A proposal for a new RPC Barrel BaBar Barrel Replacement Workshop Giancarlo Piredda INFN- Roma Slac Nov 14-15, 2002
RPC in the IFR barrel • The evil we know. • One basic question: Will they stand the rate and last long enough ? • Construction technology and QC is, thanks to BaBar, under control. • Cost (money and human resources) perfectly known. Make use of the experience made with FECap construction and installation • Assess robustness from our own experience on the chambers installed in Nov. 2000 • The necessary R&D for an optimization is completed (see D. Strom): double-gap modules working in streamer regime with a factor 4 less charge than in the actual chambers
Yes indeed, expertise exists. New FECap D.Lange/R.Contri
Barrel modules • Singles rates for barrel RPCs show a linear dependence with the luminosity for values in the current range. • The slope of the fitted straight line is higher for layers closer to the beam pipe; it gets essentially flat for outer layers, except for layer 18, where positive slopes are seen again. Sextant 5,Layer 18 Sextant 0,Layer 1 Sextant 1,Layer 10 E. Robutti
Barrel modules (cont’d) pedestals fromno-beam • Maximum slopes per module (layer 1) are ~1 kHz/1033cm–2s–1. This projects to ~40 kHz/module at L = 4 1034 cm–2s–1, or 2 Hz/cm2. • So, assuming no big non-uniformities, this should be no concern. E. Robutti
Experimental physics (observation) Barrel rates • Forward End Cap has been running at ~1-20 Hz/cm2 for 1.5 years • Even the disgraced layer17 (<6> Hz/cm2) is still 84% efficient • No other counter show any significant inefficiency • Further, FECap is strongly non uniform contrary to barrel in illumination After correcting for the ‘V-divider’ spacers/bakelite efficiency is unchanged in 1.5 year operation in forward
Theoretical physics (explanation) We have a weak explanation to offer for: -decrease of resistance of the oiled spacers (actually maybe a hint: HF) -increase of resistivity of bakelite (drying chambers) It would be nice to have a theory but honestly we do not have one even if thanks to Jerry Va’vra we have several working hints to interpret the observations.
Worst Rates key observation: rate at 4*1034 in Barrel layer 1 are lower than rates At 5*1033 in layer 15/16 of FECap Jjv/BobM.
Total Integral Rates key observation: integrated charge rate by 2010 in Barrel layer 1 will be lower than what layer 15/16 of FECap have integrated to-date Jjv/BobM.
Barrel: strawman design (I) 10 planes of chambers and 8 layers of absorber -each layer is a double-gap 3-RPC modules -larger barrel plane ~375*320 -it amounts to (10*6*3*2)=360 gas/HV module -> (10*6)=60 electronic chambers (wrt new FECap 212/116) remove corner pieces The option of inserting chambers removing 0 or 1 corner piece exists however we feel that a double gap is sufficient guarantee against the need of a deinsertion. Since it makes the electronic life much easier this is the baseline.
Barrel: strawman design (II) • -the electronics can either seat on board or be put in • minicrates outside. In both options it will be accessible • a coarse TDC will part of the project (10nsec resolution). • FEC possibly redone. -In case of external minicrates the technique is known (see FWECap) (baseline option) -On board put the electronics on the region not covered by iron and use the fact that having double gap you only need to make one of the two shorter (no efficiency loss at first order)
Barrel- double gaps chamber built in Oregon with gaps from FECap production D.Strom
Barrel- double gaps Chamber fully efficient in case of one of the two gaps fails D.Strom
SF6 to reduce the charge First attempt even too succesfull, chamber fully efficient with a charge reduced by more than a factor 3. D.Strom
Barrel construction A possibility: -build gaps and make strip planes at GT -QC/QA in Roma -electronics by Ferrara -assembly chambers in US (Princeton ?, SLAC ?) -SLAC takes care of brass as for FECap -for tests, installation and commissioning we have the FECap as guideline (SLAC,Livermore, Wisconsin, UCRiverside, Yale, Princeton,PI, RM, FE, LNF, GE) Critical path: GT availability, US assembly place
Barrel cost (RPC only) Based on FECap construction, 432 gaps (12layers of doublegaps) 20% contingency added -RPC parts and gap construction : 250k$ -Strips panels: 84k$ -Signal Cables and Minirack: 70k$ -HV connectors 15k$ -Transports : 100k$ -Electronics: (see R.Calabrese) 140k$ ~660 k$ + Assembly (3techs*2years)+ brass + installation Scale with layer number
What about General Tecnica? General Tecnica works under supervision of an INFN committee. U. Dosselli (chair of Commissione I) as chair and S. Morganti (BaBar) as responsible of production schedule. The possible production of gaps at GT has to be decided by this body. It should be possible but a tough discussion is expected. No way to start negotiations without a message that BaBar is considering this option not only as an exercise ! Alternatives will be discussed by Henry Band
Pro-Cons -Cost (the least of the three systems: <0.5M$ for the gaps) -Expertise existing -Minimal disruption to normal operation (the only realistic chance to replace something in 2004)-Avoid the IFR hybridization -Reuse of DAQ, SlowControl and core software -Profit from big effort of this summer (new HV distribution, new gas distribution) -Minimize manpower needed for construction, installation and commissioning -Detector construction subject to quality fluctuation of the material (mainly but not exclusively bakelite) -Operation in the streamer regime not fully understood
Credits (until Sept CM)more than 60 people! • Ferrara (HV) • M. Andreotti, V.Azzolini, D.Bettoni, R.Calabrese,A.Cecchi,G.Cibinetto, E.Luppi,R.Malaguti, M.Negrini,C.Padoan • Frascati (GT teststand, remediation) • L.Daniello, P.Patteri, M.Piccolo,M.Santoni • Genova (DAQ,cosmic runs) • R.Contri,M.LoVetere,S.Tosi, • Livermore(SLAC teststand) • M.Carpenter, D.Lange, D.Wright • Napoli (trigger) • D.Piccolo • Oregon(teststand,EPICS) • E. Fitzgerald, C.Potter, N. Sinev • Padova(installation) • E.Bolzan, O.Clementi,M.Negrello • Pisa (RPC production and installation, FECs) • C.Avanzini, M.Carpinelli, F.Forti, N.Neri, E.Paoloni, A.Profeti, D.Rizzi • UC Riverside(gas) • K.Wang • Roma (RPC production and installation, FECs,remediation ) • F.Bellini, A.Buccheri, G.C.,A.D’Orazio F.Ferrarotto,F.Ferroni, R.Lunadei, S.Morganti,G.Piredda, • SLAC (Cabling, installation, RPC testing) • G. Bradford, V. Coughran, M. Green, S. Jansson, S. Jones, J. Krebs, J. Krebs, G. Locke, W. Lovelace, R.Messner, R. Moore, C. Nix, G. Putallaz, H.Rogers, W. Wisniewski, S. Zalog • Yale (Barrel FECs) • M.Greene,H.Neal • Wisconsin (Cabling, GMB, gas system) • H.Band, P.Tan
Jerry Va’vra questions (I) • Freon lower the oil resistance?-SF6 increases the HF production marginally (CMS) • Does SF6 reduce the charge enough?-Reduction by a factor of 4-lifetime 4 time longer • Low rho bakelite test- We agree, shipment under way. Will any result come in due time for the decision? We have the ALICE experience here.
JV questions (II) • Bakelite resistance increase-Test humid air asap, once solved the technical problem of how to measure humidity • Whiskers control-Detection ---single rates. Discard noisy chambers • Shielding in the Forward Inner RPC-Thanks to JV & Bob Messner some additional shielding installed. Bob will be in charge for this item.
Committee Questions • Avalanche mode-see D. Strom • FECs in double gap and TDC-not a concern • Chambers production @ GT-adressed • Anything in summer 2003-to debate • Efficiency drop vs charge • Need to be clarified • SF6 test • Done (see D.Strom) • Bakelite resistance-lower than before, accurate QC • Gluing spacers to bakelite-oil-free looks impossible • Fitting in 22mm-Done (see D.Strom) • Replacement w/out removing corner blocks-Addressed • Current Barrel-new HV, gas system upgraded