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Overview of Beam-beam simulations

Overview of Beam-beam simulations. Tanaji Sen FNAL US LARP Collaboration Meeting April 23, 2008. Outline. Measurements with the wire compensator Beam transfer function comparisons Emittance growth from diffusion coefficients Physics additions to codes Future plans. Beam-beam codes.

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Overview of Beam-beam simulations

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  1. Overview of Beam-beam simulations Tanaji Sen FNAL US LARP Collaboration Meeting April 23, 2008

  2. Outline • Measurements with the wire compensator • Beam transfer function comparisons • Emittance growth from diffusion coefficients • Physics additions to codes • Future plans

  3. Beam-beam codes • FNAL: BBSIM (H.J. Kim and T. Sen) with contributions from V. Boocha, B. Erdelyi, V. Ranjbar • LBL: BeamBeam3D (J. Qiang) • SLAC: PlibB (A. Kabel)

  4. Loss rates: RHIC studies in FY08 • Deuteron-gold store in January 2008. (d: Blue, Au: Yellow ring) • 2 head-on collisions and no long-range interactions • Wire current 50A, separation changed from 26mm-50mm • Losses of deuteron beam were measured as a function of the separation BBSIM simulations of loss rate vs measurement. Onset of sharp losses well reproduced.

  5. Beam transfer function • BTF modules have been added to all 3 codes. • Useful partial validation of codes. • Measurements of deuteron BTFs in d-Au stores in 2008 provide cleaner signals than in Au-Au stores of 2007.

  6. BTF simulations : FNAL Horizontal Vertical Wire Off • Deuteron-gold store in January 2008 • Tune shift and BTF features with wire need to agree better Wire Off Wire On Wire On

  7. BTF simulations: LBL • Gold-gold store of April 25, 2007 • Difference of ~0.002 between horizontal tunes with wire on. • Simulated tune shift agrees with analytical tune shift. Without wire With wire

  8. BTF simulations: SLAC • Gold-gold run of 2007 • Reasonably good agreement in amplitude & phase BTF amplitude with wire BTF phase with wire

  9. Emittance growth from diffusion coefficients • Emittance growth may be driven by diffusive processes in the beam core. Dynamics in the tails which determines lifetime may not be diffusive • Calculate diffusion coefficients from tracking code (BBSIM) and use as input to an independent diffusion equation solver • Evolve the density and the moments to find emittance growth and lifetime over length of the store – several hours

  10. Diffusion equation • Diffusion equation in 2D action space • Tracking with BBSIM in 6D phase space to calculate diffusion coefficients. • Compared numerical diffusion coefficients with available measurements of diffusion coefficients at RHIC (R. Fliller’s thesis)

  11. Emittance growth: d-Au store Deuterons: Store 9572 • Measured horizontal emittance growth is much larger than in simulations. • Agreement with vertical emittance growth is significantly better. Vertical plane Horizontal plane

  12. Emittance growth: d-Au stores • The pattern is consistent in several stores. Horizontal emittance growth is underestimated, vertical emittance growth is more accurate. Horizontal Vertical Vertical Horizontal

  13. Physics additions to codes BBSIM (FNAL) • Coupling (Edwards-Teng) – no change to RHIC dynamic aperture • Resistive wall wakefields • Symplectic synchro-beam map Beambeam3D (LBL) • Crab cavities – first results, impact of phase noise PlibB (SLAC) • IBS – application to RHIC • Electron Lens

  14. Simulation results summary • Loss rates with wire: - Onset of loss rates with beam-wire separations is closely reproduced in BBSIM. - Similar results obtained in FY07 with earlier RHIC measurements. • BTF simulations: - Reasonable agreement without wire between meas. & sim. - Some unresolved questions with measured BTFs with the wire - Effect of coupling with wire not well understood. • Emittance growth from diffusion in d-Au stores - Significantly underestimate hor. plane. Missing IBS - Good agreement in ver. plane - Diffusion model does not predict the lifetime accurately, as expected. • First results from crab cavity (Beambeam3D). Need to be better understood.

  15. Forthcoming studies • Evaluate wire compensation in LHC and benefit to luminosity. • Simulate wire compensation in RHIC and compare with measurements in FY09 • Improve the diffusion model: add other sources of diffusion in tracking, use diffusion equation in 3D action space. Extend the comparison to other stores. • Evaluate the impact of crab cavities in the LHC with weak-strong and strong-strong simulations. Set tolerances on noise parameters.

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