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RHIC: the first polarized proton collider

RHIC: the first polarized proton collider. Mei Bai Collider Accelerator Department Brookhaven National Laboratory. Outline. General introduction of accelerator physics spin dynamics RHIC: the polarized proton collider Brief history of RHIC pp development achieved performance of RHIC pp

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RHIC: the first polarized proton collider

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  1. RHIC: the first polarized proton collider Mei Bai Collider Accelerator Department Brookhaven National Laboratory JINR, Prague, July 27, 2005

  2. Outline • General introduction of • accelerator physics • spin dynamics • RHIC: the polarized proton collider • Brief history of RHIC pp development • achieved performance of RHIC pp • highlights of RHIC pp developments • Summary JINR, Prague, July 27, 2005

  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/defocusing force in both horizontal and vertical planes • FODO cell: most popular building block for synchrotrons QF QF QD L L JINR, Prague, July 27, 2005

  4. Particle motions in a synchrotron: • Longitudinal • Synchrotron oscillation • Synchrotron tune V E t() JINR, Prague, July 27, 2005

  5. Particle motions in a synchrotron: • Transverse • Betatron oscillation: • Betatron function: the envelope of the particle’s trajectory along the machine • Beta tune: number of betatron oscillations in one orbital revolution • Transverse • Betatron oscillation: • Betatron function: the envelope of the particle’s trajectory along the machine • Beta tune: number of betatron oscillations in one orbital revolution JINR, Prague, July 27, 2005

  6. y z beam directoin x Spin dynamics:Spin motion in a circular accelerator • Thomas BMT equation • Spin tune In the frame which moves with the particle JINR, Prague, July 27, 2005

  7. Spin dynamics:Depolarization mechanism • Imperfection resonance • Coherent perturbations on the spin precession from horizontal dipole fields due to the non-zero closed orbit. • condition: • Strength: size of the closed orbit distortion • Intrinsic resonance • Coherent perturbations on the spin precession from quadrupole fields • Condition: • Strength: size of the betatron oscillation amplitude • High order resonance JINR, Prague, July 27, 2005

  8. Spin dynamics: Siberian snake • Full Siberian snake • Rotate spin vector by 180o • Cancels the perturbation on on the spin motion between snakes • spin tune in the presence of two snakes: JINR, Prague, July 27, 2005

  9. 5/6 Store working pt. Ramp working pt. 3/4 7/8 5/8 Spin dynamics: 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 JINR, Prague, July 27, 2005

  10. RHIC pp accelerator complex RHIC pC Polarimeters Absolute Polarimeter (H jet) BRAHMS & PP2PP (p) PHOBOS Siberian Snakes Siberian Snakes PHENIX (p) STAR (p) Spin Rotators (longitudinal polarization) Spin flipper Spin Rotators (longitudinal polarization) Solenoid Partial Siberian Snake Pol. H- Source LINAC BOOSTER Helical Partial Siberian Snake AGS 200 MeV Polarimeter AGS Internal Polarimeter Rf Dipole AGS pC Polarimeters Strong AGS Snake Installed and commissioned during FY04 run installed and commissioned during FY05 run JINR, Prague, July 27, 2005

  11. Siberian Snakes PHENIX (p) Spin Rotators (longitudinal polarization) Solenoid Partial Siberian Snake LINAC BOOSTER Helical Partial Siberian Snake Pol. H- Source AGS 200 MeV Polarimeter JINR, Prague, July 27, 2005

  12. Polarized proton collisions in RHIC JINR, Prague, July 27, 2005

  13. Design parameters for RHIC pp JINR, Prague, July 27, 2005

  14. Milestones of RHIC pp development JINR, Prague, July 27, 2005

  15. RHIC pp achieved performance JINR, Prague, July 27, 2005

  16. RHIC pp performance: delivered luminosity JINR, Prague, July 27, 2005

  17. RHIC pp performance in 2005: delivered luminosity Provided a total of 12.6pb-1 luminosity with longitudinal polarization at STAR and PHENIX JINR, Prague, July 27, 2005

  18. RHIC pp performance in 2005: average polarization at store 49.5% 44.5% JINR, Prague, July 27, 2005

  19. RHIC pp performance in 2005: weekly luminosity s = 410 GeV development Total hours in store: 904 Total calendar hours: 1680 Total hour for 205 GeV: 72 JINR, Prague, July 27, 2005

  20. RHIC pp performance in 2005: a typical week JINR, Prague, July 27, 2005

  21. RHIC pp performance in 2005: a typical store • The highest vacuum pressure rise was seen at • CNI polarimeter • IR10 • Still below the vacuum limit at 5x10-6 Torr • 106x106 bunches • Bunch intensity at injection: • Blue=0.99x1011, yellow=1.07x1011 JINR, Prague, July 27, 2005

  22. Snake resonance observed in RHIC ¼ snake resonance Coupled 3/14 snake resonance JINR, Prague, July 27, 2005

  23. Snake resonance observed in RHIC 7/10 snake resonance JINR, Prague, July 27, 2005

  24. Keep the spin tune as close to 0.5 as possible: snake current setting Keep the betatron tunes away from snake resonance locations: Precise tune control Tune feedback How to avoid snake resonance JINR, Prague, July 27, 2005

  25. Snake current scan in RHIC • Yellow: • no differencebetween zero orbit and flatten orbit • Blue: • wider than FY04 and than yellow • weaker resonance? JINR, Prague, July 27, 2005

  26. Highlight of RHIC pp developmentsQuest for a new working point in RHIC JINR, Prague, July 27, 2005

  27. Highlight of RHIC pp developmentsworking point exploration a snake depolarization resonance • Motivation for new working • point development: • good for polarization • transmission efficiency • good beam lifetime under • collisions • good polarization lifetime Working point during ramp good spot for polarization as well as for beam lifetime Courtesy of R. Tomas Loss rate JINR, Prague, July 27, 2005

  28. Highlight of RHIC pp developments s = 410 GeV development p=205 GeV is the compromise between machine preference and PHOBOS interest on pp physics at s=410 GeV p=217 GeV This gives the same Brho as Cu and one can avoid an additional DX magnet training achieved Intrinsic spin resonance Qx=28.73, Qy=29.72, emit= 10 JINR, Prague, July 27, 2005

  29. Highlight of RHIC pp developments s = 410 GeV development • 30% polarization was measured in both • rings at 205 GeV per beam • Two polarization ramp measurements • shows an increase of 1mm vertical rms • in yellow decreased the polarization • transmission efficiency by close to a • factor of 2 JINR, Prague, July 27, 2005

  30. Highlight of RHIC pp developments s = 410 GeV development • no polarization loss before • 100 GeV • With yellow yrms increased • by 1mm around the 1st • strong at 135GeV • Blue vertical tune moved away • from 0.7 JINR, Prague, July 27, 2005

  31. E20 5% A20 10% Two partial snake scenario Vertical betatron tune Gg Extraction 36+n intrinsic resonance Vertical component of stable spin Spin tune Courtesy of T. Roser JINR, Prague, July 27, 2005

  32. AGS cold snake development: tune scan at 36+Qy • 10% cold snake + • 5% warm snake • experimental data • agree well with spin • simulation Preliminary Courtesy of H.H. Huang JINR, Prague, July 27, 2005

  33. Summary of AGS cold snake development • 3 Tesla superconducting helical dipole snake installed in AGS • Stable operation using four cryo-coolers • Quickly reached performance of AGS without cold snake • Beam horizontal emittance is significantly smaller • Maximum measured polarization: • ~ 56% with 0.3x1011 protons per bunch • Detailed studies show expected spin behavior • Unexpected beam intensity dependence of polarization • Highest bunch intensity achieved 1.0x1011 with measured polarization of ~ 41% • Investigate various reasons • Tune spread • Insufficient correction of 9th harmonic of the vertical orbit • polarimeter saturation • Others … JINR, Prague, July 27, 2005

  34. Summary of AGS cold snake development • Several scenarios of optics correction of lattice distortions by the helical snake(s) were successfully tested. Possibly more corrections are needed to minimize the beam loss at injection which is the dominant factor in the available bunch intensity Courtesy of H.H. Huang JINR, Prague, July 27, 2005

  35. Luminosity: Goal: 150x1030 cm-2s-1 10x1030 cm-2s-1 Energy: 100 GeV 250 GeV AGS cold snake: remove the dependence of beam polarization on bunch intensity More NEG coated pipe: 110 bunches with 2x1011 protons per bunch Upgrade of RHIC pC polarimeter to avoid the deterioration of the local vacuum pressure due to excessive opening of vacuum pipe to replace the silicon detectors as well as C targets Reduce the non-linearity errors from the triplets to reduce the beam-beam effect Feedback system to combat the 10 Hz orbit jitter Outlook of RHIC polarized protons JINR, Prague, July 27, 2005

  36. Outlook of RHIC polarized protons • Luminosity: • the 10 Hz orbit jitter has been observed in RHIC. This effect leads to modulated beam-beam effect and blows up the beam emittance during a long store. JINR, Prague, July 27, 2005

  37. Polarization Goal: 70% 50% Snake current setting is critical to make sure the spin precession tune is very close to 0.5 Using the pC polarimeter to measure the turn by turn spin precession at top energy to measure the spin tune Precise tune control Ongoing improvement of the RHIC online model Better de-coupling technique Tune feedback 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 JINR, Prague, July 27, 2005

  38. Closed orbit in RHIC Flat orbit: Sum of kicks on the spin vector from quads as well as the dipole correctors = 0 Orbit through the center of bpms • under 100 GeV, the orbit correction w.r.t. • the zero orbit is sufficient for preserving • the beam polarization • going beyond 100 GeV, the spin resonances • are much stronger and simulation shows the • spin prefers the flat orbit to the zero orbit • side effects of the flat orbit • strong coupling of the betatron oscillation • enhance the imperfection resonance at a • location of JINR, Prague, July 27, 2005

  39. Summary • Over the past 5 years, all the essential hardware and diagnostic apparatus for polarization are in place and successfully commissioned. RHIC has successfully accelerated polarized protons to 100 GeV with no polarization loss. • The RHIC pp run in 2005 is the first long pp run dedicated for physics data taking. RHIC performed well. The total delivered luminosity is well within the C-AD projection. The achieved polarization is above the projection thanks to the great performance of the polarized proton source and the injectors. • The 410 GeV development demonstrated the depolarization resonance is sensitive to the orbit distortion. Machine re-alignment will be arranged during the shutdown. • With the planned measures, we expect RHIC to achieve its design goals for polarized protons in the next couple of years JINR, Prague, July 27, 2005

  40. 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. JINR, Prague, July 27, 2005

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