Chinese Physics C (HEP & NP)
Vol. 32, No. 3, Mar., 2008
Quality control and database on resistive plate chambers for the BES0 0 experiment HAN Ji-Feng(¸V¹)1,2;1) YAO Ning(w)1,3
ZHANG Jia-Wen(Ü[©)1
LIU Qian(4Ê)1,2
CHEN Jin(?)1
XIE Yu-Guang( 2)1,2
QIAN Sen(aÜ)1,2
ZHAO Jian-Bing(ëïW)1
ZHANG Qing-Min(ܬ)1,2
MA Lie-Hua(êu)1,2
1 (Institute of High Energy Physics, CAS, Beijing 100049, China) 2 (Graduate University of Chinese Academy of Sciences, Beijing 100049, China) 3 (Zhengzhou University, Zhengzhou 450052, China)
Abstract The chamber production and installation of the BES0 MUON identifier system have been finished. The cosmic ray test result after installation shows that the average efficiency is bigger than 95% and can meet the requirement of the design report. A database including all the chamber parameters and performance data has been constructed and is accessible online. The quality control procedures during the production and the database are described.
Key words resistive plate chamber (RPC), BES0, MUON identifier, quality control, database PACS 29.40.-n, 29.40.Cs
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Introduction
BES0 is a spectrometer that will work in the upgrade Beijing Electron-Positron Collider[1] . It will have superior momentum resolution for charged particles and much higher energy resolution for photons. The MUON identifier is a sub-detector which lays in the outmost part of BES0 and the main purpose is to identify muons. The muon identifier has an octagonal structure and can be divided into two parts: the barrel and the end cap. The barrel region has nine layers of resistive plate chamber (RPC)[2] super module (SM) as active muon detector and nine layers of iron plates as hadron absorbers. The end cap region has eight layers of RPC SM and nine layers of iron plates. The mass production of BES0 MUON RPC was started in June, 2004, and finished in June 2005. Approximately 1000 bare RPCs (1200 m2 ) of different sizes and shapes were constructed and a list of quality control tests were done to ensure the performance, such as the cosmic ray test for the average efficiency, the counting rate and current versus high voltage, etc. The assembling of the BES0 MUON SM was started in March 2005 and finished in October 2005.
The final front-end electronics and high voltage connector were equipped with them and a cosmic ray station was built to test the SM performance such as the efficiency, the cluster size, etc. The installation of MUON SM was started in June 2005 and finished in September 2005. One MYSQL database including the chamber parameter and performance test results was constructed.
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RPC mass production
The mass production of BES0 MUON RPC was described in Ref. [3]. The electrodes of BES0 RPC were made of bakelite plate coated with a layer of special plastic film without using linseed oil[4] , which was proved to have excellent surface quality and good performance[5—7] . Fig. 1 shows the RPC structure, which is composed of two 2 mm bakelite electrodes and one 2 mm gas gap. The 2 mm gas gap is ensured by the spacers. The central part of the spacer is 1.8 mm thick, which is used to bind the two bakelite plates together with certain amount of glues. The electrode bulk resistivity of the bakelite plate was controlled in the range of 2×1011 to 2×1013 Ω·cm at 22±2 ℃ based on the prototype R&D test result[7] ,
Received 28 April 2007, Revised 30 May 2007 1) E-mail:
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HAN Ji-Feng et alµQuality control and database on resistive plate chambers for the BES0 experiment
and the graphite surface resistivity was controlled in the range of 2×105—1×106 Ω/. Only the plates that the resistivity was within the former range were accepted to use. Fig. 2 shows the electrode bulk resistivity and graphite surface resistivity distribution of all RPCs.
Fig. 1. The cross-section view of the RPC, the thickness of the electrode plate is 2 mm, and the thickness of the gas gap is 2 mm.
Fig. 2. The electrode bulk resistivity and graphite surface resistivity distribution of all bare RPCs.
The RPC chamber was fabricated in Beijing Gaonengkedi Co. Ltd. The assembly of RPC was done in a temperature, humidity controlled and air filtered clean room to ensure the cleanness. After assembling there were many quality control procedures which were described in detail in the following.
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The first quality control procedures after assembling was the leakage test, the press test, etc., which were done in the factory by the technicians. For leakage and press test, first a positive pressure of 100 mmH2 O was put on the RPC, and the pressure variation should be less than 5 mmH2 O in a 30minute period; then a negative pressure of 50 mmH2 O was put on, and the pressure variation should be less than 5 mmH2 O in a 30 minute period, or else the RPC was rejected. The press test was used to check whether there are unglued spacers[3] . The RPC should have no more than one unglued spacers or else the RPC was rejected.
Fig. 3. The efficiency, counting rate and current distribution of all bare RPCs at 8000 V.
Then the training process was done for each RPC. The training was done with pure argon gas at the high voltage of 10 000 V for at least 24 hours until the current is less than 100 µA/m2 . For the failed RPCs another 24 hours were trained, and would be rejected if failed again. Finally the qualified RPCs that pass all the tests were delivered to IHEP for cosmic ray test. The effi-
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ciency, the counting rate and the current versus high voltage were tested by IHEP people. The working gas mixture was 50% argon, 42% C2 H2 F4 and 8% isoButane. Only the RPCs that could pass the following criteria were accepted: the efficiency plateau was longer than 600 V; at 8000 V the efficiency was higher than 85%, the counting rate smaller than 1 Hz/cm2 and the current smaller than 20 µA/m2 . The chamber parameter data and the cosmic ray test data were saved into the MYSQL database during the production and could be accessed online. Fig. 2 shows the efficiency, counting rate and current distribution at 8000 V of all bare RPC chambers.
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Super module assembling and test
Two layers of RPC and one layer of readout strip were aligned into one aluminum box to constitute one super module (SM), as shown in Fig. 4. The assembling of SM was done at IHEP by Gaonengkedi technicians. After assembling all the cables and gas pipes connected into the SM were tested to make sure they were connected properly. Then the performance of SM such as the efficiency, the cluster size, the current, etc. was tested as the final quality control procedure. The SM was tested at the working high voltage of 8000 V and using the working gas mixture of 50% argon, 42% C2 H2 F4 and 8% iso-Butane.
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For the barrel SMs, another station using barrel RPC SMs was built to test the performance of the other barrel SMs[9] . In both cases the SM was divided into small cells of the size 35 mm×35 mm and the efficiency map was calculated. The calculation was done in this way, first the cosmic ray was reconstructed for each event, then the expected hit position was calculated for the test SM, and finally the efficiency was get by comparing whether the expected hit position was fired or not. The following criteria were used to ensure qualified SMs: More than 90% of the test area’s efficiency should be higher than 95%; the current should be smaller than 20 µA/m2 . Fig. 5 shows the efficiency map, spatial resolution and cluster size distribution of one end cap SM. And Fig. 6 shows that of one barrel SM. It is found that for most areas the cell efficiency was higher than 95% except the area nearing the boundaries for both SMs.
Fig. 4. The schematic view of one SM, which contains two layers of RPC and one layer of readout strip.
One cosmic ray station using streamer tubes was built to test the performance of the end cap SM[8] .
Fig. 5. The efficiency map, spatial resolution and cluster size distribution of one end cap SM.
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HAN Ji-Feng et alµQuality control and database on resistive plate chambers for the BES0 experiment
For each SM the mean cell efficiency was calculated to represent the SM efficiency. Fig. 7 shows the SM efficiency (a) and current (b) distribution of all 64 end cap SMs and 72 barrel SMs. It is found that the current of the RPC would decrease during long term operation[4] , and that’s the reason that the SM current was much smaller than that of the bare RPC chambers in Fig. 3. The cosmic ray test results were saved into the database too.
For bare RPC chambers the material and performance of each RPC could be accessed. The material of the RPC includes the electrode bulk resistivity, graphite surface resistivity, the test temperature, humility, the installed position, etc., and the performance includes the efficiency, counting rate, current versus high voltage curve. For SMs the parameters as well as the SM cosmic ray test result were contained in the database and could be accessed on the web. The SM parameter data includes the SM size, the number of readout strips, the strip width, the installed front end electronics card, and the inner bare RPCs, etc. And the SM performance includes the efficiency map, the spatial resolution, the cluster size, etc. There are several pages about the performance distribution of all the bare RPC chambers and SMs such as the efficiency, the counting rate, the current distribution at given high voltage for all bare RPC chambers and the SM efficiency, current distribution for all SMs. The database could be accessed inside IHEP at the URL: http://muondb.ihep.ac.cn.
Fig. 6. The efficiency map, spatial resolution and cluster size distribution of one barrel SM.
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The database
The software used for the database was MYSQL, PHP and APACHE. One PC with Linux operating system was used as the server.
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Fig. 7. The SM efficiency (a) and current (b) distribution of all end cap and barrel SMs.
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Conclusion The BES0 MUON RPC has been constructed
References 1 The BES0 Detector. IHEP-BEPCII-SB-13, IHEP, Beijing 2 Santonico R, Cardarelli R. Nucl. Instrum. Methods, 1981, 187: 377 3 ZHANG Jia-Wen et al. NIM A, 2007, 580: 1250 4 ZHANG Jia-Wen et al. Nucl. Instrum. Methods A, 2005, 540: 102
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and installed. A database containing all the quality control data of MUON detector from the bare chamber production until the super module assembling and installation has been constructed.
5 ZHANG Jia-Wen et al. HEP & NP, 2003, 27(7): 615 (in Chinese) 6 ZHANG Jia-Wen et al. HEP & NP, 2003, 27(11): 1019 (in Chinese) 7 XIE Yu-Guang et al. HEP & NP, 2007, 31(1): 70 (in Chinese) 8 LIU Qian et al. HEP & NP, 2006, 30(4): 327 (in Chinese) 9 HAN Ji-Feng et al. Nucl. Instrum. Methods A, 2007, 577: 552
