Thomas RoserSPIN 2006

October 3, 2006

A Study of Polarized Proton Acceleration in J-PARC

A.U.Luccio, M.Bai, T.RoserBrookhaven National Laboratory, Upton, NY 11973, USA

A.Molodojentsev, C.Ohmori, H.SatoHigh Energy Accelerator Research Organization, Tsukuba, Ibaraki, Japan

H.HatanakaResearch Center for Nuclear Physics, Osaka University, Japan

Layout of J-PARC for polarized proton acceleration

Pol. H- Source

180/400 MeV Polarimeter

Rf Dipole

25-30% Helical Partial Siberian Snakes

pC CNI Polarimeter

Extracted BeamPolarimeter

50 GeV polarized protons for slow extracted beam primary fixed target experiments“Low” intensity (~ 1012 ppp), low emittance (10 mm mrad) beams

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 rad and 0.3 eVs for 2 1011 protons (required for polarized beam acceleration)

Linac: No depolarization RCS (25 Hz, y = 6.35, P = 3, Ekin = .18 … 3 GeV, G = 2.2 … 7.5)

5 imperfection resonances; harmonic correction needed for G = 7 Intrinsic resonances:

G = 2.65 (9- y), 3.35 (-3+ y), 5.65 (12- y), 6.35 (0+ y) Full spin flip with rf dipole: 20 Gm gives > .99 spin-flip (seems

feasible) Avoid depolarization with tune jump: y = 0.2 in 6 turns large

aperture ferrite quadrupoles with fast pulsing power supplies (difficult)

Intrinsic Spin Resonance at RCS – Rapid Cyclic Synchrotron

• emittance: 10 rad, 95%• repetition rate 25Hz• sinusoidal ramping• kinetic energy: 180MeV – 3GeV

• intrinsic resonance strength for a particle at an emittance of 10 rad

Full spin flip by a rf dipole

=2.33x10-5

=6.18x10-5

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

10 rad emittance

Issues of accelerating polarized protons in Main Ring

Beam energy: 3 50 GeV (G = 7.5 97.5) Design working point: x = 22.34; y = 20.27 Many imperfection resonances Strong intrinsic resonances No space for full snake installation

Spin tracking without partial snakes

Spin tracking of single particle at the nominal tune of the lattice.

=10 mm.mrad. No snakes.

The polarization is lost at the resonances, located at G = 3N y

Solution of accelerating polarized protons in Main Ring

Vertical component of stable spin

Fractional part ofspin tune

Injection Intrinsic resonance

G

1

0.

preaxis OT gg( )( )T

2

sptune OT gg( )( )

13.57.5 gg8 9 10 11 12 13

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

y = 20.96

x = 22.12

Spin tracking

12 particles at 4 rad(1.5 beam sigma)

Two 30% synthetic snakes

Working point: x = 22.128

y = 20.960

Possible locations of partial snakes in MR

First 30% snake Second 30% snake

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:

2

25.93

2.255.2

T

B

• horizontal orbital offset

• focusing field in both planes

• both effects become weaker at higher energy

1

5.20105.0

T

Bmxoff

Effect of Snake magnetic field on orbital motion

22

1 1

5.252.1

1

T

Bm

f x

22

1 1

5.267.0

1

T

Bm

f y

Matching of the INSA with snake at the energy =11

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

Solution of Correcting Quadrupoles

x = 22.12y = 20.96

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).

Conclusion

Possible to accelerate polarized protons of 10 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.