Proton Intensity Evolution Estimates for LHC

1. Proton Intensity EvolutionEstimates for LHC PRELIMINARY Acknowledgements to: Chiara Bracco, Elias Metral (CERN) and Thomas Weiler (Uni Karlsruhe) for simulation data. Werner Herr for collaboration on beam-beam related parameters. Bernd Dehning for input on beam loss monitors. Mike Lamont for getting me going on this work. Massimiliano Ferro-Luzzi and Roger Bailey for discussions. John Jowett for optics and layout work. Collimation Study Group and SLAC/LARP for many years of studies from many different persons and Commissioning Meeting for feedback. R. Assmann, CERN/BE 19/3/2009 LMC “Cassandra has always been misunderstood and misinterpreted as a madwoman or crazy doomsday prophetess.” L. Fitton

2. Recent Reference PhD report available for download from web site LHC collimation project: http://www.cern.ch/lhc-collimation-project/PhD/bracco-phd-thesis-2009.pdf

3. Nothing New on Limits, Except More Detail… For example, see SPC report: All the connections and expected limitations announced since many years. Phase II part of our 2003 collimation plan and effort put into place (White Paper) to find solution. Phase II prepared to maximum in the LHC tunnel (equipped slots). R. Assmann, CERN

4. LHC Proton Intensity Limit • Impossible to predict the future precisely. Especially as LHC enters into new territory with intensities above 0.5% of its nominal design value. • However, baseline assumptions have been agreed for the design of the LHC, taking into account experience with previous projects (ISR, SppS, Tevatron, HERA, …). All checked and supported by external experts. • Simulations predict performance limitation from beam losses, based on clear physics process (“single-diffractive scattering”) and limitation in off-momentum phase space coverage in LHC collimation. • Here, take baseline assumptions and assume simulations results are correct. Add some evolution to these values. Calculate performance. • Concentrate on collimation efficiency (assume impedance less severe, as predicted – or solved with transverse feedback). • All is ongoing work…

5. Result: Achievement Factor Beyond World Record in Stored Energy Looks very ambitious and successful,doesn’t it? Beat world record (mature HERA/Tevatron) in first year LHC by factor 10-20! Later you might be disappointed by this performance! better worse LHC is bigger, has much higher complexity, has magnets with lower quench limits, has deman-ding beam-beam & beam loss issues, has restricted operational flexibility from protection, …

6. Collimation: Ideal Cleaning Inefficiency versus Re(Tune Shift) R. Assmann, T. Weiler, E. Metral Ideal Performance better worse Phase I Phase II Review on April 2/3! In the following: Concentrate on Phase I Phase II worse better

7. Input: Ideal Cleaning Efficiency better Cleaning worse at high energy! More difficult to stop 7 TeV protons  no black hole available for sucking them up! worse Two cases considered: 1) Tight: Collimators always at tightest possible settings (6/7 s). Best performance but increasingly tight tolerances. Ramp and squeeze with closed collimators. 2) Intermediate: Intermediate settings with good protection and relaxed tolerances. Reduced but still good cleaning.

8. … as Inefficiency (Leakage Rate) … worse better Simulation results (points) fitted (lines) to represent energy dependence.

9. Impact of Imperfections on Inefficiency (Leakage Rate) – 7 TeV worse better PhD C. Bracco 40% intensity ideal reach

10. Impact of Alignment Errors on Inefficiency (Leakage Rate) worse Year 1 Year 2 Year 3 better Predicted inefficiency over 20 different seeds of magnet alignment errors  Always worse than ideal (as expected). PhD C. Bracco

11. Why Do We Believe Strongly in Limitation? • Because it is related to clear and well-known physics processes: • Primary collimators intercept protons and ions, as they should. • Small fraction of protons receive energy loss but small transverse kick (single-diffractive scattering), ions dissociate, … • Subsequent collimators in the straight insertion (no strong dipoles) cannot intercept these off-momentum particles (would require strong dipoles). • Affected particles are swept out by first dipoles after the LSS. Main bends act as spectrometer and off-momentum halo dump quench. • Off-momentum particles generated by collimators MUST get lost at the dispersion suppressor (if we believe in physics and LHC optics). • No hope that this is not real (e.g. LEP2 was protected against this – not included for the LHC design and too late to be added when I got involved). • Predicted for p, ions of different species (with different programs).

12. Downstream of IR7 b-cleaning Halo Loss Map Losses of off-momentum protons from single-diffractive scattering in TCP halo cryo-collimators Upgrade Scenario NEW concept transversely shifted by 3 cm without new magnets and civil engineering halo -3 m shifted in s +3 m shifted in s

13. Input: Imperfection Factor worse better Imperfections always make cleaning efficiency worse. Imperfection factor describes worsening of inefficiency! Warning: Only simulated in detail for 7 TeV. Assumed to be independent of energy.

14. Input: Quench Limit better worse Takes expected magnet quench limit and some rough dilution into account. Warning: Transient quench limit seems at least factor 2-6 lower than expected from first beam quenches. Ignored here. However, not much hope to win in the quench limit.

15. Input: BLM Threshold better Input Bernd Dehning and BLM team worse

16. Input: Dilution Factor From FLUKA results better worse Losses are diluted (lowered) by the showers! Calculated in detail by FLUKA. This factor takes this detailed dilution into account. Makes proton and FLUKA results coherent. Warning: FLUKA results only available for 7 TeV and the ideal machine. Dilution factor assumed to be independent. Can be different.

17. Putting it together: Performance Model • The various important input parameters have been put together into a preliminary performance model. • All is preliminary work. • However, should give some good idea about what we are looking at and what are the main parameters expected to limit the LHC performance. • Such an approach takes into account the agreed assumptions, the technical results and the simulations of achievable performance.

18. Result: Intensity Limit vs Loss Rate 5 TeV worse better

19. Result: Intensity Limit vs Loss Rate 7 TeV worse better

20. Remarks Beam Loss Rate • The LHC beams will have most of the time > 20h beam lifetime! • Original assumption for stored LHC beams: Min. intensity lifetime = 20 h (after 20 min about 1% of beam lost). • However, every accelerator experiences regular reductions of beam lifetime due to various reasons: • Machine changes in operational cycle: Snapback, ramp, squeeze • Crossing of high-order resonances during operational cycle. • Operator actions during empirical tuning (tune, orbit, chromaticity, coupling, …) with some small coupling of parts of beam to instabilities… • A very short drop in beam lifetime is sufficient to have a quench and to end the fill. Collimation must protect against these loss spikes. • Collimator design assumption changed to:Min. intensity lifetime = 0.2 h (after 10s about 1% of beam lost). • Based on real world experience (SppS, HERA, Tevatron, RHIC, ISR, …).

21. Examples for 0.001/s Loss Rate • It is really the loss rate that matters above a few ms. So what counts is the ratio of loss amount over loss duration (short loss spikes are very dangerous). We get the peak loss rate 0.001/s from: • 1% of beam lost in 10 s. • 0.1% of beam lost in 1 s. • 0.01% of beam lost in 100 ms. • 0.001% of beam lost in 10 ms. • Stick with the official loss rate 0.001/s from now on, adding some evolution. • Assume 0.002/s is achieved in the first year of LHC operation at 5 TeV, as shown in following slides.

22. Result: Intensity Limit vs Energy LHC could store lot’s of intensity at 1 TeV  Shows effort put on improvements!

23. Result: Limit Stored Energy vs Beam Energy x 300 LHC could store lot’s of energy at 1 TeV  Shows effort put on improvements!

24. Input: Beam-Beam Related (W. Herr) Beta* Crossing Angle (LR BB) Limit bunch intensity (head-on BB) Limit on bunch spacing (LR BB)

25. Result: Intensity Limit vs Energy R. Assmann and W. Herr beam-beam limited beam loss limited

26. Result: Limit Stored Energy vs Beam Energy R. Assmann and W. Herr beam loss limited beam-beam limited

27. Result: Peak Instantaneous Luminosity R. Assmann and W. Herr beam-beam limited beam loss limited

28. Evolution versus Time • All LHC systems are supposed to work much better than comparable systems in HERA and Tevatron in the slides before. They have been designed to do so. • However, there are no miracles (usually) and systems will not start up with their final performance. Issues must be understood and solved one by one (a 0.1% beam tail of the LHC corresponds to full Tevatron/HERA beam). • Some time evolution was added to the different parameters to reflect the experience that critical issues are usually improved with time. • Also include an upgrade scenario (Scenario 1): Collimation upgrade completed in 2013/14 shutdown. Triplet phase I upgrade. • Assume 5 TeV  6 TeV  7 TeV. Just my guess, can be changed…

29. Inputs I Ideal inefficiency Beta* Peak loss rate Limit bunch intensity

30. Inputs II BLM threshold Crossing angle Imperfection factor Dilution factor (FLUKA)

31. A Look at Tevatron Efficiency vs Time D. Still ~ factor 2 improvement per year

32. Result: Intensity versus Time (Scenario 1) PRELIMINARY Beam-beam limited Collimation limited

33. Result: Stored Energy versus Time (Scenario 1) Beam-beam limited Collimation limited PRELIMINARY

34. Result: Peak Luminosity versus Time (Scenario 1) PRELIMINARY Beam-beam limited Collimation limited

35. Scenario 2 • As before, but early collimation upgrade completed in 2011/12.

36. Result: Intensity versus Time (Scenario 2) PRELIMINARY Beam-beam limited Collimation limited

37. Result: Stored Energy versus Time (Scenario 2) PRELIMINARY Beam-beam limited Collimation limited

38. Result: Peak Luminosity versus Time (Scenario 2) Beam-beam limited Collimation limited PRELIMINARY

39. Conclusion • Nothing new on expected beam loss limitations for LHC. • Collected baseline LHC assumptions (originating from real-world collider experience: Tevatron, SppS, RHIC, HERA, LEP, SLC, PEP-2, ISR). • Put together available performance simulations around collimation and beam loss (optimistic approach). Other high intensity effects assumed OK (electro-magnetic noise, heating from image currents, instabilities, R2E, …). • Used info as input parameters to model intensity reach of the LHC. • Introduced some evolution in input parameters. BB limits from W. Herr. • Obtain performance estimates versus time based on technical arguments. • Will not claim that this is the truth but this is the best estimate that I can do and it is not in contradiction with simulations. • If different input parameters are agreed we can evaluate the effect on performance! Also allows analyzing LHC performance once we have data! • All preliminary: M. Ferro-Luzzi is coordinating a strategy note.

40. From Peak to Integrated LuminosityLEP Example Can look into a LEP model which can be applied to LHC. Note: LHC much more complex and sensitive than LEP!