VCI, 21. 2. 2001

11Werner Riegler

RPCs and Wire Chambers RPCs and Wire Chambers for the LHCb Muon Systemfor the LHCb Muon System

Overview Overview

Principles Principles

Performance Comparison: Performance Comparison:

Timing, Efficiency, Crosstalk Timing, Efficiency, Crosstalk

ConclusionConclusion

Werner Riegler, CERN

VCI, 21. 2. 2001

22Werner Riegler

The LHCb ExperimentThe LHCb Experiment

A muon trigger is given by a A muon trigger is given by a coincidence of all 5 muon coincidence of all 5 muon stations within 25ns stations within 25ns

>99% efficiency/station >99% efficiency/station in 20ns time windowin 20ns time window

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

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

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

VCI, 21. 2. 2001

33Werner Riegler

Geometry and MaterialsGeometry and Materials

2mm gas gap2mm gas gap 2mm Bakelite 2mm Bakelite = 9x10= 9x109 9 cmcm Linseed oil Linseed oil Carbon 100 kCarbon 100 k/square/square Readout pads on 200Readout pads on 200m 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

VCI, 21. 2. 2001

44Werner Riegler

SegmentationSegmentation

RPC MWPC

140-150cm

29-31cm

VCI, 21. 2. 2001

55Werner Riegler

Simulation ToolsSimulation Tools

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

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

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

Maxwell (Ansoft)Maxwell (Ansoft) weighting fields, capacitances, inductances

VCI, 21. 2. 2001

66Werner Riegler

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

Ar/COAr/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

VCI, 21. 2. 2001

77Werner Riegler

Primary Ionization, Drift, GainPrimary Ionization, Drift, Gain

20.2 clusters in 2mm for 10 20.2 clusters in 2mm for 10 GeV muon (Heed)GeV muon (Heed)

v v 100 100m/ns m/ns (50kV/cm,assumed)(50kV/cm,assumed)

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

Average total charge induced Average total charge induced by electrons =1.5pC (by electrons =1.5pC (eff eff 95cm95cm--

11)) Total avalanche charge=37pCTotal avalanche charge=37pC

21.4 clusters in 5mm for 21.4 clusters in 5mm for 10 GeV muon (Heed)10 GeV muon (Heed)

v v 90 90m/ns (8kV/cm, Magboltz)m/ns (8kV/cm, Magboltz) Proportional mode Proportional mode

Average total charge induced Average total charge induced

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

total avalanche charge=0.74pCtotal avalanche charge=0.74pC

RPC MWPC

VCI, 21. 2. 2001

88Werner Riegler

Signal CharacteristicsSignal Characteristics

RPC MWPC

Induced signals

mA A

VCI, 21. 2. 2001

99Werner Riegler

Signal CharacteristicsSignal Characteristics

Only electron signal visible Only electron signal visible

Maximum signal duration Maximum signal duration < d/v < d/v 20ns 20ns

Ions take Ions take 2 2s to Bakelites to Bakelite

Electron+ion signal visible Electron+ion signal visible tt0 0 1.5ns1.5ns

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

Ions take Ions take 20 20s to the s to the cathodecathode

RPC MWPC

VCI, 21. 2. 2001

1010Werner Riegler

Charge SpectraCharge Spectra

RPC MWPC

Saturation neglected

VCI, 21. 2. 2001

1111Werner Riegler

Intrinsic TimingIntrinsic Timing

Time r.m.s.

Efficiency Efficiency in 20ns

RPC MWPC

Time r.m.s.

VCI, 21. 2. 2001

1212Werner Riegler

ElectronicsElectronics

Intrinsic timing is of order of Intrinsic timing is of order of 3ns r.m.s.3ns r.m.s.

Longer integration time in Longer integration time in order to collect a few clustersorder to collect a few clusters

ATLAS GaAs chip: ATLAS GaAs chip: 160MHz Bandwidth 160MHz Bandwidth

CMS RPC chip: few ns CMS RPC chip: few ns rise-time rise-time

‘‘Amplifier should have the Amplifier should have the same rise-time as the RPC same rise-time as the RPC signal in order to fully exploit signal in order to fully exploit the intrinsic timing of the the intrinsic timing of the detector’ detector’

RPC MWPC

VCI, 21. 2. 2001

1313Werner Riegler

ElectronicsElectronics

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

RPC MWPC

VCI, 21. 2. 2001

1414Werner Riegler

Direct Induction CrosstalkDirect Induction Crosstalk

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

RPC MWPC

VCI, 21. 2. 2001

1515Werner Riegler

Electrical CrosstalkElectrical Crosstalk

Inhomogeneous lossless N-conductor transmission lineInhomogeneous lossless N-conductor transmission line Completely defined by capacitance and inductance matrix (NxN) Completely defined by capacitance and inductance matrix (NxN)

which can be calculated with MAXWELLwhich can be calculated with MAXWELL

RPC MWPC

VCI, 21. 2. 2001

1616Werner Riegler

Electrical CrosstalkElectrical Crosstalk

N different velocities N different velocities (modal dispersion)(modal dispersion)

For termination we For termination we theoretically need 0.5N(N+1) theoretically need 0.5N(N+1) termination resistors termination resistors

Crosstalk depends on Crosstalk depends on distance of the signal from distance of the signal from preamp preamp

For long strips crosstalk is For long strips crosstalk is smaller for slow amplifierssmaller for slow amplifiers

VCI, 21. 2. 2001

1717Werner Riegler

Electrical CrosstalkElectrical Crosstalk

Far end: Ideal termination

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

VCI, 21. 2. 2001

1818Werner Riegler

Rates+Ageing Rates+Ageing

1kHz/cm1kHz/cm22

100 Gray in 10 LHC years100 Gray in 10 LHC years Carbon layer ?Carbon layer ? Bakelite resistivity ?Bakelite resistivity ? Surface effects ?Surface effects ?

up to 100kHz/cmup to 100kHz/cm2 2 (space (space charge effects expected only charge effects expected only at 1MHz/cmat 1MHz/cm22) )

0.7C/cm wire in 10 LHC years0.7C/cm wire in 10 LHC years

RPC MWPC

Tests are ongoingTests are ongoing

VCI, 21. 2. 2001

1919Werner Riegler

Measured Performance Measured Performance

RPC Efficiency MWPC efficiency

VCI, 21. 2. 2001

2020Werner Riegler

Conclusion Conclusion Single Gap RPCs and MWPCs for the LHCb muon system have been Single Gap RPCs and MWPCs for the LHCb muon system have been

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

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

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

Apart from avalanche saturation effects the detectors can be simulated Apart from avalanche saturation effects the detectors can be simulated very well in every detail (gas, signals, crosstalk …)very well in every detail (gas, signals, crosstalk …)

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 the Double RPC layers and 4xMWPC layers fulfill the requirements for the LHCb muon system.LHCb muon 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 ….