Developments of micromegas detector at CERN/Saclay

1. Developments of micromegas detector at CERN/Saclay Shuoxing Wu 08-03-2010

2. 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

3. Part 1 Introduction to micromegas

4. Incident charged particle Gas cathode High voltage 1 Conversion gap E1 e- Micro-grille Avalanche Amplification gap Anode strip E2 Anode plane Working principle High voltage 2 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: E2 (≈ 50 kV/cm) >> E1 avalanche, electrons mulitplication.

5. Widely used in particle physics experiments: Compass: CAST@CERN: Prototype for ILC-TPC: Prototype for ILC-DHCAL:

6. The Upgrade of ATLAS muon spectrometer • LHC upgrade • LSLHC~ 10 LLHC • bunch crossing time: 50ns (25 ns) • Critical regions in ATLAS Muon Spectrometer: • EI layers: • CSC (27 m2) • EIS/L1 (54 m2) • EIS/L2 (68 m2) • EM >2: • EMS/L1 (85 m2) 6

7. 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/cm2 • Potential for going to large areas (1 m x 2 m) with industrial processes • Cost effective • Robustness 7

8. Spark in micromegas and resistive coating solution: Micro-grid Resistive film (kapton) or ink (1k-500MΩ/☐) Insulator (75 µm) Anodes Micro-grille Resistive strip (few hundreds of kΩ/☐) Anodes Micro-grille Resistive pad (few tens of kΩ/☐) Anodes Vacrel 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 MW/□ and C~1pF per pad area matches µs signal duration:

9. Part2 November test beam

10. Test beam set up: Detectors in test Non-Resistive Resistive Beam 1 mm 0.25 mm 1 mm X X Y X Y • Telescope: • 3 X-Y detectors(10 x 10 cm2) 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% CF4 + 2% isobutane SPS-H6 120 Gev π+ Y Tested detectors: Standard bulk detectors; Resistive coating detectors; Segmented mesh detector 10

11. Summary of tested detectors:

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

13. Spark counting device: C=50 pF C=50 pF Voltage-Current monitoring PC Pre-amplifer MM detector HVmesh R1=5,6 kΩ R2=5,6 kΩ C=470 pF for standard ones for resistive ones 13

14. Different sparking behaviors of standard and resistive detector: R6(1mm,400kΩ/ resistive strip) (@10KHz): Standard SLHC2 (2mm) (@10KHz): SLHC2: HV=400 V (Gain ~3000): current when sparking < 0.4 mA voltage drop< 5% R6: HV=390 V (Gain ~3000): current when sparking < 0.08 mA voltage drop<0.5%

15. Sparking behavior of resistive detector R3: Standard SLHC2 (2mm) (@10KHz): Resistive R3(2mm,2MΩ/ ) (@10KHz): SLHC2: HV=400 V (Gain ~3000): current when sparking < 0.4 mA voltage drop< 5% R3: HV=410 V (Gain ~3000): current when sparking < 0.2 mA voltage drop<2%

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

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

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

19. Detector performance at same gas gain (~3000): 19

20. 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

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

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

23. Channel-pin relation Decoding matrix: 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 33 35 37 39 41 43 45 47 49 51 53 55 57 59 61 63 64 62 60 58 56 54 52 50 48 46 44 42 40 38 36 34 65 67 69 71 73 75 77 79 81 83 85 87 89 91 93 95 96 94 92 90 88 86 84 82 80 78 76 74 72 70 68 66

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

25. 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:

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

27. 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 R6 1mm 1mm 0.25mm R6 1mm 1mm 0.25mm R3 1mm 1mm R3 1mm 0.25mm

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

29. R6 (1mm, 400KΩ/ ) efficiency : @beam intensity of 11kHz/cm2: @voltage of 400V: >98% drop<3% 29

30. Resolution: MM MM MM •Residuals of MM cluster position and extrapolated track from MM telescope: •Convolution of: - Intrinsic MM resolution - Track resolution (extrapolated) ~68mm beam MM under test 1mm 0.25 mm 1mm R6(1mm pitch, 400kΩ/ ) R3(2mm pitch, 2mΩ/ ) δ=199mm δmm=187±1.9mm δ=112mm δmm=90±0.8mm 30

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

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

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

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

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

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

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

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

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

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

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

42. 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.