Conceptual Design of A High Luminosity Medium Energy Electron-Ion Collider at JLab

1. Conceptual Design of A High Luminosity Medium Energy Electron-Ion Collider at JLab Yuhong Zhang Jefferson Lab For the JLab EIC Study Group Workshop on Partonic Transverse Momentum in Hadrons: Quark Spin-Orbit Correlations and Quark-Gluon Interactions, March 12-13, 2010 Duke University

2. Outline • Introduction • Design Considerations Advantages, Opportunities, and Design Choices • Machine Design • Near Term Goal • Energy Dependence of MEIC Luminosity • Summary

3. Introduction • JLab has been developing a preliminary conceptual design of an ElC based on the CEBAF recirculating SRF linac for nearly a decade. • Based on the requirements of the future nuclear science program, design efforts have been focused on achieving: • Ultra high luminosity (up to 1035) in multiple detectors • Very high polarization (>80%) for both electrons & light ions • ELIC design takes advantages of the existing high repetition, high polarization CW electron beam from CEBAF, a new ion complex and new collider rings. • We have made significant progress on design optimization • Investigating a medium-energy (60 x 11 GeV2) EIC as a tentative compromise between science, technology and project cost • A well-defined upgrade capability is maintained • High luminosity & high polarization continue to be the design drivers

4. 2. Design Considerations

5. ELIC Design Goal • Energy Wide CM energy range between 10 GeV and 100 GeV • Low energy: 3 to 10 GeV e on 3 to 12 GeV/c p (and ion) • Medium energy: up to 11 GeV e on 60 GeV p or 30 GeV/n ion and for future upgrade • High energy: up to 10 GeV e on 250 GeV p or 100 GeV/n ion • Luminosity • 1033 up to 1035 cm-2s-1per collision point • Multiple interaction points • Ion Species • Polarized H, D, 3He, possibly Li • Up to heavy ion A = 208, all stripped • Polarization • Longitudinal at the IP for both beams, transverse for ions • Spin-flip of both beams • All polarizations >70% desirable • Positron Beamdesirable

6. ELIC Design Considerations • Project goals • Luminosity, polarization, energy range, ion species, etc. • Cost (construction/operation), technology innovation • Future upgrade capability • Advantages (and a great opportunity) • 12 GeV CEBAF • High polarization high repetition CW electron beam • Full energy injection • New Ion Complex • High repetition ion beams with short bunch length • New collider rings • Figure-8 for high polarization

7. ELIC Design Choices Achieving high luminosity • Very high bunch repetition frequency (1.5 GHz) • Very small β* to reach very small spot sizes at collision points • Short bunch length (σz~ β*) to avoid luminosity loss due to hour-glass effect (unless other mitigation schemes used) • Relatively small bunch charge for making short bunch possible • High bunch repetition restores high average current and luminosity This luminosity concept has been tested at two B-factories very successfully, reaching luminosity above 1034 1/cm2/s • eRHIC • Low repetition rate • Super bunch charge • Long bunch length • Largeβ* • ELIC • High repetition rate • Small bunch charge • Short bunch length • Small β* • VS.

8. ELIC Design Choices (cont.) • Ring-ring vs. Linac(ERL)-ring • Linac-ring option requires very high average current polarized electron sources (100 to 10000 times state-of-art) • Linac-ring option does not help ELIC which already employs high repetition electron and ion beams  ring-ring collider • Ensuring high polarization for both electron beam and light ion beams  Figure-8 shape rings • Simple solution to preserve full ion polarization by avoiding spin resonances during acceleration • Energy independence of spin tune • g-2 is small for deuterons; a figure-8 ring is the only practical way to arrange for longitudinal spin polarization at interaction point

9. 3. Machine Design

10. MEIC: A Medium Energy EIC • Three compact rings: • 3 to 11 GeV electron • Up to 12 GeV/c proton (warm) • Up to 60 GeV/c proton (cold)

11. MEIC: Layout

12. ELIC: High Energy Upgrade Serves as a large booster to the full energy collider ring p Ion Sources SRF Linac prebooster p p MEIC collider ring ELIC collider ring e e e injector 12 GeV CEBAF Electron ring Interaction Point Ion ring Vertical crossing

13. Achieving High Luminosity MEIC design luminosity up to 1034 cm-2 s-1 Luminosity concepts • High bunch collision frequency (1.5 GHz) • Very small bunch charge (<3x1010 particles per bunch) • Very small beam spot size at collision points • Short ion bunches Keys to implementing these concepts • Making very short ion bunches with small emittance • SRF ion linac and (staged) electron cooling • Crab crossing for colliding beams Additional ideas/concepts • Relatively long bunch (comparing to β*) for very low ion energy with traveling focusing • Large synchrotron tunes to suppress synchrotron-betatron resonances • Equal (fractional) phase advance between IPs

14. ELIC Ring-Ring Design Features • Ultra high luminosity • Polarized electrons and polarized light ions • Up to three IPs (detectors) for high science productivity • “Figure-8” ion and lepton storage rings • Ensures spin preservation and ease of spin manipulation • Avoids energy-dependent spin sensitivity for all species • Present CEBAF injector meets MEIC requirements • 12 GeV CEBAF can serve as a full energy injector • Simultaneous operation of collider & CEBAF fixed target program if required • Experiments with polarized positron beam would be possible

15. 4. Near Term Goal

16. ELIC Critical Accelerator R&D • We have identified the following critical R&D for MEIC • Interaction region design with chromatic compensation • Electron cooling • Crab crossing and crab cavity • Forming high intensity, low energy ion beam • Beam-beam effect • Beam polarization and tracking • Traveling focusing for very low energy ion beam

17. Charge to JLab Machine Study Group Report of the last EICC Advisory Committee meeting Highest priority • Design of JLab EIC • High current (e.g. 50 mA) polarized electron gun • Demonstration of high energy – high current recirculation ERL • Beam-beam simulations for EIC • Polarized 3He production and acceleration • Coherent electron cooling • Mont’s Slide at Stony Brook EICC Meeting (01/11/2010) It is clearly important to produce a complete Jefferson Lab machine design over the next 9 months ---This will be our main thrusts for R&D support

18. Motivations • We are charged to deliver a detailed accelerator design of the medium energy ELIC in the next 6 months (by the next meeting of the EIC Advisory Committee), a specific requirement from the last advisory committee meeting and JLab management. • Scaling down ELIC machine parameters for the near term to make this delivering possible • Choosing key parameters within the state-of-art of existing colliders • Utilizing as many existing technologies and experiences of other colliders as possible • Keeping minimum (absolute required) R&D issues for this version • Key accelerator R&D required for forward-looking machine parameters will be pursued as a long term goal for reaching higher luminosity and better collider performance • Such R&D issues, though challenging, offer very high pay-off • Normally need long time and large resources • We are cautiously confident we can achieve these R&D goals

19. Near Term (Scaled Down) Parameters Luminosity can reach up to 0.5 ~ 1 x 1034 /s/cm2 around 60x5 GeV2

20. MEIC Machine Design Path Forward @ Full Speed • Design “contract” : Scaled down parameters (Feb. 2010) • For the near term, up to the next EICC AC meeting (Sept. 2010) • Collider Design Review Retreat (March 2, 2010) • Design Week (March 4, 5 & 7, 2010) • Identify major components and determine level of details • Farm out tasks and set up collaborations • Produce a design manual • Next level design (By June 1, 2010) • Complete the optics design (base for many simulations) • Conceptual design of major components (and parameter) • Design modification with input from User Workshops • JLab internal reviews (around June 1, 2010) • Accelerator design review (3 to 5 expert panel) • Machine cost review • First round detailed studies with simulations (By Sept. 1, 2010) • Present a reasonablely detailed design in the next EICC AC meeting • Produce an intermediate design report • Advance to the next design iteration

21. 5. Energy Dependence of MEIC Luminosity

22. MEIC Energy Range • Charges of user workshops • What nuclear science within your topic of interest can quantitatively be accomplished with the foreseen parameters? • What nuclear science within your topic of interest could quantitatively be accomplished with a change in the parameter space given, e.g. by a change in energies, a change in luminosity, a change in detector space. • MEIC design is optimized with present selected energy range • No limit/natural cut-off from a machine design perspective • Compact collider rings (and low project cost) • Easier on most accelerator issues such as electron cooling • Harder on a few accelerator issues such as colliding bunch synchronization • To assist physics discussion, we will present a semi-quantitative dependence of beam energy on MEIC luminosity

23. MEIC Luminosity: Energy Dependence • MEIC luminosity is limited by • Electron beam current  synchrotron radiation ~ Neγ4/ρ (radiation power, emittance degradation) • Proton/ion beam current  space charge effect ~ Ni/γ2 (emittance growth, tune-shift/instabilities) • (Vertical) beam-beam tune-shift (bad collisions) ~ 1/γ • Design limits (based on experience) • Electron beam SR power density: ≤ 20 kW/m • Ion beam space charge tune-shift: ≤ 0.1 • (Vertical) beam-beam tune-shift: ≤ 0.015 (proton), ≤ 0.1 (electron) • Given an energy range, MEIC collider ring is optimized with • Synchrotron radiation  prefers a large ring (for more arc bends) • Space charge effect of i-beam  prefers a small ring circumference • Multi IPs and other components require long straight sections

24. MLIC Luminosity with a Compact Collider Ring • Ring circumference (660 m) was derived as a minimum arc length (minimum cost) required to accommodate 60 GeV protons in a Figure-8 ring • Back-of-envelope estimations, using three main design limits, just as an illustration, more complicated beam dynamics issues omitted • Electron beam current decreases very fast as a function of energy (inverse fourth power) Just an illustration

25. MEIC Luminosity with a Medium Size Collider Ring • Back-of-envelope calculation, based on three main parameter limits • Luminosity of 60 GeV protons in 1 km ring is lower than that in 0.6 km ring, since space charge effect is more server in a large ring • Luminosity of 100 GeV protons is much better since space charge effect is reduced with higher energy Just an illustration

26. Compact Ring vs. Medium Size Ring • The compact MEIC ring (660 m) has a minimum arc (150 m x 2) for accommodating 60 GeV protons (8 T peak SC dipole field) • The medium size ring (in this illustration) has two 300 m arcs, nearly doubling the arc of the compact ring while two straights (150 m x 2) remain the same. Large arcs also can accommodate higher proton energy (up to100 GeV) • Ring circumference affects MEIC collider luminosity, and shifts the luminosity optimized energy range. • Doubling arc of the collider rings requires relatively small increase of MEIC machine cost (longer tunnel and more magnets), roughly 20%. MEIC has a high fixed cost for construction of ion complex front end (ion linac and boosters).

27. Summary • ELIC is designed to collide a wide variety of polarized light ions and unpolarized heavy ions with polarized electrons (or positrons). • The conceptual design takes advantages of a polarized high repetition CW electron beam from CEBAF, a new ion storage complex and new collider rings, provides opportunity of ultra high luminosity of electron-ion collisions and high beam polarization. • Present ELIC version covers an energy range up to s~1000 GeV2 with luminosity up 1034 cm-2s-1. An upgrade path to higher energies (up to 250 GeV protons and associated energy for ions) has been developed which should provide luminosity close to 1035 cm-2s-1 • MEIC design is very flexible in matching the physics requirements on energy range. The associated machine cost adjustment is moderate. • A scaled down version of MEIC parameters has been developed recently as the near term design goal, using as much as possible state-of-art technologies, thus requiring minimum R&D efforts. It was estimated that MEIC with this scaled down parameters is still able to deliver maximum luminosity above 5x1033 cm-2s-1.

28. ELIC Study Group A. Afanasev, A. Bogacz, J. Benesch, P. Brindza, A. Bruell, L. Cardman, Y. Chao, S. Chattopadhyay, E. Chudakov, S. De Silva, P. Degtiarenko, J. Delayen, Ya. Derbenev, R. Ent, P. Evtushenko, A. Freyberger, D. Gaskell, J. Grames, L. Harwood, T. Horn, A. Hutton, C. Hyde, R. Kazimi, F. Klein, G. Krafft, R. Li, L. Merminga, V. Morozov, J. Musson, A. Nadel-Turonski, M. Poelker, R. Rimmer, Y. Roblin, H. Seyed, M. Spata, C. Tengsirivattana, B. Terzic, A. Thomas, M. Tiefenback, H. Wang, C. Weiss, B. Wojtsekhowski, B. Yunn, Y. Zhang - Jefferson Laboratory staffs and users W. Fischer, C. Montag - Brookhaven National Laboratory D. Barber - DESY V. Danilov - Oak Ridge National Laboratory V. Dudnikov, R. Johnson - Muons. Inc. S.. Manikonda, P. Ostroumov - Argonne National Laboratory B. Erdelyi - Northern Illinois University V. Derenchuk - Indiana University Cyclotron Facility A. Belov - Institute of Nuclear Research, Moscow, Russia

29. ELIC Main Parameters Low energy High energy Medium energy Presented at the last EIC Collaboration Advisory Committee meeting, Nov. 2-3, Jefferson Lab