R. Assmann Collimator Functionality, Performance and First View on Set-up and Optimization R. Assmann AB/ABP, CERN External Review of the LHC Collimation Project June 30 th - July 2 nd 2004 Part of discussions on commissioning of machine protection related system: B. Dehning, B. Goddard, M. Lamont, J. Wenninger, R. Schmidt

R. Assmann Outline Functionality of the LHC collimatorFunctionality of the LHC collimator Performance estimatesPerformance estimates Set-up and optimizationSet-up and optimization ConclusionConclusion

R. Assmann The LHC Type Collimator If we say collimator:We mean a collimator with two parallel jaws! Each jaw controllable in position and angle!

R. Assmann Functionality Side view at one end Motor Temperature sensor Gap opening (LVDT) Gap position (LVDT) Resolver Reference Microphonic sensor Not shown: IN, OUT, ANTI-COLL switches! Calibration: Inside vs outside gap etc

R. Assmann Functionality Side view at one end Motor Temperature sensor Gap opening (LVDT) Gap position (LVDT) Resolver Reference Microphonic sensor Calibration: Inside vs outside gap etc

R. Assmann Basic control in-/output Basic input:Motor setting: jaw position at each end Control position and angle of each jaw independently!  Control position and angle of each jaw independently! Local resolver reading Readings:For each motor:  Local resolver reading Gap width For each end of the jaw:  Gap width Gap position  Gap position Monitoring:Temperature, switches, micro-phonic sensors

R. Assmann For set-up We can guarantee a gap in mm to several 10’s of  m! However, we must set to beam , e.g. 6  for primary collimators! Understand beta function at collimator! Must be known to 20% anyway for aperture before serious commissioning  J. Wenninger!  Collimator gaps can be set to better ± 0.6  from basic aperture tolerances! Major task for collimation set-up:  Centering of gap around the beam!

R. Assmann Inefficiency and Allowable Intensity Allowed intensity Quench threshold (7.6 × TeV) Dilution Length (50 m) Cleaning inefficiency = Number of escaping p (>10  ) Number of impacting p (6  ) Beam lifetime (e.g. 0.2 h minimum) (Luminosity)

R. Assmann How to get collimators going for phase 1 Start at low intensity:  Need for less cleaning efficiency! No collimationPilot bunch Single-stage collimation~ 500 bunches (inj) ~ 20 bunches (top)  -cleaning: 2 primary coll. momentum cleaning: 1 primary coll. Help with local tertiary coll. Limited two-stage collimationIntermediate intensities Bring on secondary coll.  -cleaning: ~ 7 TCS momentum cleaning: ~ 4 TCS Full two-stage cleaningUp to 50% of nom. intensity  -cleaning: 11 TCS momentum cleaning: 4 TCS

R. Assmann Components for the Collimation System (Phase 1) Focus of review Most difficult! Number of objects: spares Per beam: 25 collimators 3 scrapers 12 absorbers

R. Assmann Collimators / Scrapers / Absorbers Components of the collimation system are distinguished by their function: Collimators:beam protons Collimators:Elastic and inelastic interactions of beam protons. Precise devices with two jaws, used for efficient beam cleaning. Small gaps and stringent tolerances. Scrapers:beam shaping and diagnostics Scrapers:Used for beam shaping and diagnostics. Thin one-sided objects. Absorbers:mis-kicked beam showers Absorbers:Absorb mis-kicked beam or products of proton-induced showers. Movable absorbers can be quite similar in design to collimators, but mostly with high-Z jaws. Larger gaps and relaxed tolerances. Precise set-up and optimization in first line affects collimators!

R. Assmann Set-up of single collimator BLM Beam

R. Assmann Set-up of single collimator 1-by-1 procedure: 1. Lower intensity  1 stage cleaning is sufficient. 2. Scraping of beam to ~ 3  3. Move in single jaw. One edge after the other. 4. Second jaw the same way. 5. Collimator to reference position (record) and then out. 6. Next collimator…  No problem of cross-talk (do both beams at same time).  Need good BLM system (B. Dehning, B. Holzer) adjusted to set-up.

R. Assmann Set-up of single collimator BLM Beam Shower

R. Assmann Set-up of single collimator BLM Beam Shower

R. Assmann Set-up of single collimator BLM Beam Shower

R. Assmann Set-up of single collimator BLM Beam Shower

R. Assmann Set-up of single collimator BLM Beam Calibrated center and width of gap, if beam extension is known (e.g. after scraping). Advance with experience! Rely on good BLM system...

R. Assmann Advance procedures Put all collimators to same normalized setting! Assume we want to center gaps...

R. Assmann Advance procedures  Grow beam emittance... Shower

R. Assmann Advance procedures  Grow beam emittance... Shower

R. Assmann Advance procedures  Grow beam emittance... Shower

R. Assmann Advance procedures  Grow beam emittance... Shower

R. Assmann Advance procedures  Grow beam emittance... Shower

R. Assmann Advance procedures  Grow beam emittance... Shower

R. Assmann Advanced procedures In principle we could optimize many collimators at once.In principle we could optimize many collimators at once. Efficient procedures should be prepared!Efficient procedures should be prepared! Can also imagine long orbit bumps through collimation insertions with equal settings  similar to emiitance growth procedure!Can also imagine long orbit bumps through collimation insertions with equal settings  similar to emiitance growth procedure! Do at lower intensity, where one-stage cleaning is sufficient (20 nom. bunches at 7 TeV, more at injection).Do at lower intensity, where one-stage cleaning is sufficient (20 nom. bunches at 7 TeV, more at injection). Maybe less for machine protection!?Maybe less for machine protection!? Detailed simulations for these set-up procedures will be done  required and achievable tolerances (~0.1  or 20  m)!?Detailed simulations for these set-up procedures will be done  required and achievable tolerances (~0.1  or 20  m)!? SPS: Test for single collimator set-up!SPS: Test for single collimator set-up!

R. Assmann Fine tuning of performance Best cleaning efficiency to avoid quenches!Best cleaning efficiency to avoid quenches! Look at places where losses are highest!  Critical BLM’s!Look at places where losses are highest!  Critical BLM’s! Use critical BLM’s for empirical optimization of collimator settings (within limits):  Trial and error procedure!Use critical BLM’s for empirical optimization of collimator settings (within limits):  Trial and error procedure! Similar to regular machine tuining (orbit,...). Just watch out not to get the collimators damaged:  Limits on tuning range (several  ?).Similar to regular machine tuining (orbit,...). Just watch out not to get the collimators damaged:  Limits on tuning range (several  ?).

R. Assmann Loss Maps Around the Ring: Injection Q6 downstream of betatron cleaning: first SC magnet Understand effect of azimuth on quench. Help further with absorbers in IR7! Acceptable!? Understand effect of azimuth on quench. Help further with absorbers in IR7!  S. Redaelli G. Robert-Demolaize Aperture model for 27,000 m LHC with 0.1 m longitudinal resolution: ~ 270,000 loss points! Tertiary halo

R. Assmann Loss Maps Around the Ring: Collision Peaks in all triplets: Cure with tertiary collimators! Work is ongoing... 9 × 10 6 p tracked over 100 turns through each LHC element! 27,000 loss points checked in aperture! Massive computing effort: 9 × 10 6 p tracked over 100 turns through each LHC element! 27,000 loss points checked in aperture! So far only tertiary halo: Include also secondary halo. Future data generated from SIXTRACK! Tertiary halo IR8: Initial optics with  * = 1 m

R. Assmann Conclusion Preliminary thoughts on set-up and optimization.Preliminary thoughts on set-up and optimization. Evolutionary process: no collimation – 1 stage – limited 2 stage – full 2 stage. Help by tertiary collimators!Evolutionary process: no collimation – 1 stage – limited 2 stage – full 2 stage. Help by tertiary collimators! Time scale of months/years  not all collimators needed for day 1. Learn while the LHC performance is being pushed!Time scale of months/years  not all collimators needed for day 1. Learn while the LHC performance is being pushed! Set-up of single collimator: Standard procedure exists and is used successfully at other laboratories (adjust position and angle)! Test with LHC collimator in the LHC!Set-up of single collimator: Standard procedure exists and is used successfully at other laboratories (adjust position and angle)! Test with LHC collimator in the LHC! Advanced procedures: Should work to efficiently set up many collimators!Advanced procedures: Should work to efficiently set up many collimators! All of this will be simulated in detail!All of this will be simulated in detail! Goal: Procedures ready and implemented for LHC start-up in 2007! Then make them work...Goal: Procedures ready and implemented for LHC start-up in 2007! Then make them work...