AGS Polarized Proton Status and Plan

1. AGS Polarized Proton Status and Plan • Haixin Huang August 30, 2007 RSC Meeting

2. Goals of the AGS pp Run7 • The AGS pp Run was squeezed from both sides: RHIC Au operation and NSRL operation, sometimes even by BLIP. • The 11 weeks run was aimed at three goals: • Setup high Qx to overcome horizontal resonances with the two partial snakes. This requires a stronger cold snake, which in turn will make the injection tuning harder. • Investigate the possible polarization loss around the early part of the ramp, where the vertical tune is not in the spin tune gap and acceleration rate is slow. • Taking ORM data to understand the AGS lattice with and without the partial snakes.

3. Spin Tune and Fractional Vertical Tune c c c c p g . G p g - arccos(cos ( 1 ). cos( 2 ). cos( . G ) sin( 1 ). sin( 2 ). sin( )) 2 2 2 2 3 n = s p 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+.

4. Push 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 skew quads are powered to minimize the coupling. • Since the horizontal resonance strength are very weak, the horizontal tune does not need to be as close to integer as vertical tune. • A stronger cold snake (14%) is needed for both betatron tunes in the spin tune gap. • Twelve quads were added to the vertical quad string.

5. Tune Plot at Extraction Energy radial shift ( Qx:8.82-> 8.95) With normal quads Adding 12 quads

6. Betatron Tune and Spin Tune

7. Better Horizontal Polarization Profile for High nx

8. Pinj  More Polarization Loss with Stronger Snakes at Gg=7.5 Slopes: Instrumentation and/or emittance effect? Pmea=Pinj* (cos1)(cos 2)

9. Residual Vertical Intrinsic Resonance • Spin tracking only throughout the first two intrinsic resonances. • The vertical betatron tune can only be pushed into the spin tune gap after Gg=5. Two weak intrinsic resonance have been left during the acceleration. The spin tracking code did not take into account the solenoidal field gradient, sextupole component in the helical snakes. More realistic tracking is needed. F.Lin et.al PAC, Albuquerque New Mexico (2007)

10. Polarization Loss Mechanisms • Slow acceleration rate at beginning part of the ramp, large lattice distortion (stronger resonance strength) in combination of the vertical tune outside the spin tune gap. • Helical snake has significant sextupole component, which could induce spin resonance with condition such as ns =Nnxny; N nx; Nny. • Helical snake also has radial gradient in longitudinal field. A solenoid has been built in to compensate the constant longitudinal field at a given energy (chosen as Gg~9), but can not compensate the gradient component, nor at different energies.

11. Choosing Representative Data Sets • The injection and extraction mismatches are calculated for two-partial-snake scenario.  • The vertical profiles were measured several times last run (seen Fanglei’s presentation on May 31, 06 at spin meeting). I extracted the ratio of center polarization with fit vs. P_0 and averaged over several profiles. • June 19, 2007 with high horizontal tune. The six runs gave 62.7+-1.0% (intensity 0.9*1011). The source polarization was around 80% this year, which gave 0.784 as the overall ratio. • For the low Qx case, we only have an extensive runs with horizontal target, which means I will use the horizontal profile factor twice. From data taken on May 12, 2006, the average polarization was 59.5+-1.0% (intensity 1.2*1011). Given the source polarization 82%, this results the ratio of 0.726. • At extraction energy Gg=45.5, the C15 vertical component will be slightly higher than at extraction. • Take all these factors, the expected “efficiency” is shown as “Total”.

12. Expected Polarization Transmission Efficiency Some of them are due to injection/extraction mismatch; some of them are due to horizontal resonances and residual vertical resonances. There are still 8-9% (relative) unexplained polarization loss.   14%+5.9% (high nx)14%+5.9%(low nx) 10%+5.9% Inj. 0.975 0.975 0.993 Ext. 0.962 0.962 0.976 Ver. Profile 0.9582 0.958 0.9212 Hor. Profile 0.966 0.9432 0.964 C15 vs. H10 1.021 1.021 1.015 Total 0.849 0.816 0.804 Measured 0.784 0.726 0.79

13. 14% vs. 10% cold snake • 10% cold snake: • It causes less lattice distortion near injection. Larger aperture for high intensity, easier to reach high intensity. • Still some residual polarization loss due to vertical resonances. • Horizontal resonances can not be overcome with this setup. Reduce emittance by MEBT upgrade (not this summer) • 14% cold snake • It can overcome horizontal resonances (at least partially). • If the polarization loss near injection can be mitigated, it has the potential to be the better solution.

14. How ToAchieve 70% Polarization in the AGS • It has to be done with even higher intensity. • Reduce emittance growth at BtA stripping foil by altering (horizontal) beta function locally. • Reduce emittance by MEBT upgrade (not this summer). • More polarization with same intensity from the source ~ 90% (demonstrated). • Increase the AGS polarization transmission efficiency by • Keep horizontal tune high in the spin tune gap (at least partially), it has to be with a 14% cold snake. • Injection on the fly (tested in run6). This will avoid or reduce • any possible depolarization due to slow acceleration near injection around the weak spin resonances • beam loss due to the excessive time stay at injection • Possible emittance exchange due to coupling • Offline studies to understand the depolarization mechanism at low energies (Snake helical field, lattice distortion)

15. Injection on the Fly • The idea is to cross the weak intrinsic resonances near injection as quick as possible. It potentially can also maintain both horizontal and longitudinal emittances. The scheme has been tested in run6 and it worked. Due to the limited time, the reduction of horizontal emittance was not 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 and pay close attention to polarization at low energies.

16. Beta functions at LtB Foil (Courtesy of K. Brown) Using stop band quads to change beta functions locally at foil. Extensive emittance study is planned during NSRL run next month.

17. Polarization vs. Emittance at G=7.5 with CSNK On

18. Summary • With a stronger (14%) cold partial snake, moving horizontal tune into the spin tune gap in the later part of the energy ramp gives better polarization. • Extensive orbit/tune data taking for AGS modeling work. • Polarization loss observed between AGS injection and G=7.5 • significant lower acceleration rate at the beginning of the acceleration ramp • additional depolarization mechanism • the helical snake field (sextupole field, solenoid field) • others • Injection-on-the-fly can mitigate these problems. • If the polarization loss associated with stronger snake near injection is curable, the stronger snake lattice remains competitive to or even better than the 10% CSNK one.