Development of timing RPCs Presented by P.Fonte for the TOF-RPC group

CBM meeting TOF-RPC Outline Current activities of the TOF-RPC group  Test facility at ELBE/Rosendorf  Physics simulation studies  RPC properties  Analytic model of the RPC rate properties (NEW - post TSR)  Aging tests  Improvement of the rate capability  by using semiconducting glasses  by using commercially available ceramic materials (NEW)  through temperature increase  RPC layout options  Single cell chambers  Shielded timing RPCs  Multistrip counters  Readout electronics  Preamplifier/discriminator  FOPI-RPC electronics  Time measurement and digital backend

CBM meeting TOF-RPC Test facility at ELBE/Rosendorf The Rossendorf electron accelerator ELBE provides electrons up to 40 MeV in beam packets with a time spread better than 10 ps. Ready for users!

CBM meeting TOF-RPC Physics simulation ,K,p momentum distributions Occupancy on TOF plane

CBM meeting TOF-RPC RPC properties  Analytic model of the RPC rate properties (NEW)  Aging

CBM meeting TOF-RPC Primary statistics Gas response [A. Mangiarotti, P.Fonte, A.Gobbi NIM A 533(2004)16] σ τ (n 0 ’) [1/s units] n0’n0’ Ineff (%) Analytical model of the rate effect (NEW)

CBM meeting TOF-RPC Intrinsic time resolutionFluctuations in the fieldDrop in the field [Mangiarotti et al. NIM A 535 (2004) 272 ] (var E ) 1/2 /E σ τ (n 0 ’) [1/s units] Analytical model of the rate effect (NEW) For any source of E variation

CBM meeting TOF-RPC HV = 3.1 kV/gap HV = 3.2 kV/gap HV = 3.3 kV/gap HV = 3.4 kV/gap NOT FITTED! FITTED Data [re-scaled ‘prompt charge’] Analytical model of the rate effect (NEW)

CBM meeting TOF-RPC Aging ( ) - humid, cold After accumulating 800mC/cm 2 (equiv. 8.5 years of normal operation) we don't observe any systematic long-term increase of dark current with time.  made some changes on the experimental setup. 6 counters Room temperature “Standard” timing RPCs gas 85%C 2 H 2 F 4 +10%SF 6 + 5% iso-C 4 H 10, with 10% relative humidity Primary charges were created by an UV lamp No problem up to ~8 years equiv. charge (800 mC/cm 2 )

CBM meeting TOF-RPC Aging ( ) – humid, hot After more than 80 days we don’t observe any increase of the dark current. Which seems to stabilize. In chambers that operate at more than 2 kHz cm -2. And accumulated 200 mC cm -2 No problem so far (90 days = 200 mC/cm 2 ) Tenfold higher current

CBM meeting TOF-RPC Improvement of the rate capability (0.4 to 20 kHz/cm 2 foreseen, current designs: 1 kHz/cm2)  by using semiconducting glasses  by using commercially available ceramic materials (NEW!)  through temperature increase

CBM meeting TOF-RPC Rate / semiconducting glass Silicate glassPhosphate glass

CBM meeting TOF-RPC Rate / semiconducting glass

CBM meeting TOF-RPC Rate / ceramics (NEW)  Commercial “controlled resistivity” alumina, Al940CD, from Wesgo® Ceramics  Volume resistivity between 1×10 9 and 2 × 10 9  cm at room temperature.  Seems to be electronic conductor (no charge-up effects).  Good (hard, dense) surface.  Not straightforward (~1 year R&D) Benchtop test setup   22 Na Reference Chamber (identical) Test Chamber 10 cm 2 (CBM granularity) X-ray Generator Photon conversion on RPC yields an exponential pulse-charge distribution  Less favourable than the reasonable peak found in a charged beam.

CBM meeting TOF-RPC Rate / ceramics (NEW) Efficiency is kept up to 100 kHz/cm 2. Very encouraging…

CBM meeting TOF-RPC Rate / ceramics (NEW) Sigma ~ 100ps seems to be kept up to 50 kHz/cm 2 Random Coincid. Signal But background of random coincidences  fit with gaussian + symmetric exponential How does it affect the measurement of the real sigma?  visit Rosendorf… CBM goal well in reach

CBM meeting TOF-RPC Rate / Temperature Presented last meeting by D.Gonzalez

CBM meeting TOF-RPC Rate / Temperature Beam test in November When run warm (~50ºC) may comfortably reach a few 1000 Hz/cm2 Geometric acceptance ≈ 87 % Extrapolated from beam- tests on the previous HADES prototype, assuming a 25ºC temperature increase 0 75ºC=CBM goal…

CBM meeting TOF-RPC Rate / Temperature Test bench with 25 elements Heating and sensing element 20 W heater Hardware temperature limiter 1-WIRE® interface + power Thermometer Distributed temperature control system (in development) Reasonable cabling. Present accuracy ~1 ºC.

CBM meeting TOF-RPC  RPC layout options  Single cell chambers  Shielded timing RPCs  Multistrip counter

CBM meeting TOF-RPC Single cell chambers Coincides with the semiconducting glass effort

CBM meeting TOF-RPC Shielded timing RPCs Actual parts, industrially produced. Uniformity tests with 22 Na (positron  ) source Crosstalk for avalanches is below the noise level Beam test in November Final prototype of the HADES RPC-TOF wall Designed to run warm (up to 60ºC)

CBM meeting TOF-RPC Multistrip counters (FOPI) Present design: 8 gaps Very pure gaussian distribution

CBM meeting TOF-RPC Multistrip counters Single hitDouble hit 1kHz/cm 2 100Hz/cm 2

CBM meeting TOF-RPC  RPC electronics  Preamplifier/discriminator  FOPI-RPC electronics  Time measurement and digital backend

CBM meeting TOF-RPC Preamplifier / discriminator Performance of the existing front-end based on a multichip design Likely, for CBM an integrated design will be needed

CBM meeting TOF-RPC FOPI-RPC electronics TAQUILA system resolution of 33 ps demonstrated Possible concept for CBM

CBM meeting TOF-RPC Conclusion  Many developments and studies are under way in key aspects like  Aging  Physics simulation  Rate capability  System layout  Test facilities  Theoretical understanding  Some significant progress has been made.  Further results from beam tests expected later this year.