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Status of Head-on Beam-Beam Compensation

Status of Head-on Beam-Beam Compensation

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Status of Head-on Beam-Beam Compensation

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  1. US LHC Accelerator Research Program BNL - FNAL- LBNL - SLAC Status of Head-on Beam-Beam Compensation A. Valishev, FNAL 09 April 2009 LARP CM12

  2. 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 A.Valishev, LARP CM12

  3. 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 • • Near term plan: code benchmarking on a number of excercises for RHIC and LHC • Long term plan: study robustness of beam-beam compensation schemes A.Valishev, LARP CM12

  4. 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 A.Valishev, LARP CM12

  5. 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 -> BlueGene, NERSC A.Valishev, LARP CM12

  6. Beam-beam compensation parameter scan Y. Luo, BNLSixTrack A.Valishev, LARP CM12

  7. 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 < 0.5 Nip * Np Is this a tune effect? NO BBC • 1x bbc = beam-beam compensation with Ne = Nip * Np = 2*2E11 A.Valishev, LARP CM12

  8. Head-on Beam-Beam Compensation in RHICLifetrac Results (A. Valishev, FNAL) A.Valishev, LARP CM12

  9. 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 A.Valishev, LARP CM12

  10. Head-on Beam-Beam Compensation in LHCPlibB vs. Lifetrac (A. Kabel/SLAC, A. Valishev/FNAL) PlibB Lifetrac A.Valishev, LARP CM12

  11. 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 A.Valishev, LARP CM12

  12. 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. A.Valishev, LARP CM12

  13. 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 A.Valishev, LARP CM12

  14. TEL-2 Solenoid Field Profile A.Valishev, LARP CM12

  15. 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. A.Valishev, LARP CM12

  16. 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. A.Valishev, LARP CM12

  17. 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 A.Valishev, LARP CM12