A Study of Polarized Proton Acceleration in J-PARC

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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

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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
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Setup for accelerating polarized protons at J-PARC

• Optically Pumped Polarized Ion Source 1012 H-
  per 0.5 ms pulse and gt 5 Hz rep. rate, 85
  polarization (similar to KEK-TRIUMF-BNL OPPIS)
• Bunch emittance 5 p mrad 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 gt .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)

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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
?6.60x10-5
Fast tune jump?
?7.63x10-5
?2.33x10-5
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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

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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

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Solution of accelerating polarized protons in
Main Ring
ny 20.96
30
30
Gg
nx 22.12
Injection
Intrinsic resonance
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Spin tracking

• 12 particles at 4 ? mrad(1.5 beam sigma)
• Two 30 synthetic snakes
• Working point
• nx 22.128
• ny 20.960

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Possible locations of partial snakes in MR
First 30 snake
Second 30 snake
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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

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Effect of Snake magnetic field on orbital motion

• horizontal orbital offset
• focusing field in both planes
• both effects become weaker
• at higher energy

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Matching of the INSA with snake at the energy g11
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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

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Solution of Correcting Quadrupoles
nx 22.12 ny 20.96
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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).

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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 Spink using synthetic
  snakes with variable strength and a static
  lattice shows good polarization survival.