- Email: [email protected]
Test and performances of the RPC trigger chambers of the ATLAS experiment at LHC
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 533 (2004) 193–198 www.elsevier.com/locate/nima
Test and performances of the RPC trigger chambers of the ATLAS experiment at LHC G. Aiellia, M. Alviggib,c, A. Ammosovd, M. Bigliettib, E. Brambillae, P. Camarria, V. Canaleb,c, M. Capriob,c, R. Cardarellia, G. Carlinob, G. Cataldie, G. Chiodinie, A. Disimonea,f, A. Diciaccioa,f, D. della Volpeb, R. de Asmundisb, M. Della Pietrab,c, F. Grancagnoloe, E. Gorinie,g, P. Iengob,c,, B. Libertia, S. Patricellib,c, R. Perrinoe, M. Primaverae, R. Santonicoa,f, G. Sehkniadzeb, S. Spagnoloe,g, Yu. Sviridovd, V. Zaetsd a
INFN sez. Rome2, Roma, Italy INFN sez. Naples, Napoli, Italy c University ‘‘Federico II’’, Napoli, Italy d IHEP, Protvino, Russia e INFN sez. Lecce, Lecce, Italy f University ‘‘Tor Vergata’’, Roma, Italy g University of Lecce, Lecce, Italy b
Available online 26 July 2004
Abstract RPCs will be used as trigger detectors in the barrel region of the Muon Spectrometer of the ATLAS experiment at LHC. The total number of RPC units to be installed is 1088, covering a total surface of about 3500 m2 . ATLAS RPCs work in avalanche mode with C2 H2 F4 /C4 H10 /SF6 (94.7%/5%/0.3%) gas mixture. A cosmic ray test stand has been designed and built in Naples laboratories in order to carry out a complete test of the ATLAS RPC units. Since August 2002 about 300 units have been tested. A description of the test stand, test procedure and results are presented. r 2004 Elsevier B.V. All rights reserved. PACS: 29.40.Cs; 06.60.Mr Keywords: RPC; ATLAS; Muon trigger; Test
Corresponding author. INFN sez. Naples, Napoli, Italy.
E-mail address: [email protected] (P. Iengo). 0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.07.026
ARTICLE IN PRESS 194
G. Aielli et al. / Nuclear Instruments and Methods in Physics Research A 533 (2004) 193–198
1. RPCs for the ATLAS experiment The ATLAS experiment [1] uses bakelite RPCs [2] as trigger chambers in the barrel region of the Muon Spectrometer to fulfill the following requirements: high efficiency (97%) and good time resolution (2–3 ns); high rate capability, up to 100 Hz/cm2 ; measurement of the j coordinate with resolution of 5–10 mm. An RPC unit contains four gas volumes (two for BMS type) disposed on two layers. Each layer is made of two bakelite electrodes 2.0 mm thick with a bulk resistivity in the range (1–4)1010 O cm; the external faces are coated with spray graphite and then insulated with a 190 mm thick PET layer, the internal surfaces are treated with linseed oil. The electrodes are separated by specially shaped polycarbonate spacers and frame. The gas mixture is C2 H2 F4 =C4 H10 =SF6 in the percentages 94.7%, 5% and 0.3%. The pick-up electrodes are stripshaped copper panels, with a pitch ranging between 26.4 and 33.9 mm, in two orthogonal directions (Z and j), equipped with the front-end electronics. More than 1000 RPC units, covering a total surface of about 3500 m2 , will be installed in ATLAS.
signals. Data acquisition is done in common stop configuration. DAQ rate is about 8 Hz. A dedicated detector control system was developed in order to set and control all the working parameters as well as to monitor the environmental ones. All the values are continuously stored in a dedicated database allowing to get historical trends and correlations between them at any time. The high voltage applied on the chambers is corrected real time for temperature and pressure variations to standard values (T ¼ 20:5 C; P ¼ 1013 hPa).
3. Test procedure Testing a set of eight RPC units takes about one week and the test protocol contemplates the following sequential steps [5]: (1) Preliminary operations: mechanical installation, cabling and gas connection, electric test, leak test and conditioning procedure. (2) Single-rate measurement at low voltage, with threshold ranging between 0.1 and 1.5 V (with 0.1 V steps) at a fixed HV=1.0 kV.
2. The Naples cosmic rays test stand In order to perform a complete test of the ATLAS RPCs, a cosmic ray test stand [3,4] was designed and built in the Naples INFN and University ‘‘Federico II’’ laboratory. Its mechanical structure consists of 4.5 m length, 2 m wide and 3.2 m height iron made support frame where up to eight RPC units, corresponding to more than 3000 read-out channels, can be hosted and tested simultaneously. A trigger signal is provided by two scintillator planes, while two drift chambers are used as tracking system allowing a single wire resolution of 400 mm. Pulses coming from drift chambers are acquired by 1.04 ns resolution TDCs in VME standard, while single ended ECL signals from RPCs are converted to 30 ns TTL pulses and acquired by Latches VME modules at 66 MHz clock cycle. A CAMAC crate hosts 25 ps resolution TDCs for the acquisition of scintillators
Fig. 1. Current scan for four gas volumes.
ARTICLE IN PRESS G. Aielli et al. / Nuclear Instruments and Methods in Physics Research A 533 (2004) 193–198
195
1
0.8
0.8
0.6
0.6
Eff.
Eff.
Efficiency vs. HV 1
0.4 Phi
0.2
Eta
V50% 9310 V 9276 V V90-10% 665 V 657 V
0 9000
9500
10000
0.4 Phi
0.2 0
10500
Eta
V50% 9457 V 9476 V V90-10% 704 V 690 V 9000
9500
10000
10500
HV(V)
HV(V)
Layer 1 Left
Layer 1 Right
Fig. 2. Efficiency plateaux for Z and j strip panels for two gas volumes of the same unit.
BMLD-020
Thres.=1200 mV
HV=10500 V
Run Start=12/9/2002
Gas Volume Inefficiency golden = 264657
1
golden = 268215
0.9
1200
0.8 0.7
1000
0.6 0.5
800
0.4 0.3
600
0.2
400
1- ε = 2.05 %
0.1
1- ε = 1.95 %
0
500
1000
1500
2000
2500
3000
3500
4000
Ineff. points for both Eta and Phi 1
Fig. 3. Gas volume inefficiency distribution: spacers and gap frames are clearly visible.
Fig. 4. Chamber test rate at the Naples test stand since August 2002.
(3) High voltage scan with HV ranging between 1.0 and 10.5 kV (with 0.1 kV steps) at fixed threshold of 1.0 V. An example is shown in Fig. 1 where the volt–amperometric curves of four gas volumes belonging to the same unit are fitted with the sum of ohmic and exponential contributes. Typical currents at the working point are less than 10 mA. The same data-taking is used to measure the single rate scan for each strip panel as a function of the applied voltage. (4) Single-rate measurement at high voltage, with threshold ranging between 0.1 and 1.5 V (with 0.1 V steps) at a fixed HV=10.5 kV. From these
ARTICLE IN PRESS 196
G. Aielli et al. / Nuclear Instruments and Methods in Physics Research A 533 (2004) 193–198 Total number of gaps = 504 Last update on 09/09/2003 Gas Volume Efficiency
Total number of gaps = 504 Last update on 09/09/2003 Eta Efficiency Radiography
300
140
Known Problems BAD OK
Known Problems 250
BAD
120
OK 100
Gaps
Gaps
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150
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20
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95
96
97
98
0 80
99 100
82
84
86
Eff. (%)
88
90
92
94
96
98
100
Eff. (%)
Fig. 5. Statistical distribution of gas volume (left) and Z read-out (right) efficiency.
Total number of gaps = 504 Last update on 09/09/2003 V(ε=50%)
Total number of gaps = 504 Last update on 09/09/2003 V(ε =90 % ) - V(ε =10%)
120 Both Only Only
100
160
and
Both Only
140
and
Only
120
Gaps
Gaps
80
60
100 80 60
40
40 20 20 0 9100
0 9200
9300
9400
9500
9600
9700
9800
500
600
700
HV(V)
800
900
1000
HV(V)
Fig. 6. Statistical distributions for parameters V 50% and D of the plateaux curves. Dashed lines refeers to Z and j panels separately, continuous line refers to both Z and j.
measurements the threshold working range for each strip panel is established and problematic panels (showing large or zero single-rate level) are individuate. On the average a normal value of single rate below 5 Hz=cm2 per panel is found. (5) Random trigger at HV ¼ 10:5 kV and V th ¼ 1:0 V which allows to individuate noisy strips or ‘hot’ zones of the gas volumes. Typical noise level is below 10–20 Hz=cm2 .
(6) Efficiency plateau at three different thresholds (0.9,1.0 and 1.1 V) with 2500 events/m2 per fixed HV and threshold. Plateaux curves for both Z and j panels are fitted with a Fermi’s function eðV Þ ¼
A 1þ
eBðV V 50% Þ
ð1Þ
in order to extract the plateau efficiency A, the voltage at 50% of maximum efficiency V 50% and
ARTICLE IN PRESS G. Aielli et al. / Nuclear Instruments and Methods in Physics Research A 533 (2004) 193–198
the voltage range D between 10% and 90% of A. An example is shown in Fig. 2. With the same data cluster size and cluster multiplicity as a function of the applied voltages, and thresholds are also measured. (7) Radiography at HV=10.5 kV and V th ¼ 1:0 V. It consists in a high statistic data sample (25 0000 events/m2 ) to measure strip-bystrip efficiency and intrinsic inefficiency of gas volumes and of read-out panels. Fig. 3 shows a radiography result for a layer with two gas volumes. The gas volume geometrical inefficiency of 2% corresponds to spacers and frame, while the inefficiency of panel read-out is less than 1%. (8) A new current scan is performed at the end of the test in order to check the status of the currents after some days of operation. An unit is accepted only if it passes all the described tests. Test results as well as information coming from the production chain are stored on a public database managed by Naples group.
4. Test status and results The massive test at Naples stand started in August 2002, since then about 300 RPC units have been tested. Fig. 4 shows the chamber test rate up to the end of October 2003, showing that after some weeks of training the full test speed of eight chambers per week is now reached. The rejection rate is 2.5% for gas volumes having inefficient regions, high current or gas leak and 3% for readout panels having at least two dead strips. Fig. 5 show statistical distributions for gas volumes and Z strip panels efficiencies measured over 504 gas volumes. On the same plots are reported entries rejected (BAD) or accepted but with efficiency measurement affected by contingent (known) problems. A gas volume efficiency peak well above 96% is evident. Statistical distributions of the parameters extracted by fitting the plateaux curves can be built and are shown in Fig. 6. The distributions are well behaving ones indicating a good homogeneity in the working parameters of chambers constructed and tested in different times and different conditions. The goodness of the ATLAS RPCs was also
197
Fig. 7. Plateau curve measured in the 2003 H8 test-beam for a Z panel.
confirmed in the 2003 test-beam performed in the H8 area at CERN [5]. Fig. 7 shows a plateau curve measured with data acquired with a 25 ns bunched beam.
5. Conclusions A stand dedicated to the test of ATLAS RPCs is operative since August 2002 with a standardized procedure both for data acquisition and software analysis. Test rate is 8 units/week and about 300 units have been already tested. Test results and their statistical distributions show that the RPCs are well working and their performances are stable and uniform, satisfying the requirement coming from the experiment. An average rejection rate of 2.5% on gas volumes and of 3% on read-out panels was found. Good chamber performances were also measured during the 2003 H8 test-beam in a completely different environment and set-up. References [1] ATLAS Collaboration, CERN/LHCC/94-43 LHCC/P2, 1996.
ARTICLE IN PRESS 198
G. Aielli et al. / Nuclear Instruments and Methods in Physics Research A 533 (2004) 193–198
[2] ATLAS RPC Collaboration, CERN/EB-99-002, 1999. [3] A. Alviggi, et al., Nucl. Instr. and Meth. A 508 (2003) 124,159.
[4] A. Alviggi, et al., Nucl. Instr. and Meth. A 518 (2004) 79. [5] P. Iengo, Ph.D. Thesis, Universita` degli Studi di Napoli ‘‘Federico II’’, 2003.
Nuclear Instruments and Methods in Physics Research A 533 (2004) 193–198 www.elsevier.com/locate/nima
Test and performances of the RPC trigger chambers of the ATLAS experiment at LHC G. Aiellia, M. Alviggib,c, A. Ammosovd, M. Bigliettib, E. Brambillae, P. Camarria, V. Canaleb,c, M. Capriob,c, R. Cardarellia, G. Carlinob, G. Cataldie, G. Chiodinie, A. Disimonea,f, A. Diciaccioa,f, D. della Volpeb, R. de Asmundisb, M. Della Pietrab,c, F. Grancagnoloe, E. Gorinie,g, P. Iengob,c,, B. Libertia, S. Patricellib,c, R. Perrinoe, M. Primaverae, R. Santonicoa,f, G. Sehkniadzeb, S. Spagnoloe,g, Yu. Sviridovd, V. Zaetsd a
INFN sez. Rome2, Roma, Italy INFN sez. Naples, Napoli, Italy c University ‘‘Federico II’’, Napoli, Italy d IHEP, Protvino, Russia e INFN sez. Lecce, Lecce, Italy f University ‘‘Tor Vergata’’, Roma, Italy g University of Lecce, Lecce, Italy b
Available online 26 July 2004
Abstract RPCs will be used as trigger detectors in the barrel region of the Muon Spectrometer of the ATLAS experiment at LHC. The total number of RPC units to be installed is 1088, covering a total surface of about 3500 m2 . ATLAS RPCs work in avalanche mode with C2 H2 F4 /C4 H10 /SF6 (94.7%/5%/0.3%) gas mixture. A cosmic ray test stand has been designed and built in Naples laboratories in order to carry out a complete test of the ATLAS RPC units. Since August 2002 about 300 units have been tested. A description of the test stand, test procedure and results are presented. r 2004 Elsevier B.V. All rights reserved. PACS: 29.40.Cs; 06.60.Mr Keywords: RPC; ATLAS; Muon trigger; Test
Corresponding author. INFN sez. Naples, Napoli, Italy.
E-mail address: [email protected] (P. Iengo). 0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.07.026
ARTICLE IN PRESS 194
G. Aielli et al. / Nuclear Instruments and Methods in Physics Research A 533 (2004) 193–198
1. RPCs for the ATLAS experiment The ATLAS experiment [1] uses bakelite RPCs [2] as trigger chambers in the barrel region of the Muon Spectrometer to fulfill the following requirements: high efficiency (97%) and good time resolution (2–3 ns); high rate capability, up to 100 Hz/cm2 ; measurement of the j coordinate with resolution of 5–10 mm. An RPC unit contains four gas volumes (two for BMS type) disposed on two layers. Each layer is made of two bakelite electrodes 2.0 mm thick with a bulk resistivity in the range (1–4)1010 O cm; the external faces are coated with spray graphite and then insulated with a 190 mm thick PET layer, the internal surfaces are treated with linseed oil. The electrodes are separated by specially shaped polycarbonate spacers and frame. The gas mixture is C2 H2 F4 =C4 H10 =SF6 in the percentages 94.7%, 5% and 0.3%. The pick-up electrodes are stripshaped copper panels, with a pitch ranging between 26.4 and 33.9 mm, in two orthogonal directions (Z and j), equipped with the front-end electronics. More than 1000 RPC units, covering a total surface of about 3500 m2 , will be installed in ATLAS.
signals. Data acquisition is done in common stop configuration. DAQ rate is about 8 Hz. A dedicated detector control system was developed in order to set and control all the working parameters as well as to monitor the environmental ones. All the values are continuously stored in a dedicated database allowing to get historical trends and correlations between them at any time. The high voltage applied on the chambers is corrected real time for temperature and pressure variations to standard values (T ¼ 20:5 C; P ¼ 1013 hPa).
3. Test procedure Testing a set of eight RPC units takes about one week and the test protocol contemplates the following sequential steps [5]: (1) Preliminary operations: mechanical installation, cabling and gas connection, electric test, leak test and conditioning procedure. (2) Single-rate measurement at low voltage, with threshold ranging between 0.1 and 1.5 V (with 0.1 V steps) at a fixed HV=1.0 kV.
2. The Naples cosmic rays test stand In order to perform a complete test of the ATLAS RPCs, a cosmic ray test stand [3,4] was designed and built in the Naples INFN and University ‘‘Federico II’’ laboratory. Its mechanical structure consists of 4.5 m length, 2 m wide and 3.2 m height iron made support frame where up to eight RPC units, corresponding to more than 3000 read-out channels, can be hosted and tested simultaneously. A trigger signal is provided by two scintillator planes, while two drift chambers are used as tracking system allowing a single wire resolution of 400 mm. Pulses coming from drift chambers are acquired by 1.04 ns resolution TDCs in VME standard, while single ended ECL signals from RPCs are converted to 30 ns TTL pulses and acquired by Latches VME modules at 66 MHz clock cycle. A CAMAC crate hosts 25 ps resolution TDCs for the acquisition of scintillators
Fig. 1. Current scan for four gas volumes.
ARTICLE IN PRESS G. Aielli et al. / Nuclear Instruments and Methods in Physics Research A 533 (2004) 193–198
195
1
0.8
0.8
0.6
0.6
Eff.
Eff.
Efficiency vs. HV 1
0.4 Phi
0.2
Eta
V50% 9310 V 9276 V V90-10% 665 V 657 V
0 9000
9500
10000
0.4 Phi
0.2 0
10500
Eta
V50% 9457 V 9476 V V90-10% 704 V 690 V 9000
9500
10000
10500
HV(V)
HV(V)
Layer 1 Left
Layer 1 Right
Fig. 2. Efficiency plateaux for Z and j strip panels for two gas volumes of the same unit.
BMLD-020
Thres.=1200 mV
HV=10500 V
Run Start=12/9/2002
Gas Volume Inefficiency golden = 264657
1
golden = 268215
0.9
1200
0.8 0.7
1000
0.6 0.5
800
0.4 0.3
600
0.2
400
1- ε = 2.05 %
0.1
1- ε = 1.95 %
0
500
1000
1500
2000
2500
3000
3500
4000
Ineff. points for both Eta and Phi 1
Fig. 3. Gas volume inefficiency distribution: spacers and gap frames are clearly visible.
Fig. 4. Chamber test rate at the Naples test stand since August 2002.
(3) High voltage scan with HV ranging between 1.0 and 10.5 kV (with 0.1 kV steps) at fixed threshold of 1.0 V. An example is shown in Fig. 1 where the volt–amperometric curves of four gas volumes belonging to the same unit are fitted with the sum of ohmic and exponential contributes. Typical currents at the working point are less than 10 mA. The same data-taking is used to measure the single rate scan for each strip panel as a function of the applied voltage. (4) Single-rate measurement at high voltage, with threshold ranging between 0.1 and 1.5 V (with 0.1 V steps) at a fixed HV=10.5 kV. From these
ARTICLE IN PRESS 196
G. Aielli et al. / Nuclear Instruments and Methods in Physics Research A 533 (2004) 193–198 Total number of gaps = 504 Last update on 09/09/2003 Gas Volume Efficiency
Total number of gaps = 504 Last update on 09/09/2003 Eta Efficiency Radiography
300
140
Known Problems BAD OK
Known Problems 250
BAD
120
OK 100
Gaps
Gaps
200
150
80 60
100 40 50
20
0 90
91
92
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94
95
96
97
98
0 80
99 100
82
84
86
Eff. (%)
88
90
92
94
96
98
100
Eff. (%)
Fig. 5. Statistical distribution of gas volume (left) and Z read-out (right) efficiency.
Total number of gaps = 504 Last update on 09/09/2003 V(ε=50%)
Total number of gaps = 504 Last update on 09/09/2003 V(ε =90 % ) - V(ε =10%)
120 Both Only Only
100
160
and
Both Only
140
and
Only
120
Gaps
Gaps
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60
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0 9200
9300
9400
9500
9600
9700
9800
500
600
700
HV(V)
800
900
1000
HV(V)
Fig. 6. Statistical distributions for parameters V 50% and D of the plateaux curves. Dashed lines refeers to Z and j panels separately, continuous line refers to both Z and j.
measurements the threshold working range for each strip panel is established and problematic panels (showing large or zero single-rate level) are individuate. On the average a normal value of single rate below 5 Hz=cm2 per panel is found. (5) Random trigger at HV ¼ 10:5 kV and V th ¼ 1:0 V which allows to individuate noisy strips or ‘hot’ zones of the gas volumes. Typical noise level is below 10–20 Hz=cm2 .
(6) Efficiency plateau at three different thresholds (0.9,1.0 and 1.1 V) with 2500 events/m2 per fixed HV and threshold. Plateaux curves for both Z and j panels are fitted with a Fermi’s function eðV Þ ¼
A 1þ
eBðV V 50% Þ
ð1Þ
in order to extract the plateau efficiency A, the voltage at 50% of maximum efficiency V 50% and
ARTICLE IN PRESS G. Aielli et al. / Nuclear Instruments and Methods in Physics Research A 533 (2004) 193–198
the voltage range D between 10% and 90% of A. An example is shown in Fig. 2. With the same data cluster size and cluster multiplicity as a function of the applied voltages, and thresholds are also measured. (7) Radiography at HV=10.5 kV and V th ¼ 1:0 V. It consists in a high statistic data sample (25 0000 events/m2 ) to measure strip-bystrip efficiency and intrinsic inefficiency of gas volumes and of read-out panels. Fig. 3 shows a radiography result for a layer with two gas volumes. The gas volume geometrical inefficiency of 2% corresponds to spacers and frame, while the inefficiency of panel read-out is less than 1%. (8) A new current scan is performed at the end of the test in order to check the status of the currents after some days of operation. An unit is accepted only if it passes all the described tests. Test results as well as information coming from the production chain are stored on a public database managed by Naples group.
4. Test status and results The massive test at Naples stand started in August 2002, since then about 300 RPC units have been tested. Fig. 4 shows the chamber test rate up to the end of October 2003, showing that after some weeks of training the full test speed of eight chambers per week is now reached. The rejection rate is 2.5% for gas volumes having inefficient regions, high current or gas leak and 3% for readout panels having at least two dead strips. Fig. 5 show statistical distributions for gas volumes and Z strip panels efficiencies measured over 504 gas volumes. On the same plots are reported entries rejected (BAD) or accepted but with efficiency measurement affected by contingent (known) problems. A gas volume efficiency peak well above 96% is evident. Statistical distributions of the parameters extracted by fitting the plateaux curves can be built and are shown in Fig. 6. The distributions are well behaving ones indicating a good homogeneity in the working parameters of chambers constructed and tested in different times and different conditions. The goodness of the ATLAS RPCs was also
197
Fig. 7. Plateau curve measured in the 2003 H8 test-beam for a Z panel.
confirmed in the 2003 test-beam performed in the H8 area at CERN [5]. Fig. 7 shows a plateau curve measured with data acquired with a 25 ns bunched beam.
5. Conclusions A stand dedicated to the test of ATLAS RPCs is operative since August 2002 with a standardized procedure both for data acquisition and software analysis. Test rate is 8 units/week and about 300 units have been already tested. Test results and their statistical distributions show that the RPCs are well working and their performances are stable and uniform, satisfying the requirement coming from the experiment. An average rejection rate of 2.5% on gas volumes and of 3% on read-out panels was found. Good chamber performances were also measured during the 2003 H8 test-beam in a completely different environment and set-up. References [1] ATLAS Collaboration, CERN/LHCC/94-43 LHCC/P2, 1996.
ARTICLE IN PRESS 198
G. Aielli et al. / Nuclear Instruments and Methods in Physics Research A 533 (2004) 193–198
[2] ATLAS RPC Collaboration, CERN/EB-99-002, 1999. [3] A. Alviggi, et al., Nucl. Instr. and Meth. A 508 (2003) 124,159.
[4] A. Alviggi, et al., Nucl. Instr. and Meth. A 518 (2004) 79. [5] P. Iengo, Ph.D. Thesis, Universita` degli Studi di Napoli ‘‘Federico II’’, 2003.