Thomas Jefferson National Accelerator Facility Page 1 Design Status of ELIC G. A. Krafft for ELIC Design Team EIC Collaboration meeting Hampton, May 19-23, 2008

Thomas Jefferson National Accelerator Facility Page 2 ELIC Study Group & Collaborators ELIC Study Group & Collaborators A. Afanasev, A. Bogacz, P. Brindza, A. Bruell, L. Cardman, Y. Chao, S. Chattopadhyay, E. Chudakov, P. Degtiarenko, J. Delayen, Ya. Derbenev, R. Ent, P. Evtushenko, A. Freyberger, D. Gaskell, J. Grames, A. Hutton, R. Kazimi, G. A. Krafft, R. Li, L. Merminga, J. Musson, M. Poelker, R. Rimmer, Chaivat Tengsirivattana, A. Thomas, H. Wang, C. Weiss, B. Wojtsekhowski, B. Yunn, Y. Zhang - Jefferson Laboratory W. Fischer, C. Montag - Brookhaven National Laboratory V. Danilov - Oak Ridge National Laboratory V. Dudnikov - Brookhaven Technology Group P. Ostroumov - Argonne National Laboratory V. Derenchuk - Indiana University Cyclotron Facility A. Belov - Institute of Nuclear Research, Moscow, Russia V. Shemelin - Cornell University

Thomas Jefferson National Accelerator Facility Page 3Outline  ELIC: An Electron-Ion Collider at CEBAF  Basic parameters  List of recent developments/specs  Some R&D Issues  Forming Ion Beams  Electron Cooling  Crab Crossing  Summary

Thomas Jefferson National Accelerator Facility Page 4  Energy Center-of-mass energy between 20 GeV and 90 GeV energy asymmetry of ~ 10,  3 GeV electron on 30 GeV proton/15 GeV/n ion up to 9 GeV electron on 225 GeV proton/100 GeV/n ion  Luminosity up to cm -2 s -1 per interaction point  Ion Species Polarized H, D, 3 He, possibly Li Up to heavy ion A = 208, fully stripped  Polarization Longitudinal polarization at the IP for both beams Transverse polarization of ions Spin-flip of both beams All polarizations >70% desirable  Positron Beam desirable ELIC Design Goals

Thomas Jefferson National Accelerator Facility Page 5  Energy Recovery Linac-Storage-Ring (ERL-R)  ERL with Circulator Ring – Storage Ring (CR-R)  Back to Ring-Ring (R-R) – by taking CEBAF advantage as full energy polarized injector  Challenge: high current polarized electron source ERL-Ring: 2.5 A Circulator ring: 20 mA State-of-art: 0.1 mA  12 GeV CEBAF Upgrade polarized source/injector already meets beam requirement of ring-ring design  CEBAF-based R-R design still preserves high luminosity, high polarization (+polarized positrons…) Evolution of the Principal Scheme

Thomas Jefferson National Accelerator Facility Page 6 ELIC Conceptual Design 3-9 GeV electrons 3-9 GeV positrons GeV protons GeV/n ions Green-field design of ion complex directly aimed at full exploitation of science program. prebooster 12 GeV CEBAF Upgrade

Thomas Jefferson National Accelerator Facility Page 7 ELIC Ring-Ring Design Features  Unprecedented high luminosity  Enabled by short ion bunches, low β*, high rep. rate  Large synchrotron tune  Require crab crossing  Electron cooling is an essential part of ELIC  Four IPs (detectors) for high science productivity  “Figure-8” ion and lepton storage rings  Ensure spin preservation and ease of spin manipulation  No spin sensitivity to energy for all species.

Thomas Jefferson National Accelerator Facility Page 8 Achieving High Luminosity of ELIC ELIC design luminosity L~ 7.8 x cm -2 sec -1 (150 GeV protons x 7 GeV electrons) ELIC luminosity Concepts High bunch collision frequency (f=1.5 GHz) Short ion bunches (σ z ~ 5 mm) Super strong final focusing (β* ~ 5 mm) Large beam-beam parameters (0.01/0.086 per IP, 0.025/0.1 largest achieved) Need High energy electron cooling of ion beams Need crab crossing Large synchrotron tunes to suppress synchro-betatron resonances Equidistant phase advance between four IPs

Thomas Jefferson National Accelerator Facility Page 9 ELIC (e/p) Design Parameters

Thomas Jefferson National Accelerator Facility Page 10 ELIC (e/A) Design Parameters IonMax Energy (E i,max ) Luminosity / n (7 GeV x E i,max ) Luminosity / n (3 GeV x E i,max /5) (GeV/nucleon)10 34 cm -2 s cm -2 s -1 Proton Deuteron H He He C Ca Pb * Luminosity is given per nuclean per IP

Thomas Jefferson National Accelerator Facility Page 11 Electron Polarization in ELIC Produced at electron source  Polarized electron source of CEBAF  Preserved in acceleration at recirculated CEBAF Linac  Injected into Figure-8 ring with vertical polarization Maintained in the ring (to be reported by Pavel Chevtsov)  High polarization in the ring by electron self-polarization  SC solenoids at IPs removes spin resonances and energy sensitivity. spin rotator collision point spin rotator with 90º solenoid snake collision point spin rotator with 90º solenoid snake

Thomas Jefferson National Accelerator Facility Page 12 Electron Polarization in ELIC (cont.) * Time can be shortened using high field wigglers. ** Ideal max equilibrium polarization is 92.4%. Degradation is due to radiation in spin rotators. Electron/positron polarization parameters

Thomas Jefferson National Accelerator Facility Page 13 Positrons in ELIC Non-polarized positron bunches generated from modified electron injector through a converter Polarization realized through self-polarization at ring arcs

Thomas Jefferson National Accelerator Facility Page 14 Recent Developments/specs Rings Lattice design update for higher energies Interaction Region update (reduced crab…) (to be reported by Alex Bogacz, Paul Brindza) Chromaticity Correction (to be reported by Hisham Sayed) Beam-beam study/simulation (to be reported by Yuhong Zhang) IBS Study (to be reported by Chaivat Tengsirivattana) Stochastic Cooling/Stacking all species ion beams Electron Cooling specs/advances (cool protons…)

Thomas Jefferson National Accelerator Facility Page 15 Figure-8 Ion Ring (half)  Lattice at 225 GeV 42 full cells 11 empty cells 3 transition cells phase adv./cell (  x = 60 0,  y =60 0 ) Arc dipoles: : $Lb=170 cm $B=73.4 kG $rho =102 m Arc quadrupoles: $Lb=100 cm $G= 10.4 kG/cm Minimum dispersion (periodic) lattice Dispersion suppression via ‘missing’ dipoles (geometrical) Uniform periodicity of Twiss functions (chromatic cancellations) Dispersion pattern optimized for chromaticity compensation with sextupole families ( 3 × 60 0 = )

Thomas Jefferson National Accelerator Facility Page 16 Figure-8 Electron Ring (half)  Lattice at 9 GeV 54 superperiods (3 cells/superperiod) 83 empty cells Arc dipoles: : $Lb=100 cm $B=3.2 kG $rho =76 m Arc quadrupoles: $Lb=60 cm $G= 4.1 kG/cm 83 empty cells phase adv./cell (  x = 120 0,  y =120 0 ) ‘Minimized emittance dilution due to quantum excitations Limited synchrotron radiated power ( 14.3MW 1.85A ) Quasi isochronous arc to alleviate bunch lengthening (  ~10 -5 ) Dispersion pattern optimized for chromaticity compensation with sextupole families

Thomas Jefferson National Accelerator Facility Page 17 Figure-8 Rings – Vertical ‘Stacking’

Thomas Jefferson National Accelerator Facility Page 18 IP Magnet Layout and Beam Envelopes IP 10cm 1.8m 20.8kG/cm 3m 12KG/cm 0.5m 3.2kG/cm 0.6m 2.55kG/cm 8.4cm 22.2 mrad 1.27 deg 0.2m Vertical intercept 4.5m 3.8m 14.4cm16.2cm Vertical intercept 22.9cm Vertical intercept ion 5mm 4mm electron β* OK

Thomas Jefferson National Accelerator Facility Page 19 Optimization IP configuration optimization “Lambertson”-type final focusing quad  angle reduction: 100 mrad  22 mrad IR Final Quad 10 cm 14cm 3cm 1.8m 20.8kG/cm 4.6cm 8.6cm Electron (9GeV) Proton (225GeV) 2.4cm 10cm 2.4cm 3cm 4.8cm 1 st SC focusing quad for ion Paul Brindza

Thomas Jefferson National Accelerator Facility Page 20 Lambertson Magnet Design magnetic Field in cold yoke around electron pass. Cross section of quad with beam passing through

Thomas Jefferson National Accelerator Facility Page 21 β Chromaticity correction with sextupoles β- functions around the interaction region, the green arrows represent the sextupoles pairs. The phase advance, showing the –I transformation between the sextupoles pairs

Thomas Jefferson National Accelerator Facility Page 22 Local Correction of Transfer Map Initial phase space phase space after one pass through 2 IR’s No correction phase space after one pass through 2 IR’s after correction Vertical plane Δp/p~ Y Y` Phase space in both transverse planes before and after applying the sextupoles

Thomas Jefferson National Accelerator Facility Page 23 Beam-Beam Effect in ELIC Transverse beam-beam force –Highly nonlinear forces –Produce transverse kicks between colliding bunches Beam-beam effect –Can cause size/emittance growth or blowup –Can induce coherent beam-beam instabilities –Can decrease luminosity and its lifetime Impact of ELIC IP design –Highly asymmetric colliding beams (9 GeV/2.5 A on 225 GeV/1 A) –Four IPs and Figure-8 rings –Strong final focusing (beta* 5 mm) –Short bunch length (5 mm) –Employs crab cavity –vertical b-b tune shifts are 0.087/0.01 –Very large electron synchrotron tune (0.25) due to strong RF focusing –Equal betatron phase advance (fractional part) between IPs Electron bunch Proton bunch IP Electron bunch proton bunch x y One slice from each of opposite beams Beam-beam force

Thomas Jefferson National Accelerator Facility Page 24 Simulation Model –Single/multiple IPs, head-on collisions –Strong-strong self consistent Particle-in-Cell codes, developed by J. Qiang of LBNL –Ideal rings for electrons & protons, including radiation damping & quantum excitations for electrons Scope and Limitations –10k ~ 30k turns for a typical simulation run –0.05 ~ 0.15 s of storing time (12 damping times)  reveals short-time dynamics with accuracy  can’t predict long term (>min) dynamics Simulation results –Saturated at 70% of peak luminosity, 5.8·10 34 cm -2 s -1, the loss is mostly due to the hour-glass effect –Luminosity increase as electron current linearly (up to 6.5 A), coherent instability observed at 7.5 A –Luminosity increase as proton current first linearly then slow down due to nonlinear b-b effect, electron beam vertical size/emittance blowup rapidly –Simulations with 4 IPs and 12-bunch/beam showed stable luminosity and bunch sizes after one damping time, situated luminosity is 5.5·10 34 cm -2 s -1 per IP, very small loss from single IP and Single bunch operation Supported by SciDAC Beam-Beam Simulations (cont.) 4IPs, 12 bunches/beam

Thomas Jefferson National Accelerator Facility Page 25 ELIC Additional Key Issues To achieve luminosity at cm -2 sec -1 and up  High energy electron cooling To achieve luminosity at ~ cm -2 sec -1  Circulator Cooling  Crab cavity  Stability of intense ion beams  Detector R&D for high repetition rate (1.5 GHz)

Thomas Jefferson National Accelerator Facility Page 26 ELIC R&D: Forming Intense Ion Beam Use stochastic cooling for stacking and pre-cooling  Stacking/accumulation process  Multi-turn (10 – 20) injection from SRF linac to pre-booster  Damping of injected beam  Accumulation of 1 A coasted beam at space charge limited emittence  RF bunching/acceleration  Accelerating beam to 3 GeV, then inject into large booster  Ion space charge effect dominates at low energy region  Transverse pre-cooling of coasted beam in collider ring (30 GeV) ParameterUnitValue Beam EnergyMeV200 Momentum Spread%1 Pulse current from linacmA2 Cooling times4 Accumulated currentA0.7 Stacking cycle durationMin2 Beam emittance, norm.μm12 Laslett tune shift0.03 Transverse stochastic cooling of coasted proton beam after injection in collider ring ParameterUnitValue Beam EnergyGeV30 Momentum Spread%0.5 CurrentA1 Freq. bandwidth of amplifiersGHz5 Minimal cooling timeMin8 Initial transverse emittanceμm16 IBS equilibrium transverse emitt.μm0.1 Laslett tune shift at equilibrium0.04 Stacking proton beam in pre- booster with stochastic cooling

Thomas Jefferson National Accelerator Facility Page 27 Injector and ERL for Electron Cooling ELIC CCR driving injector  30 MHz, up to 125 MeV energy, 1 nC bunch charge, magnetized Challenges  Source life time: 2.6 kC/day (state-of-art is 0.2 kC/day)  source R&D, & exploiting possibility of increasing evolutions in CCR  High beam power: 3.75 MW  Energy Recovery Conceptual design  High current/brightness source/injector is a key issue of ERL based light source applications, much R&D has been done  We adopt light source injector as initial baseline design of ELIC CCR driving injector Beam qualities should satisfy electron cooling requirements (based on previous computer simulations/optimization) 500keV DC gun solenoids buncher SRF modules quads

Thomas Jefferson National Accelerator Facility Page 28 Electron Cooling with a Circulator Ring. Effective for heavy ions (higher cooling rate), difficult for protons.  State-of-Art Fermilab electron cooling demonstration (4.34 MeV, 0.5 A DC) Feasibility of EC with bunched beams remains to be demonstrated  ELIC Circulator Cooler 3 A CW electron beam, up to 125 MeV SRF ERL provides 30 mA CW beam Circulator cooler for reducing average current from source/ERL Electron bunches circulate 100 times in a ring while cooling ion beam Fast (300 ps) kicker operating at 15 MHz rep. rate to inject/eject bunches into/out circulator-cooler ring

Thomas Jefferson National Accelerator Facility Page 29 Fast Kicker for Circulator Cooling Ring Sub-ns pulses of 20 kW and 15 MHz are needed to insert/extract individual bunches. RF chirp techniques hold the best promise of generating ultra-short pulses. State-of-Art pulse systems are able to produce ~2 ns, 11 kW RF pulses at a 12 MHz repetition rate. This is very close to our requirement, and appears to be technically achievable. Helically-corrugated waveguide (HCW) exhibits dispersive qualities, and serves to further compress the output pulse without excessive loss. Powers ranging from up10 kW have been created with such a device. Estimated parameters for the kicker Beam energyMeV125 Kick angle Integrated BdLGM1.25 Frequency BWGHz2 Kicker ApertureCm2 Peak kicker fieldG3 Kicker Repetition Rate MHz15 Peak power/cellKW10 Average power/cellW15 Number of cells20 kicker Collaborative development plans include studies of HCW, optimization of chirp techniques, and generation of 1-2 kW peak output powers as proof of concept. Kicker cavity design will be considered

Thomas Jefferson National Accelerator Facility Page 30 Cooling Time and Ion Equilibrium * max.amplitude ** norm.,rms Cooling rates and equilibrium of proton beam ParameterUnitValue EnergyGeV/Me V 30/15225/123 Particles/bunch10 0.2/1 Initial energy spread* /31/2 Bunch length*cm20/31 Proton emittance, norm* mm 11 Cooling timemin11 Equilibrium emittance, ** mm 1/11/0.04 Equilibrium bunch length**cm20.5 Cooling time at equilibriummin Laslett’s tune shift (equil.) Multi-stage cooling scenario: 1 st stage: longitudinal cooling at injection energy (after transverses stochastic cooling) 2 nd stage: initial cooling after acceleration to high energy 3 rd stage: continuous cooling in collider mode

Thomas Jefferson National Accelerator Facility Page 31 ELIC R&D: Crab Crossing  High repetition rate requires crab crossing to avoid parasitic beam- beam interaction  Crab cavities needed to restore head-on collision & avoid luminosity reduction  Minimizing crossing angle reduces crab cavity challenges & required R&D State-of-art: KEKB Squashed Mode Crossing angle = 2 x 11 mrad V kick =1.4 MV, E sp = 21 MV/m

Thomas Jefferson National Accelerator Facility Page 32 Crab cavity development Electron: 1.2 MV – within state of art (KEK, single Cell, 1.8 MV) Ion: 24 MV (Integrated B field on axis 180G/4m) Crab Crossing R&D program –Understand gradient limit and packing factor –Multi-cell SRF crab cavity design capable for high current operation. –Phase and amplitude stability requirements –Beam dynamics study with crab crossing ELIC R&D: Crab Crossing (cont.)

Thomas Jefferson National Accelerator Facility Page 33 ELIC at JLab Site 920 m 360 m WM Symantec SURA City of NN VA State City of NN JLab/DOE

Thomas Jefferson National Accelerator Facility Page 34 Summary The ELIC Design Team has continued to make progress on the ELIC design  More complete beam optics  Chromaticity correction  Crab crossing and crab cavity reduction  Beam-beam effects The ELIC design has evolved  CW electron cooling with circulator ring  Ions up to lead now in design We continue design advances/optimization  Resolve (design) high rep.rate issue (high lumi vs detector)  Minimize quantum depolarization of electrons (spin matching)  Study ion stability

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