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Developments of micromegas detector at CERN/Saclay Shuoxing Wu

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Outline: Introduction to Micromegas detector 1. properties 2. main problem with micromegas November test beam 1. test beam set up 2. current-voltage monitoring 3. offline analysis 4. spark topology

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Part 1 Introduction to micromegas

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Working principle 1 ) Conversion stage: Ionization of gas by the charged particle which produces electron-ion pairs. Electrons directed by E1 (0.1 to 1 kV / cm) to the micro-grid, and cross the mesh holes. 2 ) Amplification stage: E 2 (≈ 50 kV/cm) >> E 1 avalanche, electrons mulitplication. High voltage 2 cathode Micro-grille High voltage 1 Anode strip Anode plane Incident charged particle Avalanche e-e- Conversion gap Amplification gap Gas E1E1 E2E2

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Widely used in particle physics experiments: Prototype for ILC-TPC: Compass: Prototype for ILC-DHCAL:

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The Upgrade of ATLAS muon spectrometer LHC upgrade L SLHC ~ 10 L LHC bunch crossing time: 50ns (25 ns) Critical regions in ATLAS Muon Spectrometer: EI layers: CSC (27 m 2 ) EIS/L1 (54 m 2 ) EIS/L2 (68 m 2 ) EM >2: EMS/L1 (85 m 2 ) 6

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Micromegas for ATLAS Muon upgrade Combine triggering and tracking functions Matches required performances: –Spatial resolution ~ 100 m –Good double track resolution –Time resolution ~ few ns –Efficiency > 98% –Rate capability > 5 kHz/cm 2 Potential for going to large areas (1 m x 2 m) with industrial processes –Cost effective –Robustness 7

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Spark in micromegas and resistive coating solution: A point charge being deposited at t=0, r=0, the charge density at (r,t) is a solution of the 2D telegraph equation. Only one parameter, RC (time per unit surface), links spread in space with time. R~1 M / □ and C~1pF per pad area matches µs signal duration: Micro-grid Resistive film (kapton) or ink (1k-500MΩ/ ☐ ) Insulator (75 µm) Anodes Micro-grille Resistive strip (few hundreds of kΩ/ ☐ ) Anodes Resistive pad (few tens of kΩ/ ☐ ) Micro-grille Vacrel

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Part2 November test beam

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10 Test beam set up: Telescope: 3 X-Y detectors(10 x 10 cm 2 ) manufactured at Saclay Aim: Test different resistive films detectors manufactured by Rui De Oliveira at CERN and compare behaviour to non- resistive detectors Electronics: GASSIPLEX DAQ: realised by Demokritos Gas: 95%Ar + 3% CF 4 + 2% isobutane 120 Gev π+ Y Resistive Non-Resistive XYX X Beam 1 mm0.25 mm1 mm Detectors in test Y Tested detectors: Standard bulk detectors ; Resistive coating detectors; Segmented mesh detector SPS-H6

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Summary of tested detectors: TypeNameProperties: Standard bulk:SLHC31mm pitch SLHC22mm pitch Resistive coating: R3&R42mm,2MΩ/,kapton+insulator R52mm,250MΩ/,resistive paste R61mm,400KΩ/, resistive strip R70.5mm, tens of KΩ/, resistive pad Segmented mesh S11mm pitch,8 segmentations

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12 Readout and online monitoring: Data acquistion based on Labview:Monitoring through raw data by C++/Root code: Maximum strip ID: Charge spectrum:

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13 Spark counting device: MM detector C=50 pF R1=5,6 kΩR2=5,6 kΩ C=470 pF HV mesh Pre-amplifer C=50 pFVoltage-Current monitoring PC for standard onesfor resistive ones

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Different sparking behaviors of standard and resistive detector: Standard SLHC2 (2mm) R6(1mm,400kΩ/ resistive strip) SLHC2: HV=400 V (Gain ~3000): current when sparking < 0.4 A voltage drop< 5% R6: HV=390 V (Gain ~3000): current when sparking < 0.08 A voltage drop<0.5%

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Sparking behavior of resistive detector R3: Standard SLHC2 (2mm) R3(2mm,2MΩ/ ) SLHC2: HV=400 V (Gain ~3000): current when sparking < 0.4 A voltage drop< 5% R3: HV=410 V (Gain ~3000): current when sparking < 0.2 A voltage drop<2%

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Sparking behavior of S1: Seven,eight sparking six sparking five sparking four sparking three sparking two sparking one sparking S1: Standard bulk: SLHC2 16

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Charge vs. channel ID: 17 1mm 250 m R3 R6 Pedestal shift in standard MM (telescope) due to sparks. No pedestal shift in resistive detectors (R3&R6).

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Spark rate vs mesh voltage and beam intensity: R3(2mm, 2MΩ/ ): 18 Spark rate= #sparks/#incident hadron

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19 DetectortypeSpark rateSpark current / A Voltage drop SLHC2 Standard bulk 7*E-50.45% R3 2 M Ω/ resistive kapton 9.6*E-60.22% R6 400K Ω/ resistive strip 6.4*E % R5 250 M Ω/ resistive paste 1.6*E % R7 tens of K Ω/ resistive pad 5.9*E % Detector performance at same gas gain (~3000):

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Process to analysis the data: 1. Covert raw data into root tree 1. Decoding 2. Pedestal calculation and subtraction 3. Event filtering 4. Clusterization 5. Track reconstruction 6. Efficiency and spatial resolution studies based on the track

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Binary data format: 1.run header (run ID, time, type, …..) 2. event loop: Loop over 8 detectors:.number of active strips Strip loop: Word 1: 3130…210 Word 2: 3130… Word NAS[det]: 3. run footer (event number, run end time….) 3130…210 … …1211…0 Ovf Vld strip data strip ID

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Conversion from raw data into root tree: ‘Detector’ class: { NofStrips; stripID; stripCharge; }

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Channel-pin relation Decoding matrix:

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1. Decoding: Before decoding:After decoding: Check decoding:

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2.Pedestal calculation and subtraction Charge-ID distribution:Strip out of event:Strip within event: Case of ‘noisy’ strip: Charge-ID distribution:Channel noise level:

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3. Filter event: Based on the cut on pedestal sigma, only strips with charge larger than the threshold are kept. threshold

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4. Clusterization: Strips with charge above the threshold form a ‘Cluster’( 1 gap is allowed). The cluster center is the charge-weighted barycentre of the strips, the cluster charge is the sum of strips charge within the cluster, cluster size is the number of strips within the cluster. Number of clusters in one event:Cluster size: 1mm 0.25mm R3 R6 R3 R6

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5. Track fitting: y=a*x+b, a and b are determined by minimizing the chi-square. Track angle X: Track angle Y:

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R6 (1mm, 400KΩ/ ) efficiency : >98% drop<3% intensity of of 400V:

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Resolution: beam MM MM under test MM 1mm0.25 mm1mm Residuals of MM cluster position and extrapolated track from MM telescope: Convolution of: - Intrinsic MM resolution - Track resolution (extrapolated) ~68 m R6(1mm pitch, 400kΩ/ )R3(2mm pitch, 2mΩ/ ) δ=112 m δ mm = 90±0.8 m δ=199 m δ mm = 187±1.9 m 30

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Resolution vs mesh voltage: 31 R6(1mm, 400kΩ/ resistive strip):R3(2mm, 2MΩ/ resistive kapton):

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Pillars: Track position( with hit in test detector):Track position( without hit in test detector): 32 Combination:

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Cluster size: 33 R3 : 2mm, 2 M Ω/ Resistive kapton +insulator R6 : 1mm, 400 k Ω/ Resistive strip SLHC2: 2mm standard bulk

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Number of missing strips in cluster: R6( 1mm, 400 KΩ/ ): R3( 2mm, 2 mΩ/ ): 34

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Probability to have missing strips in cluster and number of missing strips: 35

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Sparks in R7 (few tens of kΩ/ Resistive pads): 36 All the ‘sparks’ in R7:Three ‘spark’ type: ‘Spark’ amplitude distribution:

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Sparks in R5 (250 MΩ/ Resistive kapton): 37 All the ‘sparks’ in R5: ‘Spark’ amplitude distribution: Four ‘spark’ type:

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Sparks in SLHC2 (standard bulk): 38 All the ‘sparks’ in SLHC2:One ‘spark’ type: ‘Sparks’ amplitude distribution:

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Sparks in R3 (2 MΩ/ resistive kapton): 39 All ‘sparks’ in R3: ‘sparks’ amplitude distribution: One ‘spark’ type:

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Sparks in R6 (400 kΩ/ resistive strip): 40 All ‘sparks’ in R6: ‘sparks’ amplitude distribution: One ‘spark’ type:

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Spark amplitude vs voltage and beam intensity: R5 voltage:R7 voltage: SLHC2 voltage: R3 intensity:R6 voltage: R3 voltage: 41

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Conclusion: Today’s micromegas detector is facing the spark problem, resistive coating is a successful way to solve it. High efficiency achieved with a resistive strip detector R6. Good spatial resolution.

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