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11Werner Riegler

RPCsRPCs and Wire Chambers and Wire Chambersfor the for the LHCb MuonLHCb Muon System System

�� OverviewOverview

�� PrinciplesPrinciples

�� Performance Comparison:Performance Comparison:Timing, Efficiency, Timing, Efficiency, CrosstalkCrosstalk

�� ConclusionConclusion

Werner Riegler, CERN

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The The LHCb LHCb ExperimentExperiment

�� A A muonmuon trigger is given by a trigger is given by acoincidence of all 5 coincidence of all 5 muonmuonstations within 25nsstations within 25ns

�� >99% efficiency/station>99% efficiency/stationin 20ns time windowin 20ns time window

�� Time resolution <3nsTime resolution <3ns�� Up to 100kHz/cmUp to 100kHz/cm22

�� 50% Wire Chambers(50% Wire Chambers(MWPCsMWPCs))50% 50% RPCs RPCs (<1kHz/cm(<1kHz/cm22))

�� 1 Station: 4 MWPC Layers1 Station: 4 MWPC Layers or 2 RPC Layers or 2 RPC Layers

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Geometry and MaterialsGeometry and Materials

�� 2mm gas gap2mm gas gap�� 2mm Bakelite 2mm Bakelite ��== 9x10 9x109 9 ��cmcm�� Linseed oilLinseed oil�� Carbon 100 kCarbon 100 k��//squaresquare�� Readout pads on 200Readout pads on 200��m PETm PET

�� 5mm gas gap5mm gas gap�� 30 30 ��m wirem wire�� 1.5mm wire pitch1.5mm wire pitch�� Readout pads on 1.6mm G10Readout pads on 1.6mm G10

RPC MWPC

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SegmentationSegmentation

RPC MWPC

���������

�����

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Simulation ToolsSimulation Tools

�� Garfield (Rob Garfield (Rob VeenhofVeenhof))� electric fields, particle drift, induced signals….

�� Magboltz Magboltz (Steve (Steve BiagiBiagi))� transport properties of gas mixtures� Townsend coefficient and gas gain from data

�� Heed (Igor Heed (Igor SmirnovSmirnov) ) � charge deposit of fast particles in gas mixtures

�� Maxwell (Maxwell (AnsoftAnsoft))� weighting fields, capacitances, inductances

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Operating ParametersOperating Parameters

�� CC22HH22FF44/i-C/i-C44HH1010/SF/SF66 95/4/1 95/4/1

�� 10kV on carbon10kV on carbon

�� 50kV/cm in gas gap50kV/cm in gas gap

�� ArAr/CO/CO22/CF/CF44 40/50/10 40/50/10

�� 3150V on wire3150V on wire

�� 8kV/cm on cathode,8kV/cm on cathode,260kV/cm on wire260kV/cm on wire

RPC MWPC

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Primary Ionization, Drift, GainPrimary Ionization, Drift, Gain

�� 20.2 clusters in 2mm for20.2 clusters in 2mm for10 10 GeV muon GeV muon (Heed)(Heed)

�� v v �� 100100��m/m/nsns(50kV/cm,assumed)(50kV/cm,assumed)

�� Limited space charge modeLimited space charge mode-not included in simulation-not included in simulation

�� Average total chargeAverage total chargeinduced by electrons =1.5pCinduced by electrons =1.5pC((��effeff �� 95cm95cm-1-1))

�� Total avalanche charge=37pCTotal avalanche charge=37pC

�� 21.4 clusters in 5mm for21.4 clusters in 5mm for10 10 GeV muonGeV muon (Heed) (Heed)

�� v v �� 90 90��m/m/nsns (8kV/cm, (8kV/cm,MagboltzMagboltz))

�� Proportional modeProportional mode�� Average total charge inducedAverage total charge induced

on cathode = 0.37pCon cathode = 0.37pC(gain=10(gain=1055))

�� total avalanche charge=0.74pCtotal avalanche charge=0.74pC

RPC MWPC

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Signal CharacteristicsSignal Characteristics

RPC MWPC

Induced signals

mA �A

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Signal CharacteristicsSignal Characteristics

�� Only electron signal visibleOnly electron signal visible

�� Maximum signal durationMaximum signal duration< d/v < d/v �� 20ns20ns

�� Ions take Ions take �� 2 2��s to Bakelites to Bakelite

�� Electron+ion signal visibleElectron+ion signal visiblett0 0 �� 1.5ns1.5ns

�� Signal length Signal length �� 50ns 50ns(after electronics shaping)(after electronics shaping)

�� Ions take Ions take �� 20 20��s to thes to thecathodecathode

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Charge SpectraCharge SpectraRPC MWPC

Saturation neglected

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Intrinsic TimingIntrinsic Timing

Time r.m.s.

Efficiency Efficiency in 20ns

RPC MWPC

Time r.m.s.

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Electronics Electronics

�� Intrinsic timing is of order ofIntrinsic timing is of order of3ns r.m.s.3ns r.m.s.

�� Longer integration time inLonger integration time inorder to collect a few clustersorder to collect a few clusters

�� ATLAS ATLAS GaAs GaAs chip:chip:160MHz Bandwidth160MHz Bandwidth

�� CMS RPC chip: few CMS RPC chip: few nsnsrise-timerise-time

�� ‘Amplifier should have the‘Amplifier should have thesame rise-time as the RPCsame rise-time as the RPCsignal in order to fully exploitsignal in order to fully exploitthe intrinsic timing of thethe intrinsic timing of thedetector’detector’

RPC MWPC

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ElectronicsElectronics

Time r.m.s. for different preamp peaking times

RPC MWPC

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Direct Induction Direct Induction CrosstalkCrosstalk

�� For a 2.5cm strip the cluster size is For a 2.5cm strip the cluster size is ��1.2 from direct induction1.2 from direct induction(at our working point)(at our working point)

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ElectricalElectrical Crosstalk Crosstalk

�� Inhomogeneous Inhomogeneous lossless lossless N-conductor transmission lineN-conductor transmission line�� Completely defined by capacitance and inductance matrix (Completely defined by capacitance and inductance matrix (NxNNxN))

which can be calculated with MAXWELLwhich can be calculated with MAXWELL

RPC MWPC

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ElectricalElectrical Crosstalk Crosstalk

�� N different velocitiesN different velocities(modal dispersion)(modal dispersion)

�� For termination weFor termination wetheoretically need 0.5N(N+1)theoretically need 0.5N(N+1)termination resistorstermination resistors

�� Crosstalk Crosstalk depends ondepends ondistance of the signal fromdistance of the signal frompreamppreamp

�� For long strips For long strips crosstalk crosstalk isissmaller for slow amplifierssmaller for slow amplifiers

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ElectricalElectrical Crosstalk Crosstalk

Far end: Ideal termination

Preamp End: Crosstalk is minimal for Rin = 0You do NOT want to terminate there !

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Rates+Rates+AgeingAgeing

�� �� 1kHz/cm 1kHz/cm22

�� �� 100 Gray in 10 LHC years 100 Gray in 10 LHC years�� Carbon layer ?Carbon layer ?�� Bakelite Bakelite resistivityresistivity ? ?�� Surface effects ?Surface effects ?

�� up to 100kHz/cmup to 100kHz/cm2 2 (space(spacecharge effects expected onlycharge effects expected onlyat 1MHz/cmat 1MHz/cm22))

�� �� 0.7C/cm wire in 10 LHC 0.7C/cm wire in 10 LHCyearsyears

RPC MWPC

�� Tests are ongoingTests are ongoing

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Measured Performance Measured Performance

RPC Efficiency MWPC efficiency

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ConclusionConclusion�� Single Gap Single Gap RPCs RPCs and and MWPCs MWPCs for the for the LHCbLHCb muonmuon system have been system have been

studied in detail.studied in detail.�� The intrinsic time resolution is The intrinsic time resolution is �� 1.2ns for 2mm 1.2ns for 2mm RPCs RPCs and and �� 3ns for 3ns for

5mm 5mm MPWCs MPWCs (1.5mm wire pitch).(1.5mm wire pitch).�� For high threshold, For high threshold, RPCs RPCs lose their efficiency due to small pulseslose their efficiency due to small pulses

while while MWPCs MWPCs lose their efficiency due to decreasing time resolution.lose their efficiency due to decreasing time resolution.

�� Apart from avalanche saturation effects the detectors can be simulatedApart from avalanche saturation effects the detectors can be simulatedvery well in every detail (gas, signals, very well in every detail (gas, signals, crosstalkcrosstalk …) …)

�� Measurements and simulations agree well on the 10-20% level - Measurements and simulations agree well on the 10-20% level -we have a ‘clue’ what we are doing.we have a ‘clue’ what we are doing.

�� Double RPC layers and 4xMWPC layers fulfill the requirements for theDouble RPC layers and 4xMWPC layers fulfill the requirements for theLHCb muon LHCb muon system.system.

�� The crucial issue will be the long term stability of the system ….The crucial issue will be the long term stability of the system ….