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IFR Past, Present, &Future (<2005)

IFR Past, Present, &Future (<2005). Henry Band University of Wisconsin. Past RPC efficiency vs time 2000 Chambers Muon ID efficiency Present Upgrade scope Installation status Planar FEC efficiency Belt chamber hits Remediation Projections of future R&D plans.

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IFR Past, Present, &Future (<2005)

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  1. IFRPast, Present, &Future (<2005) Henry Band University of Wisconsin

  2. Past RPC efficiency vs time 2000 Chambers Muon ID efficiency Present Upgrade scope Installation status Planar FEC efficiency Belt chamber hits Remediation Projections of future R&D plans Summary of known problems Electronics Barrel cable plant FECs High Voltage Gas RPCs Oil drops Whiskers Resistivity Dark currents and noise vs time Backgrounds Outline HenryBand - U. of Wisconsin

  3. RPC Efficiency 1999-2002 -1.2 %/month Summer 1999 29-33˚ C temperatures inside BABAR steel cause high currents and force many RPCs to be disconnected RPC efficiencies continue to decline in 2000 - 2002 -0.36 %/month RPC efficiencies did not recover fully after cooling added -0.93 %/month Electronics problems HenryBand - U. of Wisconsin

  4. 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

  5. Distribution of efficiency • Two dominant trends • Most RPCs showing slow eff. loss @ 3-4% per year • Other RPCs suddenly losing all efficiency in < 2 months • 30 % of barrel RPCs have < 10% efficiency • Only a few of these understood in terms of known HV or gas problems HenryBand - U. of Wisconsin

  6. Efficiency Corrections • True RPC efficiency during collision data is worse • Backgrounds • Edge effects in algorithim Passaggio’s talk at July Col. meeting 0 10 HenryBand - U. of Wisconsin

  7. New style RPCS • 24 new RPCs were installed in Dec. 99 in the forward endcap • These RPCs had ~1/3 of the linseed oil as the original construction • The outer layers were exposed to high backgrounds and have aged quickly • The RPCs in the inner endcap have experienced low background rates and have lost efficiency @ <3%/ year • Recoverable by raising HV HenryBand - U. of Wisconsin

  8. New chambers • Inner, layers # < 17 • Outer, layers #17 and 18 Counting Rates If the hit distribution were uniform it would translate into: 0.2 Hz/cm2 /inner 0.4 Hz/cm2 /layer14 1.2 Hz/cm2 /layer 17 2.4 Hz/cm2 /layer 18 HenryBand - U. of Wisconsin

  9. New style RPCS • Layer 18 rates ~250 kHz with beam, ~60 kHz without • Large difference in efficiency with cosmics or only with beam • Layer 17 rates ~60 kHz with beam, ~20 kHz without • Reducing backgrounds a high priority HenryBand - U. of Wisconsin

  10. Efficiency plateau inner ‘new’ modules collision cosmics HenryBand - U. of Wisconsin

  11. Muon Identification • Muon identification selectors are losing efficiency as RPC efficiency drops • Impacting physics analysis Nov. 1999 Jan. 2001 Software problems Front End Electronics problems HenryBand - U. of Wisconsin

  12. RPC belt Gap #19 (new) 10cm steel 5x2.54cm brass plates (Layers 8,10,12,14,16) double gap RPC Forward Endcap Upgrade HenryBand - U. of Wisconsin

  13. Forward endcap upgrade Add absorber 5 layers 1” brass 1 external 3.5” steel plate Replace RPCs 12 single gap layers Add double gap layers 2 double gap layers Belt chambers Replace LV power supplies Other improvements Install new HV distribution Install new gas distribution Install new gas return bubblers Improve background monitoring Install shielding walls around beamline sources Repair front end electronics in the barrel Remediate Barrel RPCs Infrastructure Add 2nd monitor crate Improve online documentation Rewire barrel Canbus 2002 Access - IFR HenryBand - U. of Wisconsin

  14. All 116 RPC chambers installed, connected to DAQ and gas All connected to HV with no problems 3/96 large chambers have gas leaks Efficiency OK 5/20 belts had broken gas fittings Repaired Installed 58 minicrates 924 RPC to minicrate cables 232 minicrate to FEE Crate cables 212 HV cables >100 misc. cables, trigger, control, monitoring, temp. probes Low voltage power supplies Operational To do – Remote power switch, GMB readout Barrel FEC repair Dead + noisy + hot FECs 63/1152 in layers 1-16 5.4% was 16.2% Backgrounds Shielding installed downstream of 2 LER collimators Cables run for dedicated background scalars Outer RPCs protected by 1” or thicker steel shielding Installation Status HenryBand - U. of Wisconsin

  15. Gas distribution -FEC 8 supplies installed in FEC 8 visual return bubblers installed in FEC Electronic bubble counting return chassis late ~ 2weeks Prototype in place All scalar cables run to EH Can install ~1 hour/chassis as time allows Gas distribution -barrel 5/9 supplies and visual bubblers installed on barrel Connected to main supply 4 sextant returns and 2 sextant supplies have been connected Sextant 0 – 4/19 layers bubble Sextant 5 -12/19 layers bubble Install electronic return chassis as time allows Installation Status HenryBand - U. of Wisconsin

  16. Have attempted remediation of barrel RPCs Introduce Argon Integrate ~200 C of charge with either positive or negative HV Prior to remediation new HV connectors and distribution boxes installed in the barrel 367 HV cables spliced 24 HV distribution chassis built and installed All but 3 Barrel HV channels active (was ~3%) GMB & CANBUS lines modified Results of first remediation test in sextant 2 Remediation Status Gas flow problem ? HenryBand - U. of Wisconsin

  17. Planar Forward Endcap Before After HenryBand - U. of Wisconsin

  18. Belt Chambers Bad Fecs or mapping First run Belts Dead chamber ? HenryBand - U. of Wisconsin

  19. Next long access is summer 2005 A linear projection of present decay rate predicts 0% efficiency well before then Expect ~5% improvement in barrel RPC efficiency from remediation Expect 5% improvement in muon ID from both NN selector and fixing electronics Gains from HV and gas improvements ????? Future Barrel July 2005 HenryBand - U. of Wisconsin

  20. Outstanding issues focus on gas Flow Composition Humidity The Wisconsin/SLAC teststand will be moved to IR2 to allow tests of full sized Endcap chambers Can now measure pulse height Addition of SF6 reduces streamer size Will implement after success in the test stand Santonico has suggested another gas mix which has a much lower plateau May be useful in recovering RPCs that have died Tests of the optimal water content will likely be long term On detector work Optimize gas flow per layer Repeat temperature dependency, popped button tests R&D plans HenryBand - U. of Wisconsin

  21. RPC inefficiency has many sources not all of which are due to the RPC Electronics The barrel cable plant has been a continued headache (5 pigtails per FEC) Most of the present 5% FEC failure rate is probably cable related (was 2% in 2000) FECs in minicrates are accessible and reliable Electronics – continued Largest risk is a repeat of the background accident of last Jan. where a mis-steered beam dumped a large amout of charge into the RPCs. This apparently causes the ground to bounce destroying the ECL receivers and drivers. May knock out 8 FECs in a single failure. (clock chains) Problems, problems, problems HenryBand - U. of Wisconsin

  22. Gas Each barrel layer has 3 chambers in series in each layer with 1 input and 1 output gas line Only 60% of the barrel circuits bubble All connections are buried out of view Tests in 2000 showed no no efficiency improvement by raising gas flow Gas Again in 2000, there was no strong correlation between efficiency and gas tightness Tests up to now have focused on short <1 month time scales Raising the flow in the FWT Layer 18 improved efficiency and stabilized decay Other problems HenryBand - U. of Wisconsin

  23. High Voltage 4% of the RPCs were disconnected because of HV problems (sparking, very high currents (>200 microA) New HV trips were .5 to 1 per month. Took down 12-18 RPCs ~1/2 due to HV distribution box No HV problems in new generation RPCs! Hopefully much improved by new HV chassis Backgrounds Old Layer 18 saw soft HER synchrotron background. Deeper layers sensitive to backgrounds from LER collimators Expect factor 2-4 reduction from new shielding installation Need a factor of 10 Will require further iterations to bring under control Problems continued HenryBand - U. of Wisconsin

  24. RPC inefficiency model Bakelite Spacer • Linseed oil drops can span the RPC gap making a high resistance short which reduces the local E field below that required for streamers. • First observed in test chambers constructed shortly after the BaBar Linseed oil surface treatment under heat and HV has beaded up into drops. • The suspicion is that the oil of the original production which was intentionally applied thicker than L3 was never properly cured • Possible contamination by phthalates Graphite FR4 frame Linseed oil drops Test RPC HenryBand - U. of Wisconsin

  25. RPC surfaces Gas inlet Debri Excess oil Opposite side Whiskers HenryBand - U. of Wisconsin

  26. RPC radiography D. Piccolo May 00 8100 V 56% Ar May 99 8100 V 45% Ar HenryBand - U. of Wisconsin

  27. Bulk current increased from 1 to 200 mA on the sum of 18 modules. (measured @5kV) Streamer current increased from less than 20 mA to 80 mA or so. This goes well with the increase of single rates from ~0.05 Hz/cm2 to ~0.2Hz/cm2 for the inner layers For most of the modules the integrated charge is less than 0.1 C/cm2 Inner layers I (mA) Bulk current increases with integrated charge “Spacer” resistivity decreases, current flows through spacers and not the frame HenryBand - U. of Wisconsin

  28. 2000 generation RPCs still change with time This refers to 18 modules (<Layer 14) At day 1 I vs HV 0.1 mA @ 5000V 1.1 mA @ 7000V 13 mA/module @5kV 22 mA/module @7kV (4.5 mA of streamer) at construction time Both bulk and streamer current increased HenryBand - U. of Wisconsin

  29. Layer 18 opened • Bulk current goes to zero with nb of popped buttons • Bakelite discoloration, dried, oil residuals around buttons, no real correlation with inefficiency zones. • BAD#1 Visually ok, but bakelite resistance is huge, ~20 times > than nominal. Is bakelite too dry there ?? Graphite ok • BAD#2 Carbon discoloration on anode, missing graphite on some sections, seems graphite adhesion to bakelite has been lost at anode. Ok on the cathode side. Images of button in graphite, dried oil around buttons. • Signs of graphite deterioration on good regions HenryBand - U. of Wisconsin

  30. Summary • If efficiencies continue to decay at the present rate in summer of 2005 • Barrel 0% • Forward Endcap ~90% • Backward Endcap ~40% • Too soon to see complete benefits of recent access improvements • Best hope is to change gas mixture/humidity HenryBand - U. of Wisconsin

  31. Backup slides HenryBand - U. of Wisconsin

  32. 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

  33. 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

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

  35. 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

  36. The shifting plateau problem: a plateau collection HenryBand - U. of Wisconsin

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

  38. 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

  39. 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

  40. RPC Efficiencies HenryBand - U. of Wisconsin

  41. RPC Efficiencies HenryBand - U. of Wisconsin

  42. RPC Efficiencies HenryBand - U. of Wisconsin

  43. Radiographies 1 0 HenryBand - U. of Wisconsin

  44. Radiographies for the 24 ‘new’ modules 1 0 HenryBand - U. of Wisconsin

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