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Status of ALICE Beam Conditions Monitoring System

Status of ALICE Beam Conditions Monitoring System. ALICE Offline Week 08 October 2007. ALICE BCM. Aim detection of adverse beam conditions within the ALICE experimental region active protection of detectors (in particular the ITS) against multi-turn beam failures

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Status of ALICE Beam Conditions Monitoring System

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  1. Status of ALICE Beam ConditionsMonitoring System ALICE Offline Week 08 October 2007

  2. ALICE BCM Aim • detection of adverse beam conditions within the ALICE experimental region • active protection of detectors (in particular the ITS) against multi-turn beam failures • monitoring of background level Concept • based on pCVD diamond sensors (1 cm2 x 500 μm) • DC monitoring, integration over 40 μs, always active • initiates beam dump via Beam Interlock System if signal is above threshold • time span between occurrence of a critical situation and complete extraction of the beam 200 – 290 μs • design and components copied (to a large extent) from the LHCb BCM.

  3. TTC GMT DCS TELL1 singlemodefiber ethernet BIS Power Supplies NE12 LV CIBU reset (RG-58) HV LV BCM A BCM C multimodeopticalfibers BLM CFC card BLM CFC card

  4. Locations BCM C behind last muonabsorber (z = -19.1 m) • Whytheselocations? • nootherspaceleft on muon arm side • expectsignals due tominimumbiascollisionsand due tobackgroundeventstobeofcomparableintensity BCM A betweenCompensator Magnet and Low βshielding (z=+15.6 m)

  5. Simulations Purpose • Estimatedetectorsignalfor nominal conditions • Verifydetectorpositions Geometryof BCMs in AliRoot: 8 sensors per stationat r = 5±0.5 cm (BCM A) and r = 6±0.5 cm (BCM C) from nominal beam line ”Supports“: aluminiumtube, PCB annulus Additional BCM stationat z = + 8 m (alternative locationfor BCM A) Outerdetectors not included Detectorresponse Simulation ofhits in BCM  meancurrentestimatedfromdepositedenergy W = 13 eV,  ≈ 0.5 (CCE)

  6. Event Generation 3 contributionstoradiationenvironmenttakenintoaccount: • minimumbiaspp collisions(14 TeV) at IPAliGenPythiaR = 200 kHz • beam-gasinteractions (pOcollisionsat 7 TeV) inside experimental regionAliGenBeamGasNewR = 12 kHz/m • machinebackgroundfrom beam-gas interactions in IR2 StraightSectionAliGenHaloProtvinogas densitydistributionscenario ”3rdyear + 90 days“ Not (yet) takenintoaccount: • machinebackgroundfrom beam losses on tertiarycollimators usesourcefilesfromLHCb?

  7.  pp collisionsat IP  beam gas eventinside experimental region  machineinducedbackground Sensitive range of CFC card 10 pA – 1 mA

  8. Beam Failures FailuresatInjection FailureswithCirculating Beam Time scale several turns Scenarios various possibly dangerous for experiments: uncontrolledlocalorbitbump in combinationwith fast magnetfailure Protection detectionbysurveillancesystems (BLM, Power Interlock, BCM)beam dump via BIS Time scale < single turn Scenarios • wrongsettingsof LHC magnet(s) • failureofinjectionkicker Protection • correct settings • passive protection elements (absorbers, collimators) • all detectors in a configuration of no signal production (low bias voltage at ITS, HV below gas multiplication in gaseous detectors, limited HV in PMTs) Ref.: D. Macina,Report fromthe Joint Machine-Experiment Meeting on theexperimentsprotectionfrom beam failures, EDMS Document 856468

  9. To Do • MachineInduced Background fromlosses on TertiaryCollimators • Getestimateforthresholdsettings • Simulation ofpossible beam failurescenariosandtheirimpact on ALICE Suggestionsarewelcome!

  10. InjectionFailures • Ref: B. Pastirčák et al., Radiation fromMisinjected Beam to LHC, ALICE Internal Note 2001-03 • Failurescenarios: • grazing: fullbatch (4.13 × 1013 p) missingthe TDI beamstopper, worstcase but veryunlikely • sweep: beam passagecoincideswithkickerrise time, ≈ 20 bunchesescape TDIseveraltimes/year maincontribution • Results:Accumulated dose during 10 years due tomisinjectionis in worstcase (SPD detectorandelectronics) ≈ 1 krad (1% of total dose)

  11. InjectionFailures • Ref: B. Pastirčák et al., Radiation fromMisinjected Beam to LHC, ALICE Internal Note 2001-03 • Failurescenarios: • grazing: fullbatch (4.13 × 1013 p) missingthe TDI beamstopper, worstcase but veryunlikely • sweep: beam passagecoincideswithkickerrise time, ≈ 20 bunchesescape TDIseveraltimes/year maincontribution • Results:Accumulated dose during 10 years due tomisinjectionis in worstcase (SPD detectorandelectronics) ≈ 1 krad (1% of total dose) Longitudinal sectionthrough ALICE centralpart Energydeposition (rad) forgrazing (left) andsweep (right) impact (10 years)

  12. Collimator Background Beam halodue tocleaninginefficiencies in IR7/IR3 and beam-gas interactions in coldsectionsis lost atnextaperturelimit. Resultinglossmapsareavailable • Simulation by V. TalanovforLHCb: • particlecascadetransportedtoscoring planeatz = -1 m from IP8 • different versionsavailable (with/withoutshielding) • canbescaledwithloss rate and beam lifetime • dominatingbackgroundforLHCb

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