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A Study of Polarized Proton Acceleration in J-PARC

A Study of Polarized Proton Acceleration in J-PARC. A.U.Luccio, M.Bai, T.Roser Brookhaven National Laboratory, Upton, NY 11973, USA A.Molodojentsev, C.Ohmori, H.Sato High Energy Accelerator Research Organization, Tsukuba, Ibaraki, Japan H.Hatanaka

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A Study of Polarized Proton Acceleration in J-PARC

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  1. A Study of Polarized Proton Acceleration in J-PARC A.U.Luccio, M.Bai, T.Roser Brookhaven National Laboratory, Upton, NY 11973, USA A.Molodojentsev, C.Ohmori, H.Sato High Energy Accelerator Research Organization, Tsukuba, Ibaraki, Japan H.Hatanaka Research Center for Nuclear Physics, Osaka University, Japan

  2. Layout of J-PARC for polarized proton acceleration 50 GeV polarized protons for slow extracted beam primary fixed target experiments “Low” intensity (~ 1012 ppp), low emittance (10 p mm mrad) beams pC CNI Polarimeter Extracted Beam Polarimeter Pol. H- Source Rf Dipole 180/400 MeV Polarimeter 25-30% Helical Partial Siberian Snakes

  3. Setup for accelerating polarized protons at J-PARC • Optically Pumped Polarized Ion Source: 1012 H- per 0.5 ms pulse and > 5 Hz rep. rate, 85% polarization (similar to KEK-TRIUMF-BNL OPPIS) • Bunch emittance: ~ 5 pmrad and 0.3 eVs for 2  1011 protons (required for polarized beam acceleration) • Linac: No depolarization • RCS (25 Hz, ny = 6.35, P = 3, Ekin = .18 … 3 GeV, Gg = 2.2 … 7.5) • 5 imperfection resonances; harmonic correction needed for Gg = 7 • Intrinsic resonances: • Gg = 2.65 (9- ny), 3.35 (-3+ ny), 5.65 (12- ny), 6.35 (0+ ny) • Full spin flip with rf dipole: 20 Gm gives > .99 spin-flip (seems feasible) • Avoid depolarization with tune jump: Dny = 0.2 in 6 turns  large aperture ferrite quadrupoles with fast pulsing power supplies (difficult)

  4. Intrinsic Spin Resonance at RCS – Rapid Cyclic Synchrotron • emittance: 10 mrad, 95% • repetition rate 25Hz • sinusoidal ramping • kinetic energy: 180MeV – 3GeV • intrinsic resonance strength for a particle at an emittance of 10 mrad =6.18x10-5 Full spin flip by a rf dipole Fast tune jump? =6.60x10-5 =7.63x10-5 =2.33x10-5

  5. 10 pmrad emittance Issues of accelerating polarized protons in Main Ring • Beam energy: 3  50 GeV (G = 7.5  97.5) • Design working point: nx = 22.34; ny = 20.27 • Many imperfection resonances • Strong intrinsic resonances • No space for full snake installation

  6. Spin tracking without partial snakes • Spin tracking of single particle at the nominal tune of the lattice. • e =10p mm.mrad. No snakes. • The polarization is lost at the resonances, located at Gg = 3N ny

  7. Vertical component of stable spin Fractional part of spin tune Solution of accelerating polarized protons in Main Ring ny = 20.96 30% 30% Gg nx = 22.12 Injection Intrinsic resonance

  8. 12 particles at 4  mrad(1.5 beam sigma) Two 30% synthetic snakes Working point: nx = 22.128 ny = 20.960 Spin tracking

  9. Possible locations of partial snakes in MR First 30% snake Second 30% snake

  10. Main Ring Partial Snake • AGS type of cold snake • magnetic field strength: 3.4 Tesla • snake strength 30% (540 spin rotation angle) at injection and gets weaker at higher energy according to:

  11. Effect of Snake magnetic field on orbital motion • horizontal orbital offset • focusing field in both planes • both effects become weaker • at higher energy

  12. Matching of the INSA with snake at the energy g=11

  13. Matching snakes to the lattice • Because of the strong focusing of the snakes in both planes, they produce a substantial perturbation on the optics of the lattice at low energy, especially at injection. • Can be solved by using correcting quadrupoles at the entrance and exit of each snake to compensate the distortion, as demonstrated in the AGS. • Due to the constraint of limited space in MR, we present a solution using existing quadrupoles in MR QDT,QFP,QFT and QFS. Instead of building new quadrupoles, this solution only needs additional power supplies for these 4 magnets

  14. Solution of Correcting Quadrupoles nx = 22.12 ny = 20.96

  15. Betatron tune • No stable lattice found with MAD with both horizontal and vertical tune close to integer at injection. Real machine is probably stable (as in AGS) but tune swing is also possible. • The spin depolarization resonances in MR at low energy are very weak, and the amount of depolarization is negligible for a 10  mm-mrad beam. This allows one to ramp the two betatron tunes to (22.12, 20.96).

  16. Conclusion • Possible to accelerate polarized protons of 10p mm-mrad in the J-PARC Main Ring using two 30% partial snakes of AGS type. • The perturbation on the MR optics from snakes is significant at low energy. This can be minimized by using a correcting quadrupole doublet each at the entrance and exit of each snake. • Tracking with the code Spinkusing synthetic snakes with variable strength and a static lattice shows good polarization survival.

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