Pioneering Proton Polarization at RHIC: Milestones and Future Plans

1. Mei Bai Collider Accelerator Deptartment Brookhave National Laboratory Proton Polarization at RHIC

2. Outline • Introduction • Polarized proton setup of RHIC complex • Milestones of RHIC spin program • RHIC polarized proton status • Achieved performance at 100 GeV • Results of latest 250 GeV run • Future Plan

3. BRAHMS(p) Absolute Polarimeter (H jet) RHIC pC Polarimeters Siberian Snakes Spin flipper PHENIX (p) STAR (p) Spin Rotators (longitudinal polarization) Spin Rotators (longitudinal polarization) Solenoid Partial Siberian Snake LINAC BOOSTER Helical Partial Siberian Snake Pol. H- Source AGS 200 MeV Polarimeter AGS Polarimeters Strong AGS Snake

4. E20 5.9% A20 10~15% Polarized proton in the AGS • AGS (Alternating Gradient Synchrotron) • Energy: 2.3 GeV ~ 23.8 GeV • A total of 41 imperfection resonances and 7 intrinsic resonances from injection to extraction warm snake Spin tune has a periodicity of 3. At a location where G is an integer multipole of 3, the gap between the spin tune and the integer reaches maximum

5. Courtesy of T. Roser Spin tune with two partial snakes 36+Qy intrinsic resonance Vertical betatron tune Vertical component of stable spin Extraction Gg Spin tune

6. RHIC intrinsic resonance spectrum

7. Polarized proton setup in RHIC • RHIC: • Energy: 23.8 GeV ~ 250 GeV (maximum store energy) • A total of 146 imperfection resonances and about 10 strong intrinsic resonances from injection to 100 GeV. • Two full Siberian snakes

8. Depolarizing mechanism in the presence of snakes • Snake resonances • odd order resonance: driven by the intrinsic resonance • even order resonance: only present if • Closed orbit is not perfect • Snake configuration is not perfect current working point old working point 11/16 3/4 7/10

9. Snake resonance observed in RHIC 7/10 snake resonance polarized protons were accelerated to an energy of G=63, a location of a strong intrinsic spin resonance

10. Optimize the snake setting to have spin tune at ½ • Snake configuration • If the spin axes of the two snakes are not perpendicular • Horizontal orbital angle between snakes • if the horizontal orbits at the two snakes are not parallel • Precise vertical closed orbit control • Minimize the vertical closed orbit distortion to reduce the strength of even order snake resonances • For 100 GeV: rms distortion < 0.5mm • For 250 GeV: rms distortion < 0.3mm PRESERVING POLARIZATION IN RHIC

11. Precise optics control • Proper working point at a location with no or negligible snake resonances • Minimize the linear coupling • Keep both horizontal and vertical tune within the window where there are no snake resonances • Avoid store the beam at an energy nearby a strong intrinsic spin resonance PRESERVING POLARIZATION IN RHIC

12. Milestone of RHIC pp program

13. Polarization performance at 100 GeV • Polarization of run06, 08 and 09, measured with the absolute polarimeter using H Jet RUN 06 RUN 08 RUN 09

14. Polarization performance at 100 GeV • Polarization is preserved up to 100 GeV Polarization measured with CNI polarimeter

15. Polarization performance at 250 GeV? • Average beam polarization: ~42% • Best polarization achieved: ~54%

16. Integrated Luminosity Courtesy of P. Ingrassia

17. Remaining Challenges and plans • AGS (Alternating Gradient Synchrotron) • Horizontal resonance due to the fact that the stable spin direction is tilted slightly away from vertical due the partial snake configuration • A group of horizontal tune jump quadrupoles to jump cross all 82 horizontal intrinsic resonances • RHIC: • Polarization loss beyond 100 GeV

18. Polarization Ramp Measurement • No polarization loss up to 136 GeV • candidate of depolarization location: the three strong intrinsic resonances after • 100 GeV, around 136GeV, 199 GeV and 221 GeV

19. Polarization tune scan above 100GeV 3/4 resonance 11/16 resonance 7/10 resonance

20. Remaining Challenges and plans • Minimize polarization loss from 100GeV to 250 GeV in RHIC • New working point close to integer where no or negligible snake resonances • To run RHIC at this working point, 10 Hz triplet vibration needs to be addressed

21. Summary • Routine operation of pp collision at 100 GeV with ~ 60% polarization • First accelerate and collide pp at 250 GeV with 109 bunches, 1.2x1011 protons per bunch and an average of ~42% polarization • Demonstrated acceleration/collision of 56x56 with 1.8x1011 bunch at 250GeV. Polarization was ~30% in both rings • Future plans towards 70% polarization • Horizontal tune jump quadrupoles in the AGS • Investigate the near-integer working point at RHIC to preserve polarization beyond 100 GeV • Various techniques including orbit feedback to address the issues of • Triplet vibration • 24 hour orbital variation

22. Acknowlegement L. Ahrens, I. G. Alekseev, J. Alessi, J. Beebe-Wang, M. Blaskiewicz, J.M. Brennan, D. Bruno, J. Butler, R. Connolly, T. D’Ottavio, A. Drees, W. Fischer, G. Ganetis, C. Gardner, J. Glenn, T. Hayes, H. Huang, P. Ingrassia, D. Kyran, J. Laster, R. Lee, A. Luccio, Y. Luo, W.W. MacKay, Y. Makdisi, G. Marr, A. Marusic, G. McIntyre, R. Michnoff, M. Minty, C. Montag, J. Morris, P. Oddo, B. Oerter, J. Piacentino, F. Pilat, V. Ptitsyn, G. Robert-Demolaize, T. Roser, T. Satogata, V. Schefoer, K. Smith, D.N. Svirida, S. Tepikian, D. Trbojevic, N. Tsoupas, J. Tuozzolo, M. Milinski. A. Zaltsman, A. Zelinski, K. Zeno, S.Y. Zhang