F.R.Spada – INFN Rome I
The TRD of AMS-02 on the International Space Station
Francesca Spada
University of Rome La Sapienza & INFN Rome I
for RWTH Aachen, KNU Daegu, IEKP Karlsruhe, MIT Boston,
Università La Sapienza & INFN Roma
III Workshop on Advanced TRDs, OSTUNI – September 9, 2005
F.R.Spada – INFN Rome I
The AMS-02 experiment
• AMS-02 will fly during 3 years at a mean altitude of 400 km on the ISS (International Space Station)
• The detector has an acceptance of 0.5 m2 sr and will be used to study the flux of particles coming from space• Direct search of
Antimatter
• Indirect search of Dark Matter
AMS-02 TRD+ECAL
F.R.Spada – INFN Rome I
The AMS-02 detector
The TRD is placed on top of the detector
TRD
TOFTrigger - t = 125 ps
CRYOMAGNET and TRACKER
B = 0.9 TCharge separation = 1 up to 1 TeV
RICHFor A ≤ 27, Z ≤ 28,
separation > 3 in 1-12 GeV
ElectromagneticCALorimeter
3D sampling – lead/scintillating fibresp+ rejection > 104 in 10-300 GeV
Electronicscrates
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Outline
• The AMS-02 TRD essentials
• The radiator and the straw tubes
• The gas system
• Gas gain
• Thermal control
• Signal extraction
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ConstructionOctagon/straw tubesRWTH Aachen
Gas Supply/Circulation SystemMIT – Design CERN & MIT - Construction
Slow Control SystemMIT & INFN Rome I
TRD DAQTH Karlsruhe
F.R.Spada – INFN Rome I
The AMS-02 TRD
• Radiator: layers of fibre fleece material
increase probability of TR emission
• Interleaved with straw modules filled with high-Z gas mixture
• 20 layers arranged in a conical octagone structure in alternate projections provide 3D tracking12 middle layers in x
direction4 top + 4 bottom layers in y
direction
vacuumcharged particle
radiator
F.R.Spada – INFN Rome I
The fleece radiator
• Radiator material: LRP 375 BK (Freudenberg)
• Fleece: 10 µm thick Propylene fibres
• Density: ρ = 0.06 g/cm3
Fleece radiatorTR-yield
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The straw tubes
• 6 mm tubes filled with Xe/CO2[80:20] at a pressure of 1250
mbar
• Tubewall: 72 µm Kapton-Aluminium sandwich
• Wires: 30 µm W/Au tensioned with 100 g
• Every module contains 16 straws
• The structure is stabilized by lengthwise and crosswise stiffeners
F.R.Spada – INFN Rome I
Gas tightness
• Forseen gas storage: 8420 ℓ for Xe at 1 bar (49.5 Kg)2530 ℓ for CO2 at 1 bar (4.5 Kg)
• Measured CO2 leak rate (diffusion through the straw walls): 0.23·10-6 ℓ·mbar/s/m
• Total TRD CO2 leak rate (tubes + polycarbonate endpieces): 1.5·10−2 ℓ·mbar/s
• TRD operation pressure: 1.4 bar
a 287 ℓ loss of CO2 over 3 years
safety factor ~ 8
Double O-ring gas connectors
• Gas tightness of the straw modules over 3 years is a key point for the operation of the TRD in space
• Polycarbonate endpieces
• AW 134 glue for potting
• Copper-Tellurium crimp connectors to the electronic board
F.R.Spada – INFN Rome I
Support structure
• conical octagon structure of aluminum honeycomb with carbon fibre walls
201 cm x 62 cm, accuracy < 100 μmTotal weight: 207 kgmatches stability and lightness requirements
modules installed
aluminium + CFC support structure
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Gas gain
Quality check:
For each straw module (16 wires)• each wire sampled in 10 segments with 55Fe • calculate deviation from average gain• get RMS for each module
• reject modules with RMS>2
• To obtain the required proton rejection power, a stringent control over gas parameters is necessary• wire dependence
due to differnces in wire positioning and tensioning
F.R.Spada – INFN Rome I
Gas gain
• gas density dependence• Example:
a 3°C temperature change causes a 1% gas density variation, which implies a gas gain variation of about 5%
• Temperature variation during the orbit: from T = +35 oC to -15 oC in 15 days
• To obtain the required proton rejection power, a stringent control over gas parameters is necessary
MLIM-structure TRD
dissipativeelement
radiativelink
radiator
• Thermal stability through multilayer insulation • Temperature monitoring with 200 Dallas temperature sensors in the whole TRD
F.R.Spada – INFN Rome I
Gas system
• During the operation the gas mixture is circulated in the TRD through a manifold system from a circulation system and refilled by a supply box containing the gas tanks
TRD OCTAGON
41 segments 1.4 bar
CirculationBox
1.4 bar
Manifolds
Xe
Vessel
Mixing Vessel12 bar
CO2
Vessel
Supply Box
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Gas system – Box S
Engineering model: CERN - Flight model: ARDE Corp.
• Mixture: Xe:CO2 80:20 to 1% accuracy
Gas tanks initial content:Xe: 49.5 kg (8420 ℓ @ 1bar)CO2: 4.5 kg (2530 ℓ @ 1bar)
Xe49.5 kg
CO2
4.5 kg
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Gas System - Box C
Gas flow: 1 ℓ/h per gas circuit (41 ℓ/h)
Gas gain monitor:
• Calibration tubes coated with Fe55
• Spirometer to measures CO2 fraction
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Gas system control• Main DAQ Computer communicates via CAN bus with a control board
and then with the dedicated boards for the electomechanical devices
Electronic control
UGBS UGBC
Circulation pump Manifolds
UGFV
Xe & CO2 tanks TRD
USCM
GAS
• Also monitor of pressure and temperature in the gas system and in the TRD modules, and of the composition of the gas mixture
• In case of overpressure, or power or communication failure, actions are taken that drive the system into a safe status
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Energy deposit in the TRD
• different highly-relativistic particles leave different energy
deposits: Ephoton ≈ ▪ keV
(test beam results on a 60 cm heigth prototype)
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Proton rejection
• Energy deposit distribution is normalized, and for each track hit the probability density functions of the hit to belong to a proton or a positron track are calculated
• Combined probabilities of the event are built:
)(, ii
pe EP
• To determine whether a TRD track belongs to a proton or to a positron, a likelihood method is used
N
i ii
pepe EPW1 ,, )(
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Proton rejection
• Likelihood function: L = We /(We+Wp)
• Assuming that events with L < 0.6 are from light particles, a proton rejection factor >102 is reached up to 250 GeV with 90% electron efficiency (MC).
20 GeV Electrons
Log Likelihood Log Likelihood
160 GeV Protons
0.6 0.6
Ee-=20 GeV
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Conclusions
• AMS will perform direct search of antimatter and indirect search of dark matter measuring charged particles and nuclei up to TeV energies
• To detect positrons with a 90% efficiency, an overall proton rejection factor of 106 is needed (ECal provides 104)
• The AMS TRD will provide the additional proton rejection factor of 102
• Straw modules assembly: in progress• Gas system mechanical components and electronics: in production• Front-end electronics: undergoing space-qualification tests
READY FOR FINAL INTEGRATION OF TRD IN 2006
F.R.Spada – INFN Rome I
Front-end electronics and DAQ
Power: 20 Watt for 5248 channels
Multiplexed pulsheight only
TRD crate