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RPCs of BESIII Muon Identifier
BESIII and muon identifier
R&D
Mass production
Installation
Zhang Qingmin
Advisor: Zhang Jiawen
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The BESIII Detector
Be beam pipe
SC magnet Magnet yoke and
muonidentifier
MDC
CsI calorimeter
TOF
It is the outmost subsystem
of the BESIII detector to
measure the muons,
consisting of muon counters
and hadron absorbers, the
muon’s position and trajectory
can be obtained through
multi-layers measurements.To obtain a large solid angle coverage, the muon counters splitted off into two parts, namely barrel and endcap.Barrel has 9 layers, its inner radius is 1700mm and outer radius 2620mm. Endcap has 8 layers.
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Muon identifier ---- Barrel & Endcap
The structure of the endcap sketch map
The size of each layer of the barrel part RPC
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The prototype RPCs for the BESIII muon identifier were constructed by using resistive electrodes made from a special type of phenolic resin developed by us.
The surface quality of these plates is improved compared to other bakelite plates that have been used to construct RPCs elsewhere. A method for adjusting the resistivity of these plates was also developed.
Extensive studies were conducted by using a number of prototype RPCs in the last several years. Tests have shown prototype RPCs made by using our resistive plates without linseed oil treatment can achieve the level of performance comparable to RPCs with linseed oil treated bakelite or resistive glass electrodes.
All of the follow experiments are in streamer mode.
R&D of RPC
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R&D ---- Amplitude vs. HV
Oscilloscope traces of 100 triggered cosmic ray muons registered in a RPC prototype at 8 kV. The average signal size from a pickup electrode is about 400 mV with a 50 Ω termination. No secondary streamers were recorded
secondary streamers
450mv
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R&D ---- Eff. And Cnt. VS. HV
0
0. 1
0. 2
0. 3
0. 4
0. 5
0. 6
0. 7
0. 8
0. 9
1
5500 6500 7500 8500 9500 10500 11500
Hi gh Vol tage (V)
Effici
ency
0
0. 05
0. 1
0. 15
0. 2
0. 25
0. 3
0. 35
0. 4
Coun
ting
Rat
e (H
z/m2 )
Effi ci encyCount i ng Rate
Efficiencies and singles counting rates versus the high voltage up to 12 kV.
This plot shows the behavior of the prototype RPC under extreme high voltages.
The gas mixture used was
Ar(argon) :C2F4H2 (Freon): C4H10 (Iso-butane)= 50:42:8.
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R&D ---- prototype performance
1.18 0.044
Efficiency Plateau: 96-98%
~2KV
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neutron irradiationother
experiments
R&D ---- long-term stability
Beam test
neutron irradiation
Max: 98.8%
Min: 95.3%Average: 97.2%
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R&D ---- Threshold
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
6000 6500 7000 7500 8000 8500 9000 9500
High Voltage (V)
Eff
icie
ncy
50mv
100mv
150mv
200mv
250mv
Efficiencies versus high voltage for different
discrimination thresholds Singles counting rates versus high voltage for
different discrimination thresholds
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R&D ---- Different gas mixture
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R&D ---- Temperature
The efficiency and counting rate versus temperature.
Efficiency curve will shift to left side at high temperatures.
And the counting rate will increase exponent with temperature.
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R&D ---- Different Resistivity
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Gas vapor test
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R&D ---- Neutron irradiation
Total dose: 106rad
Efficiency: 1% ; 96%
Cnt rate: 0.18Hz/cm2
Dark current: 250% more than 1.5μA/m2
Revision time: 20days
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R&D ---- Electron Irradiation
No obvious change !
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R&D ---- γ Irradiation ( Co60 )
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Mass production
The RPC production for the BESIII muon identifier has started in middle of 2004 and finished in the early of 2005.
The average area for the endcap RPC is 1.3m2, barrel RPC 1.4m2.
The maximum area for the endcap RPC is 1.6m2, barrel RPC 2.0m2.
There are 978 RPCs and the area is about 1300m2 totally.
Each bare chamber is tested to ensure their performance is meet the requirement of the muon identifier before them assembled in the module, and all of modules are tested using cosmic rays before them installed on the BESIII.
// Maximum RPC we can make is 1.2mx2.4m. //
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Mass production ---- Bare chamber
The worker are facturing the bare chambers!
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Mass production ---- Bare chamber test
Test surrounding
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counting rate (Hz/cm2)
0.07- 0.1 0.095- 0.11
0.07- 0.1 0.08- 0.14
The performance of the RPC that just produced
HV7-8Kv,Eff 90%-95%
efficiency
HV: 7- 8Kv; Eff.>95%
Counting Rate at 7kV (Hz/cm2)
More than 95% cnt.<0.6
Efficiency at 7kV
More than 97% Eff.>90%
More than 35% Eff.>95%
Amount: 130RPCs
No
trainin
g
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Mass production ---- Bare chamber test result ---- efficiency
Training time : 1 - 3days; endcap 320RPCs, barrel 590RPCs
Endcap 7.5KvMin. 83.5%Max. 98.5%Aver.93.46%
Barrel 7.5KvMin. 85.6%Max. 99.02%Aver.95.39%
Endcap 8.0KvMin. 89.97%Max. 98.7%Aver.94.25%
Barrel 8.0KvMin. 90.38%Max. 99.2%Aver.96.4%
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Mass production ---- Bare chamber test result ---- counting rate
Training time : 1 - 3days; endcap 320RPCs, barrel 590RPCs
Endcap 7.5KvMin. 0.038Max. 0.598Aver.0.210
Barrel 7.5KvMin. 0.016Max. 0.599Aver.0.095
Endcap 8.0KvMin. 0.043Max. 0.960Aver.0.255
Barrel 8.0KvMin. 0.022Max. 0.872Aver.0.130
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Mass production ---- Bare chamber test result ---- dark current
Training time : 1 - 3days; endcap 320RPCs, barrel 590RPCs
Endcap 7.5Kv
Aver. 3.47
Barrel 7.5Kv
Aver. 1.605
Endcap 8.0Kv
Aver. 4.07
Barrel 8.0Kv
Aver. 2.415
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Temperature : 20±2ºC; Humidity≤50%; Ar:F134A:Iso=50:42:8
Reaching the efficiency plateau as the high voltage reaches 7.0kv and In the middle of the efficiency plateau (8.0KV)
Eff > 90%; Cnt. < 0.8Hz/cm2; Cur. < 10μA/m2
The resistivity range : 8x1011~5x1012Ohm
So 92% RPCs of endcap up to grade and 99% RPCs of barrel up to grade.
NOTE: All of the previous performance is signal RPC’s.
Bare chamber performance requirements
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Mass production ---- Module
The worker are assembling the modules!
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Mass production ---- Module test
Test result of an endcap module
One example of the cosmic ray test result:The plot size: 35mm*35mm;Average efficiency: 0.94Spatial resolution: 14.6mm
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…after assembling - endcap The efficiency and current distribution of all 64 endcap
modules:Note that the average efficiency is underestimated, because
the efficiency at the edge is pull down by boundary effect.Test temperature: 22-25℃
Mean 0.91 Mean 2.7 μA/m2
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Test Result after installation - endcap
Total efficiency and current of 64 endcap RPC modules after installation.Test temperature: 20-22℃
Mean 0.95Mean 1.8μA/m2
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…barrel
Module size: 3800mm*1640mmStrip length: 3800mmStrip width: 33mmAverage strip efficiency: 0.99Spatial resolution: 14.2mm
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…after assembling - barrel Total efficiency and current distribution of 72 barrel modules:
Average efficiency higher than that of endcap modules, while dark current smaller than endcap modules.
Test temperature: 22-25℃
Mean 0.98 Mean 1.1μA/m2
Barrel After installation have not been tested!
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Installation
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Installation
All except three modules have been installed!
After installing ,the endcap are being tested!
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Summary The RPCs making with new bakelite plates that we developed
have good surface quality ( ~200nm ) , it can meet with different RPC detector requirement.
The bulk resistivity range of bakelite plates is 109 ~1014Ω·cm .
The RPC avoid the problem of linseed oil and glass RPC
The RPCs have higher efficiency, lower counting rate and dark current, and good long-term stability .
The endTHANKS