1. Update on MEIC Ion Polarization Work
V.S. Morozov
Teleconference on Ion Polarization
March 25, 2015
F. Lin

2. Outline Update on the MEIC design Review of milestones
Discussion of racetrack option
Discussion of short-term plans

3. MEIC Layout & Detector Location
Cold Ion Collider Ring
(8 to 100 GeV)
Two IP locations:
One has a new detector, fully instrumented
Second is a straight-through, minor additional magnets needed to turn into IP
Ion Source
Booster
Linac
Warm Electron
Collider Ring
(3 to 10 GeV)
Considerations:
Minimize synchrotron radiation
IP far from arc where electrons exit
Electron beam bending minimized in the straight before the IP
Minimize hadronic background
IP close to arc where protons/ions exit

4. Ion Collider Ring Figure-8 ring with a circumference of 2153.9 m
Two 261.7 arcs connected by two straights crossing at 81.7
geom. match #3
disp. supp./
disp. supp./
geom. match #2
norm.+
SRF
Arc, 261.7
tune
tromb.+
match
elec. cool.
R = m
81.7
future 2nd IP
Polarimeter
det. elem.
disp. supp.
ions
beam exp./
match IP
disp. supp./
geom. match #3
disp. supp./
geom. match #1

5. Milestones of Funded 1-Year Grant
First and Second quarters
Polarization in a racetrack prebooster.
Scheme for deuteron beam in a ring.
Scheme for proton beam in a ring with solenoid.
Third and fourth quarters
Development and utilization of advanced analytical and computational methods of studying the orbital and spin dynamics in lattices of figure 8 rings with strong coupling
Complex coordinates method.
Linear theory of orbital motion.
Numerical calculations of closed orbit and linear focusing at MEIC.
Numerical calculations of spin trajectories at MEIC.
Benchmarking vs existing codes.

6. Work Plan through June 15, 2015
Finish and finalize the complete baseline scheme for ion polarization preservation and control in the MEIC ion complex including the prebooster, large booster and collider ring.
Completed. Thank you!
Preliminary demonstration of the developed scheme by numerical simulations.
Agree to contribute to a special report describing the complete polarization scheme of MEIC based on the completed work (for additional funding if after the current contract period).
Agree to update the developed scheme for the final version of MEIC (for additional funding if after the current contract period).

7. Milestones of Submitted Proposal
First and Second quarters
Systematic comparison of figure-8 and racetrack designs
Development of efficient numerical techniques for spin calculations
Spin tracking simulations
Third and fourth quarters
Spin tracking continued
Study of spin dynamics and compensation of the depolarization caused by imperfections and non-linear fields
Spin flipping

8. Spin Resonances in Racetrack
Booster Ep = 1.22 – 8 GeV, Ed = 2.03 – 8.16 GeV
Protons
~13 imperfection resonances
~26 intrinsic resonances
Deuterons
0 imperfection resonances
1 or 2 intrinsic resonances
Collider ring Ep = 8 – 100 GeV, Ed = 8.16 – 100 GeV
~175 imperfection resonances
~350 intrinsic resonances
7 imperfection resonances
~12 intrinsic resonances

9. Siberian Snake
Device rotating the spin by some angle about an axis in horizontal plane
A “full” Siberian snake rotates the spin by 180
Overcomes all imperfection and most intrinsic resonances
Spin tune with a snake
Solenoidal snake at low energies
Dipole snake at high energies

10. Racetrack Option A figure 8 comes at the price of extra arc length.
RHIC example shows that polarized protons can be accelerated to the energies of interest, however, for instance, spin flipping is not easy.
For protons, figure-8 features can be restored in a racetrack using two identical full Siberian snakes 180 bending angle apart.
All techniques and advantages of figure-8 are still valid and applicable.
Snakes at medium energies are not trivial and their orbital effects must be taken into account but this should not be a problem if the snakes are incorporated into the design ahead of time.
For deuterons, the main challenge is the collider ring.
Full snakes are not practical.
Partial snakes can be used to overcome 7 integer resonances.
Tune jump can be used to overcome a dozen or so of strong intrinsic resonances.
Control of deuteron polarization orientation in a racetrack
Vertical polarization occurs naturally.
Longitudinal polarization may be obtained by running at integer resonances (discrete energies), which also restores figure-8 features, and adiabatically rotating the polarization from vertical to longitudinal, e.g. by ramping down the partial snake and ramping up a solenoid while keeping the spin tune constant.

11. Suggested Short-Term Goals
A very high-level look at the racetrack option
Racetrack or figure-8 booster?
What would it take to turn the collider ring into a racetrack?
One or two Siberian snakes in the collider ring?
Is the energy too low for a dipole snake?
How can deuterons be handled?
Spin tracking
What should be included in the lattice?
Use linear orbital motion first?
What code to use?
What code to benchmark against?

12. Highlights of Discussion
Grant and work plan milestones
Some adjustments need to be made due to the design change
Other than that everything seems to be on schedule
Provided information about the current design
Sent current collider ring lattice and the January 15 white paper
Racetrack option
Anatoly is skeptical about polarized deuterons because of sideband synchrotron resonances
Injection energy of the collider ring is a little low for a dipole snake
Anatoly and colleagues will look at it and try to make some estimates soon
Numerical calculations of spin dynamics
Use linear orbital and spin response techniques combined with statistical methods to calculate and optimize the spin dynamics
Investigate lattice structure that compensates some of the zero-integer spin resonance strength
Verify the developed scheme by spin tracking
Not worth developing a new code
Use Zgoubi
Develop numerical tools to facilitate use of Zgoubi
IPAC preparation
Papers on a complete ion polarization scheme and numerical studies