Collimation Upgrade Plan & Questions

1. Collimation Upgrade Plan & Questions R. Assmann, CERN for the collimation team 14/6/2011 LHC Collimation Project Review

2. LHC Collimation as Staged System • LHC collimation was conceived in 2003 as a staged system. • Phase 1: • For initial beam commissioning and early years of LHC operation. • Predicted not adequate for nominal and ultimate intensity. • Designed, constructed and commissioned 2003 – 2009. • Phase 2: • Upgrade for nominal, ultimate and higher beam intensities. • Solves issues in efficiency, impedance and radiation impact. • Originally not clear what the solution would be. • By now various upgrade solutions worked out and under design. • IR upgrade: • Adaptation to changes in IR upgrades: space and losses. • Adaptation to phase space modifications (ATS, crab cavities).

3. Overall Collimation Upgrade Plan(as defined in 2009) • Interimcollimation system (2014 – 2016)Inefficiency: 0.002 % (p) b* ~ 1 – 2 m, 7 TeV Gain ~100 in R2E (IR7IR3) • L ≤ 5 × 1033 cm-2 s-1 • nominal ion intensity > 2 days per setup 2017 shutdown: IR(1)/2/(5)/7 DS Phase 2: integrated BPM’s, robust materials, red. impedance. Radiation opt. Full collimation system (2018 onwards)Inefficiency: 0.0004 % (p) b* ~ 0.55 m, 7 TeV L not limited (p and ions) 30 s per high accuracy setup Radiation optimization 2021 shutdown: tbd 2013 shutdown: IR3 DScombined cleaning, IR2 TCT’s, TCLP installation? Initial collimation system (2009 – 2012)Inefficiency: 0.02 % (p) b* ~ 1 – 1.5 m, 3.5 TeV R2E limits in IR7? > 4 days per setup Collimation IR Upgrade (2022 onwards)Low b*, 7 TeV TCT’s integrated into IR upgradeCompatibility with crab cavities

4. Prepared, Empty Secondary Collimator Slots for Phase 2 SLAC design 1st advanced phase 2 collimator CERN PHASE I TCSG SLOT EMPTY PHASE II TCSM SLOT (30 IN TOTAL)

5. Luminosity Loss limits: collimation, (UFO’s), …  D. Woll-mann, A. Rossi, G. Bellodi Triplet aperture and collimation setup accuracy  R. Bruce Beam-beam, brightness & robust-ness limits  A. Dalloc-chio (new materials)

6. Good news: • Available aperture about 50% larger than guaranteed by design (smaller orbit errors, better alignment, …). Gain here for luminosity! • Optics very well controlled (5-10% beta beat, … for b* = 1.5m). Gain here! • As expected: • Very challenging to achieve collimation & protection tolerances (only infrequent setups possible, drifts over months, …)  b* limited. • Addressed by collimators with integrated beam position pickups (almost all to be equipped). Not discussed in details for this review.

7. Good news: • Collided successfully three times nominal brightness (head-on). Long-range beam-beam soon to be checked. Gain factor 3 here, if LR beam-beam OK as well! • Under study: • Robustness of collimators for the high achieved brightness. Simulation of realistic scenarios, tests in HiRadMat facility starting in autumn. • Development of more robust collimator materials ( EuCARD/ColMat program since 2009, report A. Dallocchio). • Not discussed in details for this review.

8. Good news: • Since middle of May: ~ complete experimental assessment at 3.5 TeVdone. • Reached the design 500 kW peak beam loss (protons) at primary collimators without quench of a super-conducting magnet! • Reached 80 MJ without a single quench from stored beam losses. • Transverse damper stabilizes beam at 3.5 TeV high impedance OK. • Reached 99.995% collimation efficiency with 50% smaller gaps than design (low emittance, high impedance) and due to much less impact of imperfections than predicted (better orbit, lower beta beat, …). • Minimum beam lifetime at 3.5 TeV is ~4 times better than specified.

9. Collimation of High Power Loss No quench of any magnet!

10. Ultra-High Efficiency 99.960 % worse 99.995 % MD better

11. Achieved Stored Energy: 80 MJ 80 kg TNT

12. Stored Energy Comparedto 2010 Goals

13. Therefore some questions I • It runs so well: Do we really need to invest a lot of work for a better collimation efficiency in the first long LHC shutdown (2013/14)? • Do operational experience and MD measurements not prove to us sufficiently well that we can reach nominal 7 TeV luminosity in 2014/15 (with the efficiency of the present collimation system)? • Do the potential gains in b* and beam brightness (beam-beam) not provide an additional margin to increase luminosity (without pushing stored energy)? Reference p goal 2014 – 2017: L ≥ 1 × 1034cm-2 s-1at 7 TeV Could be reached with ~50% of nominal intensity?

14. On the Other Side • Predicted leakage mechanisms and locations are fully confirmed, both for protons and ions. • Proposed upgrade plan will gain factor ~10 in efficiency: can be used for higher stored energy and/or larger collimation gaps (relaxed tolerances and lower impedance). Lowest risk approach. • All experience relies on 3.5 TeV beam energy (higher quench margin, larger collimation gaps, lower impedance, easier operation for transverse damper, lower cross-section single-diffractive scattering, …). • All experience relies on operation with 1/2 of nominal emittance(50 ns)  beam core far away from jaw surface, lower loss spikes, more room to close collimator gaps. • It is assumed that 7 TeV beam is as stable as 3.5 TeV, that quench limits and efficiency scale as predicted and that losses do not become more localized at 7 TeV.

15. Protons: Simulations vsMeasurementB1v, 3.5TeV, β*=3.5m, IR7 B1 Cleaning Inefficiency Measured Simulated (ideal) Losses in SC magnets understood: location and magnitude

16. 3.5 TeV: Luminosity Operation Collimation Colli- mation IR7 CMS LHCb Collimation IR3 ATLAS Colli- mation IR6 Fill #1645, 200 bunches, 2.4e13 p per beam, peak luminosity 2.5e32

17. Origin of Dispersion Suppressor Losses Coll on energy Collision p – C Coll. Mat. Quad Coll Quad Coll Dipole Dipole Collision p – p Pb – Pb on energy Quad Coll Quad Coll Dipole Dipole off energy

18. Zoom IR7(and illustration of 2013 upgrade for IR3) D. Wollmann, G. Valentino, F. Burkart, R. Assmann, …

19. 99.997 %/m  99.99992 %/m Proton losses phase II: Zoom into DS downstream of IR7 quench level Very low load on SC magnets  less radiation damage, much longer lifetime. Simulation T. Weiler Impact pattern on cryogenic collimator 2 Impact pattern on cryogenic collimator 1 Simulation Cryo-collimators can be one-sided!

20. Better Efficiency and/or Lower Impedance better Impedance Target Phase 1 (full octupoles, no transv. feedback, nominal chromaticity) R. Assmann T. WeilerE. Metral WARNING: Grid simulation here for non-nominal optics and perfect machine! Ideal Inefficiency [1/m] × 2 Phase 1 Impedance Target Phase 2 (full octupoles, no transv. feedback, nominal chromaticity) Target Inefficiency (nominal intensity, design peak loss rate) Acceptable Area × 1.5 × 1.2 Gap × 1 better Phase 2 Impedance Installation of collimation phase II including collimators in cryogenic dispersion suppressors Increase gaps by factor 1.5 Nominal I. Larger triplet/IR aperture or lower b*

21. Ions: Beam 2 Leakage from IR7 Collimation (much worse, as expected)

22. Therefore some questions II • Can the upgrade of the IR3 dispersion suppressors be delayed without any danger for magnet lifetime (SC magnets as halo dumps)? • Is later upgrade work feasible in dispersion suppressors (activation)? • Are we sufficiently sure about 7 TeV beam behavior to give up the improvement in collimation efficiency and/or impedance for 2014? • Is the presently predicted “proton” safety factor ~4 above nominal intensity big enough ( assumptions and energy scaling)? • Do we need an upgrade of the IR3 dispersion suppressors for reaching nominal ion luminosity? • Will a delay of the IR3 dispersion suppressors lead to unacceptable knock-on effects for other dispersion suppressor work (IR2 for ions, IR1/5 losses into dispersion suppressors, …)? • Will decision force us to work with small emittances (impact on 25 ns)?

23. Overall Collimation Plan(possible modification, acceptable risk?) • Initialcollimation system (2014 – 2016)Inefficiency: 0.005 % (p) b* ~ 1 – 2 m, 7 TeV Gain ~100 in R2E (IR7IR3) • L ~1 × 1034 cm-2 s-1 Ion intensity and lumi limits > 2 days per setup 2017 shutdown: IR(1)/2/3/(5)/7 DS Phase 2: integrated BPM’s, robust materials, reduced impedance. Radiation opt. Full collimation system (2018 onwards)Inefficiency: 0.0004 % (p) b* ~ 0.55 m, 7 TeV L not limited (p and ions) 30 s per high accuracy setup Radiation optimization 2021 shutdown: tbd IR2 TCT’s, combined cleaning IR3, TCLP installation? Initial collimation system (2009 – 2012)Inefficiency: 0.005 % (p) b* ~ 1 – 1.5 m, 3.5 TeV R2E limits in IR7? > 4 days per setup Collimation IR Upgrade (2022 onwards)Low b*, 7 TeV TCT’s integrated into IR upgradeCompatibility with crab cavities

24. Conclusion • Equipping the IR3 dispersion suppressors with collimators improves the performance reach for LHC and has the lowest risk for LHC performance. It was defined as a minimal plan some years ago. • There are a number of recent good news at 3.5 TeVin collimation and other LHC areas that must be taken into account: • It opens the possibility to discuss delaying the IR3 collimation upgrade in the dispersion suppressors by three years. • Some important issues were summarized and some questions put up that require attention and advice. • Subsequent talks will go into more details. • Predicting performance at 7 TeV is tricky and quite involved: loss spikes, quench limit, nuclear physics p/ions, energy deposition details, small collimation gaps, high impedance, … • Your advice is very much welcome!

25. Additional Info

26. Origin of Losses in Dispersion Suppressor • Effect understood and predicted as early as 2003. • Collimators in straight sections “generate” off-momentum p and ions (effectively). • Off-momentum particles pass through straight sections and are deflected by first dipoles in dispersion suppressors. • Downstream magnets act as off-momentum halo beam dump. • SC regions off-hands: Impossible to put collimators in dispersion suppressors (as in LEP). • Clear physics sources: p have single-diffractive scattering in matter, ions dissociate/fragment! • Now confirmed by experimental data (also in horizontal plane). • Loose factor ~10 with non-smooth aperture (alignment)!

27. p – C Interaction: Multiple Coulomb &Single-Diffractive Scattering

28. Analytically Derived Simple Scaling Law (E0 = 1 TeV) MCS SD R. Assmann, Proc. HE-LHC Workshop

29. Monte-Carlo Simulation of Realistic Beam Halo and Interactions

30. Why Off-Energy Hadrons can be so Disturbing (A) Very diluted  Very low risk for quench  “Fixed” by relaxing BLM limits (small T) • Loss pattern cannot be compared to case of point scatterers like UFO’s or wire scanners  very diluted showers. • Off energy hadrons produce a very sharp impact line. • BLM’s cannot distinguish the two cases! • Important uncertainties about BLM response and thresholds with such a concentrated loss. • Plan quench tests for this case. (A) Interaction Halo/shower (B) Concentrated losses  High risk for quench  Protect by tight BLM limits (medium – large T) Point scatterer (e.g. UFO) (B) Halo/shower Interaction Low energy tail after V bend

31. 3.5 TeV: Losses in DS of IR5 (CMS) Fill #1647, 200 bunches, 2.4e13 p per beam, peak luminosity 2.5e32

32. Simple Extrapolation of Losses in Dispersion Supressor of IR5 Note: Does not include significant loads from ion operation. Does not include effect of b*. Does not include steeper scaling of losses with lumi (up to factor 5 higher  paper Annika Nordt). Win with monitor factor? Should be able to gain something with TCL/TCLP collimators (cannot fix problem due to zero dispersion).In the past strong concerns about dipoles with this load (K.H. Mess). Now OK? Clear conclusion: NOT AT ALL COMFORTABLE!

33. Quench Limit vs Energy

34. Where to Find Links to Info (New and Old)? https://espace.cern.ch/lhc-collimation-workspace Links to past meetings, minutes, presentations, …

35. Where to Find or Put Reference Info for Upgrade? https://espace.cern.ch/lhc-collimation-upgrade Minutes from collimation upgrade management meetings, agreed production and installation, tables, agreed planning, safety, …