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

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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

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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

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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

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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

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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

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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

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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

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Front-end electronics and DAQ

Power: 20 Watt for 5248 channels

Multiplexed pulsheight only

TRD crate