Overview of MEIC
Electron Collider Ring
Yuhong Zhang
Review 09/2010
Page 1
Electron Collider Ring Design Goals
• A storage ring is capable of providing the following features
Overall
• Electron energy 3 to 11 GeV
• Accepting and accumulating full energy injected electron beam from CEBAF
(No requirement of further upgrade of 12 GeV CEBAF)
• Option of “top-off” current operation
Geometric
• Be large enough to accommodate 3 IPs (detectors) and all necessary components
including RF system, spin manipulating, polarimetry, injection/ejection
• Sharing a same (figure-8 shape) footprint with the ion collider ring of 60 (30) GeV/u
protons (ions)
Beam qualities
• Be able to store a high average current (up to 3 A) and high bunch repetition rate
(up to 1.5 GHz) CW electron beam
• Be able to maintain a reasonable long beam life time
• Small transverse emittance and short bunch length
Review 09/2010
Page 2
Electron Collider Ring Design Goals (cont.)
Polarization
• high (>80%) polarization over a reasonable long period of time (>10 min)
• Longitudinal spin direction at all interaction points
• Capability of spin flipping beam
• Be able to accommodate and self-polarizing positron beam
Technical and cost-wise
• Limiting synchrotron radiation power density below 20 kW/m, and also
minimizing total radiation loss for requiring less RF power
• Constructed with warm magnets
Stability or operability
• Achieving high stability & operability through modulation optics design
• Consideration of beam control and diagnostics
• Large momentum acceptance and dynamical aperture
Review 09/2010
Page 3
Figure-8 Electron Collider Ring Footprint
Ions from
big booster
Experimental Hall
(radius 15 m)
RF (20 m)
Figure-8 crossing
angle: 2x30°
Circumference
Figure-8 crossing angle
Compton
polarimeter
(28 m)
Injection from
CEBAF
Review 09/2010
m
1000
deg
60
Symmetric arc sections
4
Quarter arc length
m
117.5
Quarter arc angles
deg
106.8
Length of Long straights
m
240
Length of short straight
m
20
Length of Spin rotator
m
50
Bending angle in spin
rotator
deg
13.2
Interaction region
m
60
Compton Polarimetry
m
28
Page 4
Comprehensive Parameter Table
Energy
GeV
5
11
Energy
GeV
5
11
Circumference
m
995
995
Total radiation power
MW
6.1
6.1
Revolution Time
μs
3.3
3.3
Radiation Power/m
kW/m
20
20
MHz
0.3
0.3
Energy loss per turn
MeV
2
43
A
3
0.13
Damping time, longitudinal
Ms
8.25
0.78
GHz
1.5
1.5
Turns
2475
232
m
0.2
0.2
4975
4975
nm
5.5
26.5
1.25
0.054
Horizontal Emitt., unnorm,
uncoupled
Horizontal Emitt., unnorm.
nm
5.5
26.5
Revolution Frequency
Beam Current
Bunch frequency
Bunch spacing
Number of bunches
Electrons per bunch
1010
m
118.5x4
118.5x4
Horizontal Emitt., norm.
μm
53.5
570
deg
240x2
240x2
Vertical Emitt., unnorm.
nm
1.1
5.3
Dipole length
m
1.5
1.5
Vertical Emitt., norm.
μm
10.7
114
Bending radius
m
36.5
36.5
Vertical emitt. /horizontal.
emitt.
0.2
0.2
Bending angle
deg
2.35
2.35
FODO
FODO
Arc length
Total arc angle
Lattice
Cell length
m
4.8
4.8
Dipole packing factor
%
62.5
62.5
Review 09/2010
Energy spread
10-3
0.71
1.6
Bunch length
mm
7.5
5.7
Page 5
Figure-8 Electron Ring Design Parameters
Energy
GeV
5
11
Energy
GeV
5
Betatron tune, horizontal
Beta-star, horizontal
mm
100
Betatron tune, vertical
Beta-star, vertical
mm
10
Horiz. beam size at IP
μm
23.5
Verti. Beam size at IP
Μm
4.7
Synchrotron tune
0.045
0.133
Arc radius
m
57
57
Beta max, horizontal
M
425
Straights, long (IR)
m
240
240
Beta max, vertical
m
612
Straights, short (snake)
m
20
20
Horiz. beam size at 1st FF
mm
1.5
GHz
1.5
1.5
Vert. beam size at 1st FF,
mm
0.82
4969
4969
3
3
17.4
17.4
RF frequency
Harmonic number
Momentum compaction
10-3
Transition gamma
Beam-stay-clear/RMS size
11
15
Aperture, horizontal
cm
2.25
Aperture, vertical
cm
1.2
Integrated RF voltage
MV
4.8
72
Synchronous phase
deg
25
30
Beam-beam tune shift, horiz.
0.03
RF momentum acceptance
10-3
4
10.6
Beam-beam tune shift, vert.
0.03
Acceptance/spread
5.6
6.7
Touschek lifetime
min
76
>2500
Natural chromaticity, y
56
S-T self polarization time
min
111
2.2
Review 09/2010
Page 6
Formation of Stored Beam in the Collider Ring
Ring
From CEBAF
SRF Linac
0.67 ns
< 3.3 ps (1 mm)
(20 cm)
Microscopic
0.2 pC
1.5 GHz
bunch duty
factor 5x10-3
Bunch frequency
Ring circumference
A
3
MHz
1497
μs
3.3
Number of bunches
10-turn injection
33.3 μs (2 pC)
Stored beam in
collider ring
Stored current
4975
Bunch charge
nC
2
Electrons/bunch
1010
1.25
Pulse train rep. rate
Hz
25
Pulse train duration
s
40
Total pulse train
cathode
40 ms
(~5 damping
times)
25 Hz
40 s
Macroscopic bunch
duty factor 8.5x10-3
• Full energy injection from CEBAF
• 10-turn injection followed by phase space damping
Review 09/2010
Linac
1000
Bunch duration (FWHM)
ps
~70
Bunch charge
pC
0.2
Electron/bunch
106
1.25
Peak current
mA
2.86
Bunch length
mm
1
Microscope duty circle
10-3
5
Macro duty circle during fill
10-3
0.85
Macro pulse aver. current
μA
300
Average current during fill
nA
250
Page 7
More Topics
• Electron collider ring optics design
Alex Bogacz
• RF systems for electron collider ring
Haipeng Wang
• Electron beam stability
Byung Yunn
• Electron beam polarization
Vasiliy Morozov
Review 09/2010
Page 8
Backup Slides
Review 09/2010
Page 9
Compton Polarimeter Layout
chicane
separates polarimetry from accelerator
scattered electron
momentum analyzed in dipole magnet
measured with Si or diamond strip detector
pair spectrometer (counting mode)
e+e– pair production in variable converter
dipole magnet separates/analyzes e+ e–
sampling calorimeter (integrating mode)
count rate independent
Insensitive to calorimeter response
Review 09/2010
Geometry:
• Total dipole chicane length = 28 m
• Dipoles = 3 m long, 2T
• Electron beam deflection between dipoles
1-2 = 94 cm
 scattered electron 6.7 cm (3.3 cm) from
beam at endpoint at asymmetry zero
crossing (green laser)
Photon detector 54 m from laser-electron
interaction point
David Gaskell
Page 10