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High Precision Wire Chambers

High Precision Wire Chambers. at LHC. Historic remarks Wire chambers at LHC Precision tracking: ATLAS Muon Drift Tubes Precision timing: LHCb Muon Trigger Chambers. Werner Riegler, CERN. The Basic Objects. Tube Geiger- Müller, 1928. Multi Wire Geometry, in H. Friedmann 1949 .

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High Precision Wire Chambers

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  1. High Precision Wire Chambers at LHC • Historic remarks • Wire chambers at LHC • Precision tracking: ATLAS Muon Drift Tubes • Precision timing: LHCb Muon Trigger Chambers Werner Riegler, CERN W. Riegler/CERN

  2. The Basic Objects Tube Geiger- Müller, 1928 Multi Wire Geometry, in H. Friedmann 1949 G. Charpak 1968 • These geometries are widely used at LHC • Basic elements are unchanged since many years • Electronics has changed considerably W. Riegler/CERN historic remarks

  3. Detector + Electronics 1925 were quite different from today ‘Über das Wesen des Compton Effekts’ W. Bothe, H. Geiger, April 1925 • Bohr, Kramers, Slater Theorie: • energy is only conserved statistically • testing Compton effect ‘ Spitzenzähler ’ W. Riegler/CERN historic remarks

  4. Detector + Electronics 1925 ‘Über das Wesen des Compton Effekts’, W. Bothe, H. Geiger, April 1925 • ‘’Electronics’’: • Cylinders ‘P’ are on HV. • The needles of the counters are insulated and connected to electrometers. • Coincidence Photographs: • A light source is projecting both electrometers on a moving film role. • Discharges in the counters move the electrometers , which are recorded on the film. • The coincidences are observed by looking through many meters of film. W. Riegler/CERN historic remarks

  5. Detector + Electronics 1929 ‘were not very different from today’ ‘Zur Vereinfachung von Koinzidenzzählungen’ W. Bothe, November 1929 Coincidence circuit for 2 tubes Geiger Müller Tubes, 1928 W. Riegler/CERN historic remarks

  6. 1930 - 1934 Cosmic ray telescope 1934 Rossi 1930: Coincidence circuit for n tubes W. Riegler/CERN historic remarks

  7. ATLAS Muon Chamber 2000 looks fairly similar to 1934 W. Riegler/CERN historic remarks

  8. Wire Chambers at LHC • Cloud Chambers, Bubble Chambers, Spark Chambers … have disappeared but wire chambers are still popular. • While the principle detecting element has changed very little, the readout electronics integration has changed dramatically. • Situation can be compared to astronomy. Telescope mirrors haven’t changed much but detecting elements (CCDs etc.) improved a lot. W. Riegler/CERN wire chamber at LHC

  9. ATLAS • Cathode Strip Chambers: • h=2.54mm, s=2.54mm • 67k cathode channels • Ar/CO2/CF4 •   60m • Thin Gap Chambers • h=1.4mm, s=1.8mm • 440k cathode and anode channels • n-Pentane /CO2 45/55 • : 99% in 25ns with single plane • Monitored Drift Tubes • R=15mm • 370k anode channels • Ar/CO2 93/7 •   80m • Transition Radiation Tracker • R=2mm • 372k anode channels • Xe/CO2/CF4 70/10/20 •   150m Other than that - Silicon and RPCs W. Riegler/CERN wire chamber at LHC

  10. CMS • Cathode Strip Chambers: • 2h=9.5mm, s=3.12mm • 211k anode channels for timing • 273k cathode channels for position • Ar/CO2/CF4 30/50/20 •   75-150m • Rectangular ‘Drift Tubes’ • w=42mm, h=10.5mm • 195k anode channels • Ar/CO2 85/15 •   250m Other than that - Silicon and RPCs W. Riegler/CERN wire chamber at LHC

  11. LHCb • Cathode Strip Chambers: • h=2.5mm, s=1.5mm • 80k cathode and anode channels • Ar/CO2/CF4 40/50/10 • t 3ns for two layers • Straw Tracker • R=2.5mm • 110k (51k) anode channels • Ar/CO2/CF4 75/10/15 •   200m Other than that - Silicon and RPCs W. Riegler/CERN wire chamber at LHC

  12. ALICE • TPC with wire chamber • 1.25-2.5mm wire pitch • 2 - 3 mm plane separation • 570k Readout Pads • Ne/CO2 90/10 •   1mm W. Riegler/CERN wire chambers at LHC

  13. Precision tracking: ATLAS muon system Precision timing: LHCb muon system W. Riegler/CERN

  14. Precision Tracking: ATLAS Muon Drift Tubes • Magnetic field • Toroidal magnetic field (0.5T) provided by 8 superconducting coils. • Three muon stations • ~1200 chambers, • Outer diameter ~20m, • Sagitta measurement  muons with pT=1 TeV/c will show a sagitta of ~500 µm •  for 10% momentum resolution we need a sagitta measurement accuracy of ~50 µm • Monitored Drift Tubes (MDT) • each chamber consists of 23 (24) layers of drift tubes ( 3cm) • chamber deformations monitored with in-plane alignment system precision tracking

  15. Principle of Operation • Ionization • muon produces 100 clusters/cm with 2-3 e- (3 bars Ar/CO2 93/7) • Electron Drift • maximum drift-time ~800ns for baseline gas • Space-drift-time-relation  radius r • obtained by auto-calibration W. Riegler/CERN precision tracking

  16. Drift Chambers • Auto-calibration of the rt-relation • start with good estimate for rt-relation • track fit  residual distribution • rt-relation corrected with the mean of the residual distribution • convergence after a few iterations • muon tracks with an angular spread (~10°) are used to avoid systematic errors •  rt-relation with a typical accuracy of 10µm precision tracking

  17. Requirements • Parameters • resolution < 80µm for a single wire •  3cm, 370 000 channels • rates up to 500 Hz/cm2 (400 kHz/tube) • total charge 1C/cm in 10 years • Choice of gas • low diffusion, fast, linear, stand 1C/cm • Ar/N2/CH4 91/4/5: fast, linear, cannot stand 1C/cm • Ar/CO2 93/7: slow, nonlinear, however the only gas known to survive 1C/cm Therefore Ar/CO2 the ATLAS baseline gas ! W. Riegler/CERN precision tracking

  18. Single Tube Performance for Ar/N2/CH4 NIMA 443(2000) 156-63 • ‘typical’ signal shape • for tp=5 and tp=15ns • many ‘spikes’ due to clustering • tp=15ns makes the signals more ‘smooth’ • Simulated and measured resolution • simulation and measurement match very well • close to the wire: primary ionization effects • far from the wire: diffusion W. Riegler/CERN precision tracking

  19. Single Tube Performance for Ar/N2/CH4 NIMA 443(2000) 156-63 • Effect of diffusion • increases with distance for the wire • Effect of charge deposit fluctuation • decreases the primary cluster and time slewing effects W. Riegler/CERN precision tracking

  20. Single Tube Performance for Ar/N2/CH4 NIMA 443(2000) 156-63 • Higher gas gain • improves resolution (less slewing effects) but no possible due to: • aging • space charge effects (gain drop) • Amplifier bandwidth • tp=5ns to tp=15ns: • only 10um difference • tp=15ns is nicer to handle W. Riegler/CERN precision tracking

  21. Rate Capability, Gain Drop NIMA 446(2000) 435-43 W. Riegler/CERN precision tracking

  22. Space Charge Effects for Ar/CO2 • In addition to gain drop: space charge changes the electric field • shift of the rt-relation • Variations of the drift field • constant space charge wouldn’t give a problem • the drift field for the electrons of one event are influenced only by neighboring ion clouds (slice of 1cm) • only a few background events influence the drift field (~6 at 1500Hz/cm) • this number of preceding events of importance is Poisson distributed • each event has a different drift field and hence a different rt-relation •  resolution deterioration • Strong gas dependence • linear gases: small effect • non-linear gases: dominating effect W. Riegler/CERN precision tracking

  23. Single Tube Performance for Ar/CO2 NIMA 446(2000) 435-43 NIMA 446(2000) 435-43 • Resolution for low rate and 1.4kHz/cm • space charge effect deteriorates the resolution • the fluctuation of the space charge is responsible • calculation matches data very well • Effect of gas gain • at low rate higher gas gain improves the reoslution • at high rate the resolution decreases W. Riegler/CERN precision tracking

  24. ATLAS MDT Front-End Electronics 3.18 x 3.72 mm Single Channel Block Diagram • 0.5m CMOS technology • 8 channel ASD + Wilkinson ADC • fully differential • 15ns peaking time • 32mW/channel • JATAG programmable Harvard University, Boston University W. Riegler/CERN precision tracking

  25. Precision Timing: LHCb Muon System • A muon trigger is given by a coincidence of all 5 muon stations within 25ns • >99% efficiency/station in 20ns time window • Time resolution <3ns • Up to 1MHz/cm2 • 50% Wire Chambers(MWPCs) • 50% RPCs (<1kHz/cm2) W. Riegler/CERN precision timing

  26. Segmentation quadrant of a single station • Segmentation in station 2 • R4: 5 x 25 cm2 • R3: 2.5 x 12.5 cm2 • R2: 1.25 x 3.15 cm2 • R1: 0.63 x 3.1 cm2 • Segmentation achieved by • connecting wires  Wire Pad • segmenting cathode  Cathode Pad • limit to segmentation of cathode pads comes from crosstalk due to direct induction (1-2cm in this case) s=1.5mm, 2h=5mm, developed by PNPI W. Riegler/CERN precision timing

  27. Single Station • One station consists of 4 gaps forming a single chamber element • Two independent front end channels per station LHCb, CERN W. Riegler/CERN precision timing

  28. Cathode Pad Readout Structure • Cathode signals are guided to the chamber side with traces on the bottom of the PCBs. • Danger of capacitive crosstalk due to high amplifier bandwidth (tp=10ns). • Input resistance must be lower than 50 • Traces were carefully designed in order to minimize crosstalk (MAXWELL). LHCb, CERN W. Riegler/CERN precision timing

  29. Full size prototype of inner region (close to beam-pipe) LHCb, CERN W. Riegler/CERN

  30. Detector Parameters • Parameters • 5mm gas gap • 30 m wire • 1.5mm wire pitch • Readout pads on 1.6mm G10 • Operating point • Ar/CO2/CF4 40/50/10 • 3150V on wire • Gain 105 • 8kV/cm on cathode, 260kV/cm on wire • Gas parameters • 21.4 clusters in 5mm for 10 GeV muon (Heed) • v  90m/ns (8kV/cm, Magboltz) • Proportional mode • Average total charge induced on cathode = 0.37pC (gain=105) • total avalanche charge=0.74pC W. Riegler/CERN precision timing

  31. Performance of a Single Gap LHCb, CERN • Intrinsic time resolution 3ns • optimum amplifier peaking time 10ns W. Riegler/CERN precision timing

  32. Efficiency and Time Resolution Double Gap Efficiency and time resolution vs. HV Efficiency and time resolution vs. threshold LHCb, CERN W. Riegler/CERN precision timing

  33. Comparison with GARFIELD • Full Simulation • primary ionization (HEED) • drift, diffusion (MAGBOLTZ) • induced signals (GARFIELD) • no parameters to tune • we understand our detector W. Riegler/CERN precision timing

  34. Measurement of Edge Effects LHCb, CERN ‘chamber ends’ 1 gap size from first obstacle ‘chamber ends’ last wire W. Riegler/CERN precision timing

  35. Front End Electronics ‘CARIOCA’ 3x4mm prototype, (2.5x3mm final) • 0.25m CMOS technology • chip is under development • 8 channel ASD • fully differential • 10ns peaking time • 30mW/channel UFRJ Rio, CERN W. Riegler/CERN precision timing

  36. Pulse Shaping results from 3 prototype chips on a chamber LHCb, CERN • detector signal has 1/(t+1.5ns) tail • dead time leads to inefficiency • shaping circuit for tail cancellation • prototype shows <50ns average dead time at the working point W. Riegler/CERN precision timing

  37. Conclusions • Wire chambers will be widely used at LHC experiments for tracking and triggering. • Ar/CO2/CF4 gas mixtures are used because of their good aging properties. • Position resolutions of 80 m per single tube and 5ns per single MWPC layer are expected even for large systems. • The basic detector elements haven’t changed much, but the front-end electronics integration is progressing fast. • The long experience with wire chambers and the fact that one can calculate and predict their behavior very accurately makes this detector a competitive candidate also for future experiments. W. Riegler/CERN

  38. Detector Simulation • Garfield (Rob Veenhof) • electric fields, particle drift, induced signals, electronics …. • Magboltz (Steve Biagi) • transport properties of gas mixtures • Heed (Igor Smirnov) • charge deposit of fast particles in gas mixtures • Very reliable simulation of all the chamber and signal processes W. Riegler/CERN

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