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

4/9/2009 A.Valishev, LARP CM12 2 E-Lens in FY09 LARP Beam-Beam Task 1.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 2.Theoretical analysis Effect of dispersion and chromaticity on RDTs, finite e-beam rigidity 3.Numerical simulations Develop and validate codes/machine models using existing experimental data Provide predictions for RHIC and LHC to support E-Lens installation The Goal: Evaluate the possible benefit to LHC (RHIC) luminosity from HO beam-beam compensation.

4/9/2009 A.Valishev, LARP CM12 3 Beam-Beam Simulation Mini Workshop BNL 12/3/ participants, 13 presentations Workshop Goals 1.Identify beam-beam related issues in LHC and RHIC that could be mitigated using e-lenses. 2.Assess the group capabilities and establish means of collaboration. 3.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

4/9/2009 A.Valishev, LARP CM12 4 Beam-Beam Simulation Mini Workshop E-Lens Physics Questions Beam-Beam effects in Tevatron and RHIC –Combination of HO and LR is important (TEV) –Separation above 6  must be maintained (TEV) –Chromatic effects are very important (TEV, RHIC) –Nonlinearities of final focus triplets significantly influence dynamics (RHIC) –Working point near 3Q x 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 N p ~5x10 11, hence HO beam-beam effect –LR collisions will make situation worse –E-Lens may be used to mitigate HO effect

4/9/2009 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

4/9/2009 A.Valishev, LARP CM12 6 Beam-beam compensation parameter scan Y. Luo, BNL SixTrack

4/9/2009 A.Valishev, LARP CM12 7 1x bbc = beam-beam compensation with Ne = Nip * Np = 2*2E11 Head-on Beam-Beam Compensation in RHIC BBSIM Results (H.-J. Kim, FNAL) Gaussian Electron Lens Same beam size as IP10's Small Ne reduces beam loss:  Ne < 0.5 Nip * Np SEFT Electron Lens Flat top edge is 4sigma Small Ne reduces beam loss much NO BBC Is this a tune effect?

4/9/2009 A.Valishev, LARP CM12 8 Head-on Beam-Beam Compensation in RHIC Lifetrac Results (A. Valishev, FNAL)

4/9/2009 A.Valishev, LARP CM12 9 Head-on Beam-Beam Compensation in RHIC BBSIM vs. Lifetrac (H.-J. Kim, A. Valishev, FNAL) Model similarities Machine optics Includes multipoles Beam parameters 3D beam-beam Model differences Initial distribution BBSIM – hollow Gaussian Lifetrac – weighted Gaussian Aperture Lattice chromaticity (sextupoles) NO BBC1/2 BBC

4/9/2009 A.Valishev, LARP CM12 10 Head-on Beam-Beam Compensation in LHC PlibB vs. Lifetrac (A. Kabel/SLAC, A. Valishev/FNAL) LifetracPlibB

4/9/2009 A.Valishev, LARP CM12 11 Recent TEL-2 Experience V. Kamerdzhiev, A. Valishev (FNAL) 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 5155, Dec 2006, 2.5E , Nov 2008, 3.3E32

4/9/2009 A.Valishev, LARP CM12 12 Recent TEL-2 Experience V. Kamerdzhiev, A. Valishev (FNAL) Dec 6, 2008, 3.5E32 No intentional tune changes Nov , 3.3E32 With intentional tune changes Valuable experience gained with e- and p beam alignment, timing, operation at high luminosity with SEFT gun.

4/9/2009 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

4/9/2009 A.Valishev, LARP CM12 14 TEL-2 Solenoid Field Profile

4/9/2009 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.

4/9/2009 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.

4/9/2009 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