1. RWA, 1/11/2007 1 Collimation Issues for the Phase 1 Insertion Upgrade R. Assmann, CERN, AB/ABP Acknowledgements to the colleagues in the LHC Collimation Working Group which worked out and presented most of the results shown here: http://www.cern.ch/lhc-collimation Acknowledgements to the colleagues in AB/ABP and AT for discussions and help in understanding the upgrade ideas. CERN, Switzerland November 1 st, 2007

2. RWA, 1/11/2007 2 1) Why Talk About Collimation? Collimation protects the machine aperture against damage and quenches. Any significant change in aperture must be revisited also from the collimation and machine protection view: possible impact on protection, loss distribution, activation, quench limitations, experimental background. Critical issues: The HERA insertion upgrade was heavily affected by unforeseen problems with beam loss and background after the upgrade. Loss in overall integrated luminosity with insertion upgrade. Give collimation input to the ongoing discussions for the phase 1 triplet upgrade such that it will be fully successful.Goal of this talk: Give collimation input to the ongoing discussions for the phase 1 triplet upgrade such that it will be fully successful. Note: MP and dump issues only mentioned as far as collimation is affected  for additional input see presentations at LUMI06 by B. Goddard and R. Schmidt.

3. RWA, 1/11/2007 3 System Design Momentum Cleaning Betatron Cleaning “Phase 1” “Final” system: Layount is 100% frozen!  Outcome of accelerator physics + energy deposition optimization

4. RWA, 1/11/2007 4 Multi-Stage Cleaning & Protection Secondary halo p p e  Primary collimator Core Unavoidable losses Shower Beam propagation Impact parameter ≤ 1  m Primary halo (p) e  Shower p Tertiary halo Secondary collimator Absorber CFC W/Cu Absorber Super- conducting magnets SC magnets and particle physics exp. Particle Beam axis Impact parameter Collimator

5. RWA, 1/11/2007 5 Functional Description Two-stage cleaning (robust CFC primary and secondary collimators). Catching the cleaning-induced showers (Cu/W collimators). Protecting the warm magnets against heat and radiation (passive absorbers). Local cleaning and protection at triplets (Cu/W collimators). Catching the p-p induced showers (Cu collimators). Intercepting mis-injected beam (TCDI, TDI, TCLI). Intercepting dumped beam (TCDQ, TCS.TCDQ). Scraping and halo diagnostics (primary collimators and thin scrapers).

6. RWA, 1/11/2007 6 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: Not allowed to use protection devices (or warm aperture limits) as a single-stage cleaning system! Setting Strategy for Collimation and Protection Elements R. Assmann, Chamonix 2005

7. RWA, 1/11/2007 7 7 TeV Settings at (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! R. Assmann, Chamonix 2005

8. RWA, 1/11/2007 8 2) Insertion Aspects for Collimation Chamonix 2003 (R. Assmann): Only way to open collimator gaps: Increase triplet aperture!Only way to open collimator gaps: Increase triplet aperture! Still true but lot’s of things understood since 2003!

9. RWA, 1/11/2007 9 2004: Addition of Tertiary Collimators Collimator settings defined with required hierarchy. Detailed loss maps for beam 1 and beam 2 produced. Halo losses in triplets (standard optics, 0.55m) up to 25 times above quench limit.Problem: Halo losses in triplets (standard optics, 0.55m) up to 25 times above quench limit. tertiary collimatorsSolution: Addition of tertiary collimators: –Make use of large aperture until D1. –Placed before D1 such that all losses are intercepted before the triplet is hit. solves loss issue –Completely solves loss issue. –Improves machine protection –Improves machine protection (allowing feasible requirements in local dump protection in IR6). experimental background –Checked for experimental background in CMS and ATLAS: Beneficial effect.

10. RWA, 1/11/2007 10 System Design Momentum Cleaning Betatron Cleaning “Phase 1”

11. RWA, 1/11/2007 11 7 TeV Proton Loss Distribution G. Robert-Demolaize et al p losses ~ inefficiency

12. RWA, 1/11/2007 12 Beam1 and Beam 2 Asymmetry Beam1, 7 TeV Betatron cleaning Ideal performance Beam2, 7 TeV Betatron cleaning Ideal performance TCDQ Quench limit (nominal I,  =0.2h) Local inefficiency: Local inefficiency: #p lost in bin over total #p lost over length of aperture bin! Quench limit (nominal I,  =0.2h) Local inefficiency [1/m]

13. RWA, 1/11/2007 13 Asymmetry IR1/IR5 Beam 1 betatron halo losses on TCT left sides of IP: –IR1:5e-4 of total halo loss –IR5:5e-6 of total halo loss Beam 2 betatron halo losses on TCT right sides of IP: –IR1: 2e-5 of total halo loss –IR5: 3e-4 of total halo loss Halo losses in experimental insertions are asymmetric. Detailed losses depend on collimator settings, phase advance and halo phase space properties. Above settings assume IR2 and IR8 collimators present and at same setting as IR1/IR5 teriary collimators. We might open them and losses in IR1/IR5 will increase (small gaps not needed in IR2/8 & trapped mode issues with higher  *, small gaps in IR2/8).  In worst case increase losses by a factor ~2.

14. RWA, 1/11/2007 14 Interim Summary I fully shadows the IR1/5 at 7 TeVPhase 1 collimation system fully shadows the IR1/5 at 7 TeV. Three components to reach this goal: –IR3/IR7 collimators –IR3/IR7 collimators set to shadow the triplet (depends on beta* and triplet aperture) against the primary and secondary halo. –Local tertiary collimators TCT –Local tertiary collimators TCT (58 mm full maximum gap) to clean tertiary halo which would otherwise be ~20 times above quench limit: 4 per IR. –Local copper absorbers TCL/TCLP –Local copper absorbers TCL/TCLP to catch showers from IP before the arc. ignoring cleaning efficiencyInsertion upgrade (ignoring cleaning efficiency limitations in IR7): open the IR3/IR7 collimators reduced impedance. –An increased minimum normalized aperture in IR1/IR5 can in principle be used to open the IR3/IR7 collimators  reduced impedance. aperture bottle-necks must be protected with tertiary collimators –Even if n1 is increased it is expected that the stringent aperture bottle-necks (including new and earlier bottle-necks) in IR1/IR5 must be protected with tertiary collimators (new types, more TCT: 4  6). Opening gaps can affect other issues (efficiency, protection, …).

15. RWA, 1/11/2007 15 2003: Reduce Impedance with Increased Gaps! F. Ruggiero, L. Vos LHC impedance without collimators Typical collimator half gap Transverse Impedance [MΩ/m] Half Gap [mm] 0 2 4 6 8 10 10 4 10 3 10 2 10 1 10 -1 factor ~ 1.6 2007: E. Metral  stable beam with 50% larger gaps from detailed analysis

16. RWA, 1/11/2007 16 2) Limitation in Cleaning Efficiency cleaning efficiency in IR1/5 is no issue any moreAs just shown, cleaning efficiency in IR1/5 is no issue any more. Fundamental limitation arises at the end of IR7Fundamental limitation arises at the end of IR7 (single-diffractive scattering + tertiary halo) after betatron cleaning. Nuclear physics routine cross-checkedNuclear physics routine cross-checked between 3 different programs. Independent studies at CERN, SLAC and IHEP agreeIndependent studies at CERN, SLAC and IHEP agree on the predicted limitations. Outside experts usually think we are even optimistic: –Loss assumptions. –Only partial errors included (loss of factor 2 seen). –Uncertainties in diffusion and halo models. –SNS has just published a paper with 5-6 times higher fractional losses in magnets than predicted in simulations. Absolute losses locally up to 20 times above specifications!

17. RWA, 1/11/2007 17 Preventing Quenches Quench limits of SC magnets given by design. criterion for preventing quenchesOverall criterion for preventing quenches: FractionalLeakageDilutionFractional quench loss rateratelengthlimit (w/o BLM threshold) MinimizeMinimizeSpread lossesinefficiencylosses Example 0.1% per s1/5,0001/(10 m)  2.0 × 10 -8 (ms) -1

18. RWA, 1/11/2007 18 Performance Prediction

19. RWA, 1/11/2007 19 Uncertainties Many uncertainties do affect results: –Uncertainty in loss assumptions. –Uncertainty in loss assumptions. Supported by external collimation review in 2004. However, some find the loss rates too low, other too high. –Impact from imperfections: –Impact from imperfections: Almost always drives efficiency down. –Required margin from BLM thresholds: –Required margin from BLM thresholds: Factor 3 announced  beam abort 3 times below quench limit. –Impact from showers: –Impact from showers: Dilutes losses  gain somewhat. –Quench limits: –Quench limits: Any reduction/increase in quench limit will reduce/improve the performance reach. We try to do the best possible simulations, given the available resources. in the field agreement on the predicted efficiency limitationExtensive cross-checks with other ongoing efforts: in the field agreement on the predicted efficiency limitation (not a single published result with a different conclusion). Being fully aware of the uncertainties, use the predictions to guide us towards achieving LHC performance goals.Approach: Being fully aware of the uncertainties, use the predictions to guide us towards achieving LHC performance goals.

20. RWA, 1/11/2007 20 7 TeV Proton Loss Prediction G. Robert-Demolaize et al Ideal case With design orbit error

21. RWA, 1/11/2007 21 Peak Inefficiency Versus Gap 0 5 10 15 20 25 Aperture primary collimator [  ] Quench limit BLM threshold? LHC nominal Phase 1 upgrade possibility (n1=9) C. Bracco et al

22. RWA, 1/11/2007 22 Other Possible Impacts from Larger Collimation Gaps in IR7 Machine Protection:Machine Protection: For example, in case of magnet trips (for example affecting x) with larger gaps: (1) the first losses are seen later. (2) dx/dt when are seen is increased.  R. Schmidt and MPWG. abort gap cleaningMomentum collimation gaps must be opened as well  impact on abort gap population (synchrotron radiation) and abort gap cleaning. Increased impact of off-momentum beta-beatIncreased impact of off-momentum beta-beat (if retraction – distance between primary and secondary jaws is kept constant).

23. RWA, 1/11/2007 23 Interim Summary 2 Cleaning efficiency in IR7driving limitationCleaning efficiency in IR7 is predicted to be the driving limitation from LHC collimation, more severe than impedance. Reducing collimator-induced impedance issue will not affect the overall limitReducing collimator-induced impedance issue will not affect the overall limit (limitations must not be added, only the bigger counts). Small gaps are required to maximize cleaning efficiencySmall gaps are required to maximize cleaning efficiency in IR7. decrease in the allowable intensityGaps can still be opened but will lead to a decrease in the allowable intensity and such to a decrease in performance. Efficiency must be addressed in addition to impedanceEfficiency must be addressed in addition to impedance. an increased aperture in IR1/5 and the “phase 1” upgrade are fully supported from collimation, as it will provide the basic possibility of opening gaps after the phase 2 upgrade.With this in mind, an increased aperture in IR1/5 and the “phase 1” upgrade are fully supported from collimation, as it will provide the basic possibility of opening gaps after the phase 2 upgrade. side effectsOther side effects of increased gaps must not be forgotten!

24. RWA, 1/11/2007 24 3) Off-Momentum Beta Beat mixes up the 6D phase spacecorrupt collimation performanceOff-momentum beat beat mixes up the 6D phase space and can corrupt collimation performance (secondary collimator becomes a primary collimator for off-momentum particles). complete for nominal opticsStudies by C. Bracco and myself complete for nominal optics. Presentation by C. Bracco next Monday in LCU meeting. first glance at preliminary results on upgrade opticsHere, first glance at preliminary results on upgrade optics that we got from R. de Maria.

25. RWA, 1/11/2007 25 Upgrade optics nominal setting (TCP@6 , TCSG@7 ....) – Horizontal Collimators Allowed phase primary collimators Allowed phase (yellow area) space should always be defined by primary collimators (red lines). It is not below  =1e-3! break-down of cleaning efficiency for off-momentum particles Could lead to break-down of cleaning efficiency for off-momentum particles! C. Bracco, R. Assmann

26. RWA, 1/11/2007 26 Upgrade optics nominal setting (TCP@6 , TCSG@7 ...) - Vertical collimators Secondary collimators become primary collimators!

27. RWA, 1/11/2007 27 Upgrade optics nominal setting (TCP@6 , TCSG@7 ....): IR7 collimators retraction Nominal retraction Secondary collimator becomes primary collimator

28. RWA, 1/11/2007 28 Upgrade optics new setting(TCP.IR7@9 , TCSG.IR7@10  TCLA.IR7@13  ): IR7 collimators Retraction Nominal retraction Secondary collimator becomes primary collimator

29. RWA, 1/11/2007 29 Interim Summary 3 noticeable but still acceptable effects from off-momentum beta- beat for the nominal LHC opticsWe see noticeable but still acceptable effects from off-momentum beta- beat for the nominal LHC optics: 30% loss in retraction. much stronger effects for upgrade opticsPreliminary results show much stronger effects for upgrade optics, up to the point where multi-stage cleaning is corrupted. Importance will depend on longitudinal beam lifetime, synchrotron losses and equilibrium beam distribution in off-momentum. Use larger retractionRemedy: Use larger retraction  increased aperture would be used (at least partially) for increased retraction (reduced gain in impedance). All collimator families must analyzed for this effect.Here we only show primary and secondary collimators. All collimator families must analyzed for this effect. optics might be adapted to minimize impactPreliminary results: further work needed and optics might be adapted to minimize impact.

30. RWA, 1/11/2007 30 4) Input and Proposals 1.The upgraded triplets should include fixed masks for the incoming beam 1.The upgraded triplets should include fixed masks for the incoming beam. This provides the best possible triplet protection and cleaning. These fixed masks should allow for easy exchange in case of damage. compatible with the 58 mm full aperture of the existing tertiary collimators 2.The upgrade optics should be compatible with the 58 mm full aperture of the existing tertiary collimators, which are located between the D1 and the D2 magnets. new tertiary collimators must be developed, tested and constructed 3.In case that requirement 2) cannot be fulfilled, limited local background control for ATLAS and CMS must either be abandoned or new tertiary collimators must be developed, tested and constructed. This affects up to eight tertiary collimators installed in IR1 and IR5. opening primary collimators in IR7 to 9  n1 = 10.5 4.The goal of providing room for opening primary collimators in IR7 to 9  is supported (50% increased collimator aperture as indicated by studies from E. Metral). This corresponds to n1 = 10.5 (up from n1 = 7) if we just scale n1. factor 2 increase in gap n1=14 5.For ultimate intensity a factor 2 increase in gap (compared to today) is needed to remove the impedance limit. This means n1=14. Stick to nominal in the next slides.

31. RWA, 1/11/2007 31 Input and Proposals continued 3.6  larger than the assumed setting of the primary collimators ≥ 12.6  6.To respect the specified hierarchy of collimator and protection settings: minimal available IR aperture after upgrade must be 2.4  to 3.6  larger than the assumed setting of the primary collimators. Required: ≥ 12.6  (this corresponds to n1 = 10.5). If we take a constant 3  increase of all gaps: ≥ 11.4 . Will provide less reduction on impedance! reduction in available aperture in adjacent magnets beam halo, beam loss maps, energy deposition, impedance and experimental background 7.The feasibility of any reduction in available aperture in adjacent magnets to the triplets must be checked with full evaluations of beam halo, beam loss maps, energy deposition, impedance and experimental background. The placement of additional tertiary collimators might be required. showers from the IP 8.The showers from the IP must be tracked into the arc to verify that the foreseen TCL/TCLP collimators are still fully adequate. 9.The performance reach of the LHC after the insertion upgrade must be calculated, taking into account also performance limitations in other areas of the machine. 9.The performance reach of the LHC after the insertion upgrade must be calculated, taking into account also performance limitations in other areas of the machine. This concerns in particular the predicted limitations due to cleaning efficiency.

32. RWA, 1/11/2007 32 Input and Proposals continued opened after a triplet upgrade various secondary effects 10.If it is assumed that the betatron collimators are opened after a triplet upgrade, then various secondary effects must be considered. In particular, it might be required to open also the momentum collimators with resulting effects on losses of off-momentum particles (synchrotron radiation losses), abort gap cleaning etc. additional triplet-induced off-momentum beta-beat 11.The compatibility of an additional triplet-induced off-momentum beta-beat with collimation must be verified. warm and cold aperture limitsshadow of machine protection collimators 12.All warm and cold aperture limits must be in the shadow of machine protection collimators, independently of the fact that warm elements cannot quench!