AGS Polarized Proton Development toward Run-9

1. AGS Polarized Proton Development toward Run-9 • Haixin Huang Oct. 3, 2008

2. Job List After Run-8 • Understand past intensity scans. Can the observed intensity dependence be explained by the emittance increase with intensity? • Spin tracking study to locate possible polarization losses along the energy ramp. • Simulation study to raise AGS vertical tune near injection into spin tune gap. • Beam study at BtA in coming weeks: to verify the BtA model and develop a match to the AGS. • MEBT upgrade in the linac to reduce emittance (mainly horizontal one). • Horizontal tune jump setup. It is an AIP project now. Haixin Huang

3. Polarization Loss Near Injection from Horizontal Resonances (Courtesy of Fanglei) Horizontal Motion only ~0.01 ~0.04 ~0.06 Haixin Huang

4. Polarization Loss Near Injection from Vertical Resonances (From Fanglei) Based on run6 tune path ~0.16 Vertical Motion only ~0.06 ~0.09 Haixin Huang

5. Possible Sources of Polarization Loss • Category the polarization loss in four parts: • Near injection due to stronger horizontal resonance strength. From Fanglei’s tracking, one can estimate the resonance strength based on known emittance and ramp rate. • Near injection due to vertical tune outside spin tune gap. Again, the resonance strength can be estimated from Fanglei’s tracking. • Spin tracking for 36+ with vertical motion only. • Simple mathcad model to estimate the overall loss due to the rest horizontal resonances with real ramp rate. • There may still be some additional polarization loss due to not perfect vertical tune path. • No emittance growth in the AGS after injection: supported by the down ramp IPM measurements. There may be injection mismatch. One can use the extraction rf off IPM measurements. Haixin Huang

6. Run6 Polarization vs. Intensity model fitting Experimental data are normalized to the 200MeV polarization and then assuming 82% AGS input. Model prediction: taken into account AGS input as 82%, spin mismatch at injection and C15. The emittance dependence on intensity was taken from fitting of measurements between 3/21/06-6/12/06: x=9.21+2.30*I; y =7.90+4.13*I, where I is intensity in unit of 1011. Haixin Huang

7. Run8 Polarization vs. Intensity (1) Haixin Huang Prediction did not agree with experimental data.

8. Emittances show much Stronger dependence on Intensity (Courtesy of Kevin Brown) Higher energy case is better but still not as good as injection with front porch. Haixin Huang

9. Run8 Polarization vs. Intensity (2) Prediction did not agree with experimental data. What are the other sources of the loss? Haixin Huang

10. Possible Polarization Losses due to Vertical tune Path Qy too low for run8, not in the model Haixin Huang

11. What the Data Is Telling Us? • Overall, the agreement of slopes between the experimental data fitting and the model is within a factor two. The steeper slope in run8 from the model is due to the stronger emittance dependence on intensity. • In addition, the model is on the high end of the data (a machine stability issue, such as vertical tune close to snake resonances, or not high enough at certain part?). • The solutions: • Start with vertical tune in the spin tune gap; • Reduce emittance (linac upgrade, beta function reduction at LtB foil; BtA lattice match). • Horizontal tune jump. Haixin Huang

12. Plans for Run-9 • Start with injection with front porch. • LINAC beam transfer line upgrade is underway. The expected benefit is to reduce horizontal emittances at the AGS by about 30% ( will have a learning curve to find the optimized parameters). • Use faster Booster acceleration rate. It was lowered since NSRL running due to P/S limit. We can run it faster now. It should not affect polarization. • Verify model of BtA line before the run (with beam) and achieve a better match at AGS injection. This would help to reduce AGS emittances. • The emittance dependence on intensity hints some space charge or instability related to brightness of the beam. H=6 for AGS injection to reduce the emittance growth. Lower the RF voltage near injection would also help. • Raise the vertical tune inside the spin tune gap near injection (from 8.88 to >8.95). Question: can this option cope with tune jump ( high vertical tune + large optics distortion due to snakes)? • Add a pair of quads to generate 82 horizontal tune jumps at all weak horizontal resonances. It is likely not available on day one (Feb. 1).

13. Source 2009 projections (Courtesy of Anatoli) After the linac LEBT/MEBT-upgrade, smaller linac emittances should give rise to smaller Booster emittances. There may not be a need of Booster scraping. Then a shorter 300 us linac pulses can be used to produce 2.0-2.5 ·1011, which should produce further emittance reduction (less time on the stripping foil) and better polarization. Haixin Huang

14. Spin Tune and Qy vs Gg (Courtesy of Nick)

15. Tune Jump for Horizontal Resonances • Add two fast quad for this purpose. • Minimum change of nx 0.04 change in 100 ms-> requires dB/dx of 0.5T/m and 300Gauss. This will quadruple the crossing speed. • Operation issue: has to be dead-reckoning of timing. For practical operation, we need to maintain the horizontal tune and radius constant throughout the ramp. • Modify existing P/S & magnet(s). New ceramic chambers have been ordered. The magnets will be assemblied at BNL. Tight schedule. It may not be ready for test on day one (Feb. 1). • Benefit on polarization transfer efficiency (horizontal 16pi beam): • Crossing Pf/Pi(peak) Pf/Pi(whole) • regular speed 0.9030.815 • Double speed 0.950 0.903 • 4X speed 0.975 0.950 Haixin Huang

16. Backup Slides Haixin Huang

17. Tune Jump Pulse Trains Haixin Huang

18. Comparison between Run6 and Run8 Haixin Huang