Performance Limit and Evolution Estimate for LHC Intensity

1. Intensity Evolution Estimate for LHC R. Assmann, CERN/BE 3/3/2009 Commissioning Meeting “Cassandra has always been misunderstood and misinterpreted as a madwoman or crazy doomsday prophetess.” L. Fitton

2. 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). Values for 7 TeV, lower energy requires more work. Assume announced quench limit! • All is ongoing work…

3. Result: Achievement Factor Beyond World Record in Stored Energy Looks very ambitious, doesn’t it? better worse Coll. Phase II Coll. Phase I

4. Recent Reference Chiara will present PhD in BE seminar on March 12th, 14h15. PhD report available for download from web site LHC collimation project: http://www.cern.ch/lhc-collimation-project/PhD/bracco-phd-thesis-2009.pdf

5. Error: Magnet Alignment Errors PhD C. Bracco

6. Impact of Imperfections on Inefficiency (Leakage Rate) worse better PhD C. Bracco

7. 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. PhD C. Bracco

8. Collimation Phase II: Ideal Cleaning Inefficiency versus Re(Tune Shift) R. Assmann, T. Weiler, E. Metral Ideal Performance better worse Phase I Phase II worse better

9. Input: Cleaning Efficiency better [%/m] Coll. Phase II Coll. Phase I worse

10. … as Inefficiency (Leakage Rate) … worse better Coll. Phase II Coll. Phase I

11. A Look at Tevatron Efficiency D. Still ~ factor 2 improvement per year

12. Input: Peak Loss Rate worse Design better

13. 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 1 second 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, …).

14. Input: BLM Threshold better Typical HERA threshold? worse

15. Putting it together: Performance Model • The various important input parameters have been put together into a preliminary performance model. • Due to the short notice for this talk, please take results with some care. I will need to check. Also, some assumptions are questionable and possibly too optimistic (BLM threshold immediately at design value). • 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.

16. Result: Intensity Evolution(preliminary) Limit from Collimation Maximum in LHC Beam-beam limited Collimation limited

17. Result: Fraction of Nominal Intensity(preliminary) World Record Stored Energy

18. Result: Fraction of Nominal Intensity(preliminary) Coll. Phase II Coll. Phase I

19. Input: Evolution of b* Triplet Phase I Present Triplets

20. Input: Evolution of Bunch Intensity

21. Result: Instantaneous Luminosity(preliminary) Not fully correct – need to improve model!

22. 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!

23. Conclusion • Put together baseline assumptions, as defined years ago and explicit supported by persons with real-world collider experience (Tevatron, SppS, RHIC, HERA, LEP, SLC, PEP-2, ISR). • Put together available performance simulations around collimation and beam loss. Other high intensity side effects assumed OK (electro-magnetic noise, heating from image currents, instabilities, …). • Used info as input parameters to model for intensity reach of the LHC. • Introduced some evolution in input parameters, based on my personal judgment and experience in various colliders. Should be discussed. • Obtain performance estimates versus time based on technical arguments. • Will not claim that this is the truth but this is the best possible estimate! • We cannot rely on hand waving arguments! Technical experts should support the assumptions in any estimate that is established!

24. “Best Possible Estimate” (Preliminary) Note, that considerable uncertainties can affect these results. However, results are not in coherent with simulation results!