beam-beam compensation at rhic larp proposal tanaji sen, wolfram fischer thanks to jean-pierre...

Beam-beam compensation at Beam-beam compensation at RHICRHIC

LARP ProposalLARP Proposal

Tanaji Sen, Wolfram FischerTanaji Sen, Wolfram Fischer

Thanks toThanks toJean-Pierre Koutchouk, Frank Jean-Pierre Koutchouk, Frank ZimmermannZimmermann

Tanaji SenTanaji Sen LHC IR Upgrades: Oct 3-4, 2005LHC IR Upgrades: Oct 3-4, 2005 22

TopicsTopics Motivation for LARPMotivation for LARP Lessons from SPS experimentsLessons from SPS experiments Lessons from RHIC experimentLessons from RHIC experiment ProposalProposal Challenges specific to the LHCChallenges specific to the LHC Need for simulationsNeed for simulations


MotivationMotivation ““Provide more luminosity earlier”Provide more luminosity earlier” Space is reserved in the LHC for the wires. An Space is reserved in the LHC for the wires. An

early test in RHIC will determine the early test in RHIC will determine the effectiveness of the compensation and effectiveness of the compensation and possibly address the challenges to the possibly address the challenges to the compensation. If effective, will allow a smaller compensation. If effective, will allow a smaller crossing angle and more beam intensitycrossing angle and more beam intensity..

Provide direction to an IR upgrade pathProvide direction to an IR upgrade path If compensation is proven to be effective, then If compensation is proven to be effective, then

the quadrupole first option seems to be a more the quadrupole first option seems to be a more natural path for the IR upgrade. Otherwise, the natural path for the IR upgrade. Otherwise, the dipole first option will be more attractive.dipole first option will be more attractive.


Lessons from the SPS Lessons from the SPS experimentsexperiments

Compensating 1 wire with Compensating 1 wire with another wire at nearly the another wire at nearly the same phase “works”same phase “works”

Compensation is tune Compensation is tune dependentdependent

Current sensitivity Current sensitivity Alignment sensitivityAlignment sensitivity Equivalent crossings in the Equivalent crossings in the

same plane led to better same plane led to better lifetimes than alternating lifetimes than alternating planesplanes

Beam lifetime Beam lifetime ττ ~ d ~ d33

d is the beam-wire distanced is the beam-wire distance Higher power law expected Higher power law expected

given the proximity of high given the proximity of high order resonancesorder resonancesBoth wires on 1 wire on

Nearly perfect compensation

No wires activated


Lessons from RHIC Lessons from RHIC experimentexperiment

Study at injection energy Study at injection energy with 1 bunch and 1 with 1 bunch and 1 parasitic interaction per parasitic interaction per beambeam

There is an effect to There is an effect to compensate, even with 1 compensate, even with 1 parasiticparasitic

Drop in lifetime seen for Drop in lifetime seen for beam separations < 7 beam separations < 7 σσ

Effect is very tune Effect is very tune dependentdependent

How important are How important are machine nonlinearities machine nonlinearities and other time and other time dependent effects?dependent effects?

Did they change with the Did they change with the beam-beam separationbeam-beam separation??


Wire compensation at Wire compensation at RHICRHIC Compensation of 1 wire Compensation of 1 wire

by another wire worked by another wire worked well in the SPS under well in the SPS under LHC conditions. LHC conditions.

Real test of the Real test of the compensation principle compensation principle requires 2 beamsrequires 2 beams

Beam studies in RHIC show that parasitic interactions have strong influence on beam loss

Favorable location for wire has been found in IR6, phase advance to parasitic ~6 degrees at top energy

Proposed wire location

Location of parasitic


Proposal - 1Proposal - 1 FY06 PlanFY06 Plan Design and construct a wire compensator (BNL)Design and construct a wire compensator (BNL) Beam-beam studies at top energy: beam separation Beam-beam studies at top energy: beam separation

and tune scan. No wire.and tune scan. No wire. Theoretical studies (analysis and simulations) to test Theoretical studies (analysis and simulations) to test

the compensation and robustnessthe compensation and robustness Install wire compensator on a movable stand in one of Install wire compensator on a movable stand in one of

the RHIC rings in 2006 shutdownthe RHIC rings in 2006 shutdown

FY07 PlanFY07 Plan Beam studies in RHIC with 1 proton bunch in at flat Beam studies in RHIC with 1 proton bunch in at flat

top and 1 parasitic interaction. top and 1 parasitic interaction. Test tolerances on: beam-wire separation, wire current Test tolerances on: beam-wire separation, wire current

accuracy, current ripple, phase advance to the wire.accuracy, current ripple, phase advance to the wire. Simulations to match experimentsSimulations to match experiments Construct and install 2Construct and install 2ndnd wire compensator and current wire compensator and current

modulator in 2007 shutdown.modulator in 2007 shutdown.


Proposal - 2Proposal - 2FY08 Plan FY08 Plan Compensation of both beams with the Compensation of both beams with the

2 wires2 wires Elliptical beams at the parasitic Elliptical beams at the parasitic

interaction – test robustness to interaction – test robustness to changes in the aspect ratiochanges in the aspect ratio

Compensation of multiple bunches in Compensation of multiple bunches in RHIC with pulsed wire current.RHIC with pulsed wire current.


RHIC proton parametersRHIC proton parameters

Beam energy [GeV]Beam energy [GeV]Bunch intensityBunch intensityTransverse emittance [mm-Transverse emittance [mm-mrad]mrad]Beta* [m]Beta* [m]RMS energy spreadRMS energy spreadRMS bunch length [m]RMS bunch length [m]Beam-beam tune shiftBeam-beam tune shift

100100 2 x 102 x 101111

1515 1.01.0 0.3 x 100.3 x 10-3-3

0.70.7 -9.8 x 10-9.8 x 10-3-3


Beam studies with 1 Beam studies with 1 wirewire Choose tunes so that only 1 beam is affected by the Choose tunes so that only 1 beam is affected by the

beam-beam interactionsbeam-beam interactions Wire strength: IWire strength: IWWL = ec NL = ec Nparapara N Npp Beam-wire distance equal to beam-beam separation. Beam-wire distance equal to beam-beam separation. Beam-wire distance > 3 Beam-wire distance > 3 σσ Minimum separation: Study the compensation over a Minimum separation: Study the compensation over a

range of separations, the minimum separation at range of separations, the minimum separation at which compensation is effective will be a measure of which compensation is effective will be a measure of the smallest crossing angle allowedthe smallest crossing angle allowed

Alignment tolerance: At fixed beam-beam separation, Alignment tolerance: At fixed beam-beam separation, find the range over which the beam-wire separation find the range over which the beam-wire separation can be varied with compensation still effective.can be varied with compensation still effective.

Tolerance on current: Vary the current until Tolerance on current: Vary the current until compensation is lostcompensation is lost

Tolerance on current jitter: Introduce current jitter, Tolerance on current jitter: Introduce current jitter, measure emittance growth. Compare with theory. measure emittance growth. Compare with theory.

Tolerance on phase advance: Move the location of the Tolerance on phase advance: Move the location of the parasitic interaction by changing the rf phase.parasitic interaction by changing the rf phase.


IssuesIssues Is cooling required with the currents to be used? If yes, Is cooling required with the currents to be used? If yes,

how will the cooling be done?how will the cooling be done? Tune and orbit correction for each beam-wire separationTune and orbit correction for each beam-wire separation What is the accuracy of the tune measuring instrument What is the accuracy of the tune measuring instrument

and the BPMs – relative to the size of the expected tune and the BPMs – relative to the size of the expected tune and orbit shiftsand orbit shifts

Over what range is the wire movable? Over what range is the wire movable? Does the wire pose an aperture restriction at small Does the wire pose an aperture restriction at small

distances from the beam?distances from the beam? In the case of a magnet failure, can the beam hit the In the case of a magnet failure, can the beam hit the

wire? Is the wire adequately protected?wire? Is the wire adequately protected? How should the effectiveness of the compensation be How should the effectiveness of the compensation be

monitored?monitored? How much machine study time should be requested for How much machine study time should be requested for

wire compensation of 1 bunch in one ring? For wire compensation of 1 bunch in one ring? For compensation of 1 bunch in both rings? For compensation compensation of 1 bunch in both rings? For compensation of several bunches?of several bunches?

Time scale of these experiments ?Time scale of these experiments ? What do simulations predict for the compensation?What do simulations predict for the compensation?


Challenges - 1Challenges - 1 Sensitivity to alignment errorsSensitivity to alignment errors Question: How do we quantify the sensitivity of the Question: How do we quantify the sensitivity of the

compensation to alignment and the precision with which compensation to alignment and the precision with which the beam-wire separation should be set ?the beam-wire separation should be set ?

Sensitivity to current jitterSensitivity to current jitter Question: How large an inductance is necessary to damp Question: How large an inductance is necessary to damp

the high frequency noise in the wire (close to the betatron the high frequency noise in the wire (close to the betatron frequency) ? Should we introduce measurable jitter to frequency) ? Should we introduce measurable jitter to induce emittance growth -> benchmark simulations?induce emittance growth -> benchmark simulations?

Sensitivity to optics errorsSensitivity to optics errors Spurious dispersion and local sources of coupling close to Spurious dispersion and local sources of coupling close to

the wire may change the efficiency of the compensation.the wire may change the efficiency of the compensation. Question: Should we attempt to create sources of optics Question: Should we attempt to create sources of optics

errors in RHIC? If yes, a) what are the important optics errors in RHIC? If yes, a) what are the important optics errors that can spoil the compensation and b) can these errors that can spoil the compensation and b) can these optics errors be created in RHIC ?optics errors be created in RHIC ?


Challenges - 2Challenges - 2 Sensitivity to phase advance errors between the Sensitivity to phase advance errors between the

parasitics and the wireparasitics and the wire Question: Is there some means by which the phase Question: Is there some means by which the phase

advance to the wire can be changed ? By how much?advance to the wire can be changed ? By how much?

Tune dependence of the compensation - RHIC tunes Tune dependence of the compensation - RHIC tunes are close to the LHC tunesare close to the LHC tunes

Question: Is it necessary to investigate the tune Question: Is it necessary to investigate the tune dependence in RHIC - over what range?dependence in RHIC - over what range?

Sensitivity to tune spread of the bunch.Sensitivity to tune spread of the bunch. Beams in RHIC and LHC will have different tune Beams in RHIC and LHC will have different tune

footprints. Is the compensation sensitive to this footprints. Is the compensation sensitive to this footprint? e.g does space charge induced tune footprint? e.g does space charge induced tune dependence on amplitude matter?dependence on amplitude matter?

Do the different rates of emittance growth in RHIC and Do the different rates of emittance growth in RHIC and LHC matter?LHC matter?


Challenges - 3Challenges - 3 Sensitivity to non-round beamsSensitivity to non-round beams Question: Can the aspect ratio at the parasitic be changed, Question: Can the aspect ratio at the parasitic be changed,

either by changing the ratio of either by changing the ratio of ββ_y*/ _y*/ ββ _x* or by changing _x* or by changing the ratio of transverse emittances e.g by scraping ?the ratio of transverse emittances e.g by scraping ?

At aspect ratio = 1.8, need a beam-beam separation of ~12σ to match the field of a round wire. Do these differences matter?


Challenges - 4Challenges - 4 How important is it to use How important is it to use

pulsed wires for pulsed wires for compensating the PACMAN compensating the PACMAN bunches, i.e. is it known that bunches, i.e. is it known that average compensation is not average compensation is not good enough for these good enough for these bunches?bunches?

If pulsed wires are required, If pulsed wires are required, what is the right frequency?what is the right frequency?

Does every PACMAN bunch Does every PACMAN bunch need a different current?need a different current?

Will such modulators and Will such modulators and power supplies be available in power supplies be available in FY07?FY07?

Wire current proportional to Npara


Simulations - 1Simulations - 1 CapabilitiesCapabilities BBSIM (FNAL) – wire module BBSIM (FNAL) – wire module

included, used for predicting included, used for predicting alignment tolerance in SPS studiesalignment tolerance in SPS studies

Frank Zimmermann & student Frank Zimmermann & student (CERN) – initial results on RHIC (CERN) – initial results on RHIC beam-beam experimentbeam-beam experiment

Beambeam3D – J. Qiang (LBL)Beambeam3D – J. Qiang (LBL) J. Shi (University of Kansas)J. Shi (University of Kansas)


Simulations - 2Simulations - 2What can we expect?What can we expect? Reproduce the results of the beam-beam Reproduce the results of the beam-beam

experiment at injection energyexperiment at injection energy Important physicsImportant physics e.g. nonlinear fields including snakes, space e.g. nonlinear fields including snakes, space

charge, IBS, tune modulation,…?charge, IBS, tune modulation,…? Simulate 1 parasitic interaction at top energy.Simulate 1 parasitic interaction at top energy. Is there a significant impact on the beam?Is there a significant impact on the beam? Variation with separation of: dynamic Variation with separation of: dynamic

aperture, emittance change, lifetime,…aperture, emittance change, lifetime,… Simulate 1 parasitic interaction and wire.Simulate 1 parasitic interaction and wire. Is compensation effective?Is compensation effective? Tolerances on: alignment, current strength Tolerances on: alignment, current strength

and jitter, phase advance errors, non-and jitter, phase advance errors, non-roundness of “strong” beam, …roundness of “strong” beam, …


SummarySummary Propose installing a wire compensator in Propose installing a wire compensator in

RHIC in 2006RHIC in 2006 Tests of the compensation principle in Tests of the compensation principle in

FY07 and beyond.FY07 and beyond. Several issues and challenges to be Several issues and challenges to be

addressed.addressed. Simulation efforts need to be Simulation efforts need to be

significantly ramped up in FY06significantly ramped up in FY06 Successful tests of wire compensation Successful tests of wire compensation

expected to improve the performance of expected to improve the performance of the LHC and help direct the upgrade the LHC and help direct the upgrade path.path.

beam-beam compensation at rhic larp proposal tanaji sen, wolfram fischer thanks to jean-pierre...

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