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?
ELIC Design Goals
 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 Conceptual Design
Green-field design of ion
complex directly aimed at
full exploitation of science
program.
12 GeV
CEBAF
Upgrade
Figure-8 Ring
Stacked vertically
Interaction Point
electron ring
Design is determined by
• Synchrotron radiation power
• Arc bending magnet strength
Ion ring
• Length of crossing straights
Vertical crossing
• Cost and fit to site
Figure-8 Ring Footprint
-40000
20000
z [cm]
10000
90 deg
0
-30000
-20000
-10000
180 m
0
-10000
-20000
10000
x [cm]
20000
30000
Small
Ring
Large
Ring
Circumference
m
2100
2500
Radius
m
152
180
Width
m
304
360
Length
m
776
920
Straight
m
362
430
40000
ELIC Baseline Design Choice
 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…)
Achieving High Luminosity of ELIC
ELIC 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 Parameters
Beam energy
GeV
Figure-8 ring
km
2.5
MHz
499
Collision frequency
250/10
150/7
100/5
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
Beam current
5/5
Vert. b-b tune-shift
Peak lumi. per IP
Luminosity lifetime
0.01/0.1
1034 cm-2s-1
hours
2.9
1.2
1.1
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
6.7
3H+1
50
7.8
6.7
3He+2
100
3.9
3.3
4He+2
75
3.9
3.3
12C+6
75
1.3
1.1
40Ca+20
75
0.4
0.4
208Pb+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 rotator
spin rotator
spin rotator with 90º
solenoid snake
collision point
collision point
collision point
spin rotator
collision point
spin rotator with 90º
solenoid snake
spin rotator
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
Solenoid
spin rotator
Vertical
bending
dipole
Vertical
bending
dipole
Spin tune
solenoid
e
Arc bending
dipoles
spin tune
solenoid
collision
point
90º 90º
Vertical
bending
dipole
e
spin tune
solenoid
collision
point
i
Solenoid
spin rotator
Spin rotators
spin tune
solenoid
Vertical
bending
dipole
Arc bending
dipoles
Polarization lifetime
• Depolarization can reduce polarization
(eg. spin flip, Sokolov-Ternov effect becomes depolarization)
• Replacement of electron/positron bunches as needed.
i
Positrons in CEBAF/ELIC
converter
10 MeV
e+
5 MeV
Polarized
source
e-
Longitudinal
emittance
filter
15 MeV
dipole
Unpolarized
source
e-
15 MeV
Transverse
emittance
filter
e-
ee
e+
e+
115 MeV
During positron production:
- Polarized source is off
- Dipoles are turned on
e-
e-e+
dipole
dipole
(B. Wojtsekhowski)
• Non-polarized positron bunches generated from modified electron
injector through a converter
• Polarization realized through self-polarization at ring arcs
Self-Polarization in ELIC (cont.)
Electron/positron polarization parameters
Parameter
Energy
Beam cross bend at IP
Radiation damping time
Accumulation time
Self-polarization time*
Equilibrium polarization, max**
Beam run time
Unit
GeV
mrad
ms
s
h
%
h
3
70
50
15
20
92
5
7
12
4
3.6
1
10
2
91.5
90
Lifetime
* Time can be shortened using high field wigglers.
** Ideal max equilibrium polarization is 92.4%. Degradation is due
to radiation in spin rotators.
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 / 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 electronpositron 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