The ALICE TPC C. Garabatos, GSI

Vienna 2004C. Garabatos, GSI Darmstadt2 TPC |  | < 0.9 (full length tracks) |  | < 0.9 (full length tracks) 845 < r < 2466 mm 845 < r < 2466 mm 2  2500 mm drift 2  2500 mm drift 88 m 3 88 m readout pads readout pads

Vienna 2004C. Garabatos, GSI Darmstadt3 Layout Inner and Outer Containment Vessels (150 mm, CO 2 ) Central electrode 100 kV Suspended field defining strips 400 V/cm Endplates housing 2  2  18 chambers

Vienna 2004C. Garabatos, GSI Darmstadt4 Challenging requirements for the gas High Multiplicities Momentum Resolution High Rate (200 Hz) dE/dx Resolution Occupancy 2 track res. Field Distortions Multiple Scattering Drift speed (max. HV) Signal/ Noise Argon Neon Hydrocarbons CO 2 CF 4 Ageing Flammability Neutrons Concentration: Gain: 2  10 4 ? ??? ? Small pads: 4  7.5 mm 2

Vienna 2004C. Garabatos, GSI Darmstadt5 Characteristics of the gas Ne-CO 2 [90-10] Non saturated drift velocity (as with Ar) : –strong dependence of V d on everything Very 'sensitive' Townsend coefficients: – strong dependence of Gain on everything (Everything: T, P, E, composition, purity,...) Poor stability: tendency to undergo self- sustained glow discharges due to minor imperfections in chamber construction  Is there any other quencher out there?

Vienna 2004C. Garabatos, GSI Darmstadt6 Yes: add Nitrogen 5% lower drift velocity or ~5% higher drift field

Vienna 2004C. Garabatos, GSI Darmstadt7 Drift velocity changes of no N 2 vs. N 2 Ne-CO 2 -N Temperature+0.37 % / K+0.34 % / K Pressure-0.15 % / mbar CO 2 concentration-7.6 % / %CO % / %CO 2 N 2 contamination-1 % / %N 2... and same diffusion coefficients, same electron absorption.

Vienna 2004C. Garabatos, GSI Darmstadt8 Gain changes of N 2 vs. no N Temperature+0.9 % / K? % / K Pressure-0.34 % / mbar? % / mbar CO 2 concentration+67, -20 % / %CO 2 +17, -14 % / %CO 2 N 2 contamination+34 % / %N % / %N 2

Vienna 2004C. Garabatos, GSI Darmstadt9 N 2 vs. no N 2 : Stability Instantaneous maximum gain Operating gain

Vienna 2004C. Garabatos, GSI Darmstadt10 Why N 2 helps with Neon: quenching (by ionisation) of Neon excited states in the avalanche

Vienna 2004C. Garabatos, GSI Darmstadt11 Chamber gain PCmonte simulations (S. Biagi) with Penning transfer, and measurements

Vienna 2004C. Garabatos, GSI Darmstadt12 Readout Chamber Production About 2/3 of the –not that conventional– wire chambers assembled and thoroughly tested Material ageing tests End of production/testing: Spring 2004

Vienna 2004C. Garabatos, GSI Darmstadt13 The Field Cage vessels with field-shaping strips Macrolon rods to support the strips to support the strips (à la NA49) to supply the HV to supply the HV and degrade it along to distribute the gas to distribute the gas (radially in/out) to distribute laser tracks to distribute laser tracks ( à la STAR) Suspended Al-mylar strips Suspended Al-mylar strips Stretched Al-mylar central Stretched Al-mylar centralelectrode Endplates to hold ROCs Endplates to hold ROCs Mechanical precision: Mechanical precision: ~200  m Ready for gas and volts: summer 2004

Vienna 2004C. Garabatos, GSI Darmstadt14 anode wire pad plane drift region 88  s L1: 5  s 200 Hz DETECTOR PADS gating grid cathodes 1 MIP = 4.8 fC S/N = 30 : 1 DYNAMIC = 30 MIP CSA SEMI-GAUSS. SHAPER GAIN = 12 mV / fC FWHM = 190 ns 10 BIT < 10 MHz BASELINE CORR. TAIL CANCELL. ZERO SUPPR. MULTI-EVENT MEMORY PASA ADC Digital Circuit (ALTRO) RAM 8 CHIPS x 16 CH / CHIP 8 CHIPS x 16 CH / CHIP CUSTOM IC (CMOS 0.35  m) CUSTOM IC (CMOS 0.25  m ) FEC (Front End Card) CHANNELS (CLOSE TO THE READOUT PLANE) FEC (Front End Card) CHANNELS (CLOSE TO THE READOUT PLANE) L2: < 100  s 200 Hz DDL (4096 CH / DDL) Power consumption: < 40 mW / channel Power consumption: < 40 mW / channel Front-end Electronics: Architecture

Vienna 2004C. Garabatos, GSI Darmstadt15 ALTRO: digital tail cancellation and baseline restoration Cosmic ray event in prototype FC

Vienna 2004C. Garabatos, GSI Darmstadt16 Electronics production status PASA chips (18000 produced), end of production: March 04 ALTRO (digital chip): chips produced by March 04 FEC 4800 boards (50 produced). Production finished Oct. 04. Automatic (robot) tests running: 1200 chips/day

Vienna 2004C. Garabatos, GSI Darmstadt17 Cooling: Temperature Stabilization and Homogeneity HV resistor rod: 4 x 8 W  water-cooled  removable  electrolysis, corrosion... all under control Very challenging: we aim at  T  0.1 K in the whole volume Thermal screens towards TRD (outer) and ITS (inner) Water-cooling of Readout Chamber Al bodies and pad planes Water cooling of FEE boards (total power 27 kW) All leakless (P < P atm ) cooling systems >400 temperature probes

Vienna 2004C. Garabatos, GSI Darmstadt18 Rays perpendicular to beam axis Effective ray  ~1mm 2 x 4 z-planes Strategic boundary crossings Additional signal from central electrode Laser System

Vienna 2004C. Garabatos, GSI Darmstadt19 Performance simulations > 97 % dN/dy = 8000 dE/dx resolution: 5.3 – 6.8 % depending on multiplicity  p/p Magnetic field 0.5 T  p/p (100 GeV) vs dN/dy: 16%  9% at dN/dy=2000

Vienna 2004C. Garabatos, GSI Darmstadt20 Space resolution from cosmic ray data Resolution in drift direction Resolution in bend direction

Vienna 2004C. Garabatos, GSI Darmstadt21 Summary A challenging, large TPC is thoroughly being constructed for ALICE High multiplicities, high occupancy, high gain  Optimised gas: Ne-CO 2 -N 2 [ ] (If you can't beat her, join her) Outlook: Dec Aug. 05: Full TPC assembly in surface 2006: TPC Installation underground 2007 START OF LHC

Vienna 2004C. Garabatos, GSI Darmstadt22 ALICE TPC Collaborators T. Alt, Y. Andres, T. Anticic, D. Antonczyk, H. Appelshäuser, J. Bächler, J. Bartke, J. Belikov, N. Bialas, U. Bonnes, R. Bramm, P. Braun-Munzinger, R. Campagnolo, P. Christakoglou, E. Connor, H. Daues, C. Engster, Y. Foka, F. Formenti, A. Förster, U. Frankenfeld, J.J. Gaardhøje, C. Garabatos, P. Glässel, C. Gregory, H.A. Gustafsson, J. Hehner, H. Helstrup, M. Hoch, M. Ivanov, R. Janik, K. Kadija, R. Keidel, W. Klempt, E. Kornaś, M. Kowalski, S. Lang, J. Lien, V. Lindenstruth, C. Loizides, L. Lucan, P. Malzacher, T. Meyer, D. Miskowiec, B. Mota, L. Musa, B.S. Nielsen, H. Oeschler, A. Oskarsson, L. Osterman, A. Petridis, M. Pikna, S. Popescu, S. Radomski, R. Renfordt, J.P. Revol, D. Röhrich, G. Rüschmann, K. Safarik, A. Sandoval, H.R. Schmidt, K.E. Schwarz, B. Sitar, H.K. Soltveit, J. Stachel, T.M. Steinbeck, H. Stelzer, E. Stenlund, R. Stock, P. Strmen, T. Susa, I. Szarka, H. Tilsner, G. Tsiledakis, K. Ullaland, M. Vassiliou, A. Vestbo, D. Vranic, J. Westergaard, A. Wiebalck, B. Windelband

Vienna 2004C. Garabatos, GSI Darmstadt23 Additional slides

Vienna 2004C. Garabatos, GSI Darmstadt24 Absorption cross-section of quenchers

Vienna 2004C. Garabatos, GSI Darmstadt25 Unprecedented gain?

Vienna 2004C. Garabatos, GSI Darmstadt26 TPC test facility measurements rms noise statistics, mean 700 e time bin pad # time bin Cosmics tracks

Vienna 2004C. Garabatos, GSI Darmstadt27 Field Cage: Central Electrode 6m wide mylar foil, glued from 3 sheets

Vienna 2004C. Garabatos, GSI Darmstadt28 SAMPLING CLOCK up to 20 MHz (5.7 MHz used) READOUT CLOCK 40 MHz 10- bit 20 MSPS 11- bit CA2 arithmetic 18- bit CA2 arithmetic 11- bit arithmetic 40-bit format 40-bit format 10-bit arithmetic ALICE TPC READOUT CHIP – Principle 16 ADCs and Digital Filter channels in one chip Algorithms and parameters reconfigurable

Vienna 2004C. Garabatos, GSI Darmstadt29 Field Cage Outer Containment Vessel

Vienna 2004C. Garabatos, GSI Darmstadt30 Readout Chamber Wire Geometry gate wires cathodes anodes pads

Vienna 2004C. Garabatos, GSI Darmstadt31 Pad Plane optimized pad sizes – 4 x 7.5 mm – 6 x 10 mm – 6 x 15 mm segmented: IROC and OROC total pads

Vienna 2004C. Garabatos, GSI Darmstadt32 Outer chamber test status

Vienna 2004C. Garabatos, GSI Darmstadt33 Tightness

Vienna 2004C. Garabatos, GSI Darmstadt34 Gain curve

Vienna 2004C. Garabatos, GSI Darmstadt35 Gain uniformity test

Vienna 2004C. Garabatos, GSI Darmstadt36 Long-term test

Vienna 2004C. Garabatos, GSI Darmstadt37 Ageing tests Tested many assembly materials: –Glues: Araldit 2012, 2013, dp190, 116 –Tedlar foil –Vacuum grease Lithelen Apiezon –Stesalit-like insulator

Vienna 2004C. Garabatos, GSI Darmstadt38 Rate of ageing in ALICE with P10

Vienna 2004C. Garabatos, GSI Darmstadt39 Ageing predictions with P10

Vienna 2004C. Garabatos, GSI Darmstadt40 Challenging requirements High multiplicities (dN/dy = 8000 originally) –High occupancy  Small pads (down to 4  7.5 mm 2 ) –E (and E  B) distortions in drift volume  No Argon Momentum resolution goal dp/p  1% – low multiple scattering gas  No Argon Event rate (up to 200 Hz) –100  s max. drift time but 100 kV max  Not much quencher allowed Good particle ID through dE/dx –signal/noise, uniformity  High enough gain

Vienna 2004C. Garabatos, GSI Darmstadt41 The gas: what is left Noble gas cannot be Argon –Positive ions too slow, Multiple scattering  Noble gas must be Neon Quencher cannot be a hydrocarbon –Flammability, Ageing, Slow proton production Quencher cannot be CF 4 (not well understood)  Quencher must be CO 2  Composition not different from [90-10] (V d =2.8 cm/  s) Low primary ionisation + small pads:  Unprecedented high gain: 2  10 4 (for TPCs)

Vienna 2004C. Garabatos, GSI Darmstadt42 Front End Card connection and cooling FEC in cooled Cu sandwich Flexible cables to PASA input Extra structure (Service Support Wheel) to hold weight of electronics

Vienna 2004C. Garabatos, GSI Darmstadt43 25 Front End Cards ALTRO PASA Power Connector Readout and Control Backplane (300 MB /sec) Readout Partition (3200 channels) FEE Components Assembly