The CMS experiment will install a RE4 layer of 144 new Resistive Plate Chambers (RPCs) on the existing york YE3 at both endcap regions to trigger high momentum muons from the proton-proton interaction. In this paper, we present the detailed procedures used in the production of new RPC gas gaps adopted in the CMS upgrade. Quality assurance is enforced as ways to maintain the same quality of RPC gas gaps as the existing 432 endcap RPC chambers that have been operational since the beginning of the LHC operation

Aleksandrov, A

Berzano, U

Calabria, C

Carrillo, C

Choi, S

Colaleo, A

Genchev, V

Hong, B

Iaydjiev, P

Jeng, YG

Kang, M

Lee, KS

Loddo, F

Maggi, M

Park, SK

Pugliese, G

Rodozov, M

Shopova, M

Sim, KS

Sultanov, G

Verwillingen, P

English

Ghent University Academic Bibliography

This content has been downloaded from IOPscience. Please scroll down to see the full text.Download details:IP Address: 157.193.59.60This content was downloaded on 25/08/2014 at 12:22Please note that terms and conditions apply. CMS endcap RPC gas gap production for upgradeView the table of contents for this issue, or go to the journal homepage for more2012 JINST 7 P11013(http://iopscience.iop.org/1748-0221/7/11/P11013)Home Search Collections Journals About Contact us My IOPscience2012 JINST 7 P11013PUBLISHED BY IOP PUBLISHING FOR SISSA MEDIALABRECEIVED: August 3, 2012ACCEPTED: October 9, 2012PUBLISHED: November 15, 2012SPECIAL ISSUE ON RESISTIVE PLATE CHAMBERS AND RELATED DETECTORS RPC2012CMS endcap RPC gas gap production for upgradeS.K. Park,a,1 S. Choi,a B. Hong,a Y. Gun Jeng,a M. Kang,a K.S. Lee,a K.-S.Sim,aA. Colaleo,b G. Pugliese,b F. Loddo,b C. Calabria,b M. Maggi,b P. Verwillingen,cU. Berzano,c C. Carrillo,e A. Aleksandrov, f V. Genchev, f P. Iaydjiev, f M. Rodozov, fM. Shopova f and G. Sultanov faDepartment of Physics and Korea Detector Laboratory, Korea University,Seoul, 136-701, KoreabUniversita e INFN, Sezione di Bari,Via Orabona 4, IT-70126, Bari, ItalycDepartment of Physics, Ghent University,Proeftuinstraat 86, BE-9000, Ghent, BelgiumdUniversita e INFN, Sezione di Pavia,Via Bassi 6, IT-Pavia, ItalyeUniversita e INFN, Sezione di Napoli, Complesso Univ. Monte S. Angelo,Via Cintia, IT-80126, Napoli, Italyf Bulgarian Academy of Sciences, Institute for Nuclear Research and Nuclear Energy,Tzarigradsko shaussee Boulevard 72, BG-1784, Sofia, BulgariaE-mail: sungpark@korea.ac.krABSTRACT: The CMS experiment will install a RE4 layer of 144 new Resistive Plate Chambers(RPCs) on the existing york YE3 at both endcap regions to trigger high momentum muons from theproton-proton interaction. In this paper, we present the detailed procedures used in the productionof new RPC gas gaps adopted in the CMS upgrade. Quality assurance is enforced as ways tomaintain the same quality of RPC gas gaps as the existing 432 endcap RPC chambers that havebeen operational since the beginning of the LHC operation.KEYWORDS: Detector design and construction technologies and materials; Resistive-plate cham-bers; Trigger detectors1Corresponding author.c© 2012 IOP Publishing Ltd and Sissa Medialab srl doi:10.1088/1748-0221/7/11/P110132012 JINST 7 P11013Contents1 Introduction 12 Production procedure 32.1 Mechanical components 32.2 Polymerization 42.3 High voltage test 53 Packing and transportation 54 Conclusions 61 IntroductionResistive Plate Chamber (RPC) is a dedicated fast muon trigger for the CMS experiment at LHC [1].Installed both in the barrel and in the endcap region it was originally planned to cover a rapidity upto η=2.1. However in the endcap region, the original four layers were reduced to three which havebeen installed on the faces of the iron return yokes. It consequently reduces the rapidity coverageup to η=1.6.Completion of the endcap RPC system with four layers will be achieved by addition of onemore RPC layer to the existing layers. The new 144 RPCs will form this additional layer calledRE4. And it will be installed on the face of the existing yoke YE3. And it will restore the triggercoverage up to η= 2.1 as planned.For the RPCs to provide an efficient muon trigger to the CMS experiment, the gas gaps mustmeet the CMS requirements for RPCs as shown in table 1. To meet these performance require-ments, we build the gaps with two most important considerations in mind: an overall mechanicalstability and an uniform electric field over the active gas volume.In the CMS RPCs, one side of the bakelite plate is coated with graphite to make the resistiveelectrode. Two resistive electrodes are separated by 2 mm spacers to form the parallel plate gasTable 1. CMS RPC requirements.Parameters Allowable rangesEfficiency >95%Time resolution 6 1 nsAverage cluster size 6 2 stripsRate capability 2 kHz/cm2Mean avalanche charge 2.5–5 pC– 1 –2012 JINST 7 P11013Figure 1. Cross sectional view of a CMS double gap RPC.Figure 2. The RPC efficiencies in terms of charge thresholds (left), and number of gaps (right).gaps. For higher trigger efficiency the RPC gaps are in double layers. The basic structure of theCMS double gap RPC is shown in figure 1.In this paper, we describe each step according to the technology that Korea Detector Labora-tory (KODEL) developed for the endcap RPCs which have been already installed and operationalsince the beginning of the LHC operation. The high quality of the CMS RPC gaps are well capturedin figure 2 as in [2].– 2 –2012 JINST 7 P11013Figure 3. Arrangement of 50 samples of bakelite pieces to check the surface resistivity.2 Production procedure2.1 Mechanical componentsThe electrode production is the first step in the production of the gas gaps. A thin layer of graphiteis coated on the bakelite sheet by a silkscreen process. The thickness of the graphite layer is wellmaintained by the 20 µm thick silk screen mesh. The surface resistivity of the graphite layer rangesfrom 100 to 250 kΩ/square. To ensure the values and homogeneity across the electrode 50 piecesof square bakelite were prepared and the surface resistivity was measured from each sample asshown in figure 3.The gas gap assembly is the next step once the electrodes are prepared. The gas gaps areassembled with two electrodes and spacers. The coin shaped spacers are placed between twoelectrodes to form a uniform separation of 2 mm between the electrodes, and the four edges of thegas gap are sealed with four edge strips. The mechanical support of the gas gap is provided by thespacers placed 10 cm apart from each other in two orthogonal directions. The edge strips that sealthe edges of the gas gap make the gas volume leak-tight. The spacers and edge strips are placedin pre-determined locations guided by a special jig and bonded to the electrodes using epoxy witha curing time of 24 hours. To achieve the maximum bonding strength between the spacers andelectrodes, the gaps are placed in a device where an additional 30 hPa pressure to ATM is applied.The mechanical stability check of the gas gap follows after 24 hours of hardening to see thestability of the bonding and the gas tightness of the gas volume. During this test the gas volumeis over-pressured with 20 hPa. For a gas gap to be qualified the loss of the measured pressure ofthe gap should be less than 0.2 hPa during a 10-minute of test period. Additional requirement forgas gaps to pass the test is that no spacers should lose its bonding strength between two electrodeswhen the 20 hPa over-pressure is applied to the gas volume. All these mechanical tests are carriedout by a robot built at KODEL and the test results as shown in figure 5 are stored in a CMS centralORACLE data base.– 3 –2012 JINST 7 P11013Figure 4. KODEL robot performing the pressure test. The dimensions of the table are 175 cm x 250 cm(top). The result of the pressure test is shown (bottom).2.2 PolymerizationThe linseed oil treatment will follow once the gas gap passes the mechanical stability test. Duringthis process the entire gas volume is filled with linseed oil. Once dried with air the oiled surfaceforms the polymerized layer. It turns out that this polymerized layer on the surface of the bakeliteinside the gas volume reduces the spurious noise by a factor of 10 in the avalanche operationmode [3]. This procedure needs a cautious preparation due to the pressure built up by the linseedoil filling the gas gap. The pressure within the gap should remain less than 20 hPa over ATM toensure that the gas gap is not over-pressured to the limit of its epoxy bonding strength.The RE4 has six different shapes and sizes. Accommodating the variety of physical dimen-sions of the gas gaps to the oil coating facility is a difficult task due to the different orientationsof the gas inlets and outlets. Also the drying period of the linseed oil surface in the gas volumebecomes a significant constraint in production schedule.– 4 –2012 JINST 7 P11013Figure 5. A wooden box is designed to provide extra protections.2.3 High voltage testThe high voltage test is the next step once the gas volume treated with linseed oil is dried. Thecurrent drawn by the gas gap with high voltage applied is a good indicator of any electrical problemsinside the gas volume.The gas mixture for the current measurement under high voltage is 95% tetrafluoroethane, 5%isobutane. The gas volume is purged at a rate of 20 l/h before applying high voltage. It amounts to15 times the volume of the gas gap. The total duration of the current measurement is about 7 daysincluding the purging time.At the beginning of the test, the high voltage is set to 1 kV to check for any electrical mis-connection. If the gaps hold at 1 kV, then every 30 minutes, the HV is increased by 1 kV up to 6kV. At each HV setting, the currents are measured and recorded in a data sheet. From 6 kV the HVis raised up to the maximum 10 kV. From 8.4 kV, the increasing step is 200 V, finer than the 1 kVstep to see the current behaviors in the operation voltages. Once the HV has reached the maximum10 kV, it is lowered to 9.6 kV for a test period of 96 hours.3 Packing and transportationEvery 60 qualified gas gaps are vertically mounted into a wooden box equipped with four pre-loaded bars which were designed to press the surface of the gas gaps horizontally. Polystyrenefoam sheets of 5mm thickness are placed between the layers of the gas gaps to absorb shockswhich could occur during transportation. Extra protection from unexpected moisture is providedby wrapping the whole 60 gas gaps with a thin vinyl film. The pipes for the gas inlets and outletsare left open to adapt to sudden variations of pressure during air transport.– 5 –2012 JINST 7 P110134 ConclusionsWe report that 144 new RPCs will be produced according to the same procedure that Korea DetectorLaboratory (KODEL) developed for the CMS endcap RPC stations of RE1, RE2 and RE3. Weconclude that the production and subsequent quality assurance described here has been proven tobe effective for the mass production of the large RPC detectors for the CMS experiment.AcknowledgmentsWe acknowledge the support of Korea University and the Korean Research Foundation.References[1] CMS collaboration, The Muon Project, Technical Design Report, CERN-LHCC 97-32, December1997.[2] S. Ahn et al., Threshold dependence of strip clusters for the forward region resistive plate chamber ofthe CMS/LHC experiment, Nucl. Instrum. Meth. A 508 (2003) 147.[3] S. Park et al., Beam test results of CMS RPCs at high eta region under high-radiation environment,Nucl. Instrum. Meth. A 533 (2004) 37.– 6 –

CMS endcap RPC gas gap production for upgrade

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CMS endcap RPC gas gap production for upgrade

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