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LHC Collimation Review 2011

LHC Collimation Review 2011. Review Committee : Tiziano Camporesi (CERN), Wolfram Fischer (BNL), Brennan Goddard (CERN), Mike Lamont (CERN), Thomas Markiewicz (SLAC), Nikolai Mokhov (FNAL), Mike Seidel (PSI, chair), Andrzej Siemko (CERN), Johannes Wessels (U. Muenster). main focus :

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LHC Collimation Review 2011

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  1. LHC Collimation Review 2011 Review Committee: TizianoCamporesi (CERN), Wolfram Fischer (BNL), Brennan Goddard (CERN), Mike Lamont (CERN), Thomas Markiewicz (SLAC), Nikolai Mokhov (FNAL), Mike Seidel (PSI, chair), AndrzejSiemko (CERN), Johannes Wessels (U. Muenster) main focus: evaluate necessity of planned upgrades of the LHC collimation system

  2. chargeforcommittee 1. Are collimation performance and limitations properly analyzed and adequately addressed by upgrade plans? 2. Can the collimation upgrade in the IR3 dispersion suppressors, presently foreseen for the 2013/4 shutdown, be delayed by three years without limiting LHC performance at 7 TeV? 3. Have any issues or risks been overlooked that should be addressed in the collimation upgrade plan?  ignorecostandmanpowereffort

  3. generalcomments • thegeneralprogresswith LHC, andparticularlyperformanceandunderstandingofthecollimationsystemareimpressive • thecommitteeisimpressedbythequalityof design- andpreperatorytechnicalworkdone on theproposedcollimators in thedispersionsuppressorregions • theagreementbetweensimulationsandobservationsregardingcollimationefficiencyandlossdistributionisexcellent in mostcases • neverthelessthepredictionofintensitylimitsat 7TeV remains a difficultproblem

  4. intensitylimit 3.5TeV resultsfrom 2011 establishintensitymarginsfor 3.5TeV wellbeyondtherequirements scalingto 7TeV predicts a marginoffourtimesthe nominal intensity

  5. assumptionsforscalingto 7TeV • minimum beam lifetimestaysconstant • but manyoperatingconditionschange (bunchspacing, bunchcharge, emittance, collimatorsettings…) • scalingofcleaningefficiencyis 0.4 fromsimulations • experimentprovokinglossesartificially on 1/3 resonancemight not reproduce real situation • scalingofquenchlimittimesdilutionlength: 0.29 • locationsofpeaklossesstaythe same

  6. concernsforoperationwithout DS collimators • with nominal intensity/emittancetheimpedancelimitfor pp isreached • performancereach will bedeterminedbytheabilitytomaintainthedemandingcollimatorhirarchyduringoperation • integratedcollimatorBPM’swouldhelp a lot

  7. concernsfor heavy ionoperation • predictedintensitylimitfrom IR3 is ¼..½ of nominal intensity, based on conservativeassumptions • theluminosity will be limited to 50% ofthe nominal bythe lack oflocalcollimatorsnexttodetectors in IR’s 1,2,5 • predictionsarelesscertainthanforprotons

  8. R2E concerns • 4 failuresobserved, withoutmitigationactionsfactor 75 expectedat nominal LHC parameters • mitigatingactionsagainstradiationdamageofelectronics in IR 7 may not besufficient • carbonsecondarycollimatorswithintegratedBPM’s will beproduced in anycaseforphase 2; if R2E problemsarise in IR7 thesecanbeinstalled in IR3 readily

  9. furtherfindings 1 • increased activation does not prevent upgrade work in LS2 2017 if work postponed, although ALARA favors LS1 2013 (factor 4) • theplanningofthecollimatorinstallationalready in LS1 2013 ischallengingandpresentsrisks • howevertheadvantagesofupgrading IR3 in 2013 are: • gainexperiencepriortoupgrading all IR’satonce • stagingthe DS collimationupgradesreducespeakworkload

  10. furtherfindings 2 • thecommitteeacknowledgesstudy on time dependent MB quenchstability • operational experience with present system at 3.5 TeV is good; few dumps from "cleaning losses“; margins are comfortable • rad damage to magnets: expect about 2.4 MGy/y if magnets run at 1/3 of quench limit; onset of problems above 10 MGy!; needs realistic FLUKA simulations • possible 'operational' mitigation measures if DS collimators NOT installed and problems seen: buttons in collimators, 50ns, improve on lifetime dips

  11. committee’sconclusions • on thebasisoftheevidencepresented, thecommitteeconcludesthatthe nominal protonintensityof LHC at 7TeV canbeachievedwithouttheinstallationof additional collimators in theIR3 dispersionsuppressionregion in LS1 • however, the eventual installationofthe DS collimators will increase operational marginsandflexibilitysignificantly

  12. recommendations 1 • mechanism for lifetime dips at 3.5 TeV should be better understood and how this scales with energy; perform studies to evaluate effects of varying operational parameters on lifetime dips • consider mitigation measures against lifetime dips, e.g. collide before squeeze • estimateradiationdamagetostabilizing material ofsuperconductingcableatcryogenictemperatures

  13. recommendations 2 • quenchlimitstudies, includingprovokingquenches, shouldbecontinuedto • benchmarksimulationpredictions • gaindatafor heavy ionoperation • establish a link to 1D beam lossmodelusedthroughoutthecollimationproject, particularly in IR3 • increaseconfidenceconcerning 7TeV predictions • FLUKA uncertaintiesconcerningsinglediffractivecrosssectionsshouldbereducedbycomparisontopPbdata

  14. recommendations 3 • investigate other upgrade options (postponing work on DS collimators until LS2) • fixed masks inside large aperture dipole magnets • possibility of 11 T magnet to replace main dipole, to make space • thin Tungsten primarycollimators • hollow e-beam • evaluate risk level with present tolerances and 0.55 m * • impedance: 7 TeV settings on the edge for stability for headtail modes and TMC; Investigate feedback? • addition of combined cleaning will maybe double the total impedance coming from the collimators due to smaller gaps...this should be properly evaluated.

  15. summary on charge 1. Are collimation performance and limitations properly analyzed and adequately addressed by upgrade plans? yes 2. Can the collimation upgrade in the IR3 dispersion suppressors, presently foreseen for the 2013/4 shutdown, be delayed by three years without limiting LHC performance at 7 TeV? yesforprotons, possibly not forions 3. Have any issues or risks been overlooked that should be addressed in the collimation upgrade plan? no

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