ELIC : A High Luminosity Ring-Ring Electron-Ion Collider at CEBAF (and Positron-Ion Collision too) Yuhong Zhang For ELIC and MEIC Study Groups International Workshop on Positrons at Jefferson Lab, March 25-27, 2009

Topics Conceptual Design of ELIC Electron Polarization and Positron Beam Low to Medium Energy Collider and Staging of ELIC

Science Motivation A High Luminosity, High Energy Electron-Ion Collider: A New Experimental Quest to Study the Glue which Binds Us All How do we understand the visible matter in our universe in terms of the fundamental quarks and gluons of QCD? Explore the new QCD frontier: strong color fields in nuclei  How do the gluons contribute to the structure of the nucleus?  What are the properties of high density gluon matter?  How do fast quarks or gluons interact as they traverse nuclear matter? Precisely image the sea-quarks and gluons in the nucleon  How do the gluons & sea-quarks contribute to the spin structure of the nucleon?  What is the spatial distribution of the gluons and sea quarks in the nucleon?  How do hadronic final-states form in QCD?

 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 10 GeV electron on 250 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, all striped  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

ELIC Conceptual Design 3-10 GeV electrons 3-10 GeV positrons GeV protons GeV/n ions 12 GeV CEBAF Upgrade Green-field design of ion complex directly aimed at full exploitation of science program. Accumulator -cooler ring & prebooster

Figure-8 Ring Small Ring Large Ring Circumferencem Radiusm Widthm Lengthm Straightm Design is determined by Synchrotron radiation power Arc bending magnet strength Length of crossing straights Cost and fit to site Stacked vertically Ion ring electron ring Vertical crossing Interaction Point

 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 (positron) 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…) ELIC Baseline Design Choice

Achieving High Luminosity of ELIC ELIC design luminosity L~ 7.8 x cm -2 sec -2 (150 GeV protons x 7 GeV electrons) ELIC luminosity Concepts High bunch collision frequency (up to 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 colliding beams Large synchrotron tunes to suppress synch-betatron resonances Equal betatron phase advance (fractional) between IPs

ELIC New Nominal Parameters Beam energyGeV250/10150/7 100/5 Figure-8 ringkm2.5 Collision frequencyMHz499 Beam currentA0.22/ / /0.38 Particles/bunch /6.91.9/ /4.8 Energy spread /3 Bunch length, rmsmm5/5 Horizontal emit., norm.μmμm0.7/510.42/ /25.5 Vertical emit., norm.μmμm0.03/ / /2.6 Beta*mm5/5 Vert. b-b tune-shift0.01/0.1 Peak lumi. per IP10 34 cm -2 s Luminosity lifetimehours24 These parameters are derived assuming a 6 m detector space, 27 mrad crab crossing angle, 10 to 14 sigma radius for aperture, 10 kW/m synchrotron radiation power density limit

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 unclean per IP

ELIC Ring-Ring Design Features  Unprecedented high luminosity  Enabled by short ion bunches, low β*, high rep. rate, large synchrotron tune  Require crab crossing colliding beam  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 electron 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.

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 IRs removes spin resonances & energy sensitivity. spin rotator collision point spin rotator with 90º solenoid snake collision point spin rotator with 90º solenoid snake

Electron Polarization in ELIC (cont.) Matching at IP  vertical in arc, longitudinal at IP  Vertical crossing bend causing energy-dependent spin rotation  Spin rotators with vertical crossing bends of IP Spin rotators Solenoid spin rotator collision point Spin tune solenoid spin tune solenoid i i e e spin 90º Arc bending dipoles Solenoid spin rotator Vertical bending dipole Polarization lifetime Depolarization can reduce polarization (eg. spin flip, Sokolov-Ternov effect becomes depolarization) Replacement of electron/positron bunches as needed.

Positrons in CEBAF/ELIC Non-polarized positron bunches generated from modified electron injector through a converter Polarization realized through self-polarization at ring arcs (B. Wojtsekhowski)

Self-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

Low to Medium Electron-Ion Collider and Staging of ELIC: Motivations A medium energy EIC becomes the low energy ELIC ion complex Science Lower energies and symmetric kinematics provide new science Valence quarks/gluon structure beyond JLab 12 GeV Asymmetric sea for x ~ M  / M N GPDs, transverse spin at x ~ 0.1 Accelerator Advantages/Benefits Bring ion beams & associated technologies to JLab Have an early ring-ring collider at JLab Provides a test bed for new technologies required by ELIC Develop expertise and experience, acquire/train technical staff

MEIC & Staging of ELIC

Medium Energy EIC Features High luminosity collider L~ 2×10 33 cm -2 s -1 (9 GeV protons x 9 GeV electrons ) CM energy region from 10 GeV (5x5 GeV) to 22 GeV (11x11 GeV), and possibly reaching 35 GeV (30x10 GeV) High polarization for both electron and light ion beams Natural staging path to high energy ELIC Possibility of positron-ion collider in the low to medium energy region Possibility of electron-electron collider (7x7 GeV) using just small 300 m booster/collider ring

MEIC Parameter Table

Key R&D Issues Forming low energy ion beam and space charge effect Cooling of ion beams Beam-beam effect Dynamics of crab crossing beams and crab cavity development Traveling focusing scheme for MEIC

Summary The ELIC collider promises to accelerate a wide variety of polarized light ions and un-polarized heavy ions to high energy, to collider with polarized electron or positron beam enabling a unique physics program The final ELIC luminosity should comfortable exceed 1x10 34 cm -2 s -1 for electron(positron)-proton collisions Low/medium energy collider (MEIC) enables rich physics program not covered by high-energy collider. The initial design studies indicated that luminosity can exceed 1x10 33 cm -2 s -1. Conceptual design iteration is still in progress. Positron beam can also be used for additional positron-ion and electron- positron collision programs. Both electron and positron beam possess high (>80%) polarization. ELIC is the primary future goal of Jlab!

ELIC Study Group A. Afanasev, A. Bogacz, J. Benesch, 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, L. Harwood, A. Hutton, R. Kazimi, G. A. Krafft, R. Li, L. Merminga, J. Musson, M. Poelker, R. Rimmer, C. 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 MEIC Study Group S. Bogacz, Ya. Derbenev, R. Ent, G. Krafft, T. Horn, C. Hyde, A. Hutton, F. Klein, P. Nadel-Turonski, A. Thomas, C. Weiss, Y. Zhang