AGS Run6 Summary

July 28, 2006RSC meeting

Haixin Huang

Challenge of the Setup• 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.

• 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 8.994 at 36+.

• Even with such strong partial snakes, 9th harmonics at 36+ could still cause polarization loss with certain orbit distortion amplitude.

• RHIC injection energy was lowered by 1 unit of Gfor better spin transmission.

Spin Tune and Fractional Vertical Tune(Junpei)

Measured Tunes along the Ramp

9.0

8.6

flattop

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

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%)

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60

-10

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60

12+

0+

Polarization as Function of Vertical Tunes

AGS Stability (Yellow Injection Measurement)

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.

Benign Intensity Dependence • We seem to have emittance growth in the vertical

dimension in the AGS as measured by the AGS IPM.• The Booster scraping is mainly affecting the vertical

emittance. • With two partial snake solution, the vertical emittance is

less a problem. That is the key to reach 65% polarization with higher intensity than the past.

Polarization vs. Intensity at Injection

No intensity dependence in this intensity range. This is very different from last year's operation with AC dipole.

YELLOW1.4*10^11: 58.48+-0.39%; 1.0*10^11: 56.60+-0.80%; 0.5*10^11: 56.58+-0.52%.

AGS1.5*1011: 59.22+-2.44%1.1*1011: 60.98+-1.71%0.6*1011: 58.43+-1.71%

Activate pp35

60

50

1.4

0.5

9th Harmonic at 36+

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

-20 -15 -10 -5 0 5

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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

(Fanglei)

G43.6 43.8 44.0 44.2 44.4 44.6 44.8 45.0 45.2 45.4 45.6 45.8 46.0 46.2 46.4 46.6 46.8 47.0

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60B Field Scan

No polarization loss across 36+Horizontal resonances stronger than warm snake only case.

G45.8 46.0 46.2 46.4 46.6 46.8 47.0 47.2

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5.9% partial snake only

Qx=8.6

Qx=8.8

Field Scan ( Warm Snake Only)

38+Qy

38+Qx

Horizontal resonances are much weaker than the counterparts of vertical ones.

55-Qy

41.4/49.8=.83

34.9/49.2=.71

Injection on the Fly • The idea is to maintain both horizontal and longitudinal

emittances. The idea has been tested and it worked. Due to the limited time, the reduction of horizontal emittance has not been observed.

• The only constraint on this mode is that one can only injection one bunch into AGS.

• We will spend more time on this scheme next run. • However, the detailed IPM emittance measurements

were done near the end of the run. First quick look suggested the emittance growth happened before 0+ where large vertical tune swing is required to push it high. More analysis on emittance growth will follow.

Horizontal Tune Near Integer • The idea is to put horizontal tune near 8 (~8.05) while maintain

vertical tune close to 9 (~9.02). 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.

• 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 and both tunes can be set to around 8.1 and 9.02. When quad current maximized at higher energies, the radius is moved to shift tune. Due to the limitation of power supply (650A in quads, unipolar sextupoles power supplies), we can only get horizontal tune to 8.1. But it proved that the idea works.

Horizontal Tune Near Integer (2)

flattop

9.0

8.1

Options for Hori. Tune Near Integer1. Purchase two new power supplies to power both

vertical and horizontal tune quads. The cost is about $300k (very rough estimate), and leading time is eight months.

2. Instead of purchasing new power supplies, using polarized proton quads (vertical) and unskew the skew quads (horizontal).

3. Using polarized proton quads (6 turns, 500A P/S ready), need cables to put 11 quads in series (~$56k cable cost). Rotate the skew quads requires 2 menX10wks plus 2 weeks survey if do all six quads. The base should still work. The copper bus have to be modified ( no quotation from central shop yet).

Options for Hori. Tune Near Integer (2)

1. The option one is going to give us capability to push both tunes near 9, though costly. Another concern is the cables (40+ years old).

2. Modeling of option two is ongoing. The skew quads rotation is labor intensive and means we will lose skew quads. Only use polarized quads at least can be used to give more vertical quad strength and no need to lower horizontal tune to raise vertical tune. Thus we can avoid the horizontal tune swing (cross 2/3 resonance) and a source of beam loss and emittance growth.

Modeling Efforts1. Analyze the difference orbit data taken at extraction

(minimum snake distortion) and injection. The analysis is going to provide information about the AGS lattice distorted by snakes.

2. Realistic spin tracking with SPINK ( snake effect on lattice changing with energy, synchrotron motion included).

3. Emittance growth observed in the AGS. Will model the emittance growth in the AGS to find the sources.

4. Another idea to reduce the horizontal resonance strength is to increase the horizontal beta function at the cold snake entrance. Modeling is needed to prove the idea with MAD and tracking first.

Better Instrumentation

1. Copy RHIC BBQ system into AGS for better tune/chromaticity/coupling measurement.

2. Develop application to do chromaticity measurement automatically along the ramp.

3. Use CNI polarimeter for emittance measurement (fast mode).

4. Improve AGS IPM to measure emittance more frequently.

5. Filters for the AtR flags will be checked during the summer.

CNI Polarimeter1. The jet run at 31.2GeV in RHIC should provide AN near

injection energy with better accuracy ( current one is with 30% systematic error).

2. We will do more ramp measurements with AGS CNI polarimeter. The target needs to stay in the beam center along the ramp and this can be achieved by feed-forward beam positions from nearby BPMs.

3. Install Am sources for 45 degree detectors. Include them in next year’s data analysis.

4. Add gear box for vertical axis to smooth the rotary motion.

5. Develop narrow targets (from 250m down to 120m) for higher intensity.

6. Mount a target with offset to measure polarization at injection.

Si Detector Acceptance (1)

Si Detector Acceptance (2) Recoil angle (θ) acceptance of the SSD:

    Δθ = 90° ± 2.7°

If we shift the target position back:

target shift     recoil angle acceptance

2 mm 92.3° > Δθ > 86.8°

5 mm 91.6° > Δθ > 86.1°

7 mm 91.1° > Δθ > 85.7°

We will install a target with a position shift to use the polarimeter at injection energy.

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 2%. We expect 72% polarization with 82% input. There is still a relative 10% polarization loss unexplained.

• The modeling (both spin and lattice) and instrumentation improvement will be our focus over the shutdown period.