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

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

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

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 = 155.5 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

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.

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).

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

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

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

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.

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?

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