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
Ralph Assmann

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…
Ralph Assmann

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

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:
collimation- project/PhD/bracco-phd- thesis-2009.pdf
Ralph Assmann

5. Error: Magnet Alignment Errors
PhD C. Bracco
Ralph Assmann

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

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
Ralph Assmann

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

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

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

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

12. Input: Peak Loss Rate
Design
worse
better
Ralph Assmann

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, …).
Ralph Assmann

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

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.
Ralph Assmann

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

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

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

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

20. Input: Evolution of Bunch Intensity
Ralph Assmann

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

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

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!
Ralph Assmann

24. “Best Possible Estimate” (Preliminary)
Year
Total number protons
% of nominal
Stored Energy [MJ]
Factor beyond Tevatron/HERA
2010
1.02E+13 3
11.5 6
2011
2.56E+13 8
28.7 14
2012
4.09E+13 13
45.9 23
2013
5.05E+13 16
56.6 28
Note, that considerable uncertainties can affect these results. However, results are not in coherent with simulation results!
Ralph Assmann