Maurice Bourquin

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The AMS Tracking Detector for Cosmic Ray Physics
in Space

• Maurice Bourquin
• University of Geneva
• On behalf of the AMS Tracker Collaboration
• New Zealand-Australia Workshop
• June 2004

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AMS Collaboration
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AMS-02 Tracker Collaboration

• Perugia INFN and University (Italy) (INFN and
  ASI)
• Geneva University (Switzerland) (SNF)
• Sun Yat-Sen University, Guangzhou (China)
• National Aerospace Laboratory (NLR) (The
  Netherlands)
• Aachen Ist Institute (Germany) (DARA)
• Montpellier (IN2P3) (France)
• Turku University (Finland) (TEKES)
• Moscow State University (Russia)
  
• South East University (Nanjing) (China)
• Institute of Space Science University of
  Bucharest (Rumania)
• Electronics in collaboration with CSIST (Taiwan)
  and MIT (USA)

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Introduction

• Applications of semiconductors for space
  experiments
• Scientific goal of this project (in broad terms)
• Study the composition of CR (charged particles)
  in the galaxy and beyond
• Few precise data on charged particles w.r.t.
  photons
• To get composition, measurements to be performed
  above atmosphere

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The International Space Station

• NASA has accepted to install AMS on ISS for 3
  years, after sucessful shuttle flight of AMS in
  1998.
• ISS not yet complete (missing ESA, Japanese
  modules, AMS,)
• Advantage for AMS power, weight, astronauts,
• C.f. failure of high-rate data link on Discovery !

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AMS on the International Space Station
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Antimatter Quest
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DarkMatter Quest
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Astrophysics motivations
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Cosmic Rays Fluxes
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Detector Requirements
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The AMS-02 Detector

• TRD e/p separation
• TOF ß and Z, sign(Z)
• Star tracker pointing
• Magnet 0.8 T, sign(Z)
• Si tracker p, Z, sign(Z)
• ACC anticoincidence system
• RICH ß and Z, sign(Z)
• ECAL e/p separation

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Superconducting Magnet
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Superconducting magnet collaboration
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Why a Silicon Tracker for AMS ?

•  
• Fulfils scientific goals
• Large surface to cover large acceptance of
  spectrometer (0.5 m2 sr)
•  
• gtgt High statistics measurement (rare
  anti-nuclei if any, exponentially decreasing CR
  spectrum)
•  
•  Excellent spatial resolution in magnetic field
  (10 µm/plane in 0.8 T)
•   gtgt High rejection power against nuclei in
  anti-nuclei search
•  
• gtgt Good identification of light isotopes
•  
• gtgt Good double-track reconstruction for
  converted photons

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Why a Silicon Tracker for AMS ?

• Large number of planes
• gtgt reduces background due to nuclear
  interactions (several indep. measurements.)
• Choice of double-sided sensors increases
  transparency of the detector (3 of a radiation
  length)
•  
• gtgt Reduces large angle scattering of nuclei
  which could simulate the curvature of
  anti-nuclei.
• Measurement of high energy converted photons
• Together with Star Tracker and GPS
• E.g. study of Gamma Ray Burst energy and time
  distributions

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Why a Silicon Tracker for AMS ?

• Well adapted to space environnement
• Space environement constraints can be met (see
  below).
• Reliability is prime consideration for mission
  success, as human intervention (almost)
  impossible.
• Safety issues take new dimensions with
  astronauts (Shuttle or Station) for mission
  safety
• gtgtuse established technologies.

 
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The AMS-02 Tracker
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Structure of an AMS Ladder
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Silicon Tracker Ladders
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Space environnement constraint
IMPACT ON SILICON TRACKER Limited
weight Sensors on thin and rigid AlC honeycomb
support planes Planes supported by
C-fiber shells and conical flanges Cables
small dimensions and weight   Limited power
Limit number of readout channels Daisy chain (
200 W) signals in bending plane and multiplexing
in non-bending one   Vibrations and
accelerations All eigenfrequencies required to
be above 50 HZ - Perform simulations
- Tests modules under vibrations
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Impact on Silicon Tracker (cont.)
Pressure changes Atmospheric pressure to
vacuum in 10 seconds Long term
outgasing all materials checked with
NASA   Limited data transfer In situ
calibration and compression of data
Local buffering for extensive
periods Temperature changes Heat removal by
conduction to radiating surfaces (the
permanent magnet in AMS-01)
by active cooling system (two-phase pumped
cooling loops to external radiators in
AMS-02) Simulations
Vacuum-thermal tests Permanent control
by thermal sensors in orbit Operation
Without human intervention (3 years for AMS)  
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STS-91 shuttle experimental flight
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The AMS-01 flight was a success
The tracker behaved perfectly well AMS
temperature and tracker noise during
STS-91 Operating temperature 20 C-5 C,
surviving temperature 20 C-20 C
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Tracker Thermal Control System
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Tracker spatial resolution
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Charge determination

• In AMS-01
• high noise level of n-side strips
• inefficient charge collection across the
  208-micrometer readout gap 
• --gt identification of nuclei up to Z8 only
  (up to Z26 for AMS-02)

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Improvements

• ? 1. Passivation of the silicon sensors to
  protects the sensors from surface damage during
  contacts with assembly tools. 
• ? 2. Redesign of sensors to increase ohmic side
  signals
• ? more uniform charge collection

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Reduction of number of n-side strips to increase
charge collection
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Improvements

• ? 3. New fabrication technology (by CSEM, now
  Colibrys) to diminish noise.  
• ? 4. More careful assembly procedures  to
  minimize mechanical, chemical and electrical
  impacts

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Improved Assembly Procedures(Ph. Azzarello
thesis)
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AMS-02 Tracker Construction
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Upilex cable on n-side
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Upilex cable on p-side and electronics
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N-side bonding jig
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Wire bonds
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Shielding wrapping
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AMS-02 tracker charge resolution

• ? Beam tests at CERN and GSI
• ? Combined results of 6 ladders

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AMS-02 tracker charge resolution

• ? Correlation of p-side and n-side measurements
  with a prototype RICH detector

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Tracker Plane AMS-02
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Tracker Reduction Board
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Antimatter Search with AMS-02 antihelium
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Darkmatter Search with AMS-02 positrons
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Space born and ground based high energy ? ray
detectors
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GLAST LAT Overview (courtesy Dr. Sugizaki)
Si Tracker 8.8?105 channels, lt160 Watts per 16
tower units 16 tungsten layers, 36 SSD layers per
one tower Strip pitch 228 µm Self triggering
3000 kg, 650 W (allocation) 1.8 m ? 1.8 m ? 1.0
m 20 MeV 300 GeV
CsI Calorimeter Hodoscopic array 8.4 X0 8
12 bars 2.0 2.7 33.6 cm

• Mega-channel particle-physics detector in orbit
• ? Low power (lt650 W)!
• Extensive data reduction on orbit!
• No maintenance!

• cosmic-ray rejection
• shower leakage
• correction

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Unidentified Sources with AMS
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Conclusions

• The AMS detector will be installed on the ISS on
  2007 for 3 years.
• Fundamental physics issues will be adressed
• Antimatter sensitivity of the order 10-9
• Dark matter searches through different signatures
  (e, p , ?, )
• Astrophysics measurements
• Charged particle tracking is done with a silicon
  microstrip detector, well adapted to work in
  space, in the high field superconducting magnet