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Accelerating Polarized Protons to High Energy

Accelerating Polarized Protons to High Energy. Mei Bai Collider Accelerator Department Brookhaven National Laboratory. Outline. General introduction of accelerator physics spin dynamics Accelerating polarized protons to high energy RHIC: the first polarized proton collider

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Accelerating Polarized Protons to High Energy

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  1. Accelerating Polarized Protons to High Energy Mei Bai Collider Accelerator Department Brookhaven National Laboratory

  2. Outline • General introduction of • accelerator physics • spin dynamics • Accelerating polarized protons to high energy • RHIC: the first polarized proton collider • brief history of RHIC pp program • achieved performance of RHIC pp • Summary

  3. Synchrotron Rf cavity • The acceleration comes from the electric field with an oscillating frequency synchronized with the particle’s revolution frequency • Alternating gradient • A proper combination of focusing and de-focusing quadrupoles yields a net focusing force in both horizontal and vertical planes • FODO cell: most popular building block for synchrotrons QF QF QD L L

  4. Particle motion in a synchrotron • Transverse • Betatron oscillation: • Betatron tune: number of betatron oscillations in one orbital revolution • Beta function: the envelope of the particle’s trajectory along the machine

  5. y z beam direction x Spin motion in a circular accelerator • Thomas BMT equation • In a perfect accelerator, spin vector precesses around its guiding field, i.e. vertical • Spin tune Qs: number of precessions in one orbital revolution. In general, • horizontal field kicks the spin vector away from its stable direction, i.e. vertical, and can lead to • Depolarization resonance when the spin vector gets kicked at a frequency close to the frequency it precesses

  6. Depolarizing spin resonances For protons, imperfection spin resonances are spaced by 523 MeV

  7. Challenge in accelerating polarized protons to high energy: preserve beam polarization • Break the resonance condition: • Full Siberian snake • Rotates spin vector by 180o • Cancels the kicks on the spin vector in between the snakes • Keeps the spin tune independent of energy • Partial snake • rotates spin vector by an angle of <180o • Keeps the spin tune away from integer • Tune jump • Jump the betatron tune as quickly as possible • Intrinsic resonance only and can cause emittance blow up

  8. Challenge in accelerating polarized protons to high energy: preserve beam polarization • Change the resonance strength • Minimize the resonance strength • Harmonic close orbit correction • Imperfection resonance • Operationally difficult for high energy accelerators • Enhance the resonance strength to achieve full spin flip with normal resonance crossing rate • Induce full spin flip using an ac dipole • Can only be applied to strong intrinsic spin resonances • not ideal for coupling resonances

  9. 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

  10. E20 5.9% A20 10~15% Polarized proton acceleration complex at BNL • 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 • One 5.9% partial snake plus one 10~15% partial snake

  11. 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

  12. Tune scan with the AGS dual snake setup • 15% cold snake +5.9% warm snake Preliminary Snake resonances Operating working point Courtesy of H. Huang

  13. Results of AGS dual snake setup • The dual snake setup in the AGS was successfully commissioned. With the four new trim quadrupoles located at the entrance and exit of the cold and the warm snakes for compensating the optics distortion from the focusing fields from the snakes, 1.5x1011 protonswith a beam polarization of 65% were accelerated with the vertical tune close to 9. H. Huang’s talk: “Polarized Proton Acceleration in the AGS with Two Helical Partial Snakes”, Oct. 2, 17:00, Hall II

  14. Polarized proton acceleration complex at BNL • 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

  15. 5/6 Store working pt. Ramp working pt. 3/4 7/8 5/8 snake depolarization resonance • Condition • even order resonance • When m is an even number • Disappears in the two snake case like RHIC if the closed orbit is perfect • odd order resonance • When m is an odd number • Driven by the intrinsic spin resonances

  16. Snake resonance observed in RHIC Coupled 3/14 snake resonance ¼ snake resonance Maximum vertical tune |Horizontal tune – 3/14|

  17. 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

  18. Keep the spin tune as close to 0.5 as possible snake current setting Keep the vertical closed orbit as flat as possible How to avoid a snake resonance Flat orbit: Sum of kicks on the spin vector from quads as well as the dipole correctors = 0

  19. Keep the spin tune as close to 0.5 as possible snake current setting Keep the vertical closed orbit as flat as possible Keep the betatron tunes away from snakeresonance locations Precise tune control How to avoid a snake resonance

  20. Polarized proton collisions in RHIC

  21. Design parameters for RHIC pp

  22. Milestones of RHIC pp development

  23. RHIC pp achieved performance Ptitsyn’s talk: “RHIC Performance with Polarized Protons in Run-6”, Oct. 2, 16:45, Hall II

  24. one week shutdown RHIC pp performance: delivered luminosity • FY05: Provided a total of 12.6pb-1 luminosity with longitudinal polarization at STAR and PHENIX • FY06: faster setup, higher luminosity and higher polarization

  25. Goal! RHIC pp performance: average store polarization FY2005 FY2006 Blue average polarization: 49.5% Yellow average polarization:44.5%

  26. RHIC pp performance: polarization transmission efficiency

  27. First look of beam polarization at 250 GeV 45%

  28. RHIC intrinsic spin resonance strength achieved Intrinsic spin resonance Qx=28.73, Qy=29.72, emit= 10

  29. Resonance around 138 GeV Polarization 250 GeV ramp measurement

  30. Luminosity: Goal: At 100 GeV: 60x1030 cm-2s-1 20x1030 cm-2s-1 (x3) Improve bunch intensity/emittance: Injector Improvement improve beam transfer efficiency Eliminate beam emittance growth during ramp Improve luminosity lifetime: 10 Hz feedback loop to fight against the 10 Hz orbit jitter: work-in-progress minimize non-linear triplet errors to improve the tolerance to beam-beam effect At 250 GeV: 150x1030 cm-2s-1(x2.5 compared w. 100 GeV) Outlook of RHIC polarized protons

  31. Polarization Goal: 70% 65% AGS: operating the AGS with both betatron tunes placed in the spin tune gap that dual snakes provide. Outlook of RHIC polarized protons

  32. Polarization Goal: 70% 65% AGS: operating the AGS with both betatron tunes placed in the spin tune gap that dual snakes provide RHIC: Snake current setting is critical to make sure the spin precession tune is very close to 0.5 Multiple techniques of measuring spin precession tune in RHIC are under development. Precise tune control Tune+decoupling feedback system comissioned in FY06 Precise orbit control Re-alignment of the machine Improve the quality as well as the robustness of the BPM system to achieve the rms value of the orbit distortion below 0.3mm Outlook of RHIC polarized protons

  33. Summary • Over the past 5 years, all the essential hardware and diagnostic apparatus for polarized beam were put in place and successfully commissioned. RHIC has successfully accelerated polarized protons to 100 GeV with no polarization loss. • The performance of RHIC pp in Run 2006 was greatly improved due to the great success of the AGS dual snake setup as well as the improvement of RHIC systems. • The 500 GeV development demonstrated a beam polarization of 45% at 250 GeV and also identified the location of depolarizing resonances. • With the success in the AGS and improvements in RHIC, the RHIC 2006 has achieved a faster setup as well as higher luminosity.

  34. Acknowledgement L. Ahrens, I.G. Alekseev, J. Alessi, J. Beebe-Wang, M. Blaskiewicz, A. Bravar, J.M. Brennan, D. Bruno, G. Bunce, J. Butler, P. Cameron, R. Connolly, J. Delong, T. D’Ottavio, A. Drees, W. Fischer, G. Ganetis, C. Gardner, J. Glenn, T. Hayes, H-C. Hseuh. H. Huang, P. Ingrassia, U. Iriso-Ariz, O. Jinnouchi, J. Laster, R. Lee, A. Luccio, Y. Luo, W.W. MacKay, Y. Makdisi, G. Marr, A. Marusic, G. McIntyre, R. Michnoff, C. Montag, J. Morris, A. Nicoletti, P. Oddo, B. Oerter, J. Piacentino, F. Pilat, V. Ptitsyn, T. Roser, T. Satogata, K. Smith, D.N. Svirida, S. Tepikian, R. Tomas, D. Trbojevic, N. Tsoupas, J. Tuozzolo, K. Vetter, M. Milinski. A. Zaltsman, A. Zelinski, K. Zeno, S.Y. Zhang.

  35. Beam intensity AGS bending magnet field 9.0 Vertical betatron tune (8.98) 8.8 Horizontal betatron tune 8.6 Results of AGS dual snake setup Courtesy of L. Ahrens and K. Brown

  36. How to avoid a snake resonance • Keep the spin tune as close to 0.5 as possible • snake current setting • set the vertical tune to • 0.745 • measure the beam • polarization with • different snake current • expect no depolarization • if the corresponding spin • tune is very close to 0.5

  37. 10% Cold snake 5.9% Warm snake P P 15% Cold snake 5.9% Warm snake Target position Target position AGS Horizontal resonance The tilted stable spin direction also causes about ~5% depolarization at the locations of horizontal tunes Courtesy of F. Lin: “Exploration of Horizontal Intrinsic Spin Resonance in the AGS”, April 22, C14.00005

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