ELIC: A High Luminosity Ring-Ring Electron-Ion Collider

at CEBAF(and Positron-Ion Collision too)

Yuhong ZhangFor 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 MotivationA 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 • 1033 up to 1035 cm-2 s-1 per interaction point

Ion Species• Polarized H, D, 3He, 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

30-250 GeV protons

15-100 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

-20000

-10000

0

10000

20000

-40000 -30000 -20000 -10000 0 10000 20000 30000 40000

z [cm]

x [cm]430 m 180 m

90 deg

Figure-8 Ring FootprintSmall Ring

Large Ring

Circumference m 2100 2500

Radius m 152 180

Width m 304 360

Length m 776 920

Straight m 362 430

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 ELICELIC design luminosity

L~ 7.8 x 1034 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 (σz ~ 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 ParametersBeam energy GeV 250/10 150/7 100/5

Figure-8 ring km 2.5

Collision frequency MHz 499

Beam current A 0.22/0.55 0.15/0.33 0.19 /0.38

Particles/bunch 109 2.7/6.9 1.9/4.1 2.4/4.8

Energy spread 10-4 3/3

Bunch length, rms mm 5/5

Horizontal emit., norm. μm 0.7/51 0.42/35.6 0.28/25.5

Vertical emit., norm. μm 0.03/2.0 0.017/1.42 0.028/2.6

Beta* mm 5/5

Vert. b-b tune-shift 0.01/0.1

Peak lumi. per IP 1034 cm-2s-1 2.9 1.2 1.1

Luminosity lifetime hours 24

• 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

Ion Max Energy(Ei,max)

Luminosity / n (7 GeV x Ei,max)

Luminosity / n(3 GeV x Ei,max/5)

(GeV/nucleon) 1034 cm-2 s-1 1033 cm-2 s-1

Proton 150 7.8 6.7

Deuteron 75 7.8 6.73H+1 50 7.8 6.7

3He+2 100 3.9 3.34He+2 75 3.9 3.312C+6 75 1.3 1.1

40Ca+20 75 0.4 0.4208Pb+82 59 0.1 0.1

* 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 rotatorspin rotator

spin rotatorspin rotator

collision point

spin rotator with 90º solenoid snake

collision point

collision point

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

collision point

Spin tune solenoid

spin tune solenoid spin tune

solenoid

spin tune solenoid

ii

ee

spin

90º 90º

Arc bending dipoles

Arc bending dipoles

Solenoid spin rotator

Vertical bending dipole

Vertical bending dipole

Vertical bending dipole

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

115 MeV

converter

e-

e-15 MeV

5 MeVe+

e-

e-

e-

e+

10 MeV

15 MeV

e-

e+e+

Polarized source

dipole

Transverse emittance

filter Longitudinal emittance

filter

dipole dipole

e-

e-

e+

e-

e-

-e

e+

Unpolarized source

During positron production: - Polarized source is off - Dipoles are turned on

(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.

Parameter Unit Energy GeV 3 5 7 Beam cross bend at IP mrad 70 Radiation damping time ms 50 12 4 Accumulation time s 15 3.6 1 Self-polarization time* h 20 10 2 Equilibrium polarization, max** % 92 91.5 90 Beam run time h Lifetime

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

ScienceLower energies and symmetric kinematics provide new science• Valence quarks/gluon structure beyond JLab 12 GeV• Asymmetric sea for x ~ M / MN

• 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~ 2×1033 cm-2s-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 1x1034 cm-2s-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 1x1033 cm-2s-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 LaboratoryV. Danilov - Oak Ridge National Laboratory V. Dudnikov - Brookhaven Technology GroupP. Ostroumov - Argonne National LaboratoryV. Derenchuk - Indiana University Cyclotron FacilityA. 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