Post on 09-Jan-2016
description
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.