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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
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

the basic objects
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

detector electronics 1925
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

detector electronics 19254
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

detector electronics 1929
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

1930 1934
1930 - 1934

Cosmic ray telescope 1934

Rossi 1930: Coincidence circuit for n tubes

W. Riegler/CERN

historic remarks

atlas muon chamber 2000
ATLAS Muon Chamber 2000

looks fairly similar to 1934

W. Riegler/CERN

historic remarks

wire chambers at lhc
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

atlas
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

slide10
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

slide11
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

alice
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

slide13

Precision tracking: ATLAS muon system

Precision timing: LHCb muon system

W. Riegler/CERN

precision tracking atlas muon drift tubes

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

principle of operation
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

drift chambers

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

requirements
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

single tube performance
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

single tube performance19
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

single tube performance20
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

rate capability gain drop
Rate Capability, Gain Drop

NIMA 446(2000) 435-43

W. Riegler/CERN

precision tracking

space charge effects
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

single tube performance23
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

atlas mdt front end electronics
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

precision timing lhcb muon system
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

segmentation
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

single station
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

cathode pad readout structure
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

detector parameters
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

performance of a single gap
Performance of a Single Gap

LHCb, CERN

  • Intrinsic time resolution 3ns
  • optimum amplifier peaking time 10ns

W. Riegler/CERN

precision timing

efficiency and time resolution
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

comparison with garfield
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

measurement of edge effects
Measurement of Edge Effects

LHCb, CERN

‘chamber ends’ 1 gap size from first obstacle

‘chamber ends’ last wire

W. Riegler/CERN

precision timing

front end electronics carioca
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

pulse shaping
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

conclusions
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

detector simulation
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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