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ELIC Luminosity and Electron Cooling Ya. Derbenev and Y. Zhang

EIC Collaboration MeetingStony Brook University, January 10 to 12, 20101OutlineIntroduction

ELIC Luminosity Concept

Forming and Cooling of Ion Beams

Conceptual Design of ERL Circulator Cooler

Key Enabling Technologies and R&D

Summary21. Introduction3Introduction: ELIC LuminosityIt is true that ELIC *=5 mm is a factor of 25 to 50 smaller than other hadron collidersHowever this is not whole storyBunch repetition rate fc and bunch charges Nh, Ne also play very important role in ELIC design

IntroductionFrom the beginning, ELIC design effort has been focused on achieving very high luminosity, above 1034 /cm2/s, over a wide range of center-of-mass energy.

ELIC design concept is based on very high bunch repetition rate (for hadron colliders), very small beam spot sizes at collision points (*=5 mm)very short ion bunch (~5 mm RMS)All proven in existing (lepton) colliders

Staged electron cooling is essential for such luminosity concept.

The design is optimized for taking maximum advantages of CEBAF high repetition CW electron beam a new facility of ion complex.

For electron cooling, all technology issues are either already solved or have promising concepts

52. ELIC Luminosity Concept6B-Factories Success As A Role ModelB-factories (PEPII & KEKB, etc)

Asymmetric high energy lepton colliders (energy and beam current)

Pioneered a class of new technologies (crab cavity, etc.)

Highly succeed interaction region design

Unprecedented high luminosity, already over 2x1034 /cm2/s, the present world record

Planning for upgrade (Super-B factory) for reaching luminosity above 1036 /cm2/s, with more technology innovations (crab waist, etc.)7Key Factors for B-Factories Unprecedented High LuminosityVery high bunch repetition rate (~ 500 MHz)

Very small * (~6 mm) to reach very small spot sizes at collision points

Very short bunch length (z~ *) to avoid luminosity loss due to hour-glass effect (unless other mitigation schemes are used)

Very small bunch charge for making very short bunch possible

High bunch repetition restores high average beam current and luminosity

Nature provides a very powerful helping hand -- synchrotron radiation damping,

8B Factories and Super-B Factories

A factor of 30 reduction9How to Repeat B-Factories Success for Electron-ion Collision ELIC?Do exactly the same things for electron/ion beamsVery high bunch repetition (~499 MHz up to 1.5 GHz)Very small * for reaching very small bunch spot at collision points

Fortunately, we are able to make this happenElectron beam from CEBAF is already a high repetition CW beam (up 1.5 GHz) Proton/ion beams from a new ion complex, which allows us to specially design to deliver same high repetition beams

But very unfortunately, Nature does not provide a radiation damping to ion beam in our desired energy range, we must introduce one10Choice of Short Ion Bunch with Small ChargeELIC design choice (with a very small *) A very short bunch length (same as *) to minimize luminosity loss due to hour-glass effectA small bunch charge to keep relatively small charge density for avoiding bad beam instabilityAchieve high average beam current through high bunch repetition with relative small bunch charge

A short ion bunch with high charge (and high charge density) can lead to many bad things such as increasing single bunch instabilities, hard to form & cool, and heat-up by strong IBS .

A long bunch, though can hold high charge, needs additional mitigations such as traveling final focusing, an unnecessary technical complication. 11ELIC Design Parameters Beam EnergyGeV250/10150/760/560/312/3Collision freq.MHz499Particles/bunch10101.1/3.10.5/3.250.74/2.91.1/60.47/2.3Beam currentA0.9/2.50.4/2.60.59/2.30.86/4.80.37/2.7Energy spread10-4~ 3RMS bunch lengthmm555550Horz. emit., norm.m0.7/510.5/430.56/850.8/750.18/80Vert. emit. Norm.m0.03/20.03/2.870.11/170.8/750.18/80Horizontal beta-starmm1257525255Vertical beta-starmm5Vert. b-b tuneshift/IP0.01/0.10.015/.050.01/0.03.015/.08.015/.013Laslett tune shift p-beam0.10.10.10.0540.1Peak Lumi/IP, 1034cm-2s-1114.11.94.00.59High energyMedium energyLow energyCurrent focus12Comparison of ELIC & eRHIC Ion beamsBottom line:ELICeRHICFactorsKEK BSuperBCoherent electron coolingYes(2005)Luminosity (1034)1/cm2/s~4~40.010.32.1>100Bunch repetitionMHz50015008.71338 to 115509476Bunch ChargenC1.70.5732321/19 to 1/573.2 / 2.34.6 / 2.6proton/bunch10101.10.3720201/19 to 1/572 / 1.56.2 / 3.5Bunch lengthmm55200491/40 to 1/1066Particle linear density1013 /m0.220.070.10.52 to 1/7 0.31 / 0.7Horizontal & vertical *mm5/255/255002505.9 / 1200.2 / 20Similar or smaller charge densityELICHigh repetition rateSmall bunch charge Short bunch length Small * eRHICLow repetition rate Super bunch charge Long bunch length, Large *VS.ELIC protons/bunch adjusted appropriatelyWith a smaller charge density, ELIC ion beam formation/cooling & dynamics should not be significantly different, if not better. 13Achieving High LuminosityELIC design luminosityL~ 1035 cm-2 s-1 for high energy (250 GeV x 10 GeV)L~ 4x1034 cm-2 s-1 for medium energy (60 GeV x 3 GeV)

ELIC luminosity ConceptsHigh bunch collision frequency (0.5 GHz, can be up to 1.5 GHz)Short ion bunches (z ~ 5 mm) (also much smaller bunch charge)Relative long bunch (comparing to beta-star) for very low ion energyStrong final focusing (*y ~ 5 mm)Large beam-beam parameters (~0.01/0.1, 0.025/.1 largest achieved)

Need electron cooling of ion beamsNeed crab crossing colliding beams

Large synchrotron tunes to suppress synchrotron-betatron resonances Equal (fractional) betatron phase advance between IPs 14Special Considerations for ELICElectron and ion beams are still quite differentElectron/positron beams have (radiation) damping, ion beams dont (achieving & preserving the beam quality)

Electron/positron beams have full energy injection, ion beams dont (forming a stored beam)

B-factories and EIC are also differentDistance between the final focusing magnets and a collision point in EIC is much larger than the B-factory, so chromaticity is huge.Electron CoolingSRF Linac, Staged CoolingChromatic Compensation153. Forming and Cooling of ELIC Ion Beams 16Length (m)Max. Energy (GeV/c) Cooling SchemeElectron Energy (MeV)ProcessSource/SRF linac0.2Full strippingPre-booster (Accumulator Ring)~1003DC electron0.1Stacking/accumulatingEnergy boostingLow energy ring (booster)~64012Electron(ERL)1.6 & 6.5 Fill ring/Energy boostingRF bunching (for collision)Medium energy ring~64060Electron (ERL)6.5 & 33Energy boostingRF bunching (for collision)sourceSRF Linacpre-booster-Accumulator ringBooster-low energy collider ringMedium energy ion collider ringTo high energy ion collider ring(for Full Energy EIC@JLab)coolingForming Ion Beams With CoolingMature or state-of-art, except this 17Stacking/cooling Ion Beam in Pre-booster/Accumulator Ring Accumulation of 1 A coasted beam in pre-booster Polarized p, d: stripping injection from negative ion source after linacOther ions: must use DC electron cooling

Multi-turn (~10) pulse injection from linacDamping/cooling of injected pulseAccumulating beam at space charge limited emittance

Accelerating to 3 GeV/c Fill large booster/low energy collider ring, then accelerate Switch to collider ring for energy booster, RF bunching and initial/continuous cooing CircumferenceM~80Arc radiusM~3Crossing straight lengthM2 x 15Energy/uGeV0.2 -0.4Electron current A1Electron energyMeV0.1 - 0.2Cooling time for protonsms10Stacked ion currentA1Norm. emit. After stackingm16An advanced conceptOvercoming space charge by accumulating low temperature, large area beam in ring with circular betatron modesPre-booster/Accumulator-ring An advanced stacking/cooling concept:Overcoming space charge, by accumulating low temperature, large area beam in ring with circular betatron modesInitial, Final & Continuous Cooling of Ion Beam in ELIC Collider RingGeV/MeVInitial Coolingafter boost & bunchingColliding ModeMomentumGeV/MeV12 / 6.5560 / 32.6760 / 32.67Beam currentA0.6 / 30.6 / 30.6/ 3Particles/Bunch10100.74 / 3.750.74 / 3.750.74 / 3.75Bunch lengthmm200 / 200 (coasted)10 / 30 5 / 15Momentum spread10-45 / 15 / 13 / 1Horizontal emittance, norm.m410.56Vertical emittance, norm.m410.11Lasletts tune shift (proton)0.0020.0060.1Cooling length/circumferencem/m15 / 64015 / 64015 / 640Cooling times921620.2IBS growth time (longitudinal)s0.9194. Conceptual Design of ERL Circulator Electron Cooler20Design Choice of ELIC e-CoolerDesign Requirements and ChallengesElectron beam currentup to 3 A CW beam at 499 MHz repetition rateAbout 5 nC bunch charge (possible space charge issue at low energy)About 260 kC/day from source/injector (state-of-art is 0.2 kC/day)

Energy of cooling electron beamup to 6.7 MeV for cooling low energy (12 GeV/c) ELICup to 33 MeV for cooling medium energy (60 GeV/c) ELIC

Beam powerNeed 100 to 400 MW for cooling 60 to 250 GeV/c ELIC

Design Choice: ERL Circulator Cooler (ERL-CC)Energy Recovery SRF Linac (ERL) to solve RF power problemCirculator-cooler ring for reducing average current from source/ERL

ERL-CC can provide the required high cooling current while consuming low RF power!

High Current & Lifetime of injectorHigh RF Power21ERL Based Circulator e-Coolerion bunchelectron bunchElectron circulator ringCooling sectionsolenoidFast beam kickerFast beam kickerSRF Linacdumpelectron injectorenergy recovery pathCirculator ring by-pass Path length adjustment(synchronization)22ELIC Cooler Design ParametersMax/min energy of e-beamMeV33/8Electrons/bunch10103.75bunch revolutions in CCR~300Current in CCR/ERLA3/0.01Bunch repetition in CCR/ERL MHz500/1.67CCR circumferencem80Cooling section lengthm15Circulation durations27Bunch lengthcm1-3Energy spread10-41-3Solenoid field in cooling section T2Beam radius in solenoidmm~1Beta-functionm0.5Thermal cyclotron radiusm2Beam radius at cathodemm3Solenoid field at cathodeKG2Lasletts tune shift @60 MeV0.07Longitudinal inter/intra beam heatings200Number of turns in circulator cooler ring is determined by degradation of electron beam quality caused by inter/intra beam heating up and space charge effect. Space charge effect could be a leading issue when electron beam energy is low.

It is estimated that beam quality (as well as cooling efficiency) is still good enough after 100 to 300 turns in circulator ring.

This leads directly to a 100 to 300 times saving of electron currents from the source/injector and ERL.235. Key Technologies and Critical R&D24Enabling Technologies and R&DMaking of a cooling electron beamA high bunch-charge and high repetition source/injectorEnergy recovery linac Fast kicker

Stability of cooling beam in a circulator ringSingle (electron) & coupled (electron-ion) instabilitiesLong term space charge effect & beam quality degradationBeam heat-up by IBS

Efficiency of cooling at medium ion energyCooling rate as a function of energy (state-of-art is 4 MeV at Fermilab)Cooling efficiency as a function of turns in the circulator ringStaged cooling (at injection & final energy, during collision)

New Concepts and SchemesFlat-to-round beam transform and reduction of space charge effect25Electron Source/InjectorELIC CCR driving injector10 mA@1.667 MHz, up to 33 (125) MeV energy 5 nC bunch charge, magnetizedChallengesSource life time: 0.86 kC/day (state-of-art is 0.2 kC/day) source R&D, & exploiting possibility of increasing evolutions in CCR Conceptual designHigh current/brightness source/injector is a key issue of ERL based light source applications, much R&D has been doneWe adopt light source injector as a baseline design of CCR driving injector Beam qualities should satisfy electron cooling requirements (based on previous computer simulations/optimization) Bunch compression may be needed. 300keV DC gunsolenoidsbuncherSRF modulesquads26Energy Recovery LinacSRF ERL based FEL High average power, up to14 kW (world record)mid-infrared spectral regionExtension to 250 nm in the UV is plannedPhotocathode DC injector, 10 mA class CW beam, sub-nC bunch chargeBeam energy up to 200 MeV, energy recoveryNext proposal: 100kW average power, 100 mA CW beam. ERL, nC-class bunch charge

JLab FEL ProgramEnergy RecoveryEnergyMeV80-200Charge/bunchpC135Average currentmA10Peak currentA270Beam powerMW2Energy spread%0.5Normalized emittancem-rad70% desirable

Positron Beam desirable

ELIC Design Goals36EIC@JLab: Low to Medium Energy

Three compact rings: 3 to 11 GeV electron Up to 12 GeV/c proton (worm) Up to 60 GeV/c proton (cold)EIC@JLAB: Low to Medium Energy

polarimetryELIC Ring-Ring Design FeaturesUnprecedented high luminosityElectron cooling is an essential part of ELICUp to four IPs (detectors) for high science productivityFigure-8 ion and lepton storage rings Ensure spin preservation and ease of spin manipulation No spin sensitivity to energy for all species.Present CEBAF injector meets storage-ring requirements12 GeV CEBAF can serve as a full energy injector to electron ringSimultaneous operation of collider & CEBAF fixed target program.Experiments with polarized positron beam are possible. 39Circulator Ring & SynchronizationTransverse focusing latticeSynchronizationBunch spacing depends on beam energy. There is about 1.8 mm difference when energy is boosted from 12 to 60 GeV/c A 10m dog-lag lattice or loops in arc must be introduced to ensure electron-ion synchronization at cooling section.

Maximum deflecting angle is 13, providing total 26cm path length adjustment. Bunch In/out kicking An ultra fast kicker switches electron bunches in and out circulator ring.

Deflecting angle should be large enough to separate outgoing bunches from circulating bunches and be further deflected by a dipole

Duration of kicking should be less than bunch spacing (~1/500MHz = 2 ns)energyMeV33Kick angle0.04Integrated BDLGM400Frequency BWGHz2Kicker aperturecm2Repetition RateMHz1.67PowerkW13Kicker Parameter40