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Beam and ageing tests with a highly-saturated avalanche gas mixture

VIII Workshop on Resistive Plate Chambers and Related Detectors Seoul 10-12 October. Beam and ageing tests with a highly-saturated avalanche gas mixture for the ALICE p-p data taking Francesca Poggio.

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Beam and ageing tests with a highly-saturated avalanche gas mixture

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  1. VIII Workshop on Resistive Plate Chambers and Related Detectors Seoul 10-12 October • Beam and ageing tests with • a highly-saturated avalanche gas mixture • for the ALICE p-p data taking • Francesca Poggio • Alessandria - Italy, Dipartimento di Scienze e Tecnologie Avanzate dell’Università del Piemonte Orientale • P. Cortese and G. Dellacasa • Clermont-Fd - France, LPC, IN2P3/CNRS and Univerité Blaise Pascal • A. Baldit, V. Barret, N. Bastid, G. Blanchard, P. Crochet, F. Daudon, A. Devaux, P. Dupieux, • P. Force, B. Forestier, S. Grigoryan, F. Guerin, R. Guernane, C. Insa, F. Jouve, F. Manso, • P. Rosnet, L. Royer and P. Saturnini • Torino - Italy, INFN and Dipartimento di Fisica Sperimentale dell’Università di Torino • R. Arnaldi, E. Chiavassa, A. Colla, N. De Marco, A. Ferretti, M. Gagliardi, M. Gallio, R.Gemme, P. Mereu, • A. Musso, C. Oppedisano, A. Piccotti, F. Poggio, E. Scomparin, G. Travaglia, E. Vercellin and F. Yermia • members of the ALICE collaboration

  2. ALICE: A LargeIonColliderExperiment ALICE: heavy ion dedicated experiment at LHC-CERN g Ar-Ar, Pb-Pb g p-p: reference data for A-A collisions = 5.4-14 TeV per nucleon pair Muon Forward Spectrometer: identification of muon pair from J/ and  decay Muon Trigger System: detector g RPC detailed description in F.Yermia’s talk

  3. heavy-ion collisions • performance • position resolution: few mm • cluster size: 1.4 (1 cm strip) • muon detection efficiency 95% • time resolution 1-2 ns • rate capability 200 Hz/cm2 R.Arnaldi et al., Nucl. Instr. And Meth. 451 (2000) 462 R.Arnaldi et al., Nucl. Instr. And Meth. 457 (2001) 117 R.Arnaldi et al., Nucl. Instr. And Meth. 490 (2002) 51 • ageing • test on 50x50 cm2 prototypes: all RPCs work satisfactorily up to 100 Mhit/cm2R.Arnaldi et al., Nucl. Instr. And Meth.A 533 (2004) 112 • test of a pre-production RPC (RPC1, 70x210 cm2): works satisfactorily up to 100 Mhit/cm2 collision system max luminosity (cm-2 s-1) months max hit rate (Hz/cm2) integrated hits (106/cm2) integrated hits in the most irradiated zone of the most irradiated RPCs is~100 Mhit/cm2, 10 years Pb-Pb 1027 6 3 18 Ar-Ar 0.6x1029 2 24 48 d-Pb 1.1x1029 2 15 30 streamer gas mixture 50.5% Ar, 41.3% C4H10, 7.2% C2H2F4, 1% SF6 - RH=50%

  4. p-p data taking • mean rate: <2 Hz/cm2 • hot spot (beam-gas interaction) : • 10 Hz/cm2 g 1-2 RPCs • data taking: 107 s/year • integrated hits: • ~20 Mhit/cm2 per year • ~100 Mhit/cm2 per year in the hot spot the occupancy is much smaller in p-p w.r.t. heavy-ions g larger cluster size can be accepted in p-p the expected trigger rate is lower in p-p, i.e. the pt cut on single muon can be relaxed g space resolution requirements less stringent in p-p see Yermia PhD Thesis, ALICE-INT-2003-041

  5. highly-saturated avalanche operation very different requirements for Pb-Pb wrt p-p…. Pb-Pb p-p d-Pb small Cluster size good position resolution Detector lifetime Ar-Ar Front End Electronics:ADULT (A DUaL Threshold Technique) see F.Yermia’s talk possibility to employ the same FEE foreseen for the streamer mode (discrimination threshold = 80 mV), simply by lowering the discrimination threshold to the minimum possible value of 10 mV (this imposes the use of the external thresholds and conseguently a more complicated setupin the trigger apparatus) study of a highly-saturated avalanche gas mixture with signal amplitude higher than 10 mV NOTE: the highly-saturated avalanche gas mixture will be referred from now on as maxi-avalanche

  6. preliminary studies with cosmic rays g efficiency and streamer contamination correlation: DV=600 V between the knee and a maximum streamer contamination of about 20% the test allowed to select a maxi-avalanche gas mixture: 88% C2H2F4, 10% C4H10, 2% SF6 - RH=50% test on 50x50 cm2 RPC (Clermont-Ferrand laboratory) • FEE thresholds set at 10 mV • efficiency • the shape of each signal is sampled each ns to study amplitude, timing and released charge: • streamer comtamination

  7. beam test setup (CERN: GIF + SPS-X5) • RPC1 (70x210 cm2), pre-production: • 88% C2H2F4, 10% C4H10, 2% SF6 - RH=50% • strip width g 1, 2 and 4 cm concrete wall 50 cm concrete blocks S3+S4 (10x10 cm2) S1+S1 (10x10 cm2) g source µ beam g DWC 2 DWC 1 DWC 3 efficiency plateau measurement for the detection of muons (m beam from SPS-X5) scanning the whole surface of the RPC RPC1 horz. + vert. movement

  8. beam test: results (I) source-on 80 Hz/cm2 source-off • the detector showed a stable behaviour with: • dark current (source off)  1 mA • dark single rate (source off)  0.1 Hz/cm2 • current drawn with source-on  1/3 of the current drawn in streamer for the same irradiation conditions • time resolution  1-2 ns • efficiency close to 100%, no plateau displacement due to the irradiation rate: • 4 efficiency calculation methods: • Coincidence Register • tracking with DWC • total • core (higher beam irradiation rate) • outer circle (lower beam irradiation rate) • T/p correction: HVeff=HV0*(T/T0)*(p0/p) with T0=293.15 K, p0=970 mbar

  9. beam test: results (II) Cluster size at working point HV 1 cm strips Cluster-size strip width streamer mode maxi-avalanche mode 1 cm 1.35 1.7 2 cm 1.33 1.41 4 cm 1.12 1.18 2 cm strips 4 cm strips HV (V) zero corresponds to the knee

  10. beam test: gas analysis during the test g analysis of the exhaust gas were performed both for streamer and maxi-avalanche operation of the RPC positive message in view of ageing : w.r.t. streamer, maxi-avalanche operation gives a smaller content of impurities and a spectacular decrease of HF content

  11. ageing test setup (CERN GIF) Trigger Scintillators (10x30 cm2) Cu shield Pb filters (custom) we monitor the test from Turin and Clermont-Ferrand in remote Other detectors under test Gamma Irradiation Facility 137Cs source Eg= 662 keV RPCs (50x50 cm2) not in scale Pb shield current, rate and efficiency: continuously monitored with source on + periodical data-taking with source off ohmic current (HV=7000 V): 2times/day NOTE gas flow: 2-3 vol/h, open loop • monitor the efficiency for the detection of cosmic ray under -induced counting rate

  12. small prototype 1: ageing results • problem: after a first period (~100 Mhit/cm2), we observe, from time to time at high rates (~120 Hz/cm2): • a fast increase of the current that gives instability • after HV off the RPC recovers a normal behavior • (high efficiency, low dark current and low dark rate) • the instability is given by a local dischargeg local increase of the temperature measured during the a current increase (+17°C on ~7 cm2) • the current trend during the instability seems to have a strict correlation with: g highrate: 120 Hz/cm2 • ghigh working point: HV~10900 V • (gas mixture: 88% C2H2F4, 10% C4H10 and 2% SF6 – RH=50%) • after ~225 Mhit/cm2(~34 mC/cm2): • dark current ~1 mA and dark rate <1 Hz/cm2 • no efficiency loss without and with g irradiation (120 Hz/cm2) • efficiency stable at ~94% • m beam from SPS-X5: the mean efficiency over the whole surface • at HV=10900 V (working point) is ~95%

  13. we decrease the SF6 percentage to lower the working point beam test on 2 small prototypes (50x50 cm2) to check the performances with the gas mixture: 89.7% C2H2F4, 10% C4H10 + 0.3% SF6 – RH=50% to make a direct comparison with the gas mixture with 2% SF6: performances: cluster size: 1.8 (1 cm strip) time resolution: 1-2 ns efficiency: in all position the efficiency plateau reaches 95-96% no significant differences with respect to the gas mixture with 2% SF6 working HV~10000-10100 V(800 V lower) streamer contamination <20% gas mixture modification

  14. small prototype 2: results HV decreased during summer time period (temp. up to 28°C) (HV = 10050&9950 V, effective voltage) HV = 10050 V HV = 9950 V high rate and current, high ohmic current: problem with the refrigerator used to add water in the gas mixture ! remote operations after ~440 Mhit/cm2 (corresponding to ~66 mC/cm2) 1. dark current <2-3 mA 2. dark rate <1-2 Hz/cm2 3. no efficiency loss without irradiation, slight efficiency loss with high irradiation rate (100 Hz/cm2)

  15. small prototype 3: results HV decreased during summer time period (temp. up to 28°C) (HV = 10100&10000 V, effective voltage) HV = 10100 V HV = 10000 V • high current: problem due to an external discharge (rate constant) • the insulation has been improved ! remote operations after ~410 Mhit/cm2 (corresponding to ~62 mC/cm2) 1. dark current ~1-2 mA, Imax 6 mA 2. dark rate <1 Hz/cm2 3. no efficiency loss without irradiattion, slight efficiency loss with high irradiation rate (80 Hz/cm2)

  16. efficiency plateaux working point for ageing working point for ageing after 310 Mhits/cm2 (47 mC/cm2) after 255 Mhits/cm2 (34 mC/cm2) small proto 2 rate 60 Hz/cm2 small proto 3 rate 50 Hz/cm2 • no plateau displacement without and with g irradiation (50-60 Hz/cm2) • the efficiency over the whole surface of both RPCs has been recently measured g ~93-95%

  17. conclusions • streamer gas mixture g heavy ion collisions • the results obtained with performance and ageing tests (on prototypes and final RPC), show that the requirements for 10 years of heavy-ion operation are totally fulfilled • highly-saturated avalanche gas mixture g p-p collision • it is possible to operate the RPCs with the same FEE foreseen for the streamer mode • performance: tests on prototypes and final RPC • threshold: 10 mV • cluster size: 1.8 (1 cm strip) • time resolution: 1-2 ns • ageing: the 2 tested prototypes work satisfactorily up to about 410-440 Mhit/cm2fulfilling the requirement: • for ~4-4.5 years of the p-p program for the most irradiated RPC • for ~20 years of the p-p program for other RPCs • the test is going on…

  18. Backup slide

  19. Muon Trigger System ~ 6.5 m single-gap Resistive Plate Chambers(General Tecnica) 4 planes, 72 RPCs in all each module is ~ 70x280 cm2, 2 mm gas gap ~ 5.5 m Front End Electronics: ADULT (A DUaL Threshold Technique) with variable threshold see F.Yermia’s talk Trigger detectors requirements: • large detection area • muon detection efficiency 95% • low sensibility to  and neutrons • time resolution 1-2 ns • good granularity (2·10-3 hits/cm2) • rate capability 100 Hz/cm2 • (max 24 Hz/cm2 Ar-Ar) • spatial resolution better than 1 cm • for the Trigger selectivity in A-A

  20. outline • preliminary test with cosmics (Clermont Ferrand laboratory): • RPC 50x50 cm2 • signal shape and amplitude • efficiency vs streamer contamination • beam test (X5-SPS) on a pre-production RPC: • RPC1, 70x270 cm2 • efficiency&current, cluster size and gas analysis • ageing test (GIF): • RPC 50x50 cm2 (small prototype 1) • beam test (X5-SPS) • 2 RPC 50x50 cm2 (small prototype 2&3) • ageing test (GIF): • 2 RPC 50x50 cm2 (small prototype 2&3) 88% C2H2F4 10% C4H10 2% SF6 89.7% C2H2F4 10% C4H10 0.3% SF6

  21. R&D on RPC for the Muon Trigger System for ALICE experiment in view of p-p data taking Yermia Frédéric IEEE - Nuclear Science Symposium 2004 Gaseous Detectors session

  22. Signal amplitude with cosmics I Signal Shape Amplitude (V) vs. time (ns) • Tests with cosmics allowed to select twoHighly-quenched gas mixtureswith goodperformances in conjunction with our FEE: • C2H2F4(89.5%)+i-C4H10(10%)+SF6(0.5%) • C2H2F4(88%) + i-C4H10(10%) + SF6(2%) Large avalanche signal Amplitude (V) 20 ns SET UP 60 mV Time (ns) RPC 50X50 cm2 2 cm strips Both FEE thresholds are set at 10 mV The finger scintillator is centered on the 3 strips Signals taken directly from 3 strips sent to the FEE (eff.) and to the DAQ (hexadecimal file analysis) Signals shape were sampled each ns Delayed streamer 160 mV Time (ns) Prompt streamer 160 mV Time (ns)

  23. Signal amplitude with cosmics II • Charge on the 3 strips ( in negative values) • Progression of the streamer contamination Nb of events HV 11 100 V HV 11 100 V HV 11 200 V HV 11 200 V HV 11 300 V HV 11 300 V HV 11 400 V HV 11 400 V HV 11 500 V HV 11 500 V Charge (pC) knee 11 100 V

  24. Signal amplitude with cosmics III Amplitude & timing vs. charge HV = 11 100 V HV = 11 500 V -20 pC Nb of events Nb of events Amplitude (V) Amplitude (V) Peak time (ns) Peak time (ns) Charge (pC) Charge (pC)

  25. 12.5 % 38.5 % 8 % 21 % 60.5 % knee Requirements fulfilled w.r.t. the FEE and the plateau width

  26. beam test, setup - FEE 4 cm 2 cm 1 cm FEB and FEA strip X g horizontal strip Y g vertical

  27. instability problem (I) ~10 cm ~10 cm hp: local discharge g the temperature in correspondence of the discharge point should increase appreciably RPC without external mechanics, with the ground side fully covered by thermosensitive adhesives

  28. instability problem (II) 4.5 cm during a sudden current increase T35 °C with the thermosensitive adhesive 6.5 cm during a sudden current increase T up to 42°C in the hot spot (measured with an IR thermometer) upper left corner source on the back mean T 25 °C over the whole surface (measured with an IR thermometer) RPC

  29. streamer contamination % of streamer in the 25 tested positions at 3 different HVeff (10000 V, 10100 V and 10200 V) obtained with thresholds setting: • X plane: 8 mV • Y plane: 80 mV the distributions of these values are shown in next slide NOTE: recent measurement shows a factor 2

  30. streamer contamination distribution

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