Status of Headon BeamBeam Compensation

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Status of Head-on Beam-Beam Compensation
US LHC Accelerator Research Program
BNL - FNAL- LBNL - SLAC
A. Valishev, FNAL 09 April 2009 LARP CM12
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E-Lens in FY09 LARP Beam-Beam Task
The Goal Evaluate the possible benefit to LHC
(RHIC) luminosity from HO beam-beam compensation.

• Experimental studies at the Tevatron
• Installation of the Gaussian profile gun is
  planned
• Will allow to experiment with beam to beam
  alignment tolerances
• Possibly attempt tune footprint suppression
• Identify operational problems
• Provide data for comparison with simulations
• Theoretical analysis
• Effect of dispersion and chromaticity on RDTs,
  finite e-beam rigidity
• Numerical simulations
• Develop and validate codes/machine models using
  existing experimental data
• Provide predictions for RHIC and LHC to support
  E-Lens installation

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Beam-Beam Simulation Mini WorkshopBNL 12/3/2008

• 11 participants, 13 presentations
• Workshop Goals
• Identify beam-beam related issues in LHC and RHIC
  that could be mitigated using e-lenses.
• Assess the group capabilities and establish means
  of collaboration.
• Establish near and long term simulation program,
  set priorities and schedule.
• We addressed a list of about ten questions. Full
  report is available at
• http//larpdocs.fnal.gov/LARP-public/DocDB/ShowDoc
  ument?docid907
• Near term plan code benchmarking on a number of
  excercises for RHIC and LHC
• Long term plan study robustness of beam-beam
  compensation schemes

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Beam-Beam Simulation Mini WorkshopE-Lens Physics
Questions

• Beam-Beam effects in Tevatron and RHIC
• Combination of HO and LR is important (TEV)
• Separation above 6s must be maintained (TEV)
• Chromatic effects are very important (TEV, RHIC)
• Nonlinearities of final focus triplets
  significantly influence dynamics (RHIC)
• Working point near 3Qx requires resonance
  suppression (RHIC)
• Head-on compensation in RHIC
• Strength of beam-beam effects depends on choice
  of parameters
• Benefits of E-Lens have to be evaluated
• Expectation for Beam-Beam effects in LHC
• LPA upgrade scenario Np 5x1011, hence HO
  beam-beam effect
• LR collisions will make situation worse
• E-Lens may be used to mitigate HO effect

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Available Computing Tools

• Short-term simulations
• BBSIM (T. Sen, H.-J. Kim, FNAL)
• SixTrack (N. Abreu, Y. Luo, BNL)
• Long-term (weak-strong macro particle simulation
  codes)
• BBSIM (T. Sen, H.-J. Kim, FNAL)
• LIFETRAC (A. Valishev, FNAL)
• PlibB (A. Kabel, SLAC)
• SixTrack (Y. Luo, G. Robert-Demolaize, BNL)

Heimdall cluster 16x4 cpu
NERSC (?)
BOINC -gt BlueGene, NERSC
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Beam-beam compensation parameter scan
Y. Luo, BNLSixTrack
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Head-on Beam-Beam Compensation in RHICBBSIM
Results (H.-J. Kim, FNAL)

• SEFT Electron Lens
• Flat top edge is 4sigma
• Small Ne reduces beam loss much

• Gaussian Electron Lens
• Same beam size as IP10's
• Small Ne reduces beam loss
• Ne lt 0.5 Nip Np

Is this a tune effect?
NO BBC

• 1x bbc beam-beam compensation with Ne Nip
  Np 22E11

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Head-on Beam-Beam Compensation in RHICLifetrac
Results (A. Valishev, FNAL)
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Head-on Beam-Beam Compensation in RHICBBSIM vs.
Lifetrac (H.-J. Kim, A. Valishev, FNAL)

• Model differences
• Initial distribution
• BBSIM hollow Gaussian
• Lifetrac weighted Gaussian
• Aperture
• Lattice chromaticity (sextupoles)

• Model similarities
• Machine optics
• Includes multipoles
• Beam parameters
• 3D beam-beam

NO BBC
1/2 BBC
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Head-on Beam-Beam Compensation in LHCPlibB vs.
Lifetrac (A. Kabel/SLAC, A. Valishev/FNAL)
Lifetrac
PlibB
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Recent TEL-2 ExperienceV. Kamerdzhiev, A.
Valishev (FNAL)
5155, Dec 2006, 2.5E32

• TEL-2 was installed in 2006
• By then, adverse beam-beam effects shifted to
  protons!
• Specifically, bunch 12 in the train had
  considerably higher losses due to lower vertical
  tune
• In 2008 after improvements in the machine optics
  bunch 12 is no longer different at luminosities
  up to 3.3E32
• Requested several high initial luminosity stores
• Started preparations to test Gaussian gun

6598, Nov 2008, 3.3E32
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Recent TEL-2 Experience V. Kamerdzhiev, A.
Valishev (FNAL)
Nov 22 2008, 3.3E32 With intentional tune changes
Dec 6, 2008, 3.5E32 No intentional tune changes
Valuable experience gained with e- and p beam
alignment, timing, operation at high luminosity
with SEFT gun.
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Experiment with Gaussian Gun at Tevatron(A.
Valishev, A. Romanov, FNAL)
The new gun was trained and emission
characteristic was measured together with the
beam profile. Still awaiting an opportunity to
install into TEL-2, at least 12 hour tunnel
access is required
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TEL-2 Solenoid Field Profile
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Gaussian TEL-2 Head-on Tune Spread (A. Valishev,
A. Romanov, FNAL)
Changes in beam shape (right) and tune spectra
(left) due to imperfection of guiding solenoidal
field.
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Possibility of Head-on Compensation with SEFT(A.
Valishev, A. Romanov, Fermilab)
Changes in beam shape (right) and tune spectra
(left) due to imperfection of guiding solenoidal
field. It is feasible to generate noticeable tune
spread with the existing gun. Experiment is in
progress.
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Summary

• Reasonable agreement have been achieved between 3
  simulation groups for RHIC beam-beam
  compensation. A more rigorous comparison is in
  progress
• Adverse beam-beam effects are observed for RHIC
  upgrade parameters
• Extent of EL beam-beam compensation is sensitive
  to the choice of e- and p beam parameters
• Two codes have been configured to run the same
  LHC case
• Beam-beam induced losses are more pronounced than
  in the RHIC case better opportunities for
  compensation
• Gaussian gun could not be installed in TEL-2
  (restricted access time)
• Calculations show that SEFT gun can generate
  sizeable tune spread attempt to demonstrate
  this will be made during remaining Tevatron run
  in FY09