Intensity Evolution Estimate for LHC

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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
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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, doesnt it?
better
worse
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-the
sis-2009.pdf
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Error Magnet Alignment Errors
PhD C. Bracco
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Impact of Imperfections on Inefficiency (Leakage
Rate)
worse
better
PhD C. Bracco
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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
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Collimation Phase II Ideal Cleaning Inefficiency
versus Re(Tune Shift)
R. Assmann, T. Weiler, E. Metral
Ideal Performance
worse
Phase I
Phase II
better
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Input Cleaning Efficiency
better
/m
Coll. Phase II
Coll. Phase I
worse
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as Inefficiency (Leakage Rate)
worse
better
Coll. Phase I
Coll. Phase II
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A Look at Tevatron Efficiency
D. Still
factor 2 improvement per year
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Input Peak Loss Rate
worse
better
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Remarks Beam Loss Rate

• The LHC beams will have most of the time gt 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 toMin.
  intensity lifetime 0.2 h (after 10s about 1 of
  beam lost).
• Based on real world experience (SppS, HERA,
  Tevatron, RHIC, ISR, ).

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Input BLM Threshold
better
Typical HERA threshold?
worse
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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.

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Result Intensity Evolution(preliminary)
Limit from Collimation
Maximum in LHC
Collimation limited
Beam-beam limited
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Result Fraction of Nominal Intensity(preliminary
)
World Record Stored Energy
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Result Fraction of Nominal Intensity(preliminary
)
Coll. Phase I
Coll. Phase II
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Input Evolution of b
Present Triplets
Triplet Phase I
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Input Evolution of Bunch Intensity
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Result Instantaneous Luminosity(preliminary)
Not fully correct need to improve model!
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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!
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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!

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