4 th EIC Workshop Hampton University, VA Richard Milner 1 Electron-Ion Collider Accelerator Workshop Summary and Outlook EIC biennial meeting Hampton, VA May 2008 R. Milner MIT Presentation based on work and contributions from L. Merminga, V. Litvinenko, V. Ptitsyn, C. Tschalär, E. Tsentalovich, Y. Zhang and their colleagues

4 th EIC Workshop Hampton University, VA Richard Milner 2 Concepts 20 – 100 GeV c.m. Energy eRHIC (BNL) Ring-ring Electron linac – ion ring ELIC (JLab) Ring-ring Polarized electron gun development Conclusions and outlook Outline

4 th EIC Workshop Hampton University, VA Richard Milner 3 Lepton Beam Facilities Quarks discovered Gluon momentum distribution measured Nucleon spin structure studied

4 th EIC Workshop Hampton University, VA Richard Milner 4 High luminosity – e-nucleon collisions/(cm 2 s) Polarized electron and positron beams Polarized nucleon (proton, deuteron, 3 He) beams Heavy ion beams (He to Uranium) Integrated luminosity: 50 fb -1 over about a decade Concepts: Ring-ring: e - / e + storage ring intersects ion storage ring Linac-ring: e - from ERL intersect ion storage ring Physics considerations

4 th EIC Workshop Hampton University, VA Richard Milner 5 Challenges and Limitations 1. Luminosity Ring-ring colliders Beam-beam tune shift ξ limited Empirical limits: ξ e ≤ 0.1 ; ξ i ≤ Linac- ring Colliders No electron tune shift limit (“once through” beam) Polarized electron current I e limited (polarized source) Ion emittance є i limited →cooling IP beam spot limited: є e,β e,β i

4 th EIC Workshop Hampton University, VA Richard Milner 6 2. Polarization Proton and 3 He beams from polarized sources Siberian snakes prevent depolarization during acceleration Ring-ring: Polarized electrons from laser driven GaAs source, low current (≤ 1mA ; 70-80% pol.) Non-depolarizing accelerator (linac, fig.-8 syncrotron) Stack and store in “spin transparent” ring Positrons from positron source (unpolarized) accelerate, stack into storage ring, self-polarize (Sokolov-Ternov) Linac-ring: Polarized electrons from ultra-high current GaAs source (≥ 100mA ; 70-80% pol.) Accelerate in ERL, intersect ion ring, recover beam energy (>1 GW) Challenges and Limitations (contd.)

4 th EIC Workshop Hampton University, VA Richard Milner 7 eRHIC ring-ring layout GeV polarized protons; GeV/n ions, He-U Polarized 3 He source 5-10 GeV electrons/positrons

4 th EIC Workshop Hampton University, VA Richard Milner 8 eRHIC (BNL) Ring-Ring EIC Electron/positron storage ring 5-10 GeV 1.2 km circumference (1/3 RHIC) optimized for: cost, synchrotron light power, e + polarization time “Superbends” for optimal emittance, pol. time at all energies Full-energy injection: recirculating linacs, or fig.-8 fast synchrotron; Positron source Polarized injection; optimized ring; top-off mode “Spin transparent” lattice, no vertical bends, spin resonances, ~ 5 min. self-polarization time Ring circumference adjustable to ion energy (RHIC orbital frequency) - “Trombone”

4 th EIC Workshop Hampton University, VA Richard Milner 9 eRHIC ring-ring parameters High energy setupLow energy setup pepe Energy, GeVGeV Number of bunches Bunch spacingns71 Particles / bunch Beam currentmA % normalized emittance  mm·mrad 155 Emittance  x nm Emittance  y nm  x* m  y* m Beam-beam parameter  x Beam-beam parameter  y Bunch length  z m Polarization% Peak Luminosity10 33 cm -2 s

4 th EIC Workshop Hampton University, VA Richard Milner 10 Status Lattice design concept → finalize spin tracking, beam-beam effects Injection concept → cost optimization Interaction point concept → optimize with detector designs No major R&D Solid cost estimate

4 th EIC Workshop Hampton University, VA Richard Milner 11 PHENIX STAR e-ion detector eRHIC eRHIC ERL-based Design Four recirculation passes Main ERL (1.9 GeV) Low energy recirculation pass Beam dump Electron source Possible locations for additional e-ion detectors

4 th EIC Workshop Hampton University, VA Richard Milner 12 Advantages & Challenges of ERL based eRHIC This scheme takes full advantage of cooling of the hadron beams Uses RHIC tunnel for the return passes. High luminosity up to cm -2 sec -1 Allows multiple IPs Allows higher range of CM-energies with high luminosities Full spin transparency at all energies No machine elements inside detector(s) No significant limitation on the lengths of detectors Energy of ERL is simply upgradeable Polarized electron gun requirements x100 to 1000 above existing Needs completion of e-cooling R&D (CeC and conventional)

4 th EIC Workshop Hampton University, VA Richard Milner ERL-based eRHIC Parameters High energy setupLow energy setup pepe Energy, GeV Number of bunches166 Bunch spacing, ns71 Bunch intensity, Beam current, mA Normalized 95% emittance, p mm.mrad Rms emittance, nm  *, x/y, cm Beam-beam parameters, x/y Rms bunch length, cm201 1 Polarization, % Peak Luminosity, 1.e33 cm -2 s -1 Aver.Luminosity, 1.e33 cm -2 s Luminosity integral /week, pb

4 th EIC Workshop Hampton University, VA Richard Milner 14 Main R&D Items Electron beam R&D for ERL-based design: –High intensity polarized electron source Development of large cathode guns with existing current densities ~ 50 mA/cm 2 with good cathode lifetime. –Energy recovery technology for high power beams Multicavity cryomodule development; BNL test ERL; loss protection; instabilities. –Development of compact recirculation loop magnets Design, build and test a prototype of a small gap magnet and its vacuum chamber. –Evaluation of electron-ion beam-beam effects, including the kink instability and e- beam disruption Main R&D items for ion beam: –Polarized 3 He production (EBIS) and acceleration –166 bunches General EIC R&D item: –Proof of principle of the coherent electron cooling

4 th EIC Workshop Hampton University, VA Richard Milner 15 ERL Test Facility 50 kW MHz system Cryo-module SRF cavity 1 MW MHz Klystron e - 2.5MeV Laser SC RF Gun e MeV Beam dump Cryo-module e MeV Merger system Return loop test of high current (~ 0.5 A) high brightness ERL operation 5-cell cavity SRF ERL test of high current beam stability issues highly flexible lattice 704 MHz SRF gun test Start of commissioning in D.Kayran’s talk at the Parallel session 5 cell SRF cavity arrived in BNL in March 2008.

4 th EIC Workshop Hampton University, VA Richard Milner 16 eRHIC Recirculation passes  Separate recirculation loops  Small aperture magnets  Low current, low power consumption  Minimized cost 5 mm 10 GeV (20 GeV) 8.1 GeV (16.1 GeV) 6.2 GeV (12.2 GeV) 4.3 GeV (8.3 GeV) Common vacuum chamber Approved LDRD for the compact magnet development

4 th EIC Workshop Hampton University, VA Richard Milner 17 Interaction Region Design Present IR design features:  No crossing angle at the IP  Detector integrated dipole: dipole field superimposed on detector solenoid.  No parasitic collisions.  Round beam collision geometry with matched sizes of electron and ion beams.  Synchrotron radiation emitted by electrons does not hit surfaces in the detector region.  Blue ion ring and electron ring magnets are warm.  First quadrupoles (electron beam) are at 3m from the IP  Yellow ion ring makes 3m vertical excursion. (Blue) ion ring magnets (Red) electron beam magnets (Yellow) ion ring magnets Detector HERA type half quadrupole used for proton beam focusing C.Montag’s talk at the Parallel session

4 th EIC Workshop Hampton University, VA Richard Milner 18 Novel features Coherent electron cooling - the key for many novel features in eRHIC Choosing the focus: ERL for electrons –Advantages and challenges of ERL driver spin transparency –R&D items for ERL-based eRHIC eRHIC is the future of RHIC: eRHIC staging –Energy challenge –20 GeV e x 325 GeV p and 30 GeV e x 125 GeV/n heavy ions –Loss on synchrotron radiation –Polarized beam current Luminosity challenge: –Can eRHIC deliver cm -2 sec -1 luminosity? –High rep-rate, crab cavities, coating RHIC arc vacuum chambers and more Other novelties and oldies –Low (350 MHz) RF frequency, no 3 rd harmonic, higher real estate gradient –Small magnets for re-circulating passes, resistive-wall losses –e-lens or fast a quads for matching ERL beam –compact and flexible separators and combiners –Possibility of eRHIC II up-grade V. Litvinenko

4 th EIC Workshop Hampton University, VA Richard Milner 19 Stage I -RHIC with ERL inside RHIC tunnel Medium energy EIC with 2 GeV IP2 Asymmetric detector 0.95 GeV SRF linac 100 MeV ERL 2 GeV e-beam pass through the detector 3 vertically separated passes at 0.1 GeV, 1.05 and 2 GeV Don’t forget the polarized electrons! V. Litvinenko Lively discussion on Tuesday afternoon Many issues raised Consideration will continue

4 th EIC Workshop Hampton University, VA Richard Milner 20 Proof of Principle test for Coherent Electron Cooling IR-2 in RHIC

4 th EIC Workshop Hampton University, VA Richard Milner 21 eRHIC polarized electron gun (linac-ring) Extremely high current demand !!! I(average) ~ 500 mA I(peak) ~ 200 A High polarization → strained GaAs → QE ~ 0.1% Average laser power ~ 800 W Such lasers do not exist. Possible solutions: a) array of diode lasers b) dedicated FEL – almost unlimited laser power, tunable

4 th EIC Workshop Hampton University, VA Richard Milner 22 Damage location Electrons follow electrical field lines, but ions have different trajectory. Usually, they tend to damage central area of the cathode. Laser spot Cathode Damage groove JLAB data Ring-like cathodes ? E. Tsentalovich, MIT-Bates

4 th EIC Workshop Hampton University, VA Richard Milner 23 Axicon Beam Profile

4 th EIC Workshop Hampton University, VA Richard Milner 24 QE change (small spot in the corner) Run C

4 th EIC Workshop Hampton University, VA Richard Milner 25 Lifetime

4 th EIC Workshop Hampton University, VA Richard Milner 26 Cathode Cooling Water in Water out HV Laser Manipulator Cathode Crystal

4 th EIC Workshop Hampton University, VA Richard Milner 27 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

4 th EIC Workshop Hampton University, VA Richard Milner 28 High Luminosity with ELIC ELIC design luminosity L~ 7.7 x cm -2 sec -2 (150 GeV protons x 7 GeV electrons) ELIC luminosity design considerations 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 synch-betatron resonances Equidistant phase advance between four IPs

4 th EIC Workshop Hampton University, VA Richard Milner 29 ELIC Design Parameters IonMax Energy (E i,max ) Luminosit y/n (7GeVxE i,m ax ) Luminosity /n (3GeVxE i,ma x /5) (GeV/n)10 34 cm -2 s cm -2 s -1 Proton Deuter on H He He C Ca Pb e/p e/A

4 th EIC Workshop Hampton University, VA Richard Milner 30 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.  Present CEBAF gun/injector meets storage-ring requirements  The 12 GeV CEBAF can serve as a full energy injector to electron ring  Simultaneous operation of collider and CEBAF fixed target program.  Experiments with polarized positron beam are possible.

4 th EIC Workshop Hampton University, VA Richard Milner 31 Figure-8 ring z [cm] x [cm] 362 m 152 m 80 deg Figure-8 Ring - Footprint Small Ring Large Ring Circumferencem Radiusm Widthm Lengthm Straightm Ion ring electron ring Vertical crossing Interaction Point Design is determined by Synchrotron radiation power Arc bending magnet strength Length of crossing straights Cost and fit to site Stacked vertically

4 th EIC Workshop Hampton University, VA Richard Milner 32 Electron polarization in ELIC Producing at source  Polarized electron source of CEBAF  Preserved in acceleration at recirculated CEBAF Linac  Injected into Figure-8 ring with vertical polarization Maintaining in the ring  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 snake solenoid spin rotator collision point spin tune solenoid i i e e spin 90º Electron/positron polarization parameters * Time can be shortened using high field wigglers. ** Ideal max equilibrium polarization is 92.4%. Degradation is due to radiation in spin rotators.

4 th EIC Workshop Hampton University, VA Richard Milner 33 ELIC R&D Requirements To achieve luminosity at cm -2 sec -1 and up  High energy electron cooling To achieve luminosity at ~ cm -2 sec -1  Crab cavity  Stability of intense ion beams  Beam-beam interactions  Detector R&D for high repetition rate (1.5 GHz)

4 th EIC Workshop Hampton University, VA Richard Milner 34 ELIC R&D: Electron Cooling  Issue To suppress IBS, reduce emittances, provide short ion bunches. Effective for heavy ions (higher cooling rate), difficult for protons.  State-of-Art Fermilab e-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 Non-polarized source (present/under developing) can deliver nC bunch SRF ERL able to provide high average current CW beam Circulator cooler for reducing average current from source/ERL Electron bunches circulate 100 times in a ring while cooling ion beam

4 th EIC Workshop Hampton University, VA Richard Milner 35 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 ELIC crab cavity Requirement 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

4 th EIC Workshop Hampton University, VA Richard Milner 36 Comparison of GeV E CM Colliders Projected performance eRHIC ELIC Ring-ringLinac-ring Electron energy GeV Pol. Positron energy GeV Unpol. Positron energy GeV Proton energy GeV Ion energy GeV/n Luminosity /cm 2 s Collision rate MHz14(28) 1500

4 th EIC Workshop Hampton University, VA Richard Milner 37 Required R&D eRHIC ELIC Ring-ring Linac-ring Ring-ring p/ion-beam Raise bunch rep rate to 14 (28) MHz polarization > 70% Injector, Fig.8 lattice beam current 0.5A Electron cooling Stochastic cooling for є ≤ 4 nm Coher. el. Cooling? OSC for 250 GeV? Crab crossing cavities Electron cooling to 225 GeV Coherent el. cooling? OSC ? e-beamSpin trackingPol. source 260mA ERL 2.6 GW beam 15 km recirculator Spin tracking Vertical bens Interaction Region Integrating IP and detector design “close-packed” Low – β IP region 1500 MHz concept ? pulse rate C. Tschalär (MIT-Bates)

4 th EIC Workshop Hampton University, VA Richard Milner 38 Conclusions Promising and exciting developments world-wide of high-luminosity polarized electron-ion colliders. U.S. nuclear physics accelerator physics capabilities very well matched to needs NSAC Long-Range Plan recommends accelerator R&D funding for eRHIC and ELIC. Intensive EIC R&D effort required to realize aim of single EIC machine design by ~ Continued cooperation and careful coordination essential to get there.

4 th EIC Workshop Hampton University, VA Richard Milner 39 Perspective To get to next base in realizing EIC, we need to be in position to request a green light at the next long range plan ~ This requires a strong science case, a single machine design and firm cost. This will be needed in ~ 2012, four years from now! We have a unified scientific collaboration working on the science case. Could we have a unified EIC accelerator design group to come to a single machine design?