1. P. Chevtsov for the ELIC Design Team
Electron Spin Rotation and Matching Schemes for ELIC, a High Luminosity Ring-Ring Electron-Ion Collider
P. Chevtsov
for the ELIC Design Team
SPIN2008, Charlottesville, VA, 6-11 October 2008

2. Outline Introduction ELIC Electron Ring Spin Rotation Scheme
ELIC Spin Matching Optics Scheme
Some ELIC Spin Preparation and Manipulation Issues
Summary

3. ELIC ELIC is an Electron-Ion Collider based on CEBAF
GeV protons
GeV/n ions
ELIC
12 GeV
CEBAF
upgrade
3-9 GeV electrons
3-9 GeV positrons
ELIC is an Electron-Ion Collider based on CEBAF
upgraded to 12 GeV.

4. ELIC The CEBAF accelerator with its polarized source will
GeV protons
GeV/n ions
ELIC
12 GeV
CEBAF
upgrade
3-9 GeV electrons
3-9 GeV positrons
The CEBAF accelerator with its polarized source will
serve as a full energy injector into an electron storage ring
providing required beam current, energy, and polarization.

5. ELIC Electron and ion storage rings are designed as Figure-8
GeV protons
GeV/n ions
ELIC
12 GeV
CEBAF
upgrade
3-9 GeV electrons
3-9 GeV positrons
Electron and ion storage rings are designed as Figure-8
shaped double rings.

6. ELIC Both rings share the same tunnel, with the electron ring above
GeV protons
GeV/n ions
α=0.022
ELIC
12 GeV
CEBAF
upgrade
3-9 GeV electrons
3-9 GeV positrons
Both rings share the same tunnel, with the electron ring above
the ion ring. To collide with ions, electrons are bent
vertically with a crossing angle of 22 mrad.

7. ELIC Design Goals Energy Luminosity Ion Species Polarization
Center-of-mass energy between 20 GeV and 90 GeV
energy asymmetry of ~ 10,
 3 GeV electrons on 30 GeV protons/15 GeV/n ions up to
9 GeV electrons on 225 GeV protons/100 GeV/n ions
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
Spin-flip of both beams
All polarizations >70% desirable
Polarized Positron Beam desirable

8. ELIC Electron Ring Spin Rotation Scheme

9. Electron Polarization in ELIC
Polarized electrons are produced in the CEBAF electron polarized source.

10. Electron Polarization in ELIC
High polarization of electrons is preserved during their acceleration in CEBAF.

11. Electron Polarization in ELIC
Polarized beams are injected into the ELIC Figure-8
shaped ring with vertical polarization.

12. Electron Polarization in ELIC
Spin is vertical in arcs and longitudinal at IPs IP IP IP IP
Electron Polarization in ELIC

13. Electron Polarization in ELIC
Vertical crossing bends cause energy-dependent
spin rotations
α=0.022 IP IP IP IP
Electron Polarization in ELIC 13

14. Electron Polarization in ELIC
We need spin rotators that do not change the beam orbit
and provide longitudinal spin at IPs at all available electron
beam energies (3-9 GeV)
α=0.022 IP IP IP IP
Electron Polarization in ELIC 14

15. Sol1 φ1
Sol2 φ2
α=0.022 B1 B2 α1 α2
SR1

16. Sol1 φ1
Sol2 φ2
α=0.022 B1 B2 α1 α2
anomalous magnetic moment of the electron

17. Sol1 φ1
Sol2 φ2
α=0.022 B1 B2 α1 α2

18. α1 α2 Sol1 φ1 Sol2 φ2 α=0.022 B1 B2 B2: γaα2=π/2 at 9 GeV - α2=0.077

19. Sol1 φ1
Sol2 φ2
α=0.022 B1 B2 α1 α2
3 GeV – 9 GeV

20. Sol1 φ1
Sol2 φ2
α=0.022 B1 B2 α1 α2
SR1

21. SR1
SR2

22. SR1
SR2

23. SR1*
SR1
SR2

24. ELIC Electron Ring Optics

25. A great effort has been made to ensure the “spin transparency” and spin matching in ELIC.

26. To avoid depolarization, the optics must be arranged in the way that
perturbations caused by the elements in the whole system
compensate each other.

27. to ½, which compensates most of the spin perturbations.
electron ring IP IP IP IP
- spin tune solenoids
- electron spin direction
- spin rotators
Spin tune solenoids are used to make machine spin tune equal
to ½, which compensates most of the spin perturbations. 27

28. vertical bends and solenoids.
electron ring IP IP IP IP
- spin tune solenoids
- electron spin direction
- spin rotators
The most critical components of the ELIC electron ring are
vertical bends and solenoids. 28

29. Solenoid (φ – spin rotation)v e-

30. Solenoid (φ – spin rotation)v e-
X-Y beam coupling

31. Decoupling insertion between two solenoids
V.Litvinenko, A.Zholents, 1980

32. quadrupoles v e-

33. Some ELIC Spin Preparation
and Manipulation Issues

34. Polarized electrons are available immediately from CEBAF.
12 GeV CEBAF
upgrade
3-9 GeV electrons
Polarized electrons are available immediately from CEBAF.

35. To take the advantage of the Sokolov-Ternov effect,
12 GeV CEBAF
upgrade
3-9 GeV electrons
To take the advantage of the Sokolov-Ternov effect,
electrons are injected into the ELIC with the direction of
polarization that is opposite to the direction of
guiding magnetic field.

36. Positrons in ELIC
Non-polarized positron bunches are generated from a modified CEBAF electron injector through a converter
Polarization is realized through self-polarization in ring arcs
115
MeV
converter e - 15 5 e+ 10
unpolarized
source
polarized
dipole
Transverse
emittance
filter
Longitudinal
emittance filter
During positron production:
- Polarized source is off
- Dipoles are turned on

37. spin flipping
RF dipoles inducing spin resonance frequencies

38. spin flipping
CEBAF

39. Summary
A concept of spin rotators, which do not change the beam orbit for the ELIC electron ring at all available energies has been developed
Such rotators and spin stabilizing solenoids build up a very efficient spin manipulation system for the ELIC electron ring
The work on spin matching beam transport optics in progress

41. Electron Polarization in ELIC (cont.)
Electron/positron polarization parameters
* Time can be shortened using high field wigglers.
** Ideal max equilibrium polarization is 92.4%. Degradation is due
to radiation in spin rotators.

42. the spin precession due to
B depends on the beam
energy ()
the spin precession due to
B|| is energy-independent
anomalous magnetic moment of the electron
θsp α
The spin precession angle θsp in a dipole magnet with respect to the electron momentum vector is equal to aγα, where α is the dipole bending angle.

43. spin rotation angle φsp= (1+a) BL/B0ρ  BL/B0ρ
Solenoid v e- L
spin rotation angle φsp= (1+a) BL/B0ρ  BL/B0ρ
where B0ρ (T.m) = P (GeV/c)