RPCs of BESIII Muon Identifier

BESIII and muon identifier

R&D

Mass production

Installation

Zhang Qingmin

Advisor: Zhang Jiawen

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.

Muon identifier ---- Barrel & Endcap

The structure of the endcap sketch map

The size of each layer of the barrel part RPC

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

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

R&D ---- Eff. And Cnt. VS. HV

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5500 6500 7500 8500 9500 10500 11500

Hi gh Vol tage (V)

Effici

ency

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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.

R&D ---- prototype performance

1.18 0.044

Efficiency Plateau: 96-98%

~2KV

neutron irradiationother

experiments

R&D ---- long-term stability

Beam test

neutron irradiation

Max: 98.8%

Min: 95.3%Average: 97.2%

R&D ---- Threshold

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6000 6500 7000 7500 8000 8500 9000 9500

High Voltage (V)

Eff

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ncy

50mv

100mv

150mv

200mv

250mv

Efficiencies versus high voltage for different

discrimination thresholds Singles counting rates versus high voltage for

different discrimination thresholds

R&D ---- Different gas mixture

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.

R&D ---- Different Resistivity

Gas vapor test

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

R&D ---- Electron Irradiation

No obvious change !

R&D ---- γ Irradiation ( Co60 )

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. //

Mass production ---- Bare chamber

The worker are facturing the bare chambers!

Mass production ---- Bare chamber test

Test surrounding

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

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%

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

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

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

Mass production ---- Module

The worker are assembling the modules!

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

…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

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

…barrel

Module size: 3800mm*1640mmStrip length: 3800mmStrip width: 33mmAverage strip efficiency: 0.99Spatial resolution: 14.2mm

…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!

Installation

Installation

All except three modules have been installed!

After installing ,the endcap are being tested!

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