Overview of Beam-beam Overview of Beam-beam simulationssimulations

Tanaji SenTanaji SenFNALFNAL

US LARP Collaboration MeetingUS LARP Collaboration MeetingApril 23, 2008April 23, 2008

OutlineOutlineMeasurements with the wire compensatorMeasurements with the wire compensatorBeam transfer function comparisonsBeam transfer function comparisonsEmittance growth from diffusion Emittance growth from diffusion

coefficientscoefficientsPhysics additions to codesPhysics additions to codesFuture plansFuture plans

Beam-beam codesBeam-beam codesFNAL: BBSIM (H.J. Kim and T. Sen)FNAL: BBSIM (H.J. Kim and T. Sen)

with contributions from with contributions from

V. Boocha, B. Erdelyi, V. RanjbarV. Boocha, B. Erdelyi, V. RanjbarLBL: BeamBeam3D (J. Qiang)LBL: BeamBeam3D (J. Qiang)SLAC: PlibB (A. Kabel)SLAC: PlibB (A. Kabel)

Loss rates: RHIC studies in FY08Loss rates: RHIC studies in FY08

Deuteron-gold store in January Deuteron-gold store in January

2008. (d: Blue, Au: Yellow ring)2008. (d: Blue, Au: Yellow ring)

2 head-on collisions and no long-2 head-on collisions and no long-

range interactionsrange interactions

Wire current 50A, separation Wire current 50A, separation

changed from 26mm-50mmchanged from 26mm-50mm

Losses of deuteron beam were Losses of deuteron beam were

measured as a function of the measured as a function of the

separationseparation

BBSIM simulations of loss rate vs measurement. Onset of sharp losses well reproduced.

Beam transfer function Beam transfer function

BTF modules have been added to all 3 BTF modules have been added to all 3 codes.codes.

Useful partial validation of codes.Useful partial validation of codes.Measurements of deuteron BTFs in d-Au Measurements of deuteron BTFs in d-Au

stores in 2008 provide cleaner signals stores in 2008 provide cleaner signals than in Au-Au stores of 2007.than in Au-Au stores of 2007.

BTF simulations : FNALBTF simulations : FNAL

Deuteron-gold store in January 2008Deuteron-gold store in January 2008 Tune shift and BTF features with wire need to agree betterTune shift and BTF features with wire need to agree better

Horizontal Vertical

Wire OnWire On

Wire OffWire Off

BTF simulations: LBLBTF simulations: LBL

Gold-gold store of April 25, 2007Gold-gold store of April 25, 2007 Difference of ~0.002 between horizontal tunes with wire Difference of ~0.002 between horizontal tunes with wire

on.on. Simulated tune shift agrees with analytical tune shift.Simulated tune shift agrees with analytical tune shift.

Without wire With wire

BTF simulations: SLACBTF simulations: SLAC

Gold-gold run of 2007Gold-gold run of 2007 Reasonably good agreement in amplitude & phaseReasonably good agreement in amplitude & phase

BTF amplitude with wire BTF phase with wire

Emittance growth from diffusion Emittance growth from diffusion coefficientscoefficients

Emittance growth may be driven by Emittance growth may be driven by diffusive processes in the beam core. diffusive processes in the beam core. Dynamics in the tails which determines Dynamics in the tails which determines lifetime may not be diffusivelifetime may not be diffusive

Calculate diffusion coefficients from Calculate diffusion coefficients from tracking code (BBSIM) and use as input to tracking code (BBSIM) and use as input to an independent diffusion equation solveran independent diffusion equation solver

Evolve the density and the moments to Evolve the density and the moments to find emittance growth and lifetime over find emittance growth and lifetime over length of the store – several hourslength of the store – several hours

Diffusion equationDiffusion equation

Diffusion equation in 2D action spaceDiffusion equation in 2D action space

Tracking with BBSIM in 6D phase space to Tracking with BBSIM in 6D phase space to calculate diffusion coefficients. calculate diffusion coefficients.

Compared numerical diffusion coefficients Compared numerical diffusion coefficients with available measurements of diffusion with available measurements of diffusion coefficients at RHIC (R. Fliller’s thesis)coefficients at RHIC (R. Fliller’s thesis)

]2[2

1JyyyJyJyxyJxJxxxJxt DDD

Emittance growth: d-Au storeEmittance growth: d-Au store

Measured horizontal emittance growth is much larger than in simulations.Measured horizontal emittance growth is much larger than in simulations. Agreement with vertical emittance growth is significantly better. Agreement with vertical emittance growth is significantly better.

Horizontal plane Vertical plane

Deuterons: Store 9572

Emittance growth: d-Au storesEmittance growth: d-Au stores

The pattern is consistent in several stores. Horizontal emittance growth is The pattern is consistent in several stores. Horizontal emittance growth is underestimated, vertical emittance growth is more accurate. underestimated, vertical emittance growth is more accurate.

Horizontal

VerticalHorizontal

Vertical

Physics additions to codesPhysics additions to codes

BBSIM (FNAL)BBSIM (FNAL) Coupling (Edwards-Teng) – no change to RHIC dynamic Coupling (Edwards-Teng) – no change to RHIC dynamic

aperture aperture Resistive wall wakefieldsResistive wall wakefields Symplectic synchro-beam mapSymplectic synchro-beam map Beambeam3D (LBL)Beambeam3D (LBL) Crab cavities – first results, impact of phase noiseCrab cavities – first results, impact of phase noise PlibB (SLAC)PlibB (SLAC) IBS – application to RHIC IBS – application to RHIC Electron Lens Electron Lens

Simulation results summarySimulation results summary Loss rates with wire: Loss rates with wire: - Onset of loss rates with beam-wire separations is closely - Onset of loss rates with beam-wire separations is closely

reproduced in BBSIM. reproduced in BBSIM. - Similar results obtained in FY07 with earlier RHIC - Similar results obtained in FY07 with earlier RHIC

measurements. measurements. BTF simulations: BTF simulations: - Reasonable agreement without wire between meas. & sim.- Reasonable agreement without wire between meas. & sim. - Some unresolved questions with measured BTFs with the - Some unresolved questions with measured BTFs with the

wirewire - Effect of coupling with wire not well understood.- Effect of coupling with wire not well understood. Emittance growth from diffusion in d-Au storesEmittance growth from diffusion in d-Au stores - Significantly underestimate hor. plane. Missing IBS- Significantly underestimate hor. plane. Missing IBS - Good agreement in ver. plane- Good agreement in ver. plane - Diffusion model does not predict the lifetime accurately, as - Diffusion model does not predict the lifetime accurately, as

expected. expected. First results from crab cavity (Beambeam3D). Need to be First results from crab cavity (Beambeam3D). Need to be

better understood. better understood.

Forthcoming studiesForthcoming studies Evaluate wire compensation in LHC and benefit Evaluate wire compensation in LHC and benefit

to luminosity.to luminosity. Simulate wire compensation in RHIC and Simulate wire compensation in RHIC and

compare with measurements in FY09compare with measurements in FY09 Improve the diffusion model: add other sources Improve the diffusion model: add other sources

of diffusion in tracking, use diffusion equation in of diffusion in tracking, use diffusion equation in 3D action space. Extend the comparison to other 3D action space. Extend the comparison to other stores. stores.

Evaluate the impact of crab cavities in the LHC Evaluate the impact of crab cavities in the LHC with weak-strong and strong-strong simulations. with weak-strong and strong-strong simulations. Set tolerances on noise parameters. Set tolerances on noise parameters.