1. RWA LTC 27.10.04 Preliminary results from SPS collimator MDs LTC 27.10.04 R. Assmann for the collimation team

2. RWA LTC 27.10.04 People involved in collimator design/construction/testing team effortThis has been an outstanding team effort over the last 12 months! Work by: O. Aberle, G. Arduini, R. Assmann, A. Bertarelli, T. Bohl, L. Bruno, H. Burkhardt, S. Calatroni, F. Caspers, E. Chiaveri, B. Dehning, A. Ferrari, E.B. Holzer, J.B. Jeanneret, L. Jensen, M. Jimenez, R. Jones, M. Jonker, T. Kroyer, M. Lamont, M. Mayer, E. Metral, R. Perret, L. Ponce, S. Redaelli, G. Robert-Demolaize, S. Roesler, F. Ruggiero, D. Schulte, H. Tsutsui, P. Sievers, R. Steinhagen, V. Vlachoudis, L. Vos, J. Wenninger, F. Zimmermann,... Not including work on LHC collimation design!

3. Goals of SPS Tests 1.SPS ring: Show that the LHC prototype collimator has the required functionality and properties (mechanical movements, tolerances, impedance, vacuum, loss maps, …). Show that an LHC collimator jaw survives its expected maximum beam load without damage to jaw material nor metallic support nor cooling circuit (leak). 2. TT40 extraction: Show that an LHC collimator jaw survives its expected maximum beam load without damage to jaw material nor metallic support nor cooling circuit (leak). Crucial project milestoneMechanical engineering (installation 18Aug04) Tolerances Prototype production Control and motorization Set-up of a single LHC collimator with beam (APC April 04)

4. RWA LTC 27.10.04 Beam conditions Beams prepared by G. Arduini, J. Wenninger and OP team Low intensity MD: Monday Oct 11 th Bunch population1.1e11 p Number of bunches1-16 Beam energy270 GeV Emittance~ 1  m H beam size at collimator ~ 0.4 mm Beam orbit stability~ 10  m High intensity MD:Monday Oct 18 th Bunch population1.1e11 p Number of bunches288 Beam energy270 GeV Emittance~ 3.75  m H beam size at collimator ~ 0.7 mm Robustness test:Monday Oct 25 th

5. RWA LTC 27.10.04 Configuration Collimation team:Collimator in P5 of SPS BLM team:8 downstream BLMs Together:1 Hz DAQ and plotting in control room BLM team

6. RWA LTC 27.10.04 Different issues 1.Functionality and basic collimator control 2.Set-up and beam-based alignment of jaw (includes BLM diagnostics) 3.Halo dynamics 4.Impedance and trapped modes 5.Heating of collimator 6.Vacuum and e-cloud (outgassing) 7.Effects on BPM’s and orbit feedback

7. RWA LTC 27.10.04 1. Functionality: Mechanical movement and tolerances FULLY operational wayCollimators moved in a FULLY operational way: no limits or unexpected difficulties encountered! ~ 1 mmClosest gap of ~ 1 mm achieved with circulating beam! Mechanical tolerances and angular alignment at the ~ 100  m level! Much smaller gaps than required in the 7 TeV LHC have been achieved with the LHC collimator prototype and circulating beam!  Much smaller gaps than required in the 7 TeV LHC have been achieved with the LHC collimator prototype and circulating beam! ± 100  m ± 20  mKnowledge of full collimator gap (excluding human math errors): Absolute± 100  m Reproducibility± 20  m Anti-collision settings1.188/1.146/1.160 mm Gap known to 100  m with excellent reproducibility (20  m) over 16 h (motor setting reproducibility)!  Gap known to 100  m with excellent reproducibility (20  m) over 16 h (motor setting reproducibility)! Reduce number  Some sensors useful others less useful: Reduce number of sensors!

8. RWA LTC 27.10.04 2a. Set-up and beam-based alignment of jaw Gap width Gap center First basic set-up (100  m accuracy) within 50 min!

9. RWA LTC 27.10.04 2b. Set-up and BBA: Typical BLM signal for move of jaw 10-20 seconds Observation of BLM signal tails:Up to 10-20 seconds in length BLM teamBeam related true signal BLM team:Many measurements  Beam related true signal!

10. RWA LTC 27.10.04 2c. Studies of BLM systematics Time L. Ponce et al

11. RWA LTC 27.10.04 2d. Set-up and BBA: High precision set-up LHC requirement: Center gap around beam with ~ 25  m accuracy for nominal  * (beam-based alignment). SPS beam: 120 h beam lifetime (de-bunched beam?) orbit stable to 5  m  ideal tuning conditions... to 100  m is OK!... to 50  m is difficult!... to 10-20  m is impossible?Observation: Beam-based alignment...... to 100  m is OK!... to 50  m is difficult!... to 10-20  m is impossible? Understand effect to improve beam-based set-up!

12. RWA LTC 27.10.04 3a. Halo dynamics: Re-shaping After 10-20 seconds: New stable shape Problem: Re-shaping of beam with collimator in!? –Edge 1 jaw 1 creates sharp edge and stays in! –Rectangular distribution close to edge unstable! –Particles in sharp edge diffuse and are lost! –No sharp edge for precise alignment of edge 2 jaw 1 or jaw 2! –Similar effects observed in ISR, SPS,... No sharp edges! Collimator jaw Beam distribution

13. RWA LTC 27.10.04 3b. Measurement of repopulation rate – jaw positions 2.7 mm ≈ 6.5  Move from 7.7 mm (~ 19  ) back and forth to 2.7 mm (~ 6.5  ). Wait different times in between. Observe beam loss. Left jaw Right jaw Dump beam on collimator G. Robert-Demolaize et al

14. RWA LTC 27.10.04 3c. Measurement of repopulation rate - BLM signals G. Robert-Demolaize et al DC coll at 19  DC coll at 6.5  G. Robert-Demolaize et al

15. RWA LTC 27.10.04 3d. Measurement of repopulation rate – low intensity analysis  Shows how much beam diffuses out of sharp edge versus time! G. Robert-Demolaize et al

16. RWA LTC 27.10.04 3e. Measurement of repopulation rate – high intensity analysis G. Robert-Demolaize et al

17. RWA LTC 27.10.04 3f. Beam distribution close to the edge after 30 seconds G. Robert-Demolaize et al 50  m 1 mm

18. RWA LTC 27.10.04 3g. DC beam loss versus collimation depth ~ 10  ~ 20  More beam losses with collimator jaws further in: Enhanced diffusion rate? S. Redaelli et al

19. RWA LTC 27.10.04 4a. Impedance and trapped modes Impedance is a limitation for the LHC collimators. Impedance depends on collimator gap. Measurement is simplified as impedance can controlled through gap. Different measurements tried: Tune shifts, orbit kicks, trapped modes, growth rates,...

20. M.Gasior, R.Jones, CERN-AB-BDI Direct Diode Detection Base-Band Q-Measurement Collimator MDs #2 – (some) BBQ results Collimator cycled between  51 mm and 3.86 mm (5h04)  51 mm and 2.86 mm (5h35)  51 mm and 2.46 mm (5h43)  51 mm and 2.06 mm (5h50)  51 mm and 1.86 mm (5h58) LARGE gap SMALL gap

21. M.Gasior, R.Jones, CERN-AB-BDI Direct Diode Detection Base-Band Q-Measurement Collimator MDs #2 – (some) BBQ results  Collimator cycled (at ca 4h33) between the gap of 51 mm and 2 mm.  Tune frequency was changing by 10 Hz, i.e. 2.3  10 -4 (  f rev ) BBQ system245 MHz system 245 MHz system confirms data (F. Caspers/T. Kroyer) Also: Standard tune measurments (H. Burkhardt)

22. M.Gasior, R.Jones, CERN-AB-BDI Direct Diode Detection Base-Band Q-Measurement Collimator MDs #2 – (some) BBQ results

23. RWA LTC 27.10.04

27. 4b: Trapped modes Collimators were equipped with RF pickups to measure trapped modes. Measurement with and without beam by F. Caspers and T. Kroyer. Observation: There are trapped modes. They are excited by beam. No effect on collimator temperature or beam stability observed. Detailed analysis required. Fritz has won a bottle of Champaign and 20 straws... F. Caspers & T. Kroyer

28. RWA LTC 27.10.04 5. Heating of collimator (high intensity) No sign of problematic heating... Maximum increase 10 deg for closing gaps quickly!? No over- or under-design of collimator cooling...

29. RWA LTC 27.10.04 6. Vacuum and e-cloud No sign of vacuum pressure increase. No sign of local e-cloud at the collimator.

30. RWA LTC 27.10.04 7. Effects on BPM’s and orbit feedback Scraping of up to 5e12 protons at 270 GeV. No effect observed on downstream BPMs and overall orbit feedback (R. Steinhagen & J. Wenninger). Orbit feedback stabilized to 10  m orbit drifts. However, increased noise observed on BLM (equivalent to 10  m jaw steps and consistent with BPM noise). FB ON

31. RWA LTC 27.10.04 Robustness test in TT40 Beam accidentBeam accident just before sending first beam to collimator. Septum/power supply problem (  Jan). Safe extraction of nominal LHC beam for another trial? Collimator in TT40 saw no beamCollimator in TT40 saw no beam (except showers from accident). collimator safetyConcerns about collimator safety: –Lot’s of calculations and lab measurements  We are convinced it will survive without damage (both jaw and water cooling circuit)! –We had vacuum/radiation protection/cooling water experts on stand-by in the control room for an eventually needed emergency intervention. –Was not needed for the collimator but was helpful for fast recovery of the SPS. Try again the robustness testTry again the robustness test: We are convinced there will be no problem. However, there can always be a bad surprise  Test now with SPS beam so we can still correct problems! real mess to only find it in the LHC  If there is an unexpected problem it would be a real mess to only find it in the LHC!

32. RWA LTC 27.10.04 Preliminary conclusions Collimator design has been validated successfully Collimator design has been validated successfully in beam operation: Fully functional deviceFully functional device with no significant hardware problems. Reduce number of sensorsReal world performance provides knowledge base for possible savings:  Reduce number of sensors to required minimal level (save budget). Small gapsgood accuracy and tolerancesSmall gaps (smaller than in LHC) established with good accuracy and tolerances (circulating beam for 1 mm gap). Impedance measurements confirm predictionsImpedance measurements confirm predictions:  Phase 2 collimators are required for above 50% of nominal intensity (resources???). beam-based jaw alignmentintermediate precisionSet-up and beam-based jaw alignment worked at intermediate precision:  Need to advance quantitative understanding of halo dynamics for  * below ~ 1m with high precision jaw set-up (resources???). Collimator design does not require any modificationsCollimator design does not require any modifications (except maybe some material for absorbing trapped modes, if found dangerous). now be produced robust and powerful tools for the LHCCollimators will now be produced and we are convinced that phase 1 collimators will be robust and powerful tools for the LHC (robustness test should still be done)!

33. RWA LTC 27.10.04 Gap center and width versus time

34. RWA LTC 27.10.04