSECONDARY TOPICS::
Antiproton fluxAntiproton fluxPositron charge ratioPositron charge ratiope /
p
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Particle Number (3 yrs)
Energy Range
Protons 3.108 80 MeV – 700 GeVAntiprotons >3.104 80 MeV – 190 GeVElectrons 6.106 50 MeV – 2 TeVPositrons >3.105 50 MeV – 270 GeVHe 4.107 80 MeV/n – 700 GeV/nBe 4.104 80 MeV/n – 700 GeV/nC 4.105 80 MeV/n – 700 GeV/nAntihelium Limit
7.10-8 80 MeV/n – 30 GeV/n
•‘Semi-Polar’ orbit (700) Low energy particles•Wide energy range + 3 years mission Reliable measurements
Expected Fluxes in 3 YearsExpected Fluxes in 3 Years
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TRD• Threshold device. Signal from e±, no signal from p,p• 9 planes of Xe/Co2 filled straws (4mm diameter). Interspersed with carbon fibre radiators crude tracking.• Aim: factor 20 rejection e/p (above 1GeV/c) (2. 105 with calorimeter)Si Tracker + magnet• Measures rigidity • 5 Nd-B-Fe magnet segments (0.4T)• 6 planes of 300m thick Si detectors• ~3m resolution in bending view demonstrated, ie: MDR = 740GV/c •+/-10 MIP dynamic range
Time-of-flight• Trigger / detects albedos / particle identification (up to 1 GeV/c) / dE/dx • Plastic scintillator + PMT• Timing resolution = 120ps
Si-W Calorimeter• Measures energies of e±. E/E = 15% / E1/2 + 5%• Si-X / W / Si-Y structure.• 22 Si / 21 W 16X0 / 0.90
• Imaging: EM - vs- hadronic discrimination,longitudinal and transverse shower profile
Anticoincidence system• Defines acceptance for tracker• Plastic scintillator + PMT
Pamela SubdetectorsPamela Subdetectors
Acceptance ~20.5 cm2sr
1.2 m
Mass ~450 kg
Pamela SubdetectorsPamela Subdetectors
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The PAMELA Magnetic Spectrometer• Magnetic SystemMagnetic System
– It produces an intense magnetic field region where charged particles follow curved trajectories
• Tracking SystemTracking System– It allows to determine six points in the high field region
to reconstruct the particle trajectory and so its momentum and charge sign
ee++BB
• Momentum p m v• Charge sign (e+/e-)
(p/p)
If B uniform and perpendicular to p, then qBrp
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A glossary of magnetic spectrometersfor cosmic rays studies
ee++BB
• Momentum p = qBr (r=radius of curvature)• Rigidity R = p/q = Br• Deflection = 1/R = q/p
• R/R = = R ( = constant point’s measurement error)
• Maximum Detectable Rigidity (MDR) : 1
RR
MDRR
spatial spatial resolutionresolution
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• 5 magnetic modules• permanent magnet assembled
in an aluminum mechanics– Nd-Fe-BNd-Fe-B alloy
• magnetic cavity sizes:– (132 x 162)(132 x 162) mmmm22 x 445 x 445 mmmm
• field inside the cavity:– 0.48 T0.48 T at the center
• places for detector planes and electronics boards lodging
• Geometric Factor: 20.5 cm20.5 cm22srsr
• Black IR absorbing painting (not shown in the picture!)
MAGNETIC SYSTEMMAGNETIC SYSTEM
The PAMELA Magnetic Spectrometer
Geometry of a magnetic block
Permanent magnet elements
Aluminum frame
The “Magnetic TowerMagnetic Tower”
Base Plate prototype
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The PAMELA Magnetic System
Magnetic field Magnetic field measurementmeasurement
• Gaussmeter F.W. Bell equipped with 3-axis probe mounted on a motorized positioning device (0.1mm precision)
• Measurement of the three components in 6736767367 points 5mm apart from each other
• Average field along the central axis of the magnetic cavity: 0.43 T0.43 T
• Good uniformity !Good uniformity !
Main field component along the Main field component along the cavity axis cavity axis
Main field component for z=0 (I) Main field component for z=0 (I) Main field component for z=0 (II)Main field component for z=0 (II)
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The PAMELA Tracking System
• 6 detector planes
• each plane: composed by 3 “ladders”
• the “ladder”: 2 microstrip silicon sensors + 1 hybrid circuit with front-end electronics (VA1 chip)
• silicon sensors: double sided; double metalization; integrated decoupling capacitance
• resolutions:
• MDR > 740 (GV/c)740 (GV/c)
The TRACKERThe TRACKER TheThe detector planesdetector planesTheThe “ladder”“ladder”
TheThe silicon sensorsilicon sensor
m13 m,3 yx
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RequirementsRequirements::
• Very small power consumption (60 W all included for 36864 readout channels)
• Very low noise (3 m resolution required!!!!)
• Redundancy and safety (satellite experiment)
• Protection against highly ionizing cosmic rays (Mainly Single Event Effect tests)
• Very big data reduction (4 GB/day of telemetry, 5 Hz trigger rate, 30 GB/day of data, >90% reduction is mandatory)
SolutionsSolutions::
• CMOS low power analog and digital electronics
• VA1 chips: ENC = 185 e- + 7.5 e- C(pF)Small input Capacitance (<20pF)Decoupling between front-end and read-out
• Big modularity, hot/cold critical parts
• Selection of components (dedicated tests)Limiting circuits on the power linesArchitectural `tricks’ (error correction codes, majority logic etc.)
• 12 dedicated DSP (ADSP2187) with highly efficient compression alghoritm
Few words on the electronics….
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Tracker front-end: thermal test
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Silicon gluing pointsSiliconic glue
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First resonance frequency: 340 Hz!!!!Test plane survived to +6db spectrum (10.4 g rms) and repeated 50 g/5 ms + 40g/1 ms shocks
Vibrations tests in Galileo (Florence)
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No Zero Suppression (Losses of particles in case of bad strips or change in the pedestals!!!)
We use a reversible alghoritm (Zero Order Predictor, ZOP)
eventstripADC event
strip - PEDstrip - CNevent
eventstripis distributed around 0
First word is transmittedFollowing word is transmitted if above/below n A word is transmitted with the corresponding address if the preceding one was not transmitted
If a cluster is identified (eventstrip > N )
+/- 2 strips are transmitted
ZOP compression algorithm
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Compression
time<1ms
Compression
factor>96%
First Plane
Last Plane
• Decompressed data o Non compressed data
Signal/Noise
• Decompressed data o Non compressed data
Resolution x (m)
Some results on the compression…
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2002: production of flight model detector planes2002: production of flight model detector planesPerformances obtained with cosmic rays in Firenze : s/n for MIP
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July 2000: CERN SPSJuly 2000: CERN SPSSpatial resolutionSpatial resolution
(July 2000 beam test with 5 ladder prototype MS)
50/
04.077.2
nsmx
20/
2.01.13
nsmy
• FINAL LADDERS
• FINAL ELECTRONICS
• SMALLER MAGNETIC SYSTEM
DISTRIBUTIONDISTRIBUTIONR q p
p/p versus pp/p versus p
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SignalSignalnon bending view bending view
Signal/NoiseSignal/Noises/n 26 s/n 52300 GeV/c Electron event300 GeV/c Electron event
non bending view bending view
During the last test (June 2002) the spectrometer flight model has been tested to determine the performances
July 2002: CERN SPSJuly 2002: CERN SPS