1 / 30

BaBar Experience with RPCs: A snapshot of our present knowledge

BaBar Experience with RPCs: A snapshot of our present knowledge. Henry Band University of Wisconsin. The BaBar detector at the PEPII B factory has operated a ~2000 m  RPC detector since 1999 These RPCs operating in the streamer regime have proven very sensitive to temperature

genna
Download Presentation

BaBar Experience with RPCs: A snapshot of our present knowledge

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. BaBar Experience with RPCs:A snapshot of our present knowledge Henry Band University of Wisconsin

  2. The BaBar detector at the PEPII B factory has operated a ~2000 m RPC detector since 1999 These RPCs operating in the streamer regime have proven very sensitive to temperature Both RPC current and efficiency have suffered apparently irreversible changes (new results show hope of reversing changes) Examination of opened RPCs show clear problems with the linseed oil coating A few new RPCs with thinner oil coatings were installed in late 00 Although LHC RPCs operate in avalanche mode, our experience may be relevant to this next generation of RPC detector IFR RPCs History of IFR construction Initial efficiency measurements Operational problems Unstable temperature and currents Declining efficiency Detector studies BaBar Test stands Other RPC Autopsy photos Inefficiency Model New RPCs Characteristics Operation BaBar plans Introduction HenryBand - U. of Wisconsin

  3. Instrumented Flux Return 342 barrel RPCs 432 endcap RPCs 32 cylindrical RPCs Electronics 3300 Front end cards ~ 40 mV threshold 16 channels connected to alternate strips 1 TDC measurement 1 scalar Gas 35% Freon 134a, 4.5% iso-butane, 60.5% Argon 2-3 volume changes/day High Voltage > 50 10 kV HV pods Instrumented Flux Return HenryBand - U. of Wisconsin

  4. IFR Collaboration • INFN Lab.-Frascati -F. Anulli, R. Baldini, A. Calcaterra, D. Falciai, G. Finocchiaro, P. Patteri, I. Peruzzi, M. Piccolo, Y. Xie, A. Zallo, R. de Sangro • INFN-Bari - A. Palano • INFN-Genova-S. Bagnasco, A. Buzzo, G. Crosetti, M. Lovetere, M. Macri, S. Passaggio, F. Pastore, M.G. Pia, E. Robutti, A. Santroni, S. Tosi • INFN-Napoli-T. Cartaro, N. Cavallo, G. DeNardo,F. Fabozzi, C. Gatto, , L Lista, P. Paolucci, D. Piccolo, C. Sciacca • LLNL -R. Bionta, V. Brigljevec, D. Lange, D. Wright • U. of Wisconsin-H. Band, A. Eichenbaum,J. Johnson • U. Oregon - J. Brau, R. Frey, E. Grauges-Pous, M. Iwasaki, N. Sinev, D. Strom • Yale U - T. Moore, H. Neal • INFN-Roma - F. Ferroni, S. Morganti, G. Piredda, • INFN-Pisa - M. Carpinelli, F. Forti • Consulting experts • C. Lu -Princeton University, J. Va’vra -SLAC, M. Lazzari - Turin HenryBand - U. of Wisconsin

  5. IFR Construction Endcap RPCs 0.9m 1.5-2.7 m Barrel RPCs 1.25m  1.9-3.2 m 3 chambers per layer 3 RPC modules / chamber 2RPC modules / chamber HenryBand - U. of Wisconsin

  6. Operates in limited streamer mode Parallel high resitivity plates (Bakelite  1011 -1012  cm ) Graphite ~100 k/ According to the General Tecnica factory the RPCs were filled 3 times with a mixture of 70% linseed oil and 30% n-pentane. Air was then flushed through the RPC for several days. Strip pitch Barrel 20-33 mm (), 38 mm (z) Endcap 26 mm(y), 38 mm (x) Changes from L3 RPCs Polycarbonate buttons with lip replaced G10 cylindrical button Single layer with strips on both sides No mechanical envelope Nonflammable gas - low iso-butane %, CBrF3 replaced by Freon 134a C2H2F4 Gas mixture in % BABAR RPC HenryBand - U. of Wisconsin

  7. Bakelite Surface Changguo Lu Linseed oil coating smoothes surface imperfections No oil New Babar RPCs BaBar original HenryBand - U. of Wisconsin

  8. RPCs chosen for BaBar 1/95 Mature technology Good L3 experience RPC Production 7/96- 10/97 RPC QA tests - Frascati I < 18 A and efficiency > 95% Chamber assembly SLAC 12/96 - 12/97 Chamber tests at SLAC 5/97 – 12/97 Initial tests High Temperatures - 30 C High Currents ~100 A Efficiency > 95% Assembly/test area air conditioned 7/97 Chamber insertion 6/97 -12/97 Cabling and Fecs installed from 10/97 Complete Barrel and Forward E.C. 11/98 Barrel cosmic ray tests 12/98 Sharply increasing current observed when doors closed and LV on Backward E.C. completed 4 / 99 First beam May 99 99% of RPCs working 96% of Fecs working Heating from electronics & ambient hall raise steel T to 29-34 HV current limitations force reduction in # of RPCs < I >  70 -210 A barrel ~70 Endcap Complete barrel cooling 10/99 Install Endcap cooling 1/00 - 4/00 <I> 60A barrel ~40 Endcap Average Efficiency remain ~85% IFR History HenryBand - U. of Wisconsin

  9. RPC tests at Frascati, 1997 • HV modules shipped to LNF. • Longitudinal strips were applied. • Modules packed into boxes • Cosmic ray tests were made to characterize each module • Gas Ar 45%, Freon 50%, isobutane 5% Hz A HenryBand - U. of Wisconsin

  10. Efficiency - LNF Efficiency of barrel modules 11 10  HenryBand - U. of Wisconsin

  11. LNF data / Construction • Neither the measured current or singles rate was found to depend on bakelite resistivity • Singles rate < 1kHz /m2 • Current 3-20 A • RPCs air shipped to SLAC • HV modules assembled 2 or 3 to a chamber • 2nd view strips applied • SLAC cosmic rays tests • Completed and tested chambers inserted into BABAR steel • After erection of BABAR steel - installed • DAQ cabling • HV cabling • Gas connections HenryBand - U. of Wisconsin

  12. June 1999 • By May 99 IFR cabling complete • RPC efficiencies good • But - warning signs • Some RPCs with > 100 A were disconnected • Limited HV current capability • FECs inside steel produce 2.3 W of heat each • Total power into barrel ~2.6 kW • Poor heat transfer to outside • With collision data • Barrel heats up ~.4 C/day • IR hall temperature climbs during summer  77%  91%  93% HenryBand - U. of Wisconsin

  13. HV currents & temperatures 99 RPC current vs. time Barrel temperatures vs. time +10%/ day @7800 V Barrel face +0.4 C / day FEC power turned off 1 meter inside @6000 V HenryBand - U. of Wisconsin

  14. RPC Efficiency 99 • Climbing temperatures forced the disconnection of more RPCs • Cooling system being prototyped • Average currents were • 70 A(sextant 4) -210 A (sextant 0) • 65 A Forward endcap • 70 A Backward endcap • Because of voltage drops across a ~1.5 M resistor in the HV distribution network, the voltage on working RPCs was reduced by 100-300 volt • Additional inefficiency from more conventional sources • HV shorts 3% • Gas leaks <2% • Dead front end electronics <2% HenryBand - U. of Wisconsin

  15. Water cooling • Tests of prototype cooling loops in sextant 1 started in mid June • Additional loops installed in August • Full barrel installation of copper loops brazed into BABAR steel- Oct. 99 • Completed endcap cooling system - Jan. 00 • Remove ~ 10kW heat • Stabilized temperature and RPC currents • Barrel temps. ~19-21°, were 29-33° in summer 99 • Endcap temps 22- 24° HenryBand - U. of Wisconsin

  16. Cooling / HV Currents 2000 HenryBand - U. of Wisconsin

  17. RPC efficiency 00 Gas change -1.4% /month -0.56%/month -1.4% /month HenryBand - U. of Wisconsin

  18. RPC efficiency 99-00 Barrel Forward E.C. Backward E.C.  91%  93% June 99  77%  81%  86%  85% Jan. 00  81%  75%  71% July 00 HenryBand - U. of Wisconsin

  19. RPC efficiency 01 • Efficiency loss is correlated with previous efficiency HenryBand - U. of Wisconsin

  20. Individual time histories HenryBand - U. of Wisconsin

  21. Realization that the RPC efficiencies did not recover spurred detector studies During the 99-00 data run access to the RPCs was limited Physical removal of any RPC would require > 1 month access Limited tests were carried out during accesses or on a few chambers Lowered barrel temp. to 17 C. Reversed HV Increased gas flow Lowered discriminator threshold Put weights over inefficient regions No effect Gas composition was regularly tested No evidence of water vapor Detector studies A wide spread of plateau curves were measured. HenryBand - U. of Wisconsin

  22. RPC radiography D. Piccolo The RPC efficiency was mapped in 2D showing irregular regions of reduced efficiency. HenryBand - U. of Wisconsin

  23. RPC radiography (2) D. Piccolo May 00 8100 V 56% Ar May 99 8100 V 45% Ar HenryBand - U. of Wisconsin

  24. IFR efficiencies status I. Peruzzi HenryBand - U. of Wisconsin

  25. IFR Construction Quality I. Peruzzi Quality distribution vs production box Fraction of good chambers not uniformly distibuted in time Production problems? HenryBand - U. of Wisconsin

  26. Test stands were restarted or started at several locations Frascati Napoli SLAC U. of Oregon SLAC test stand utilized 9 post BABAR production RPCs which had been used in background tests The RPCs were subjected to a heating cycle at 36 C. Permanent changes in both current and efficiency were seen Several RPCs were opened Large oil drops spanning the 2 mm gap were found. Test stands HenryBand - U. of Wisconsin

  27. A. Soha SLAC/Wisconsin Test Stand A 32 C. 28 C 36 C. 29 C. HenryBand - U. of Wisconsin

  28. Linseed oil surface treatment under heat and HV has beaded up into drops. Some drops span the RPC gap making a high resistance short which reduces the local E field below that required for streamers. Both HV current and efficiency are irreversibly changed The new shape of the buttons may be more likely to trap oil The number and location of the blobs explains both the RPC to RPC variation and the efficiency holes Gas leaks, HV shorts, and point discharges also contribute IFR inefficiency model Bakelite Spacer Graphite FR4 frame Linseed oil drops Test RPC HenryBand - U. of Wisconsin

  29. Oil Stalagmite Formation Changguo Lu • In lab tests using freshly painted bakelite (uncured) the application of 4-5 kV resulted in the movement of the oil and the formation of stalagmites within hours. • In BaBar RPCs the oil is more viscous and the time scale is presumably much longer. HenryBand - U. of Wisconsin

  30. Effect of Oil bridge Changguo Lu HenryBand - U. of Wisconsin

More Related