1. R. Assmann Collimators and Beam Absorbers for Cleaning and Machine Protection Ralph Assmann Workshop Chamonix XIV 17-21.01.2005 Acknowledgements to the members of the Collimation Project, the Collimation WG and the Machine Protection WG!

2. R. Assmann Collimators and Protection Devices Collimators:  20 + 15 per beam (TCP, TCSG + TCSM)Collimators:  20 + 15 per beam (TCP, TCSG + TCSM) –Interact with primary, secondary or tertiary beam halo. –Scattering devices for spoiling and inducing inelastic interactions for protons lost from the beam! –Precise devices with two jaws, used for efficient beam cleaning. Small gaps and stringent tolerances. –Absorb little energy. Very robust. Movable absorbers:  20 per beam (TCT, TCLA, TCLP)Movable absorbers:  20 per beam (TCT, TCLA, TCLP) –Interact with shower products from p-p and p-collimator interactions. –Devices for absorbing the lost energy. –High-Z jaws. Larger gaps and more relaxed tolerances. Diluters:  4 + 7 per beam (TDI, TCLI, TCDQ + TCDI)Diluters:  4 + 7 per beam (TDI, TCLI, TCDQ + TCDI) –Interact with mis-kicked beam or irregular beam tails (injection and dump protection). –Strong dilution (emittance blow-up) and partial absorption of energy Scrapers:  3 per beam (TCHS)Scrapers:  3 per beam (TCHS) –Thin one-sided objects. Used for beam shaping and diagnostics. CLEANING (continuous) PROTECTION (accidents) SPECIAL (exceptional)

3. R. Assmann Detailed Table 138 collimator locations In total 138 collimator locations in LHC and transfer lines! ~ 145 m Installed active length of ~ 145 m plus ~70 m overhead (215 m total) Injection: up to 39 collimators per beam Top energy:up to 41 collimators per beam

4. R. Assmann Sophisticated Cleaning Design in IR3 and IR7 Line input file for FLUKA generated from collimation halo tracking program. Automatic generation of FLUKA geometry with dynamic placement of collimators. Powerful tool  Automatic generation of full LHC FLUKA geometry on the horizon? V. Vlachoudis et al Cleaning optics in collaboration with TRIUMF! Not more than 1 out of 10000 impacting protons may escape the cleaning system at 7 TeV: Cleaning  S. Redaelli

5. R. Assmann Phase Space Coverage Injection Beam 3  envelope coverage of phase space Decent coverage of phase space: first be intercepted at a collimator or absorber or diluter Beam will likely first be intercepted at a collimator or absorber or diluter (also for asymptotic orbit change)! BLM’s at collimator protect against beam loss! Not very comfortable margin though (profit from tighter settings)! Cold aperture

6. R. Assmann Limitations from Collimation & Protection in Commissioning Towards Nominal Performance Beam-induced damage to the machine (collimators):  Robust collimators! Quenches or beam loss related aborts:  Efficient cleaning! Experimental background :  Efficient cleaning! Instabilities :  Impedance from collimators! Limitation in operational efficiency! Limitation in intensity/luminosity!

7. R. Assmann Efficiency is Already Optimized in Design Phase - Robust collimators - Robustness maximized with C-C jaws and powerful water cooling!

8. R. Assmann Design Verification with Beam Test Two prototype collimators installed.Two prototype collimators installed. SPS ring:SPS ring: –Functional test –Beam-based alignment with small gaps –Measurement of impedance, HOM, vacuum, e-cloud,... TT40:TT40: –Robustness test with 2.4 MJ/mm 2 All VERY successful! S. Redaelli

9. R. Assmann Robustness Test C-C jaw C jaw TED Dump 450 GeV 3 10 13 p 2 MJ 0.7 x 1.2 mm 2 no change in jaw dimensionsJaw impact could be measured during all expected hits: no change in jaw dimensions (nothing fell off) 1mm gap after testClosure of two jaws to 1mm gap after test (no large debris). Take out collimator in January and inspectTake out collimator in January and inspect. Analyzing measurements of temperature, vibration and sound. ~ Tevatron beam ~ ½ kg TNT Microphone

10. R. Assmann Jaws after Shock Impact

11. R. Assmann Damage Limits in Present design Danger to regular machine equipment and metallic absorbers:Danger to regular machine equipment and metallic absorbers: –Above 1e12 p at injection: 4e-3 of beam –Above 5e9 p at 7 TeV: 2e-5 of beam Danger to C-C collimators/absorbers:Danger to C-C collimators/absorbers: –Above 3e13 p at injection:10% of beam –Above 8e11 p at 7 TeV:3e-3 of beam Maximum allowed loss rates at collimators (goal):Maximum allowed loss rates at collimators (goal): –100 kW continuously. –500 kW for 10 s (1% of beam lost in 10s). –1 MW for 1 s. Commissioning must respect these limits: we cannot relax more!Commissioning must respect these limits: we cannot relax more!

12. R. Assmann Impedance Limit for Movable Devices Collimators and absorbers are close to beam: A resistive wall impedance is induced (gap size depends on  *)!Collimators and absorbers are close to beam: A resistive wall impedance is induced (gap size depends on  *)! C-C material has reduced electrical conductivity (price to pay for a robust system). Fix with phase 2 advanced collimators.C-C material has reduced electrical conductivity (price to pay for a robust system). Fix with phase 2 advanced collimators. Increase from collimators (nominal settings) for the imaginary part of the effective vertical impedance:Increase from collimators (nominal settings) for the imaginary part of the effective vertical impedance: –8 kHz: factor 3 for injection factor 69 for 7 TeV –20 kHz: factor 3 for injection factor 145 for 7 TeV Large increase in impedance must be actively counteracted by transverse feedback and octupoles!Large increase in impedance must be actively counteracted by transverse feedback and octupoles!

13. R. Assmann F. Zimmermann et al Collimator-Induced Tune Change (Changing Collimator Gap) Gap: 2.1 51 mm So-called BBQ device (M. Gasior & R. Jones) SPS tune depends on collimator gap! M. Gasior, R. Jones et al

14. Elias Métral, LTC, 08/12/2004 25 ns 50 75 150 300 900 Single bunch Stability diagram (maximum octupoles) and collective tune shift for the most unstable coupled-bunch mode and head-tail mode 0 (1.15e11 p/b at 7 TeV) Effect of the bunch spacing… Vertical plane STABLE  Even single bunch unstable for nominal  *!

15. R. Assmann Setting Strategy for Collimation and Protection Elements at Injection Plateau Clear requirements for settings: LHC ring aperture sets scale a ring  tight LHC aperture Protection devices must protect ring aperture a prot < a ring  protect against injected beam; take into account accuracies Secondary collimators tighter than protection a sec < a prot  avoid too much secondary halo hitting protection devices Primary collimators tighter than secondary a prim < a sec  primary collimators define the aperture bottleneck in the LHC for cleaning of circulating beam!Clear requirements for settings: LHC ring aperture sets scale a ring  tight LHC aperture Protection devices must protect ring aperture a prot < a ring  protect against injected beam; take into account accuracies Secondary collimators tighter than protection a sec < a prot  avoid too much secondary halo hitting protection devices Primary collimators tighter than secondary a prim < a sec  primary collimators define the aperture bottleneck in the LHC for cleaning of circulating beam! These conditions should always be fulfilled: Avoid using protection devices as a single-stage cleaning system!These conditions should always be fulfilled: Avoid using protection devices as a single-stage cleaning system!

16. R. Assmann Settings during injection (in    ) a abs = ~ 10.0  Active absorbers in IR3 and IR7 a sec3 =9.3  Secondary collimators IR3 (H) a prim3 =8.0  Primary collimators IR3 (H) 7.5  a ring =7.5  Ring cold aperture 6.8  a prot = 6.8  TDI, TCLI (V)protection elements 7.0  a prot ≥ 7.0  TCDQ (H) protection element 6.7  a sec =6.7  Secondary collimators IR7 5.7  a prim = 5.7  Primary collimators IR7 4.5  6.9  a TL =4.5  Transfer line collimators (ring protection at 6.9  )  Tight settings below “canonical” 6/7  collimation settings! Tighter for larger beta beat (smaller cold aperture)!

17. R. Assmann Settings at 7 TeV (in    nominal   ) a abs = ~ 20.0  Active absorbers in IR3 a sec3 =18.0  Secondary collimators IR3 (H) a prim3 = 15.0  Primary collimators IR3 (H) a abs = ~ 10.0  Active absorbers in and IR7 8.4  a ring = 8.4  Triplet cold aperture 8.3  a prot = 8.3  TCT protection and cleaning at triplet 7.5  a prot ≥ 7.5  TCDQ (H) protection element 7.0  a sec = 7.0  Secondary collimators IR7 6.0  a prim = 6.0  Primary collimators IR7  “Canonical” 6/7  collimation settings are achievable!

18. R. Assmann Setting versus energy

19. R. Assmann Collimator Set-up and Extrapolation to High Intensity Several procedures are used: Collimator touching beam and observation with BLM’s, scraping of intensity, transmission measurement, … See also talks by S. Redaelli and V. Kain!Several procedures are used: Collimator touching beam and observation with BLM’s, scraping of intensity, transmission measurement, … See also talks by S. Redaelli and V. Kain! All these methods set up the collimators in a single stage process!All these methods set up the collimators in a single stage process! Intensities must be limited because of reduced cleaning efficiency with single stage cleaning process.Intensities must be limited because of reduced cleaning efficiency with single stage cleaning process. Reference collimator and beam positions will be recorded at low intensity and must be re-established at high intensity!Reference collimator and beam positions will be recorded at low intensity and must be re-established at high intensity! Cleaning set-up relies on excellent stability and reproducibility of machine, even while current is changed significantly!Cleaning set-up relies on excellent stability and reproducibility of machine, even while current is changed significantly! Limited empirical optimization at top energy is possible!Limited empirical optimization at top energy is possible! Can we conceive a high current set-up for collimation? (also request from external review)Can we conceive a high current set-up for collimation? (also request from external review)

20. R. Assmann Commissioning of Cleaning System 43 Pilot No collimation Single-stage cleaning Two-stage cleaning (phase 1) Two-stage cleaning (phase 2)

21. R. Assmann Commissioning a Single-Stage Cleaning/Protection System with Circulating Beam 1.Put 3 betatron primary collimators to coarse 6  setting (single-stage cleaning always in cleaning insertions). Put 1 momentum primary collimators to 8.5 . 2.Put 8 TCLA absorbers in cleaning insertions to coarse 9  position (shadow SC arc aperture and capture shower debris). 3.Set up 1 TDI and 1 TCLI for injection protection (collimators can be out during set-up). 4.Set up 1 TCDQ for dump protection. 5.Accumulate and ramp. 6.Set up up to 8 TCT’s at top energy to protect triplets. 22 movable elements per beamincreased margin for set-up errors and transient beam changes This system involves 22 movable elements per beam with increased margin for set-up errors and transient beam changes (orbit, beta-beat): Injection: 3.0 mm margin instead of 1.0 mm margin 7 TeV:0.6 mm margin instead of 0.2 mm margin Fully functional 1 stage cleaning with injection and dump protection, as well as full protection of triplets! Fully functional 1 stage cleaning with injection and dump protection, as well as full protection of triplets! It’s surely worth it! ~1 day per beam Required time for set-up: ~1 day per beam based on SPS experience! Extend towards two-stage system by moving in secondary collimators! Reduce margin!

22. R. Assmann How to Overcome Beam Loss Limitations? 1.Increase available aperture for the beam (work on orbit and beta beat). 2.Improve stability of the machine (lower loss rates). 3.Improve cleaning efficiency (close collimators  reduce tolerances, increase impedance, increase complexity). 4.Decrease intensity. Sorted in order of priority for collimation/machine protection! Solution 4 reduces the performance and is only the last resort! It is the easy way! For above ~ 5-10% of nominal intensity we need to work hard on all topics 1-3! For above ~ 5-10% of nominal intensity we need to work hard on all topics 1-3! Don’t cut too many corners in the early commissioning! Need estimate on beta beat and orbit during different phases of commissioning! For detailed scenarios: Need estimate on beta beat and orbit during different phases of commissioning!

23. R. Assmann The Human Side of Machine Protection People can have deep insight and great ideas: We are the only chance to make the accelerator work!People can have deep insight and great ideas: We are the only chance to make the accelerator work! People can have very bad ideas and do stupid actions: We are the greatest risk to the accelerator! We can destroy the accelerator in a second!People can have very bad ideas and do stupid actions: We are the greatest risk to the accelerator! We can destroy the accelerator in a second! The machine protection enforcement The “boss” ONE central application We can try to avoid unnecessary problems:  ONE central application for all movable elements in LHC and TL’s! Close integration  Close integration into online knowledge of orbit, optics, … Interlocking. definition of responsibility  Clear and formal definition of responsibility for functions, optimization, operation, … Redundant checking  Redundant checking of machine status, e.g. positions of collimators/absorbers/diluters! (“Trust is good but control is better”)

24. R. Assmann Using Sensors to Monitor Jaw Positions Side view at one end Motor Temperature sensor Gap opening (LVDT) Gap position (LVDT) Resolver Reference Microphonic sensor Vacuum tank

25. R. Assmann Baseline Control Architecture Motor Drive Control Position Readout and Survey Environmental Survey System Collimator Supervisory System Central Control Application Function of motor setting, warning levels, dump levels versus time. Motor parameters (speed, …). Beam-loss driven functions. BLM’s BPM readings Timing From MP channel: Intensity, energy,  * Warning & error levels. Info and post mortem. Temperature sensors (jaw, cooling water, …) Vibration measurements & water flow rates Vacuum pressure & radiation measurements Motor status & switches Abort Functions (motor, warning, dump level). Info and post mortem. All position sensors. STOP Function motor. Motor parameters. Measurements. Post mortem. Warnings. Motor and switches. Abort Preliminary by R. Assmann, M. Jonker, M. Lamont  Detailed design by R. Losito et al

26. R. Assmann Motivation for this Controls Approach Experience shows that advanced and automatic collimator control algorithms must be used (TEVATRON, RHIC):Experience shows that advanced and automatic collimator control algorithms must be used (TEVATRON, RHIC): –BLM-based setting: “Move until BLM #i reads value X.” –Automatic movements for beam-based alignment requires functions. –Functions also allow fastest possible and most tolerant squeeze (move collimators during squeeze)  useful once we are in routine operation? –Full integration into machine control and machine protection required, while preserving maximum flexibility for optimization of cleaning. Break complicated system into manageable packages:Break complicated system into manageable packages: –Central Control Application to generate simple or complicated functions and to provide dump and warning levels. –Collimator Drive Control: Simple system which provides minimum required control (motor movement). Without MP functionality. Can be specified quickly and bought from external company. MUST be ready in early 2007. –Position Readout & Survey and Environmental Survey System: Independent checks with various sensors. Provides position verification and protection functionality. Developed at CERN and expected to mature with beam experience. –Collimator Supervisory System: System for many collimators (1-2 per IR) with interface to other systems (e.g. BLM’s). Provides advanced features. Expected to develop with needs of LHC operation.

27. R. Assmann Summary: Preparing Commissioning of Absorbers, Collimators and Diluters Collimation (phase 1) and protection design with movable devices essentially finalized! Coherent settings have been worked out.Collimation (phase 1) and protection design with movable devices essentially finalized! Coherent settings have been worked out. Detailed commissioning models require scenarios for evolution of beta beat and orbit during the commissioning (we need to know what we have to protect)!Detailed commissioning models require scenarios for evolution of beta beat and orbit during the commissioning (we need to know what we have to protect)! Now define control algorithms up to middle of 2005 for most movable collimators, absorbers and diluters in the LHC and the transfer lines! Additional manpower after “warning message” in Chamonix 2004 will arrive and will be essential for our success!Now define control algorithms up to middle of 2005 for most movable collimators, absorbers and diluters in the LHC and the transfer lines! Additional manpower after “warning message” in Chamonix 2004 will arrive and will be essential for our success! –Goal: Simple low level scheme with advanced medium and top level! –Functions can be used! Proposals:Proposals: –Separate set of BLM’s for collimator tuning! Don’t mix machine protection and cleaning problems! –Further tests with SPS beam in 2006 (final motors, sensors, control, …) are proposed. –Include proposed one-stage cleaning and protection into early commissioning plan! –Include MD time for phase 1 limitations and phase 2 tests into 2008 schedule! Decision 2008! –Only ONE central control for collimators/absorbers/diluters! No special commissioning tools! –Very limited tools for control of experimental background: Input required from experiments!