Polarized Proton Acceleration in the AGS with Two Helical Partial

Snakes

October 2, 2006SPIN 2006

H. Huang, L.A. Ahrens, M. Bai, A. Bravar, K. Brown, E. D. Courant, C. Gardner, J.W. Glenn, A.U. Luccio, W.W. MacKay, V. Ptitsyn, T. Roser, S. Tepikian, N. Tsoupas, J. Wood, K. Yip, A. Zelenski, K. Zeno

Depolarizing Resonances in the AGS Imperfection Resonances

arising from sampling of error fields, fields due to closed orbit errors, etc. G=n (integer) G=5,6,…45 partial snake(s) Spin tune is given by coss=cos (/2) cos G s can not be an integer, avoided all imperfection resonances Vertical Intrinsic Resonances

arise from sampling of focusing fields due to finite beam emittance. G=kPy Strong ones: G=0+y,12+y,36y AC dipole, strong partial snakes Weak ones: G=24y,48-y fast crossing speed , strong partial snakes Horizontal Intrinsic Resonances

1. horizontal non-vertical stable spin direction due to strong partial snake interaction with horizontal motion.

2. betatron motion coupled to the vertical betatron motion by coupling elements: solenoid, helical magnet.

G=kx fast crossing speed, strong partial snakes

Partial Snake Resonances

strength proportional to nearby intrinsic resonance strength. G=kPmy , m>1 avoid the resonance tunes

Spin Tune and Fractional Vertical Tune

With two helical magnets installed, the lattice is largely distorted at low energies. It took quite a lot efforts to set the vertical tune close to integer. Vertical tune is higher than 8.98 at all major intrinsic resonances. It is even as high as 8.99 at 36+.

Ramp Measurement

RHIC injection energy was lowered by 1 unit of G for better spin transmission. Note that there is not much data before G=7.

Vertical Tunes8.84 8.86 8.88 8.90 8.92 8.94 8.96 8.98 9.00

0+

36+

Vertical Tunes8.84 8.86 8.88 8.90 8.92 8.94 8.96 8.98 9.00

Pol

ariz

atio

n (

%)

-10

0

10

20

30

40

50

60

-10

0

10

20

30

40

50

60

12+

0+

Polarization as Function of Vertical Tunes

Snake resonance effect is clearly seen.

9th Harmonic at 36+

Vertical sin 9th harmonic amplitude at 36+ (mm)

-20 -15 -10 -5 0 5

Pol

ariz

atio

n

-10

0

10

20

30

40

50

60

70

Estimated imperfection resonance strengths with large sin 9th harmonics. As can be seen, with 8mm sin 9th harmonic amplitude, the resonance strength is comparable to the 16% partial snake in the AGS. With certain phase between them, the effect of partial snakes is canceled by the large orbit distortion at G=45 (near 36+y).

Measured polarization as function of the sine 9th harmonic amplitude at 36+y. The dashed

line is to guide the eyes. The location of the polarization dip agrees with model prediction.

(Mei)

Horizontal Polarization Profile

3 2 1 0 1 2 30.5

0.6

0.7

0.8

0.9

1

1.11.1

0.5

P1 82 x 10 1 ( )

w2

w2 w3

w2 w3P2 82 x 20 2 ( )

v2

v2 v3

v2 v3

3.3. x q1 q1 q1 x u1 u1 u1

Polarization

Target Position (mm)

15% Cold Snake

10% Cold Snake

4 3 2 1 0 1 2 3 40

2 105

4 105

6 105

0.7 106

33.586

f1 x( )

w5

w5 w6

w5 w6f2 x( )

v5

v5 v6

v5 v6

44 x q1 q1 q1 x u1 u1 u1Target Position (mm)

Normalized

Rate

15% Cold Snake10% Cold Snake

The horizontal resonance effect is measurable over the whole ramp. The following snake setup gave the best polarization: 10% cold snake, 5.9% warm snake.

 2002 2003 2004 2005 2006

Intensity (1011) 0.7 0.7 0.7 1.0 1.5

Polarization 30% 40% 50% 50% 65%

AGS Polarization Evolution

Slow ramp rate

Normal ramp rate

New warmsnake

Cold snake

BoosterScraping

Source polarization and intensity gradually improved over this period.

Horizontal Tune Near Integer • The idea is to put horizontal tune near 9 (~8.95) while

maintain vertical tune close to 9 (~8.98). Both tunes are within the spin tune gap.

• With the fractional part of the two tunes are so close, the coupling has to be corrected very well. The old solenoid snake will be ramped to overcome the coupling.

• Since the horizontal resonance strength are very weak, the horizontal tune does not need to be so as close to integer as vertical tune.

• The idea has been tested with beam. With added strength from nearby quad strings, we should be able to put the tunes into the gap as needed.

Horizontal Tune Near Integer (2)

Horizontal Tune Near Integer (3)

Summary• 65% polarization with 1.51011 intensity achieved with two partial

snakes in the AGS. • The following snake setup gave the best polarization: 10% cold

snake, 5.9% warm snake.• Added four compensation quads for warm snake worked very well.

The lattice is easier to handle than last year without them. • The intensity dependence is very benign with this setup. • There is polarization loss of 5% due to each of vertical and

horizontal resonances. The injection and extraction mismatch is about 1%. We expect 73% polarization with 82% input. There is still an relative 10% polarization loss unexplained.

• Move horizontal tune into the spin tune gap next run.• Spin tracking effort is underway to understand the polarization loss. • More polarization ramp measurements during next run.

Spare slides

AGS Stability

RHIC injection measurements with very long measuring time. Averaged over 420 million events. Error bar for each bunch is 4.7%. Trying to look for AGS variation from shot to shot. Need more statistics.

pC CNI Polarimeter in the AGS

ultra-thin Carbon ribbon (target)5 g/cm2

250 m wide

~32 cm

Si strip detectors12 vertical strips

read-out withwaveform digitizers

beamdirection

beam

24 mm

12 mm

p p

left right

Ramp Measurement (2)

With total of eight runs, the error bars are already quite small. If data from 45 degree detectors are included, they can be further reduced.