polarized HCAL ECAL2 ECAL1 HCAL1

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1 GEM Detectors for COMPASS CERN-EP/TA1 16 May 2 Solid State Detectors Seminar Outline ffl The COMPASS experiment ffl Gas Electron Multiplier basics ffl Discharge studies ffl Design of detectors ffl Construction ffl Quality control ffl Readout electronics ffl Performance in the beam ffl Summary and Outlook

2 The Physics Program COmmon Muon and Proton Apparatus for Structure and Spectroscopy Muon beam ffl Gluon polarization G=G Photon-gluon fusion ffl Longitudinal and transversal spin distribution ffl Polarization of Λ and Λ Hadron beam ffl Study of charm hadrons ffl Study of hadron structure with virtual photons Primakoff scattering ffl Exotic hadrons (glueballs, hybrids)

3 The Spectrometer Fixed target experiment at the SPS of CERN polarized target SM1 RICH1 µ filter 1 SM2 RICH2 µ filter 2 ECAL2 HCAL2 ECAL1 HCAL1 Magnets Tracking RICH ECAL HCAL µ filter Target: Polarized 6 LiD, liquid hydrogen, active charm target Tracking: large area small area before SM1 Drift chambers Micromegas, Si, SciFi after SM1 Straws, MWPC GEM, Si, SciFi Particle Id: 2 RICH with MWPC + CsI photocathode pads Calorimetry: Muon Id: after walls after 2nd wall RICH 1 C 4 F 1 RICH 2 C 2 F 6 + Ne electromagnetic, hadronic ECAL lead glass + PbWO 4 HCAL lead/scintillator Muon filter walls concrete + iron Drift tubes (ffi 3cm) Scintillator hodoscopes

4 Tracking Beam parameters Muon beam Hadron beam μ +,μ p; K; ß x y (RMS) (mm 2 ) 7:8 7:8 1:5 1:1 x y (RMS) (mrad) :4 :8 :29 :48 Momentum (GeV/c) Flux (per spill) Trigger rates Muon program 1 khz Hadron program 1 1 khz Requirements for Small Area Trackers ffl High rate capability ffl High spatial resolution ffl Large active area ffl "Massless detectors" ) Micropattern gas detectors Micromegas 12 muon program GEM 2 hadron + muon program

5 GEM Principle Typical dimensions: D = 7 μm d = 6 μm p = 14 μm Kapton Gas Electron Multiplier [F. Sauli, NIM A386, 531 (1997)] Cu ffl Thin polymer (Kapton) foil, typ. 5 μm thick ffl Metal-clad on both sides, typ. 5 μm Cu ffl Perforated by large number of holes, typ. 1=cm 2 : photolithography + etching process ffl U ο 5 V between electrodes ) high electric field inside holes: Proportional avalanche multiplication

6 GEM-based Detector ffl Gain is a property of GEM foil ) little dependence on external fields (mechanical tolerances!) ffl Signal on readout electrode entirely due to electron collection ffl No slow ion tail, no ion feedback ffl Possibility to cascade several GEM foils ) higher gain ffl Separation of gas amplification and readout stage ) high flexibility! ffl Readout electrodes remain on ground potential

7 GEM Detectors - Properties High rate capability > 1 5 Hz=mm 2 No aging observed up to 1 mc=mm 2

8 Choice of Gas Filling TRIPLE GEM; 241 Am Source D= 3mm, T =T =I=1mm 1 2 E = 2 kv/cm D E =E =E = 3.5 kv/cm T1 T2 I TGEM gain-volt gas 1 4 Ar-iC 4 H 1 (9-1) Ne-iC 4 H 1 (9-1) Ar-CO 2 (7-3) V GEM (Volts) Requirements for use in high rate HEP applications: ffl Non-polymerizing (aging!) ffl Large drift velocity ffl Low diffusion ffl High gain at low operating voltages ffl Non-flammable ) Ar/CO 2 (7%/3%)

9 Gas Discharges ffl Due to manufacturing defects ) QC ffl Due to nuclear interactions on exposure to heavily ionizing tracks Systematic investigation of ffl Probability of discharge ffl Energy/charge released in a discharge ) Strategies to optimize GEM detectors for successful operation under harsh COMPASS conditions

10 Defects in GEM Foils

11 Discharge Probability 1 1 cm 2 GEM, 5:5MeV ff ( 241 Am) Effective gain 1 4 Single GEM Double GEM Triple GEM U GEM (V) Discharge probability / α Single GEM Double GEM Triple GEM Effective gain

12 Discharge Energy I 1 1 cm 2 DGEM, sectorized, 5:3 8:8MeV ff ( 228 Th) Voltage (V) sector: C=1.4 nf sectors: C=2.8 nf -1 3 sectors: C=4.1 nf sectors: C=5.5 nf (a) E ind =4.9 kv/cm Time (µs) 5-5 Voltage (V) (b) Time (µs) 3 sectors: C=4.1 nf E ind =1.1 kv/cm

13 Discharge Energy II Discharges in GEM only ffl Charge released depends on capacitance between electrodes ffl Fraction of charge collected depends on induction field ffl Duration ο 2 ns ) Q ο 2:5 1 nc Full discharges to readout strips ffl Charge released determined by capacitance and potential difference between readout and lower GEM electrode (C ο 6 pf for 1 1 cm 2 GEM; U ο 8 2 V) ffl Charge Q ο 5 12 nc, current I ο 1A ) Protection of FE chip necessary!

14 Probability of Full Discharges 1 1 cm 2 DGEM, sectorized, 5:3 8:8MeV ff ( 228 Th) Probability of propagation Sectors: C=5.5 nf 3 Sectors: C=4.1 nf 2 Sectors: C=2.8 nf 1 Sector : C=1.4 nf E ind (kv/cm) ffl Probability of propagation depends on E ind and energy of primary discharge (GEM capacitance) ) Can be decreased by decreasing sector size: 13 sectors instead of 5

15 Sharing of Gain 1-2 DGEM Ar-CO DGEM disch asym voltage CERN-EP-TA1 GDD 2/8/ 1-3 G= G=1 4 G= V/V 1 1 Equal (U 1 -U 3 )/U 2 =% Unbal. (U 1 -U 3 )/U 2 = 18% Unbal. (U 1 -U 3 )/U 2 = 39% Discharges per min x1 4 1.x1 5 Eff. Gain Asymmetric gain sharing between GEMs =) probability of discharges lower by 2 orders of magnitude at given gain

16 design I Triple GEM: Probability of discharge at given gain lower by more than one order of magnitude compared to DGEM Sectorized foils: Decrease energy stored in GEM foils ffl Charge released in a GEM discharge smaller ffl Probability of propagating discharge lower "Beam killer": Central area of 5cm ffi can be deactivated Readout: 2-dim, strips, 4 μm pitch Thickness of detector: 15 mm ) Active area 3:7 3:7cm 2

17 design II

18 Two-dimensional Readout 35 m 8 m 4 m Production process [A. Gandi, R. de Oliveira, CERN-EST] ffl Two orthogonal sets of parallel Cu strips, engraved on two sides of Cu-clad Kapton foil (5 μm thin): 8 μm width on upper side 35 μm width on lower side 4 μm pitch ffl Gluing of Kapton foil onto a thin insulating support (fiber glass) ffl Chemical removal of Kapton in the interstices between the strips on the upper side ) Bottom layer of strips is opened to charge collection ffl Charge sharing 1 : 1 between upper and lower layer achieved by adjusting strip widths

19 Construction of GEM detectors ffl Carried out by K. Dehmelt [Univ. Mainz] and M. van Stenis [CERN-EP/TA1] in TA1 cleanroom: class < 1, humidity + temperature controlled ffl Protective clothing: overall, shoe-covers, hair-covers, facial masks, gloves

20 Construction Tools & Materials Tools: designed by M. Delattre and M. van Stenis ffl Alignment plate and gluing tool ffl Heating cover with N 2 flow ffl HV test box with N 2 flow Materials: Glue: ARALDIT AY13 + HD991 (ratio 1:4) Support: μm Stesalit on 3mm Honeycomb Nomex Drift foil: 5 μm Cu on 5 μm Kapton GEM foils: 2 5 μm Cu on 5 μm Kapton Frame: 3mm Stesalit Spacer grid: 2mm Vetronite Sealant: Polyurethane Nuvovern LW (2 comp.) Strip PCB: 2 5 μm Cu on 5 μm Kapton, 6 μm NoFlow glue, 12 μm Stesalit Shielding 5 μm Aluminum

21 Triple GEM Material Budget Part Material = of X GEM Cu: 6 5 μm (X = 14:3mm) : Kapton: 3 5 μm (X = 286 mm) :8.42 Total: 2.1 Drift Cu: 5 μm.35 Kapton: 5 μm.17 Total:.52 Grid G1: 3 2mm (X = 194 mm) :8 Total:.25 PCB Cu (8 μm strips): 5 μm :2.7 Cu (35 μm strips): 5 μm :75.26 Kapton: 5 μm :2.3 G1: 12 μm.62 NoFlow Glue: 6 μm (X = 2 mm).3 Total: 1.28 Shield Al: 5 μm (X = 89 mm) Total:.6 Total: 4.21 HC NOMEX: 2 3mm (X = mm) Total:.46 Skins G1: 4 12 μm Total: 2.47 Total: 7.14

22 Construction Steps I Assembly starts from drift side: ffl Glue Stesalit skins onto honeycomb (33 33 cm 2 ) ffl Glue drift foil onto honeycomb sandwich ffl 3mm frame with gas distribution channels Seal with Polyurethane Clean in ultrasonic bath Test for HV stability (up to 5kV) Glue gas input pipe ffl Glue frame onto drift foil

23 Construction Steps II Pre-tension GEM foil ffl Stretch GEM foil over transfer frame ffl Glue GEM foil onto transfer frame ffl HV test

24 Construction Steps III Glue GEM foil ffl Mount drift honeycomb on alignment plate, fix with vacuum ffl Apply glue to the frame using gluing wheel ffl Align GEM on transfer frame to honeycomb using pins ffl Apply weight to the transfer frame to stretch GEM ffl Cut out GEM from transfer frame ffl HV test

25 Construction Steps IV Glue spacer grid ffl Apply glue to the spacer grid using gluing wheel ffl Mount drift honeycomb on alignment plate, fix with vacuum ffl Align spacer grid to honeycomb using pins ffl Apply weight to the spacer grid ffl HV test

26 Construction Steps V Large honeycomb, Strip PCB ffl Insert gas outlet piece into honeycomb ffl Glue Stesalit skins onto honeycomb (5 5 cm 2 ) ffl Strip PCB: Measure strip pitch and deviation from parallelism Check for shorts ffl Glue strip PCB onto honeycomb sandwich ffl Close detector by gluing drift stack onto large honeycomb using alignment pins inserted into large honeycomb

27 GEM quality control I Optical transparency ) relative alignment of holes in two Cu electrodes

28 GEM quality control II HV test: ffl up to 6 V before mounting ffl up to 55 V after each gluing step ) monitor leakage currents of sectors, shorts

29 HV Distribution 3x { 1M.5 M Drift 1 M 24 M 1M 1 M 12 M 1 M 1 M 1 M 1 M Center on/off GEM 3 ffl Resistor network instead of individual power supplies ffl Main chain defines fields between foils and gain in GEM ffl Individual protection resistors on upper GEM side: 1 MΩ ) Most of the potential drop on upper side in case of discharge! Limitation: max. 5V potential drop under exposure to high intensity beam (1 8 s 1, G = ) ffl Operational even with permanent short in one sector: small drop of potential in remaining sectors can be compensated by slightly increased HV ffl Room for improvement: sectorization on both sides of the GEM foils

30 Detector Quality Control Gas leak test (pure CO 2 ) HV distribution boards: ffl Chemical cleaning of boards after assembly of resistors ffl Coating of boards with HV-proof varnish ffl Test of each individual board before mounting HV stability: ffl Test of each individual GEM foil before mounting HV boards (pure CO 2 ) ffl Test for external discharges at nominal voltage (pure CO 2 ) ffl Test for internal discharges at nominal voltage (Ar/CO 2 ) Detector performance: ffl Check for shorts in readout circuit ffl Gain map with 8:9keV X-rays, using standard laboratory preamplifier/amplifier

31 Uniformity of Gain and Resolution Cu X-ray spectra (8:9 kev) in 4 4 points over each detector for both strip layers Entries Histogram X 7 6 Gain = E/E =.2 Entries Histogram X 7 6 Gain = E/E =.222 Entries Histogram X 7 6 Gain = E/E =.227 Entries Histogram X 7 6 Gain = E/E = Energy [a. u.] Energy [a. u.] Energy [a. u.] Energy [a. u.] Entries Histogram X 6 5 Gain = E/E =.21 Entries Histogram X 6 5 Gain = 15.4 E/E =.211 Entries Histogram X 6 5 Gain = E/E =.26 Entries Histogram X 6 5 Gain = E/E = Energy [a. u.] Energy [a. u.] Energy [a. u.] Energy [a. u.] Entries Histogram X Gain = E/E =.189 Entries Histogram X Gain = E/E =.214 Entries Histogram X 6 5 Gain = E/E =.24 Entries Histogram X 6 5 Gain = 12.2 E/E = Energy [a. u.] Energy [a. u.] Energy [a. u.] Energy [a. u.] Entries Histogram X 7 6 Gain = 989. E/E =.198 Entries Histogram X 6 Gain = 95.5 E/E =.215 Entries Histogram X 6 Gain = E/E =.25 Entries Histogram X 6 Gain = 18.6 E/E = Energy [a. u.] Energy [a. u.] Energy [a. u.] Energy [a. u.] Maps of relative gain and energy resolution GainMap Avg = Min = Max = Avg = 2.7 Min = 18.9 Max =

32 Gain Calibration Effective gain: measure current on readout strips I as a function of count rate R under irradiation with 8:9keV X-rays G = I e NR ; e N : primary charge Gain calibration at points with maximum and minimum gain Gain Max Gain Min Gain U TOP TGEM11

33 GEM Readout "Deadtime-less" frontend electronics ) Pipeline APV25-S: CMS Si microstrip tracker FE chip ffl Analogue pipeline ASIC fabricated in :25 μm CMOS technology ffl Preamplifier + shaper (5 ns peaking time) ffl 192 memory cells / channel ffl Samples written at 4 MHz ffl FIFO depth 31 events ) Latency up to 4 μs ffl MUX output t, sec t, sec noise [e -- ] 3 2 PreMux128 5e e -- /pf 1 APV25 278e e -- /pf capacitance [pf] 4 5

34 Front-end Electronics FE-card: 3 APV chips, glass pitch adapter, 22 pf capacitors, BAV99 double diodes for input protection Readout chain: München) designed and built by I. Konorov (TU

35 COMPASS SAT Beam Tests CERN PS-T11: 1 6 p; ß=spill, 3:6GeV=c 3 triple GEM detectors: ffl 2 fully equipped with electronics (372 channels) ffl 1 half equipped with electronics (768 channels) 1 Si microstrip detector: ffl 5 7cm 2, double-sided, 3 μm thick ffl 5 μm strip pitch (234 channels) TGEM11 TGEM1 p, Scintillator Silicon Scintillator Scintillator

36 Cluster Amplitudes Single cluster, U = 45 V (G ο 8) TGEM11 counts Cluster charge coordinate 12 1 Chi2 / ndf = / 564 Prob = 1.14e-17 Constant = ± Mean = 94.7 ±.612 Sigma = ± cluster charge (8 µ m strips) counts Cluster charge coordinate 1 1 Chi2 / ndf = / 569 Prob = 6.135e-9 Constant = 52.9 ± Mean = 99.2 ±.757 Sigma = 39.2 ± cluster charge (35 µ m strips) ffl Strip noise: 15 e (8 μm), 125 e (35 μm)

37 Cluster Amplitude Correlation Cluster charge correlation cluster charge (35 µ m strips) cluster charge (8µ m strips) 5 Cluster charge ratio Chi2 / ndf = / 39 counts Chi2 / ndf = / 39 Prob = Constant = ± Mean =.9273 ±.8237 Sigma =.9221 ± cluster charge (8µ m) / (35µ m) strips TGEM11 ffl Charge sharing between strip planes ο 1 ffl Narrow correlation between amplitudes: ff = :9 ) Resolve hit ambiguities

38 Hit Map hit position (35 µ m strips) Hit map hit position (35 µ m strips) Hit map hit position (8 µ m strips) hit position (8 µ m strips) Image of scintillator used for triggering clearly visible Deactivation of central part works eæciently Inactive regions underneath spacer grid GDD GDD GAS GAS DETECTORS DETECTORS DEVELOPMENT DEVELOPMENT

39 Cluster Size Cluster: ffl strip amplitude > 3ff i ffl cluster amplitude > 5 p Pi ff2 i Cluster FWHM coordinate Cluster size coordinate counts 12 1 counts cluster FWHM (8µ m strips) cluster size (8µ m strips) Cluster FWHM coordinate 1 Cluster size coordinate 1 counts counts cluster FWHM (35µ m strips) cluster size (35µ m strips)

40 Efficiency 8 μm strip layer: TGEM11 Efficiency S/N U GEM 35 μm strip layer: Efficiency S/N U GEM

41 Hit Correlations TGEM11 SIL6, two projections Hit correlation Hit correlation

42 Time Resolution APV25: 3-sample readout, rising edge of signal Timing TGEM1 pr1 (Biggest Cluster) Late 34. Late Fit Result x = ±.15 σ = 18.2 ± entries 1 8 Fit Result x = ±.13 σ = 18.5 ± entries time [ns] Late time [ns] Late Fit Result x = ±.1 σ = ± entries 1 8 Fit Result x = ±.9 σ = ± entries time [ns] time [ns]

43 Summary GEM detectors meet requirements for tracking devices in modern HEP experiments: ffl high rate capability ffl no aging observed ffl large active area ffl thin, little material ffl cheap COMPASS adopted GEM detectors for SAT: ffl cm 2 active area ffl 2-dimensional projective readout Optimization ffl triple GEM amplification ffl sectorization of GEM foils ffl asymmetric gain sharing ffl input protection for FE chip APV25 S Beam test of detectors ffl no loss of electronic channels ffl low noise ffl efficiency plateau reached at gain ο 8, S=N ο 18 ffl narrow correlation of pulse heights ffl time resolution < 15 ns

44 Outlook Production of GEM detectors for COMPASS ffl Ongoing at CERN-EP/TA1 ffl 9 detectors of final design assembled ffl test procedures for QC of components and detectors defined Goal for 21: 14 detectors (7 % of total) The Group C. Altunbas, K. Dehmelt, J. Friedrich, B. Grube, S. Kappler, B. Ketzer, I. Konorov, S. Paul, A. Placci, L. Ropelewski, F. Sauli, H.-W. Siebert, F. Simon, M. van Stenis Special Thanks M. Sanchez (PCB design), R. de Oliveira (GEM production), G. Hall, M. Raymond (APV design), A. Honma, K. Mühlemann (Bonding), L. Schmitt (DAQ), TUM Si group