The magnetic spectrometer of the PAMELA satellite experiment

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The magnetic spectrometer of the PAMELA satellite
experiment

• INTRODUCTION
• DESCRIPTION OF THE MAGNETIC SPECTROMETER
• Silicon Sensors
• Mechanics
• Electronics
• TESTS RESULTS
• CONCLUSIONS

• Oscar Adriani
• INFN Sezione di Firenze / Dipartimento di Fisica
  dellUniversita di Firenze
• The PAMELA collaboration

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The PAMELA experiment
MAIN TOPICS

• fluxes measurement
• Search for light Antinuclei
• Modulation of GCRs in the Heliosphere
• Solar Energetic Particles (SEP)
• Earth Magnetosphere
• spectra 80 MeV/c 190 GeV/c
• e spectra 50 MeV/c 270 GeV/c

SECONDARY TOPICS
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Expected Fluxes in 3 Years
Particle Number (3 yrs) Energy Range
Protons 3.108 80 MeV 700 GeV
Antiprotons gt3.104 80 MeV 190 GeV
Electrons 6.106 50 MeV 2 TeV
Positrons gt3.105 50 MeV 270 GeV
He 4.107 80 MeV/n 700 GeV/n
Be 4.104 80 MeV/n 700 GeV/n
C 4.105 80 MeV/n 700 GeV/n
Antihelium 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

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Satellite and Orbit
Resurs DK1

• Earth observation role
• 350 / 610 km
• Inclination 70o

• Soyuz 2 launcher
• Baikonur launch site
• Launch date mid 2003
• 3 year mission

Pamela operational
During 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

• Total mass 380kg / 345W power budget
• Dedicated telemetry down-link (4Gbyte per day)

350 - 600 km
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The PAMELA detector

• MAIN SUBDETECTORS
• TOF
• TRD
• Magnetic Spectrometer
• Calorimeter
• Neutron Detector

Magnetic Spectrometer
TRD
TOF
RESURS DK1
Neutron Detector
Electromagnetic Calorimeter
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Principle of Operation
Triggervelocity
g measurement
p measurement
E measurement Particle id.
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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)

• Anticoincidence system
• Defines acceptance for tracker
• Plastic scintillator PMT

• Time-of-flight
• Trigger / detects albedos / particle
  identification (up to 1 GeV/c) / dE/dx
• Plastic scintillator PMT
• Timing resolution 120ps

• Si Tracker magnet
• Measures rigidity
• 5 Nd-B-Fe magnet segments (0.4T)
• 6 planes of 300mm thick Si detectors
• 3mm resolution in bending view demonstrated,
  ie MDR 740GV/c
• /-10 MIP dynamic range

• Si-W Calorimeter
• Measures energies of e.
• DE/E 15 / E1/2 5
• Si-X / W / Si-Y structure.
• 22 Si / 21 W ? 16X0 / 0.9l0
• Imaging EM - vs- hadronic discrimination,longitu
  dinal and transverse shower profile

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The PAMELA Magnetic Spectrometer

• Magnetic System
• It produces an intense magnetic field region
  where charged particles follow curved
  trajectories
• Tracking System
• It allows to determine six points in the high
  field region to reconstruct the particle
  trajectory and so its momentum and charge sign

• Momentum p m g v
• Charge sign (e/e-) (p/p)
• If B uniform and perpendicular to p, then

B
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A glossary of magnetic spectrometersfor cosmic
rays studies

• Momentum p qBr (rradius of curvature)
• Rigidity R p/q Br
• Deflection h 1/R q/p
• DR/R Dh/h R Dh (Dh constant ? points
  measurement error)
• Maximum Detectable Rigidity (MDR)

spatial resolution
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The PAMELA Magnetic Spectrometer

• 5 magnetic modules
• permanent magnet assembled in an aluminum
  mechanics
• Nd-Fe-B alloy
• magnetic cavity sizes
• (132 x 162) mm2 x 445 mm
• field inside the cavity
• 0.48 T at the center
• places for detector planes and electronics boards
  lodging
• Geometric Factor 20.5 cm2sr
• Black IR absorbing painting (not shown in the
  picture!)

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The PAMELA Magnetic System
Magnetic field measurement

• Gaussmeter F.W. Bell equipped with 3-axis probe
  mounted on a motorized positioning device (0.1mm
  precision)
• Measurement of the three components in 67367
  points 5mm apart from each other
• Average field along the central axis of the
  magnetic cavity 0.43 T
• Good uniformity !

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The PAMELA Tracking System
The TRACKER

• 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 gt 740 (GV/c)

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• SILICON SENSORS
• Double Sided (x y view)
• Double Metal (No Kapton Fanout)
• AC Coupled (No external chips)
• Produced by Hamamatsu

Geometrical Dimensions 70.0 x 53.3
mm2 Thickness 300 mm Leakage Current lt 3
mA Decoupling Capacitance gt 20 pF/cm Total
Defects lt 2 p side Implant Pitch 25
mm Readout Pitch 50 mm Biasing Resistance
(FOXFET) gt 50 MW Interstrip Capacitance lt 10
pF n side Implant Pitch 67 mm Readout
Pitch 50 mm Biasing Resistance (PolySilicon) gt
10 MW Interstrip Capacitance lt 20 pF
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SILICON SENSORS DEFECTS
Request to Hamamatsu Defects lt 2 Defects
Short Circuit of AC coupling (Most common, not
destructive) Short between adjacent
strips Open circuit on metal lines
It seems to be perfect BUT
The first batch was OK (Prototype ladders were
perfect, bad strip lt 2) We started the mass
production Huge number of bad strips
(gt10)!!!!! 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)
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Implanted strip
Implanted strip
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The PAMELA Tracking System
FRONT-END VA1 chip
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The mechanical assembly

• 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 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 mm) Mylar foil is glued on the
plane to increase the safety of the whole
spectrometer during integration and flight
phases No coating on the bonding
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The first detector plane
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Siliconic glue
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Vibrations tests in Galileo (Florence)
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The test plane electronics lodging on the
magnetic system
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Few words on the electronics. (a dedicated talk
will be necessary!)

• Requirements
• Very small power consumption
• (60 W all included for 36864 readout channels)
• Very low noise
• (3 mm 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, gt90 reduction is mandatory)

• Solutions
• CMOS low power analog and digital electronics
• VA1 chips (ENC 185 e- 7.5 e-C(pF))
• Small input Capacitance (lt20pF)
• Decoupling between front-end and read-out
• Big modularity, hot/cold critical parts
• Selection of components (dedicated tests)
• Limiting circuits on the power lines
• Architectural tricks (error correction codes,
  majority logic etc.)
• 12 dedicated DSP (ADSP2187) with highly efficient
  compression alghoritm

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ZOP compression algorithm
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) Deventstrip ADC eventstrip - PEDstrip -
CNevent Deventstrip is distributed around
0 First word is transmitted Following word is
transmitted if above/below n s . . A word
is transmitted with the corresponding address if
the preceding one was not transmitted If a
cluster is identified (Deventstrip gt N s) ? /-
2 strips are transmitted
On 2000 Beam Tests 94.6 compression
factor no loss of resolution no loss of
efficiency 3.3 kB/event (tracker)
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The magnetic spectrometer during the last beam
test at CERN (July 2002)
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July 2000 CERN SPS

• FINAL LADDERS
• FINAL ELECTRONICS
• SMALLER MAGNETIC SYSTEM

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2002 production of flight model detector planes
Performances obtained with cosmic rays in Firenze
s/n for MIP
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July 2002 CERN SPS
During the last test (June 2002) the spectrometer
flight model has been tested to determine the
performances
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Some results on the compression
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CONCLUSIONS

• The PAMELA magnetic spectrometer is now ready for
  the final assembly phase
• The tracking capabilities have been accurately
  studied in several beam tests at CERN PS and SPS
  since 1998
• (s/n)x ? 52 , (s/n)y ? 26 for MIP
• spatial resolution
• MDR gt 740 (GV/c)
• The whole detector will be assembled starting
  from next week in the laboratory of Roma Tor
  Vergata