Conditioning of MWPCs for the LHCb Muon System

1
Status of the Test System of the MWPC for the
LHCb Muon System
Andre Massafferri (Universita Tor Vergata
INFN sezione II - Roma)
V. Bocci, R. Nobrega (Universita La Sapienza
INFN sezione I - Roma) G. Carboni, E. Santovetti
(Universita Tor Vergata INFN sezione II -
Roma)
IEEE San Diego 2006
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MWPC in Muon System
LHCb an experiment for precise
measurements of CP violation and B mesons rare
decays

• MWPC task
• Fast muon triggering
• Muon identification
• 5 Stations divided in 4 Regions
• 19 different geometries
• 1368 chambers
• More than 120K channels

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Goal
Friendly and automatic procedure for diagnose
of errors of the Chamber Electronics
system Check of our 1368 MWPC ( 128000
channels) before installation Database for
Online Monitoring
Topics
1 - Chamber Front-End Electronic (FEE) 2 -
Test setup and description 3 - Results 4 -
Cross check using cosmics 5 - Conclusion
4
MWPC Design

• 40 pF lt Cdet lt 220 pF (geometry)
• Wire (Anode) Pad (Cathode) readout
• 4-gaps MWPC
• gap size 5 mm (wire plane centered)
• gas mixture Ar/CO2/CF4 (40555)
• wire spacing 2 mm, mechanical tension 65 gr
• HV 2.650 KV
• gas gain G 50 000
• gain uniformity 30

M3R3 panel
M5R3 full equipped
6 FEEs
Faraday cage
Single pad
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Chamber Front-End Electronics (FEE)
Chamber 2 bigaps
Spark protection board
Single pad
Ch A
LVDS READOUT Ch(AB)
CONTROL
logic
SPB
Ch B
CONTROL
2 CARIOCAs DIALOG FEE (CARDIAC)

• DIALOG 16 chs control
  chip
• 8-bits DACs for threshold voltage
• width and delay adjustment
• masking
• 24-bits scaler
• pulse injection feature
• access via LVDS-based I2C protocol

• CARIOCA 8 chs current-mode Ampl
• signal amplification
• tail cancellation
• base line restoration
• digitalization into LVDS lines

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FEE characteristic I
Anode Q gt 14 fC Cathode Q gt 8 fC
charge
µ signal
Capacitance (pF)
Qth
noise
Min Det charge
dead region
time
Capacitance (pF)
AFTER TEST FEE DATABASE

• Band-width 10 / 25 MHz
• depending on Polarity
• Sensitivity 16 to 8 mV/fC
• ENC 0.3 to 2 fC
• Min Detectable charge about 40 mV/sens

Capacitance (pF)
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FEE characteristic II

• The Discriminator
• Differential Threshold Voltage
• Less sensitive to Noise
• Vth Nominal 0 to 1.3 V
• Vth Effective Abs(VrefA VrefB)
• VrefA VrefB obtained from Vth Nominal
• OffSet
• (Vth Nominal _at_ Min Vth Effective)
• 740 to 860mV

VrefA
VrefB
Vth Eff
Vth Nominal
Noise Rate
Rate method
Analysis of Noise X Threshold
offset Vth Nominal
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Test Setup

• Full Equipped Chamber (UNDER TEST)

• Control FEE via I2C (Service Board CANopen)
• Internal Counters (Dialog feature)
• External Counters (ACQ Gate Boards and
  USB-VME)
• BarCode Reader

UNDER TEST
FEE
MWPC

• PC (WIN, Visual C ROOT)
• Barcode and Test Program

FEE
FEE
FEE
8X
USB
16X
Service Board (SB) controls FEE in the
experiment. ACQ is a 64-channels VME module used
as external counter. Gate Board translates the SB
gate signal sent to the FEE to be used also by
the ACQ.
Gate Board Task
FEE
LVDS
input
ACQ
TTL
output
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The Test Protocol
SOFTWARE
GOAL
USER TASK
Association of Chamber to FEE boards
LOCATION DATABASE Extraction of Chamber and
FEE parameters
Read the Chamber and FEE barcodes
In dressing area (1) Preparation
Check LVDS output line Check
Chamber-FEE association Search for Dead
Channels Estimate Cdet (Rate Method)
Search for Short-Circuit Search for
Open Channels Check Level Noise _at_ 3
specific
thresholds

Press
Initialize
In test area (2) Test Procedure
Complete Test
Read Chamber barcode
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First Step
Check LVDS output line
Cable Checking
Check if cables are swapped It can be useful to
check cables in pit
Pulse Injection Test
Check if FEE is working properly (pulse
injection, internal counters, output
lines) Inject 500 pulses to all
channels Reading by dialog ACQ
counters Comparison
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Second Step
Check Chamber-FEE association
Search for Dead Channels
Threshold Scan Test
Check the Position of FEE comparison of OFFSET
values obtained here to the ones found on FEE
database Check dead FEE channels by the simple
existence of Noise (min 3 pts)
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Third Step Cdet
Estimate Cdet (Rate Method)
Search for Short-Circuit Search for Open
Channels
Threshold Scan Test
The detector capacitance determines the
noise level since it acts as a series noise source
SPB 2 nF
-Vth2
2 ENV2
Rate Nexp
bigap
functions
Noise fit
offset
Min Det signal
ENC(Cdet) Sensitivity(Cdet)
Offset Min detect signal
ENV
Cdet
Short-Circuit Noise (2nF)Noise (300pF)
saturation due CARIOCA
band-width Open Channel Cdet 0pF
easy to discriminate even for M2R2
40pF
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Third Step Cdet
Criteria
ltCdetgt s
D1
channels
Cdet
D2
Mostly associated to setup itself
D1 gt 2.5 s D2 gt 3 s or
ERROR
Cdet gt 300 pF or Cdet lt 20 pF
Very important Alarms !
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Fourth Step
Check Level Noise _at_ 3 specific
thresholds
Criteria for Noise Rate at 3 specific
Thresholds
OK / WARNING / ERROR

if Rate gt 1 KHz
Electronic Noise can be 100 Hz / channel 1 KHz
in Noisy channels is acceptable Chamber Eff gt99
_at_ Th 8 fC (cathode) 14 fC (anode)
threshold
Cathode Readout 6 7 8 fC
Anode Readout 10 12 14 fC
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Results Format DATABASE
PLots Histograms
Diagnostic file

• Histograms of the main output parameters
• Graph of the Noise X Thr of all FEE/channels
• OffSet signature
• Vertex position (cross of each combination of
  two channels)
• Acquisition facility any threshold/gate-time/
  bigap-logic
• PLOT

• Detailed description of all steps through the
  pre-defined ranges of OKs , Warnings, Errors
  messages

Output file

• List of 33 relevant parameters, including FEE
  database.
• Allow further comparisons

Leds Buttons
Info Where is the problem !
OK Warning ERROR
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Results First Chambers tested _at_ LNF
100 - M5R4 Cdet (sim) 220 pF 22 - M3R3
Cdet (sim) 140 pF 06 - M5R2 Cdet (sim) 120
pF
Cdet
128 - chambers
About 10 needed some intervention pointed out by
the Test System Mostly Change FEE
(dead,noisy) Also
bad connection, SPB, I2C (chain)
Alarms !
We upgrade MaxNoiseRate 20 MHz to detect it
Those tests were performed using a MaxNoiseRate
cut 2 MHz
Recently we have observed a FEE patology that
distorted the Th-Scan at high Noise Rate
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More Plots
M5R4 M3R3 M5R2
OffSet
Noise _at_ th 10 fC 6 fC
10 KHz
Noise _at_ th 12 fC 7 fC
Noise Rate of 4 M5R4 chambers 12 CARDIACs _at_
th 14fC
1 KHz
Noise _at_ th 14 fC 8 fC
100 Hz
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Cross-Check using Cosmics

• Cosmic Acquisition is being done at CERN on
  chambers tested in LNF

2 chambers without PLATEAU
HV scan, gas, Operational Threshold signal
coincidence between 2 Bigaps 15 M5R4 analysed
up to now 100 of the defects found were
successfully detected by the Upgraded Test System
High Cdet signature More Statistic (mainly
with other chamber types) must be collected
Low Eff channel
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Conclusions

• Automatic and fast (5-10 minutes) system has been
  implemented to be used also for non-experts
• System has shown to be very effective on 130 INFN
  chambers tested fundamental guide to fix
  problematic chambers (10)
• Cosmic Acquisition pointed an unexpected kind of
  problem in 0.5 of the channels. A retest using
  the Upgraded version of Test System has been able
  to discriminate all those channels
• Now we have 4 systems operating CERN (2), LNF
  (1) and in the pit (1)
• We aim to minimize drastically the installation
  of chambers with problems