1. Critical beam losses during Commissioning & Initial Operation Guillaume Robert-Demolaize (CERN and Univ. Joseph Fourier, Grenoble) with R. Assmann, S. Redaelli, C. Bracco & T. Weiler; thanks to B. Dehning, B, Holzer & L. Ponce

2. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 2 OUTLINE Introduction Loss distribution from betatron cleaning Minimum workable BLM system for collimation studies Conclusion – Future studies

3. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 3 Introduction Purpose of the LHC Collimation system: provide cleaning efficiency and protection, using collimators and absorbers ~ 40 elements per ring => ~ 40 elements per ring are being implemented in the machine (Phase 1 of the system) About 3700 Beam Loss Monitors (BLMs) can be counted around the two rings of the machine => do we need all BLM information to understand the cleaning performance and losses from the “leaking halo” ?

4. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 4 Base principles of the LHC collimation system Collimators intercept beam halos (first, secondary, …) with some leakage which gets lost around the ring: the cleaning inefficiency of the system is then defined as: The leakage lost over a given length of the machine (10 cm in our studies) is then counted as local cleaning inefficiency (unit = m -1 ). sufficient to useonly a limited number of BLMs for commissioning the collimation system Goal of this presentation is to show that it is sufficient to use only a limited number of BLMs for commissioning the collimation system.

5. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 5 Critical BLMs for collimation There are two types of critical BLMs for the collimation system: => critical loss locations characterize the efficiency of our system: can we identify those critical locations (= BLMs) ?? -- BLMs at the collimators: needed from early on for the set-up of the collimators (experiments in SPS performed successfully in Fall 2004 for the first time), -- BLMs at loss locations of “leakage halo”: the halo exiting IR3/IR7 is lost in characteristic locations and not spread everywhere around the ring (implying all BLMs should be used) => critical loss locations characterize the efficiency of our system: can we identify those critical locations (= BLMs) ??

6. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 6 How to address this question Performing full simulations with ALL movable LHC Collimation System equipments: 41 collimators/absorbers per ring for Phase 1. Only betatron cleaning is considered in the following for on-momentum beam halo Check leakage halo losses in cold elements of the machine Notes: * results presented for Beam 1 only (Beam 2 tracking in preparation) * heavy computing effort in resources and time (CPU limited) * local energy deposition: FLUKA takes our data as input * losses at collimators: induced showers can propagate downstream

7. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 7 CPU usage 2 students - 2 fellows Tracking on 64+ CPUs ← limit of Collimation allocated CPUs ← granted by share with experiments

8. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 8 OUTLINE Introduction Loss distribution from betatron cleaning Minimum workable BLM system for collimation studies Conclusion – Future studies

9. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 9 Parameters for obtaining loss maps Data done for the two types of tracked halo (horizontal and vertical) and the two optics defined as reference cases: -- injection optics: 450 GeV,  * = 17 m at all IPs, -- collision optics: 7 TeV,  * = 0.55 m at IP1 & IP5 (else 10 m). Intermediate  * values can be studied if necessary (in case of big losses in experimental insertions). Assumed quench limit values:  10 -3 m -1 (injection)  2 x 10 -5 m -1 (collision) Results presented in the following slides focus on the horizontal halo only.

10. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 10 Collimators settings – Injection (1/2)

11. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 11 Collimators settings – Injection (2/2)

12. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 12 Collimators settings – Top energy (1/2)

13. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 13 Collimators settings – Top energy (2/2)

14. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 14 Error scenarios In the following we consider free orbit oscillations, always at the worst phase (found in simulation scan), following 2 scenarios: Static case: -- collimators are always re-centered around the perturbed orbit -- the error amplitude can reach the estimated aperture tolerances of 4 mm (injection optics) / 3 mm (collision optics) Dynamic case: -- collimators are still centered on the nominal closed orbit -- peak amplitude of error is ~ 1.5 

15. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 15 Loss map – 450 GeV Ideal case => Ideal case: below the quench limit (factor 5); not true during start-up though ▬► halo ↕ x 5

16. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 16 Sample perturbed orbit ▬► halo ↑ │ │ ± 4 mm │ ↓

17. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 17 Loss map – 450 GeV Perturbed orbit – worst phase, 4 mm amplitude => Loss of a factor 2 in efficiency at worst locations !!! ▬► halo ↕ x 2.5

18. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 18 Going downstream from IR7 ▼ ▼ ▼▼▼▼▼ => Same loss locations !!! Modulation of the peaks: a way to measure orbit ??? ▼ ▼ ▼ ▼ ▼ ▼ ▼ ▼ high dispersion ↓ high dispersion + high  ↓ ↓ ↓ ↓ Ideal case 4 mm orbit ▼ = critical BLM

19. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 19 Effect of optic (dispersion) => Losses due to first high dispersion location !!! Characteristic loss locations can be understood from halo properties and optics. ↑ peak loss location

20. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 20 Why off-momentum losses for on-momentum primary halo ? Collimators in IR7 intercept off-axis particles => induced proton-collimator material interaction follows several processes. Single-diffracting scattering Single-diffracting scattering: generates off-momentum halo => always lost at one of the first high dispersion points: critical locations for limiting losses are therefore well defined (as seen in the IR7 +Arc 7-8 case) Sets fundamental limitation of the LHC betatron cleaning insertion: single-diffracting scattering can never be avoided !!!

21. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 21 IR8 + Arc 8-1 ▼ ▼ ▼ ▼ Ideal case 4 mm orbit

22. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 22 Effect of optic (beta) => Losses due to high betatron location !!! ← peak loss location

23. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 23 IR1 Ideal case 4 mm orbit

24. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 24 IR2 Losses here are due to scattering from TDI TDI.4L2 TCLIA.4R2 Ideal case 4 mm orbit

25. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 25 IR3 ▼ ▼ Remember: only betatron cleaning Ideal case 4 mm orbit

26. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 26 IR4 Ideal case 4 mm orbit

27. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 27 IR5 Ideal case 4 mm orbit

28. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 28 IR6 ▼ Losses at the TCDQ equipment: → problem of local showers downstream of it under study Ideal case 4 mm orbit ▼ 13 critical BLMs identified => We made one turn after IR7: 13 critical BLMs identified at injection (in addition to the ones foreseen at the locations of collimators ).

29. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 29 Going further in error amplitude │ │ ← specified orbit │ + 80 % + 130 %

30. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 30 7 Tev Study IR2, IR5 & IR8: nominal crossing schemes IR1: where orbit perturbation is applied halo ▬► Static orbit: ± 4 mm in the arcs, ± 3 mm in the insertions (many thanks to W. Herr !!!).

31. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 31 Going downstream from IR7 ▼ ▼ ▼ ▼ ▼ ▼ ▼ ▼ ▼ ▼ ▼ ▼ Ideal case With orbit error ↓ high dispersion high dispersion + high  ↓ ↓ ↓ ↓ => From below quench limit to about twice above; additional BLMs show up, but most of them are at the same locations than injection case.

32. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 32 IR8 + Arc 8-1 ← TCTs: generate a new quartiary halo => critical BLMs to be located here as well ▼ ▼ ▼▼ ▼ ▼ Ideal case With orbit error

33. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 33 IR1 Ideal case With orbit error ← TCTs

34. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 34 IR2 ← TCTs Ideal case With orbit error

35. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 35 IR3 Remember: only betatron study so far Ideal case With orbit error

36. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 36 IR4 Ideal case With orbit error

37. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 37 IR5 Ideal case With orbit error ← TCTs

38. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 38 IR6 Losses at the TCDQ equipment: → problem of local showers downstream of it under study Ideal case With orbit error => After one complete turn: 18 critical locations (in addition to collimator ones and at the triplets)

39. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 39 Dynamic scenario - Process Dynamic studies: collimators are not re-centered around the perturbed orbit. Purpose of this scenario: check the sensitivity of the system to fast orbit changes => how does the system behave if a secondary collimator gets closer to become a primary (back to a single-stage system) ? What is the effect on the cleaning efficiency ? In the following, only the collision optics case is presented (results for injection optics still being analyzed).

40. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 40 Effect on the cleaning system - Lattice TCP.C6L7TCSG.B4L7TCSG.6R7 ↓ zero orbit change ↑ critical secondary

41. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 41 Loss Map for a 0.95  offset (only IR7 elements) => Loss of a factor 4 in local cleaning efficiency in IR7 !!! same critical locations !!! ↓

42. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 42 OUTLINE Introduction Loss distribution from betatron cleaning Minimum workable BLM system for collimation studies Conclusion – Future studies

43. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 43 Requirements for commissioning For commissioning of the LHC and its collimation system, one needs to be sure to operate in safe conditions => with the results presented here, we can already point out critical locations !! The determined positions and peak values of losses can then be used to define a minimum workable LHC BLM system for collimation studies.

44. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 44 Summary table for injection black: nominal & perturbed case red: only in nominal case + collimator locations + critical locations for IR3 => 13 critical locations in total

45. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 45 Summary table for collision black: nominal & perturbed case red: only in nominal case blue: only in perturbed case + collimator locations + triplets + critical locations for IR3 identical as in the injection case => 18 critical locations in total, 6 of which being identical as in the injection case !!

46. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 46 Critical loss locations

47. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 47 Longitudinal distribution of beam losses – detailed studies for BLM positioning Dipole: all along the magnet Quadrupole: up to the middle of the magnet

48. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 48 Remarks Early scenario checked (as seen in R. Assmann’s previous talk) as well: identical loss locations expect certainly some few additional high loss locations Cases studies here refer to closed orbit perturbation spread all along the lattice: do not take into account possible local bumps in orbit !!! => expect certainly some few additional high loss locations. injection optics: many regions, not that critical injection optics: many regions, not that critical collision optics: few regions, more critical

49. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 49 OUTLINE Introduction Loss distribution from betatron cleaning Minimum workable BLM system for collimation studies Conclusion – Future studies

50. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 50 Conclusion The tools we developed allow us to study where the most critical regions of the machine are expected: -- for both mode of operation of the LHC (injection & collision), with still other optics possible, -- for any given scenario of beam losses, to check how flexible the system can be depending on the mode of operations. detection and monitoring of these critical regions shall be achieved to allow efficient commissioning of the LHC Collimation System In close collaboration with the BLM team, detection and monitoring of these critical regions shall be achieved to allow efficient commissioning of the LHC Collimation System.

51. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 51 Conclusion SC ring losses: 25 per ring + 8 triplet locations Collimator losses: 41 collimator locations at Phase 1 => would it be sufficient to rely on the information delivered by the BLM located at the closest quadrupole magnets ? Out of these 74 locations, only 3 of them are not yet foreseen as BLM locations: MB9, MB11 and MB13 downstream of IP7 => would it be sufficient to rely on the information delivered by the BLM located at the closest quadrupole magnets ? Results will be used to prepare commissioning tools: number of channels displayed, etc…

52. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 52 Future works Static case at collision optics: in this talk, we set IR1 as the disturbed insertion => estimation of losses for other IRs ?? Dynamic studies: check of the influence on efficiency at injection still ongoing; accident cases can de derived from this scenario (e.g. a secondary IR7 collimator becoming a primary) Other error models are foreseen to be studied, mainly beta- beating tolerances, inclusion of the map of non-linearities of the LHC magnets, more complete imperfection models.

53. GRD, Chamonix XV 2006Critical Beam Losses during Commissioning and Initial Operation53

54. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 54 BACKUP SLIDES

55. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 55 Critical BLMs for collimation S. Redaelli, Chamonix 2005

56. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 56 Parameters for obtaining loss maps Quench limit values used in the following are derived from the values of the loss rates at the quench limit as given in the LHC Project Report 44: (assuming simplified quench limits)

57. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 57 Cases studied so far Various models are available; to compare with the Perfect Machine case, we started studying the effect of Closed Orbit variation, depending on: -- the phase of the error with respect to the IR7 insertion, -- the amplitude of this error, -- the speed of this error: is the perturbation fast enough so that collimators become off-centered from the new closed orbit ? => 2 scenarios: static study and dynamic study

58. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 58 Beam Loss Tracking A package of state-of-the-art 6D tracking tools has been set up in 2005, which includes: -- scattering routines applied to all of the 43 equipments foreseen for Phase 1 of the Collimation System, -- LHC aperture model with a 10 cm resolution level, -- full 6D treatment of error models (closed orbit deviation, beta- beating, magnet non-linearities) => this talk will focus on the critical beam loss locations due to various closed orbit error scenarios

59. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 59 Static case – Injection Optics Aim: scan all possible phases between [ -π ; + π ] and find the worst one, i.e. the one phase for which the highest local loss peak comes the closest to the design quench limit. Once this phase is found, do a scan over the amplitude of the closed orbit deviation (peak value of the error always taken in the arc as reference).

60. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 60 Peak losses - local

61. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 61 First Step – Scan in Phase

62. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 62 List of “golden” BLMs - Injection 12 critical positions listed: Q11 @ right of IR3 DFBA behind Q5 @ right of IR6 Q11, MB13, Q13, Q23, Q27, Q31 @ right of IR7 Q33, Q29, Q25 @ left of IR8 Q2 before D1 @ right of IR8 Q6 @ right of IR8

63. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 63 Loss map – 7 Tev Ideal case => Ideal case: just below the quench limit downstream of IR7 !!!! ▬► halo

64. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 64 Worst phase – Static case, Collision optics The static scenario for a closed orbit perturbation at collision optics is different than the previous study, the maximum tolerance in orbit distortion being: -- ± 4 mm in the arcs -- ± 3 mm in the insertion regions In the collision scheme we consider, IR1 & IR5 are squeezed: in the following we will consider a maximum perturbation in the arcs and IR1 and an orbit corrected to the nominal schemes in all other IRs.

65. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 65 Loss map – 7 TeV Perturbed orbit – worst phase for IR1 scenario => Now a factor 2 over quench limit at worst locations !!! ▬► halo

66. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 66 Collision Optics – 7 TeV Perturbed orbit – phase with high IR3 losses => Getting closer to quench limit in IR3: Q6 (left) !!!

67. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 67 Effect of optic parameters => Losses due to first high dispersion location !!!

68. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 68 Effect of optic parameters

69. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 69 List of “golden” BLMs – 7 TeV 17 critical positions listed: Q6 @ left of IR3 Q8, MB9, Q9, MB11, BS.11, Q11, Q13, Q19, Q21, Q27 @ right of IR7 Q33, Q25, Q17 @ left of IR8 Q16, Q30 @ right of IR8 Q22, Q14 @ left of IR1

70. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 70 Dynamic scenario – Considered cases TCP.C6L7.B1 TCSG ↔ DX = 0.95 s +6 s +7 s -6 s -7 s

71. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 71 Dynamic scenario – Considered cases TCP.C6L7.B1 TCSG ↔ DX = 1.1 s +6 s +7 s -6 s -7 s TCSG becomes a primary collimator => In that case, the TCSG becomes a primary collimator !!!

72. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 72 Second step – Phase selection

73. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 73 Effect on the cleaning system – Cleaning Inefficiency for a 0.95 s offset factor 2 in cleaning efficiency => At 10 s, we loose a factor 2 in cleaning efficiency !!!

74. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 74 Critical loss locations Injection optics: -- the critical losses are distributed over the end of IR7, the Arc 7-8 and IR8, -- the IR2 region should also be monitored: losses there are due to interaction of secondary halo particles with the TDI collimator, protecting the machine from Beam 1 injection errors, -- the IR3 region (dedicated to momentum cleaning) should also be monitored: studies presented here only consider on- momentum particles, and loss spikes can already be noticed.

75. GRD, Chamonix XV 2006 Critical Beam Losses during Commissioning and Initial Operation 75 Critical loss locations Collision optics: -- static scenario: * critical losses are at the very beginning of the dispersion suppressor downstream of IR7, * some other noticeable spikes are seen in arcs 7-8 and 8-1, but none in IR8, * for some particular situation, we also noticed high losses at the Q6 of IR3: this location should as well be monitored -- dynamic scenarios: this case shows how much the system relies on a good control of the orbit => for a 0.95 s offset at the worst location in IR7, the cleaning efficiency drops by a factor 2 (significant at collision optics).