1. Complete Baseline Scheme for Ion Polarization Preservation and Control in the MEIC Ion Complex
Yu.N. Filatov, A.M. Kondratenko, M.A. Kondratenko
Science and Technique Laboratory Zaryad, Novosibirsk, Russia
translated and presented by V.S. Morozov
JLab
MEIC R&D meeting, February 19, 2015
F. Lin

3. …
~13 pages

4. Contents of the Report Introduction
Colliders with “preferred spin axis” and “transparent to the spin”
Strength of the zero-integer spin resonance in a figure-8 collider
Ion polarization in the MEIC accelerator complex
Preservation of the ion polarization in the prebooster and large booster
Ion polarization control in the collider ring
Calculation of the ion polarization in the collider’s experimental straight
Spin flipping in the ion collider ring
Conclusions

5. Introduction Polarization design requirements
High polarization (over 70%) for protons or light ions (d, 3He++, and possibly 6Li+++)
Both longitudinal and transverse polarization at all interaction points
Sufficiently long polarization lifetime
Spin flipping at a high frequency
Figure 8 features advantageous for satisfying the design requirements
The spin tune is energy independent but is equal to zero
The figure-8 topology eliminates the effect of arcs on the spin motion
Control the polarization of any particle species including deuterons, using longitudinal fields of small integrated strength (weak solenoids)
Control the polarization at the interaction points without essentially any effect on the beam’s orbital characteristics
Elegant solution to the problem of ion acceleration completely eliminating resonant beam depolarization
Allows one to easily adjust the polarization in any direction at any orbital location
necessary when transferring the beam from one ring into another or when measuring the polarization by polarimeters
Allows for an easy manipulation of the spin direction at an interaction point during an experiment
Spin-flipping system with a spin reversal time of less than a second
Polarized beam studies in MEIC at an unprecedented precision level

6. Collider Types Colliders (accelerators) with preferred spin direction
Conventional accelerator
Collider with a single Siberian snake
Collider with two Siberian snakes with their axes at 90
Colliders (accelerators) transparent to the spin
Conventional accelerator (resonant case)
Collider with two identical Siberian snakes
Collider in the shape of a figure 8
The most natural representative of a collider “transparent to the spin”
Unique opportunities with colliders (accelerators) transparent to the spin
Efficient control of the ion polarization using small magnetic field integrals
10 Tm vs ~100 and 2500 Tm for protons and deuterons, respectively, at 100 GeV/c
Polarization control at the interaction points during experiments
Efficiently control using “weak” fields, which have essentially no effect on the beam’s orbital characteristics
Spin reversal in less than a second

7. Zero-Integer Spin Resonance
The frequency spectrum of the spin motion in a figure 8 consists of integer-multiple harmonics of the particle revolution frequency
Zero-integer resonance strength determines polarization stability
Resonance strength components
Coherent part
Due to additional dipole and longitudinal fields along the closed orbit
Linear effect
Can be compensated, compensation technique is well known and has been successfully used, for instance, at the AGS
Incoherent part
Nonlinear effect
Much weaker than the coherent part

8. Ion Polarization in MEIC
Polarization preservation during acceleration
Ion source
Ion linac
Prebooster
Large booster
Ion collider ring
Polarization control in the ion collider ring

9. Polarization in Prebooster and Large Booster
Figure 8 eliminates spin resonance crossing during acceleration
Polarization stabilized by a single weak solenoid
Polarization is longitudinal in the solenoid straight, which can be used for polarization matching
Spin tune shift by the solenoid must greatly exceed the zero-integer spin resonance strength
Required solenoid field integral does not exceed 2 Tm, compare to a full Siberian snake of 75 and 250 Tm for protons and deuterons, respectively, at 20 GeV

10. Optical Effect of Solenoid
Linear optics without solenoid
Linear optics with solenoid
Betatron tune shift

11. Ion Polarization Control in Collider Ring
3D spin rotator consisting of weak dipoles and solenoids
Any polarization orientation
No effect on the optics
Three modules for control of the three polarization components
Fixed orbit bumps of ~12 mm
Spin rotations for a certain polarization direction

12. Ion Polarization Control in Collider Ring
Field integrals as functions of energy for deuterons assuming 0.58 bends and a spin tune of 2.510-4
Field integrals as functions of energy for protons assuming 0.58 bends and a spin tune of 0.01
Lattice integration
Each module is ~6 m long

13. Calculation of Deuteron Polarization
Schematic of the experimental straight with bend locations
Deuteron polarization along the collider ring

14. Calculation of Proton Polarization
Proton polarization in the experimental straight

15. Spin Flipping
The universal 3D spin rotator can be used to flip the polarization
Consider e.g. longitudinal polarization at the IP at 100 GeV/c
Polarization is flipped by reversing the fields of the solenoids in the radial and longitudinal spin control modules
Polarization is preserved if
The spin tune is kept constant
No resonant depolarization
The rate of change of the polarization direction is slow compared to the spin precession rate
>0.1 ms for protons and >3 ms for deuterons

16. Conclusions Figure 8 design allows for
use of weak solenoids for polarization control at high energies of any particle type including deuterons;
seamless integration of the spin control elements into the collider lattice with fixed closed orbit and no optics distortion;
elimination of the resonant depolarization at all stages of the beam acceleration from the linac to the collider ring;
adjustment of any polarization orientation at any orbital location (spin matching at injection into the different accelerator complex components, polarimetry, spin flipping);
manipulation of the particle spin during an experiment without affecting the beam orbital properties, which provides a capability of carrying out polarized beam experiments at a new precision level;
compensation of the manufacturing and alignment errors of the lattice magnetic elements, which additionally substantially enhances the precision of polarized beam experiments;
ease of adjusting the spin dynamics to meet any experimental requirements, which may arise in the future.