MICROMEGAS per l’upgrade delle Muon

Chambers di ATLAS per SLHC

Arizona, Athens (U, NTU, Demokritos), Brookhaven, CERN, Harvard, Istanbul (Bogaziçi, Doğuş), Naples, Seattle, USTC

Hefei, South Carolina, St. Petersburg, Shandong, Thessaloniki

M.Alviggi, GR1-Napoli, 16 dicembre 2008Thanks to P.Iengo per la maggior parte dei plot

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Micromegas as candidate technology

• Combine triggering and tracking functions

• Matches required performances:– Spatial resolution ~ 100 m

(track< 45°)– Good double track resolution– Time resolution ~ few ns– Efficiency > 98%– Rate capability > 5 kHz/cm2

• Potential for going to large areas ~1m x 2m with industrial processes

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Prototype P1

• Standard bulk micromegas fabricated at CERN-TS/DEM

• Homogeneous stainless steel mesh

• 325 line/inch = 78 m pitch• Wire diameter ~25 m• Amplification gap = 128 m• 450mm x 350mm active area • Different strip patterns (250, 500,

1000, 2000 µm pitch; 450mm and 225 mm long)

• Drift gap: 2-5 mm

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Test beam set up

P1 tested @ CERN H6 beam line in November 2007 & June to August 2008 120 GeV pion beam Scintillator trigger External tracking with three Si detector modules (Bonn Univ.); independent DAQ Three non-flammable gas mixtures with small isobutane admixture used in 2008:

Ar:CO2:iC4H10 (88:10:2), Ar:CF4:iC4H10 (88:10:2), Ar:CF4:iC4H10(95:3:2) Data acquired for 4 different strip patterns and 5 impact angles (0 to 40 degrees)

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2007 Test beam set up 2008 Test beam set up

Readout

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32 channels

DAQ based on ALTRO CHIP

Micro

Megas

trigger

Two inverted diodes for spark protectionZero channels died

FEC 32 channels200 ns integration time64 charge samples/ch100 ns/sample 15 pre-samples1 ADC count ~ 1000 e-

DAQ PC (ALICE DATE)

Typical ADC spectra Noise subtraction (from 12 pre-samples) Cluster position from center of gravity

Cluster charge (ADC counts)

Cluster charge distribution Gas mixture: Ar:CF4:iC4H10 (88:10:2) Drift gap 5 mm; drift field = 200 V/cm Strip pitch = 250 µm Horizontal axes: ADC count ADC count = 1000 electrons

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HVmesh = 460 V

Gain measurement from HVmesh scan Exponential gain increase Stable operation (small spark rate) for gain

of 3–5 · 103

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Spatial resolution

• Si tracker σextr≈ 50 µm

• MM cluster position Convoluted

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Strip pitch: 250 µmGas: Ar:CF4:iC4H10 (88:10:2)Track impact angle: 90°

Convoluted resolution of Si tracker + extrapolation σ(Si+MM) = 63 µm

MM intrinsic resolution σ(MM) ≤ 40 µm

Spatial resolution … more

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‘x-raying’ the micromegas

Look for areas where micromegas is inefficient, i.e. tracks in Si tracker with no hits in the micromegas pattern of pillars

Equipped micromegas area (8 mm)

2.54 mmPillar distance

Si tracks

…Micromegas as a TPC

• A time resolution of a nanosecond results in space points with a resolution along the drift direction of 100 µm

• Each micromegas gap delivers a set of space points, the more the track is inclined the more space points are available

• Solves the problem of spatial resolution for large track inclination

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Therefore… Robust detector Works with non-flammable gases Spatial resolution is excellent with small

strip pitch MM as TPC will give track segments &

excellent space resolution; needs time measurement (ns)

Electronics should measure time, may relax on charge

Trigger capability to be proven with faster electronics

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What next ?

Test beam stopped ; setting up cosmics test stand in lab@CERN and in few other labs (Naples,Demokritos) optimize gas mixtures wrt drift velocity, diffusion, primary ionization, sparks, ageing…

Analysis of test beam data taken in 2008 with goals: Definition of readout segmentation Definition of requirements for r/o electronics

Construction and test of 1300 x 400 mm2 prototype (Rui de Oliveira)

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The 50% prototype Active area: 1.3 x 0.4 Segmented mesh (cut) to

reduce mesh capacity 250 and 400 µm strip

pitches Long and short strips Construction has started in

CERN/TS-DEM Expect MM board to be

ready by early 2009 Chamber to be completed

spring 2009 Test beam in May 2009

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The stretched micromegas mesh on its frame

Backup

• Richieste CSN1• RD51

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17ns*100

σ = 30 nsσm ≈ 1.2 ns

Inclined tracks

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Impact angle: 50°ClusterFirst strip

Last strip

Micromegas as TPC (II)

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Track under 50° with relative time info

Software tool• Software tool* for

quasi online and off-line reconstruction (based on ROOT)

• Permits alignment of Si tracker modules with MM chamber

• Combines data from Si tracker and MM

• ‘online’ resolution• Also: simple event

display

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*) Thanks to Woo Chun Park (U. South Carolina)

Simple event display

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Si module6

Si module1 Si module3

Micromegas

Spatial resolution – ‘online’ Residuals of MM cluster position and

extrapolated track from Si Convolution of:

– Intrinsic MM resolution– Tracker resolution (extrapolation)– Multiple scattering

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Si trackerMicromegas

Beam

Gas: Ar:CF4:iC4H10 (88:10:2)Drift field: 200 V/cm

Strip pitch: 250 umStrip width: 150 um

Strip pitch: 500 umStrip width: 400 um

Strip pitch: 1000 umStrip width: 900 um

mm

mm

mm

: 85 umMM: 60 um

: 212 umMM: 203 um

: 102 umMM: 82 um

⎬ ~60 µm