MEIC Accelerator Design
Yuhong Zhang
MEIC Ion Complex Design Workshop
Jan. 27 & 28, 2011
Outline
• Introduction
• Luminosity Concept and Design Choices
• Machine Design Status
• Ion Complex
• Summary
Introduction
Future Nuclear Science
Program at JLab
• JLab has been developing a preliminary design of an EIC based on the
CEBAF recirculating SRF linac for nearly a decade
• Requirements of the future nuclear science program drives JLab EIC
design efforts to focus on achieving
• ultra high luminosity per detector (up to 1035) in multiple detectors
• very high polarization (>80%) for both electrons & light ions
• Over the last 12 months, we have made significant progress on design
optimization
• The primary focus is on a Medium-energy Electron Ion Collider (
the best compromise between science, technology and project cost
– Energy range is up to 60 GeV ions and 11 GeV electrons
• A well-defined upgrade capability to higher energies is maintained
• High luminosity & high polarization continue to be the design drivers
) as
Accelerator R&D EICAC Recommendations
• Highest priority
– Design of JLab EIC
–
–
–
–
–
EICAC Report, Feb. 2010
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
• High priority, but could wait until decision made
– Compact loop magnets
– Electron cooling for JLab concepts
– Traveling focusing scheme (it is not clear what the loss in performance
would be if it doesn’t work; it is not a show stopper if it doesn’t)
– Development of eRHIC-type SRF cavities
• Medium priority
– Crab cavities
– ERL technology development at JLab
Short Term Design “Contract” & Technical Strategy
• The accelerator team is committed to produce a complete MEIC design
with sufficient technical details according to recommendations of EICAC
• The short term design “contract” for an EIC with the following features
•
•
•
•
CM energy up to 51 GeV: up to 11 GeV electron, 60(30) GeV proton (ion)
Upgrade option to high energy
3 IPs, at least 2 of them are available for medium energy collisions
One full acceptance detector, the other detector can be optimized for high luminosity
with a large acceptance
• Luminosity up to 1034 cm-2s-1 per collision point
• High polarization for both electron and light ion beams
This “contract” will be renewed every 6 to 12 months with major revision
• We are taking a conservative technical position by limiting many MEIC
design parameters within or close to the present state-of-art in order to
minimize technical uncertainty
• Maximum peak field of ion superconducting dipole is 6 T
• Maximum synchrotron radiation power density is 20 kW/m
• Maximum betatron value at FF quad is 2.5 km
Highlights of Last Twelve Months of
MEIC Design Activities
• Continuing design optimization
– Tuning main machine parameters to serve better the science program
– Now aim for high luminosity AND large detector acceptance
– Simplified design and reduced R&D requirements
• Focused on detailed design of major components
–
–
–
–
Completed baseline design of two collider rings
Completed 1st design of Figure-8 pre-booster
Completed beam polarization scheme with universal electron spin rotators
Updated IR optics design
• Continued work on critical R&D
– Beam-beam simulations
– Nonlinear beam dynamics and instabilities
– Chromatic corrections
Luminosity Concept
and Design Choices
B-Factories As Role Models
PEPII & KEKB
• Highly asymmetric lepton-lepton colliders
(energies and beam currents)
• Pioneered a class of new technologies
(crab crossing with crab cavities, etc.)
• Highly succeed interaction region design
• The present world record of high
luminosity, already above 2x1034 /cm2/s
Super-B and SuperKEKB
• Upgrades are planed and accelerator R&D
are currently underway
• Aiming for luminosity above 1036 /cm2/s
• More technology innovations, most
importantly, crab-waist scheme for
interaction region
Comparison between e+e- Collider &
Traditional Hadron-Hadron Colliders
Key factors for high luminosities in B-factories
•
•
•
•
•
Very high bunch repetition (~ 500 MHz), thus very large number of bunches
Very small β* (~6 mm) to reach very small spot sizes at collision points
Very short bunch (σz~β*) to avoid luminosity loss due to hour-glass effect
Small bunch charge (~5x109) for making very short bunch possible
High bunch repetition restores high average beam current and luminosity
KEK-B & PEPII
Traditional
hadron collider
A factor of
Bunch repetition frequency
~ 500 MHz
5 to 10 MHz
50
Number of bunches in ring
> 2000
A few and up to 100
20 to 50
Particles per Bunch
Bunch length
Beta-star
Beam-beam tune-shift
Luminosity per IP
A few of 10
10
A few of 10
11
1/10
0.5 cm
70 to 100 cm
1/100
0.5 to 1 cm
30 to 100 cm
1/100
0.1
0.025
4
2x10
34
Up to a few of 10
32
50 to 100
Collider Luminosity & Beam-Beam Tune-shift
• Luminosity of a collider with head-on
collisions is
L
fc Ne N p
4 x* *y
assuming colliding bunches are short,
and their spot sizes are matched at
collision points.
• Presumably, a higher luminosity could
be achieved with
– High collision frequency
– High bunch charges
– Small spot sizes at collision points
• These parameters are usually limited
by collective beam effects. The most
important one is beam-beam effect
• The beam-beam tune-shift
 y, p 
rp N e
p
 y*, p
2 *y ( x*   *y )
• The luminosity can be rewritten as
 p N p f c y , p
 *y
L
(1  * )
*
2rp  y , p
x
• High beam-beam tune-shift means high
luminosity
• However, achievable beam-beam tuneshifts are limited by many factors, such
as nonlinear b-b forces, nonlinear
dynamics in the storage rings, etc
• Typical achieved maximum values of
beam-beam tune-shift
– Electron ~ 0.15
– Proton
~ 0.03 to 0.04
Optimization of Collider Luminosity
• Route for high luminosities
– Highest allowable beam-beam tune-shifts (in y-direction for flat beam)
• limited by nonlinear beam-beam forces and others
– Highest allowable beam current (bunch charge x repetition rate)
• electron current limited by synchrotron radiation
• proton current limited by space charge tune-shifts and many others
– Smallest beta star
• limited by bunch length (hour-glass effect)
• Unless special IR designs (traveling focusing, crab waist)
• High beam current considerations
– High bunch charge/low frequency vs. low bunch charge/high frequency
Large bunch charge is unfavorable to single bunch instabilities,
space charge tune-shift, and small beta-star
• High aspect rate
make interaction region design much easier
MEIC Design Choice
• A great opportunity at JLab
– Electron beam: 12 GeV CEBAF delivers a high repetition (up to 1.5 GHz) high
polarized CW beam, can be used as a full energy injector
– Proton/ion beam: a new green-field ion complex, can be specially designed to
match ion beams to the electron beam
 We should be able to duplicate the great
success of e+e- colliders in the EIC!
• MEIC colliding ion beams
–
–
–
–
–
High bunch repetition rate, up to 1.5 GHz
Small proton bunch charge, a few of 109,
Short bunch length, down to 1 cm,
Small linear charge density
Small beta-star, same to bunch length
comparing to eRHIC





115 times higher
57 times smaller
5 times smaller
7 times smaller
25 times smaller
Why Linac(ERL)-Ring is Not Good for MEIC?
• Advantage of an linac-ring collider
electron beam can tolerate much larger beam-beam disruption, therefore, one
can achieve a high luminosity in principle.
 y ,e 
re N p
e
 y*,e
re N p

2 *y ( x*   *y ) 2 e y (1   x* /  *y )
D y,x 
2 re N p z
 e *y ( x*   *y )
• Reducing proton spot sizes (emittances)
Needs strong cooling, could be very difficult to achieve
• Increasing proton bunch charge
Single bunch effects such as space charge tune shift could get much worse
• Longer bunch length
High charge density may be mitigated by increasing the bunch length,
Beta-star has to be increase to avoid the hour-glass effect,
Large beta-star reduce some of the luminosity gain of the linac-ring approach.
• The linac-ring approach could provide some advantages, especially for
traditional regime of collider design, when bunch is long anyway, and
beam current is low, therefore increasing of proton bunch charge is
possible. However, a very strong cooling is required. That is not MEIC.
Technical Challenges for ERL-Ring Design
• The JLab EIC design started with an ERL-Ring collider initially.
• It is a natural approach since JLab already has a CEBAF recirculated linac,
and is also a world leader in ERL technology
• We had recognized the high current polarized electron sources issue, about
2000 times beyond start-of-art, associated to a ERL-ring design approach.
• A circulator-ring had been suggested to the ERL-Ring design of ELIC to
reduce the electron current from polarized gun by a factor of 100. However,
the remaining electron source R&D is still challenging
• JLab eventually abandoned the circulator-ring based ERL-ring approach for
MEIC because
– It requires a significant R&D on polarized electron source
– It requires development of high-energy, high-current, multiple-pass ERL and
circulator ring technologies
– It requires a proof of new (linac-ring) collider concept
– It doesn’t provide a significant increase of luminosity for MEIC design
parameter regime
Current MEIC Design
 Energy
MEIC Design Goals
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-2 s-1 per 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 of ions
• Spin-flip of both beams
• All polarizations >70% desirable
 Positron Beam desirable
MEIC : 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)
MEIC : Detailed Layout
warm ring
cold ring
ELIC: High Energy & Staging
Straight section
Serves as a large booster to
the full energy collider ring
Arc
Stage
Max. Energy
(GeV/c)
p
e
Medium
96
11
High
250
20
Ring Size
(m)
Ring Type
IP #
p
e
1000
Cold
Warm
3
2500
Cold
Warm
4
MEIC Design Parameters For
a Full-Acceptance Detector
Proton
Electron
Beam energy
GeV
60
5
Collision frequency
GHz
0.75
0.75
Particles per bunch
1010
0.416
2.5
Beam Current
A
0.5
3
Polarization
%
>70
~ 80
Energy spread
10-4
~3
7.1
RMS bunch length
mm
10
7.5
Horizontal emittance, normalized
µm rad
0.35
54
Vertical emittance, normalized
µm rad
0.07
11
Horizontal β*
cm
10
10
Vertical β*
cm
2
2
Vertical beam-beam tune shift
0.014
0.03
Laslett tune shift
0.07
Very small
7
3.5
Distance from IP to 1st FF quad
Luminosity per IP, 1033
m
cm-2s-1
5.6
MEIC Design Parameters For
a High-Luminosity Detector
Proton
Electron
Beam energy
GeV
60
5
Collision frequency
GHz
0.75
0.75
Particles per bunch
1010
0.416
2.5
Beam Current
A
1
3
Polarization
%
>70
~ 80
Energy spread
10-4
~3
7.1
RMS bunch length
mm
10
7.5
Horizontal emittance, normalized
µm rad
0.35
54
Vertical emittance, normalized
µm rad
0.07
11
Horizontal β*
cm
4
4
Vertical β*
cm
0.8
0.8
Vertical beam-beam tune shift
0.007
0.03
Laslett tune shift
0.014
Very small
4.5
3.5
Distance from IP to 1st FF quad
Luminosity per IP, 1033
m
cm-2s-1
14.2 (20)
MEIC & ELIC: Luminosity Vs. CM Energy
https://eic.jlab.org/wiki/index.php/Machine_designs
MEIC Ring-Ring Design Features
• Ultra high luminosity
• Polarized electrons and polarized light ions
• Up to 3 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
possible
• Experiments with polarized positron beam would be possible
Figure-8 Ion Rings
• Figure-8 optimum for polarized ion beams
– 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
– No technical disadvantages
– Only disadvantage is small cost increase
MEIC Ion Beams &
Ion Complex
Design Goal of MEIC Ion Complex
• Developing a conceptual design for a technical sound and cost
effective ion complex for the MEIC project
• The MEIC ion complex should be able to deliver a required colliding
ion beam for a successful operation of a medium energy EIC
– Polarized light ions (>75% in the collider) & un-polarized heavy ions
– Colliding beam current up to 1 A (~5x109 protons/bunch)
– Compatible with a bunch repetition frequency of 750 MHz
• Capable of being upgraded to 1.5 GHz
– RMS bunch length of 5 to 10 mm for colliding beams
– Emittance at injection of <5 mm-mrad
– Round beams at injection
– Compatible with a luminosity lifetime of ~10 hours Highly polarized light ions
and un-polarized heavy ions
Difference Between B-factories & MEIC
• Leptons and ion beams are still quite different
– Lepton beams have (radiation) damping, ion beams don’t
issue: achieving & preserving the beam quality
Staged electron cooling
– Leptons beams have full energy injection, ion beams don’t
issue: how to form a high intensity short bunch ion beam
SRF Linac, electron cooling
during accumulation
• B-factories and EIC are also different
– Distance between the final focusing magnets and a collision point in
EIC is much larger than the B-factories, so chromaticity is huge.
Chromatic compensation
MEIC Ion Complex As We Envisioned
Cooling
(for accumulation)
source
SRF
Linac
Large boosterLow energy
collider ring
Pre-boosterAccumulator ring
Maximum
Energy (GeV/c)
Cooling
(for collision beam)
Cooling
cooling
Medium energy
collider ring
Processes
Source/SRF linac
0.2
Full stripping
Prebooster/Accumulator-Ring
3 to 5
DC electron
Stacking/accumulating
Large booster
Low energy ring
12 to 20
Electron
(for collision)
RF bunching (for collision)
Medium energy ring
60 to 100
Electron
RF bunching (for collision)
Electron Cooling of Colliding Ion Beams
10 m
injector
SRF ERL
dumper
• Electron cooler is located at center
for figure-8 ring
• Compact cooler design
• Doubled length of cooling section,
therefore the cooling rate
• Reduces number of circulation
Horizontal
longitudinal
Cooling
(Derbenev)
IBS
(Piwinski)
IBS
(Derbenev)
s
s
s
7.8
86
66
51
MEIC Study Group
A. Afanasev, S. Ahmed, A. Bogacz, J. Benesch, P. Brindza, A. Bruell, L. Cardman, J.
Chen, Y. Chao, S. Chattopadhyay, E. Chudakov, 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. A. Krafft, R. Li, F. Marhauser, L.
Merminga, V. Morozov, J. Musson, P. Nadel-Turonski, F. Pilat, M. Poelker, R.
Rimmer, T. Satogata, M. Spata, B. Terzic, M. Tiefenback, A. Thomas, H. Wang, C.
Weiss, B. Wojtsekhowski, B. Yunn, Y. Zhang - Jefferson Laboratory staff and users
W. Fischer, C. Montag - Brookhaven National Laboratory
M. Sullivan - SLAC
D. Barber - DESY
V. Danilov - Oak Ridge National Laboratory
V. Dudnikov - Brookhaven Technology Group
P. Ostroumov, S. Manshikonda - Argonne National Laboratory
B. Erdelyi - Northern Illinois University and Argonne National Laboratory
H. Sayed – Old Domino University
Backup Slides
Summary
• MEIC is optimized to collide a wide variety of polarized light ions and
unpolarized heavy ions with polarized electrons (or positrons)
• MEIC covers an energy range matched to the science program proposed by
the JLab nuclear physics community (~4200 GeV2) with luminosity up to
3x1034 cm-2s-1
• An upgrade path to higher energies (250x10 GeV2), has been developed
which should provide luminosity of close to 1035 cm-2s-1
• The design is based on a Figure-8 ring for optimum polarization, and an ion
beam with high repetition rate, small emittance and short bunch length
• Electron cooling is absolutely essential for cooling & bunching the ion beam
• We have identified the critical accelerator R&D topics for MEIC, and are
presently working on them
• Our present MEIC design is mature and flexible, able to accommodate
revisions in design specifications and advances in accelerator R&D
MEIC is the future of Nuclear Physics at Jefferson Lab
Collaborations Established
• Interaction region design M. Sullivan (SLAC)
• ELIC ion complex front end
P. Ostroumov (ANL)
(From source up to injection into collider ring)
– Ion source
– SRF Linac
V. Dudnikov, R. Johnson (Muons, Inc)
V. Danilov (ORNL)
P. Ostroumov (ANL), B. Erdelyi (NIU)
• Chromatic compensation
A. Netepenko (Fermilab)
• Beam-beam simulation
J. Qiang (LBNL)
• Electron cooling simulation
D. Bruhwiler (Tech X)
• Electron spin tracking
D. Barber (DESY)
Future Accelerator R&D
We will concentrate R&D efforts on the most critical tasks
Focal Point 1:
Sub tasks:
Complete Electron and Ion Ring designs
Finalize chromaticity correction of electron ring and
complete particle tracking
Insert interaction region optics in ion ring
Start chromaticity correction of ion ring, followed by particle
tracking
Focal Point 2:
Sub tasks:
IR design and feasibility studies of advanced IR schemes
Develop a complete IR design
Beam dynamics with crab crossing
Traveling final focusing and/or crab waist?
Future Accelerator R&D
Focal Point 3:
Sub tasks:
Forming high-intensity short-bunch ion beams & cooling
Ion bunch dynamics and space charge effects (simulations)
Electron cooling dynamics (simulations)
Dynamics of cooling electron bunch in ERL circulator ring
Led by Peter Ostroumov (ANL)
Focal Point 4:
Sub tasks:
Beam-beam interaction
Include crab crossing and/or space charge
Include multiple bunches and interaction points
Additional design and R&D studies:
Electron spin tracking, ion source development
Transfer line design
MEIC Luminosity: 1 km Ring, 8 Tesla
Assuming maximum peak field of ion magnet 8 Tesla,
highest proton energy can be 96 GeV
Large acceptance
High luminosity
Proton
Energy
Electron
Energy
S
CM
Energy
Luminosity
(L=7m, β*=2cm)
Luminosity
(L=4.5m, β*=8mm)
GeV
GeV
GeV2
GeV
1033 cm-2s-1
1033 cm-2s-1
96
3
1152
34.0
12.5
30.4
96
4
1536
39.2
10.0
25.0
96
5
1920
43.8
6.6
16.4
96
6
2340
48.0
2.6
6.6
96
7
2688
51.9
1.2
2.9
96
9
3456
55.8
0.3
0.74
96
11
4224
65.0
0.1
0.2
ELIC Luminosity: 2.5 km Ring, 8 Tesla
Proton
Energy
Electron
Energy
s
CM
Energy
Large acceptance
Luminosity
(L=7m, β*=2cm)
High luminosity
Luminosity
(L=4.5m, β*=8mm)
GeV
GeV
GeV2
GeV
1033 cm-2s-1
1033 cm-2s-1
250
3
3000
54.8
8.3
20.7
250
5
5000
70.7
18.5
46.4
250
6
6000
77.5
20.2
50.5
250
7
7000
83.7
20.7
64.5
250
8
8000
89.5
18.9
57.6
250
9
9000
94.9
15.8
39.6
250
11
11000
104.9
7.5
18.8
250
20
20000
141.4
3.1
6.2
Proton
Energy
Electron
Energy
Ring
Circumference
Luminosity
(L=7m, β*=2cm)
Luminosity
(L=4.5m, β*=8mm)
GeV
GeV
m
1033 cm-2s-1
1033 cm-2s-1
30
3
2500/2500
1.1
2.6
30
3
1000/2500
2.1
4.9
• The second option is using 1 km medium-energy ion ring for higher proton beam
current at 30 GeV protons for lowering the space charge tune-shift
MEIC Adopts Proven Luminosity Approaches
High luminosity at B factories comes from:
•
•
•
•
•
Very small β* (~6 mm) to reach very small spot sizes at collision points
Very short bunch length (σz~ β*) to avoid hour-glass effect
Very small bunch charge which makes very short bunch possible
High bunch repetition rate restores high average current and luminosity
Synchrotron radiation damping
 KEK-B and PEPII already over 21034 cm-2 s-1
KEK B
MEIC
Repetition rate
MHz
509
1497
Particles per bunch
1010
3.3/1.4
0.42/1.25
Beam current
A
1.2/1.8
1/3
Bunch length
cm
0.6
1/0.75
Horizontal & vertical β*
cm
56/0.56
10/2 (4/0.8)
Luminosity per IP, 1033
cm-2s-1
20
5.6 (14.2)
JLab believes these ideas should be replicated in the
next electron-ion collider
( ): high-luminosity detector
MEIC Design Details
Our design is mature, having addressed (in various degrees of
detail) the following important aspects of MEIC:
•
•
•
•
•
•
•
•
•
•
•
•
•
Electron and ion beam optics
Electron cooling
ERL circulator cooler
Electron polarization, universal spin rotator
Beam synchronization
Electron beam time structure & RF system
IR design and optics
Beam-beam simulations
Tracking and dynamical aperture
Beam stability
Forming the high-intensity ion beam: ion SRF linac, ion pre-booster
Synchrotron radiation background
Detector design
Figure-8 Electron Collider Ring
MEIC: Reaching Down To Low Energy
electron ring
(1 km )
low energy IP
A compact (~150 m) ring
dedicated to low energy ion
Compact
low energy
ion ring
Medium energy IP
• Space charge effect is the leading factor for limiting ion beam
current and luminosity
• A small ring with one IP, two snake, injection/ejection and RF
• Ion energy range from 12 GeV to 20 GeV
• Increasing ion current by a factor of 6, thus luminosity by 600%
Electron Collider Ring
Electron ring is designed in a modular way
• two long (240 m) straights (for two IPs)
• two short (20 m) straights (for RF module), dispersion free
• four identical (120º) quarter arcs, made of 135º phase advance FODO cell with
dispersion suppressing
• four 50 m long electron spin rotator blocks
One quarter arc
OptiM - MAIN: - C:\Working\ELIC\MEIC\Optics\Electron Ring_1000\quart_arc_in_per.opt
0.15
15
Mon Jun 28 19:23:50 2010
1.1 m
1.25 T (2.14 deg)
Quad
0.4 m
9 kG/cm
DISP_X&Y[m]
Dipole
0
Field
0
Length
BETA_X&Y[m]
135º FODO Cell for arc
0
Cell
BETA_X
BETA_Y
DISP_X
DISP_Y
4m
2 dis. sup.
cells
0.15
2 dis. sup.
cells
26 FODO cells
OptiM - MAIN: - C:\Working\ELIC\MEIC\Optics\Electron Ring_1000\cell_in.opt
0.5
Mon Jun 28 19:11:11 2010
OptiM - MAIN: - C:\Working\ELIC\MEIC\Optics\Electron Ring_1000\cell_in.opt
15
Mon Jun 28 19:07:51 2010
120
Figure-8 Collider Ring - Footprint
phase adv/cell: 1350
10000
PHASE_X&Y
DISP_X&Y[m]
BETA_X&Y[m]
8000
6000
4000
2000
x [cm]
-20000
0
-15000
-10000
-5000
-2000
0
5000
10000
15000
20000
0
BETA_X
BETA_Y
DISP_X
DISP_Y
4.03051
0
0
0
-4000
0
Q_X
Q_Y
4.03051
-6000
-8000
-10000
z [cm]
circumference ~1000 m
Electron Polarization in Figure-8 Ring
electron spin in
vertical direction
ions
Universal Spin
Rotators
spin tuning
solenoid
electron spin in
vertical direction
Self polarization time in MEIC
GeV
Hours
3
14.6
4
3.5
5
1.1
6
0.46
9
0.06
11
0.02
• Polarized electron beam is injected at full energy
from 12 GeV CEBAF
• Electron spin is in vertical direction in the figure-8
ring, taking advantage of self-polarization effect
• Spin rotators will rotate spin to longitudinal
direction for collision at IP, than back to vertical
direction in the other half of the ring
Universal Spin Rotator
espin
from arc
spin
8.8º
4.4º
OptiM - MAIN: - C:\Working\ELIC\MEIC\Optics\5GeV Electe. Ring\sol_rot_2.opt
Solenoid 2
BL = 28.712 Tesla m
Spin rotation
BDL
spin
rot.
BDL
arc
bend 1
src
bend 2
GeV
rad
Tm
rad
Tm
rad
rad
3
π/2
15.7
0
0
π/3
π/6
4.5
π/4
11.8
π/2
23.6
π/2
π/4
6
0.63
12.3
π-1.23
38.2
2π/3
π/3
9
π/6
15.7
2π/3
62.8
π
π/2
12
0.62
24.6
π-1.23
76.4
4π/3
2π/3
0
spin
rot.
0
Solenoid 1
BETA_X&Y[m]
E
5
15
Tue Jul 13 22:27:07 2010
0
BETA_1X
BETA_2Y
BETA_1Y
BETA_2X
solenoid
4.16 m
17.9032
decoupling
quad insert
M=
C
0
0
-C
solenoid
4.16 m
Electron Beam Time Structure & RF System
From
CEBAF SRF
Linac
0.67 ns
(20 cm)
1.5 GHz
<3.3 ps
(<1 mm)
0.2 pC
Microscopic bunch
duty factor 5x10-3
MEIC
10-turn injection
33.3 μs (2 pC)
RF operation frequency
MHz
1.497
Total Power
MW
6.1
Harmonic number
RF Voltage
40 ms
(~5 damping times)
25 Hz
Beam current
Energy loss per turn
4969
MV
4.8
A
3
MeV
2
R/Q
3000 “pulses” =120 s
HOM Power
Accelerating voltage
gradient
Unloaded Q
Number of cavities
90
kW
2
MV/m
1
1.2×109
16
Possible Electron Ring RF Systems
CESR
PEP II
BESSY
RF may prefer 748.5 MHz (coupler limits)
Beam Synchronization
• Electron speed is already speed of light at 3 to 11 GeV, ion speed is not, there is 0.3% variation of
ion speed from 20 to 60 GeV
• Needs over 67 cm path length change for a 1000 m ring
• Solution for case of two IPs on two separate straights
– At the higher energies (close to 60 GeV), change ion path length
 ion arc on movers
– At the lower energies (close to 20 GeV), change bunch harmonic number
 Varying number of ion bunches in the ring
• With two IPs in a same straights  Cross-phasing
• More studies/implementation scheme needed
Harmonic Number vs. Proton Energy
n
β=(h-n)/h
γ
Energy
(GeV)
0
1
inf
Inf
1
0.9998
47.44
43.57
2
0.9996
33.54
30.54
3
0.9993
27.39
24.76
4
0.9991
23.72
21.32
5
0.9989
21.22
18.97
6
0.9987
19.37
17.24
eRHIC e-Ring Path Length Adjustment
(eRHIC Ring-Ring Design Report)
Ion SRF Linac (First Cut)
RFQ IH
(3 m) (9 m)
QWR
(24 m)
IS MEBT
QWR
(12 m)
Up to Lead
208Pb
MeV/u
100
Maximum beam current
averaged over the pulse
Pulse repetition rate
mA
2
Hz
10
Pulse length
ms
0.25
Maximum beam pulsed
power
Fundamental frequency
kW
680
MHz
115
m
150
Total length
DSR
(50 m)
Stripper
Ion species
Ion species for reference
design
Kinetic energy of lead ions
HWR
(24 m)
• Accelerating a wide variety of polarized
light ions and unpolarized heavy ion
• Up to 285 MeV for H- or 100 MeV/u for
208Pb+67
• Requires stripper for heavy ions (Lead)
for efficiency optimization
QWR
HWR
DSR
MEIC Ion Pre-booster
ARC1
SS3 Dispersive
SS1 Dispersive
ARC3
ARC4
ARC2
Drift (arc)
m
0.35
Drift (SS)
m
3
Quad
m
0.4
Max Quad Field (arc)
T
0.81
Dipole
m
2
deg
11.47
Bending angle
Total length
m
300
Straight (long)
m
2x57
Straight (short, in arc)
m
2x23
deg
95.35
Figure-8 angle
Max particle γ
4.22
Transition γ
5.4
Momentum compaction
0.0341
Detector Concept and IR Layout
central detector with endcaps
large aperture
electron quads
dipole
IP
dipole
small diameter
electron quads
~50 mrad crossing
Solenoid yoke + Muon Detector
Tracking
5 m solenoid
Pawel Nadel-Turonski
EM Calorimeter
Hadron Calorimeter
Muon Detector
RICH
HTCC
EM Calorimeter
Solenoid yoke + Hadronic Calorimeter
RICH
low-Q2
electron detection
small angle
hadron detection
ion quads
ultra forward
hadron detection
dipole
( )   
2
*
BETA_X&Y[m]

*

*2
3.52
 *
 6 102 m
-2

2 10
ff
 IR
 x*  10cm
 y*  2cm
 max g0FF
Natural Chromaticity:
IP
x = -47
0
0
f
0
BETA_X
BETA_Y
FF doublets
DISP_X
f2 1
f

* f *
DISP_X&Y[m]
800
5
IR Optics (electrons)
DISP_Y
l * = 3.5m
19
y = -66
Synchrotron Radiation Background
50 mrad
38
P+
8.5x105
2.5W
Photons incident on various
surfaces from the last 4 quads
4.6x104
240
2
FF2
FF1
40 mm
30 mm
50 mm
e-1
1
2
3
4
5
3080
Rate per bunch incident on the surface
> 10 keV
Beam current = 2.32 A
2.9x1010 particles/bunch
M. Sullivan
July 20, 2010
F$JLAB_E_3_5M_1A
Rate per bunch incident on the detector
beam pipe assuming 1% reflection
coefficient and solid angle acceptance of
4.4 %
Michael Sullivan, SLAC
Beam-Beam Studies
• Simulating the beam-beam effects becomes critically important as part of the
feasibility study of this conceptual design
• Staged approach to simulations:
– Current: isolate beam-beam effects at IP (idealized linear beam transport)
– Next: incorporate non-linearity in the beam transport around the ring
• Main points of this stage of beam-beam simulations:
– Developed a new, automated search for working point based on an
evolutionary algorithm (near half-integer resonance: exceeds design luminosity
by ~33%)
– Short-term stability verified to within capabilities of strong-strong code
– As beam current is increased, beam-beam effects do not limit stability
– Beam-beam effects are not expected limit the capabilities of the MEIC
Electron Beam Stability
The following issues have been studied:
• Impedances
• Inductive impedance budget
• Resistive wall impedance
• CEBAF cavity
• HOM loss
• Single bunch instabilities
• Multibunch instabilities
• Intrabeam scattering
• Touschek scattering
• Beam-gas scattering
• Ion trapping & fast beam-ion
instability
• Electron clouds
• As long as design of vacuum chamber
follows the examples of ring colliders,
especially B-factories, we will be safe
from the single bunch instabilities.
• No bunch lengthening and widening due
to the longitudinal microwave instability
is expected
• No current limitation from transverse
mode coupling instability.
• The performance of MEIC e-ring is likely
to be limited by multi-bunch instabilities.
Feedback system able to deal with the
growth has to be designed.
• All ion species will be trapped. Total
beam current limitation and beam
lifetime will depend upon the ability of
the vacuum system to maintain an
acceptable pressure, about 5 nTorr in the
presence of 3 A of circulating beam.
ERL Circulator Cooler
Design goal
• Up to 33 MeV electron energy
• Up to 3 A CW unpolarized beam
(~nC bunch charge @ 499 MHz)
• Up to 100 MW beam power!
Solution: ERL Circulator Cooler
Electron
circulator
ring
• ERL provides high average current CW
beam with minimum RF power
• Circulator ring for reducing average
current from source and in ERL
(# of circulating turns reduces ERL
current by same factor)
Technologies
• High intensity electron source/injector
• Energy Recovery Linac (ERL)
• Fast kicker
Forming the High-Intensity Ion Beam
low energy ring cooling
SRF Linac
source
pre-boosterAccumulator ring
Medium energy
collider ring
Energy (GeV/c)
Stacking proton beam in ACR
Circumference
Energy/u
Cooling electron current
Cooling time for protons
Stacked ion current
Norm. emit. after stacking
Cooling
m
GeV
A
ms
A
µm
100
0.2 -0.4
1
10
1
16
Process
Source/SRF linac
0.2
Full stripping
Prebooster/Accumulator-Ring
3
DC electron
Stacking/accumulating
Low energy ring (booster)
12
Electron
RF bunching (for collision)
Medium energy ring
60
Electron
RF bunching (for collision)
Stacking/accumulation process





Multi-turn (~20) pulse injection from SRF linac into the prebooster
Damping/cooling of injected beam
Accumulation of 1 A coasted beam at space charge limited emittance
Fill prebooster/large booster, then accelerate
Switch to collider ring for booster, RF bunching & staged cooling
MEIC Critical Accelerator R&D
We have identified the following critical R&D for MEIC:
•
•
•
•
•
•
•
Interaction region design and limits 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
Level of R&D
Low-to-Medium Energy
(12x3 GeV/c) & (60x5 GeV/c)
High Energy
(up to 250x10 GeV)
Challenging
Semi
Challenging
Likely
Know-how
IR design/chromaticity
Electron cooling
Traveling focusing (for very low ion energy)
IR design/chromaticity
Electron cooling
Crab crossing/crab cavity
High intensity low energy ion beam
Crab crossing/crab cavity
High intensity low energy ion beam
Spin tracking
Beam-Beam
Spin tracking
Beam-beam
MEIC Enabling Technologies
•Pushing the limits of present accelerator theory
– Issues associated with short ion bunches (e.g.. cooling)
– Issues associated with small β* at collision points
• Focus on chromatic compensation
– Beam-beam effects
•Development of new advanced concepts
– Dispersive crabbing
– Beam-based fast kicker for circulator electron cooler
Achieving High Luminosity
MEIC design luminosity
L~ 6x1033 cm-2 s-1 for medium energy (60 GeV x 3 GeV)
Luminosity Concepts
•
•
•
•
High bunch collision frequency (0.5 GHz, can be up to 1.5 GHz)
Very small bunch charge (<3x1010 particles per bunch)
Very small beam spot size at collision points (β*y ~ 5 mm)
Short ion bunches (σz ~ 5 mm)
Keys to implementing these concepts
• Making very short ion bunches with small emittance
• SRF ion linac and (staged) electron cooling
• Need crab crossing for colliding beams
Additional ideas/concepts
• Relative long bunch (comparing to beta*) for very low ion energy
• Large synchrotron tunes to suppress synchrotron-betatron resonances
• Equal (fractional) phase advance between IPs
Straight Section Layout
y
z
Minimizing crossing angle
reduces crab cavity challenges
straight section
spin
rotator
e
arc dipoles
vertical
bend
vertical
bend
collision
point
spin
rotator
e
collision
point
i
~0.5 m
~0.5 m
arc bend
i
vertical spin vertical
bend rotators bend
Vertical crossing
angle (~30 mrad)
Optional 2nd detector
Interaction Region
~ 60 m
IP
FODO Crab
cavity
Chrom Matching FF
quads
Detector
space
FF
Matching Chrom Crab FODO
quad
cavity
MEIC Science Drivers
Key issues in nucleon structure & nuclear physics
• Sea quark and gluon imaging of nucleon with GPDs (x >~ 0.01)
• Orbital angular momentum, transverse spin, and TMDs
• QCD vacuum in hadron structure and fragmentation
• Nuclei in QCD: Binding from EMC effect, quark/gluon radii from coherent
processes, transparency
• High luminosity > 1034: Low rates, differential
measurements
• CM energy s~1000 GeV2: Reach in Q2, x
• Detectability: Angular coverage, particle ID,
energy resolution
 favors lower & more
symmetric energies
ECM (GeV)
50 fb-1
120
xmin ~ 10-4
gluon
100
saturation
8
0
60
4
0
2
0
0
xmin ~ 10-3
quarks,
gluons in
nuclei
DIS
nucleon
structure
exclusive,
electroweak
processes
Machine/detector requirements
MEIC
xmin ~ 10-2
1
R. Ent
10
MEIC
sin2θ
W
100
∫L dt (fb-1)