1. Electron Ring Optics Design
Alex Bogacz
for MEIC Collaboration
Center for Advanced Studies of Accelerators
MEIC Review
September 2010

2. Figure-8 Collider Rings
total ring circumference ~1000 m
60 deg. crossing
Collider Ring size is a compromise between synchrotron radiation and space charge
3-11 GeV electrons
20-60 GeV ions (with 6 Tesla dipoles)

3. Collider Ring Architecture
Larger Figure-8 Rings (~1000 m circumference)
6 Tesla bends for ions at 60 GeV
Additional straights to accommodate ‘snakes’ (ions) and RF (electrons)
Horizontal IR crossing, dispersion free straights
Spin Rotators (4) at arcs ends
Electron Collider Ring based on emittance preserving Optics
FODO (1350 phase adv/cell)
FMC/DBA Optics
TEM Optics?

4. Electron Ring - 1350 FODO Cell
E = 11 GeV 15
0.15
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y
0.5
PHASE_X&Y
Q_X
Q_Y
phase adv/cell: Dfx,y= 1350
Arc dipoles:
$Lb=110 cm
$B=12.5 kGauss
$ang=2.14 deg.
$rho = 29.4 meter
Arc quadrupoles
$Lq=40 cm
$G= 9 kG/cm
1350 FODO offers emittance preserving optics – 〈H〉 minimum for FODO lattices
Synchrotron radiation power per meter less than 20 kW/m

5. Emittance preserving Optics 15
0.3
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y
1350 FODO
F ~〈H〉
Minimized 〈H〉 over bends
H = gD2 + 2aDD’ + bD’2
F  100
Equilibrium rms emittance at 5 GeV: ex = 1.87 ×10-8 m

6. Quarter Arc Achromat 60 × 1.1 meter dipoles 120 deg. Arc15
0.15
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y
120 deg. Arc
2 dis. sup. cells
2 dis. sup. cells
26 FODO cells
60 × 1.1 meter dipoles

7. Electron Ring - Arc Optics
260 15
0.15
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y
240 deg. Arc
quarter Arc – 120 meter
Straight – 20 meter
quarter Arc – 120 meter

8. Electron Half-Ring - Lattice 15
0.15
-0.15
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y ×2
Arc ‘inward’ – 260 m
Straight – 234 m
Ring circumference – 988 m

9. Spin Rotator - Ingredients…
320
230 15
0.15
-0.15
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y
Arc end
4.4 0
8.8 0
Spin rotator ~ 46 m
BL = 11.9 Tesla m
BL = 28.7 Tesla m

10. Locally decoupled solenoid 15 5
BETA_X&Y[m]
BETA_1X
BETA_2Y
BETA_1Y
BETA_2X
BL = 28.7 Tesla m
solenoid m
solenoid m
decoupling quad insert
M = C
- C

11. Locally decoupled solenoid 15 1 -1
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y
BL = 28.7 Tesla m
solenoid m
solenoid m
decoupling quad insert
M = C
- C

12. Spin Rotator - Optics 5 GeV 4.4 0 8.8 0 Spin rotator ~ 46 m
374
288 30 1 -1
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y
4.4 0
8.8 0
Spin rotator ~ 46 m
BL = 11.9 Tesla m
BL = 28.7 Tesla m

13. Emittance preserving Optics46
28.5 20 1 -1
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y
BL = Tesla m
Solenoid 2
Solenoid 1
8.8 deg. bend
Minimized 〈H〉 over bends
H = gD2 + 2aDD’ + bD’2

14. Spin Rotator Pair - Optics
5 GeV
374
288 30 1 -1
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y
575
490 30 1 -1
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y
4.40
8.80
BL = 11.8 T m
BL = 28.7 T m
-4.40
-8.80
BL = T m
BL = T m

15. Lower emittance - upgrade path
E = 5 GeV
E = 11 GeV 15
0.3
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y 15
0.3
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y
1350 FODO
FMC Cell
F = 100
F = 30
exeg = 1.87 ×10-8 m
Minimize 〈H〉 over bends
H = gD2 + 2aDD’ + bD’2

16. Extreme emittance preserving Optics
E = 11 GeV
FMC Cell
TEM like Cell 15
0.3
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y
4.06 20
0.2
BETA_X&Y[m]
DISP_X&Y[m]
BETA_X
BETA_Y
DISP_X
DISP_Y
F = 30
F = 3

17. Summary
Complete design of Figure-8 Collider Rings (~ 1000 m circumference)
Emittance preserving Arcs based on 1350 FODO lattice
Compact spin rotators ‘meshed’ into the arcs
No dispersion suppression at arc end
Locally decoupled solenoid inserts
Beyond 1350 FODO Optics in the arcs
FMC Optics
TEM Optics?