Proton%20Intensity%20Evolution%20Estimates%20for%20LHC

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Proton Intensity EvolutionEstimates for LHC
PRELIMINARY

• R. Assmann, CERN/BE
• 19/3/2009
• LMC

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.
Cassandra has always been misunderstood and
misinterpreted as a madwoman or crazy doomsday
prophetess. L. Fitton
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Recent Reference
PhD report available for download from web site
LHC collimation project http//www.cern.ch/lhc-co
llimation-project/PhD/bracco-phd-thesis-2009.pdf
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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).
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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, as predicted or solved
  with transverse feedback).
• All is ongoing work

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Result Achievement Factor Beyond World Record in
Stored Energy
Looks very ambitious and successful,doesnt
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,
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Collimation Ideal Cleaning Inefficiency versus
Re(Tune Shift)
R. Assmann, T. Weiler, E. Metral
Ideal Performance
worse
Phase I
Phase II Review on April 2/3!
In the following Concentrate on Phase I
Phase II
better
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Input Ideal Cleaning Efficiency
Cleaning worse at high energy!
More difficult to stop 7 TeV protons ? no black
hole available for sucking them up!
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.
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as Inefficiency (Leakage Rate)
worse
better
Simulation results (points) fitted (lines) to
represent energy dependence.
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Impact of Imperfections on Inefficiency (Leakage
Rate) 7 TeV
worse
better
PhD C. Bracco
40 intensity ideal reach
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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 ? Always worse than ideal
(as expected).
PhD C. Bracco
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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).

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Downstream of IR7 b-cleaning
Halo Loss Map
Losses of off-momentum protons from
single-diffractive scattering in TCP
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
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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.
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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.
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Input BLM Threshold
better
Input Bernd Dehning and BLM team
worse
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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.
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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.

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Result Intensity Limit vs Loss Rate 5 TeV
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Result Intensity Limit vs Loss Rate 7 TeV
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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 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 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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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.

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Result Intensity Limit vs Energy
LHC could store lots of intensity at 1 TeV ?
Shows effort put on improvements!
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Result Limit Stored Energy vs Beam Energy
x 300
LHC could store lots of energy at 1 TeV ? Shows
effort put on improvements!
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Input Beam-Beam Related (W. Herr)
Beta
Crossing Angle (LR BB)
Limit bunch intensity (head-on BB)
Limit on bunch spacing (LR BB)
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Result Intensity Limit vs Energy
R. Assmann and W. Herr
beam-beam limited
beam loss limited
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Result Limit Stored Energy vs Beam Energy
R. Assmann and W. Herr
beam loss limited
beam-beam limited
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Result Peak Instantaneous Luminosity
R. Assmann and W. Herr
beam-beam limited
beam loss limited
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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

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Inputs I
Ideal inefficiency
Beta
Peak loss rate
Limit bunch intensity
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Inputs II
BLM threshold
Crossing angle
Imperfection factor
Dilution factor (FLUKA)
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A Look at Tevatron Efficiency vs Time
D. Still
factor 2 improvement per year
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Result Intensity versus Time (Scenario 1)
PRELIMINARY
Collimation limited
Beam-beam limited
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Result Stored Energy versus Time (Scenario 1)
Collimation limited
Beam-beam limited
PRELIMINARY
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Result Peak Luminosity versus Time (Scenario 1)
PRELIMINARY
Collimation limited
Beam-beam limited
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Scenario 2

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

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Result Intensity versus Time (Scenario 2)
PRELIMINARY
Collimation limited
Beam-beam limited
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Result Stored Energy versus Time (Scenario 2)
PRELIMINARY
Collimation limited
Beam-beam limited
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Result Peak Luminosity versus Time (Scenario 2)
Collimation limited
Beam-beam limited
PRELIMINARY
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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.

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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!