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Observation of Snake Resonances at RHIC

Observation of Snake Resonances at RHIC. M. Bai , L. Ahrens, J. Alessi , E. Courant, A. Drees , W. Fischer C. Gardner, R. Gill, J. Glenn, H. Huang, V. Litvinenko A. Luccio , Y. Luo , F. Pilat , W. W. MacKay, Y. Makdisi A. Marusic , M. Minty, C. Montag , V. Ptitsyn , T. Roser

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Observation of Snake Resonances at RHIC

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  1. Observation of Snake Resonances at RHIC M. Bai, L. Ahrens, J. Alessi, E. Courant, A. Drees, W. Fischer C. Gardner, R. Gill, J. Glenn, H. Huang, V. Litvinenko A. Luccio, Y. Luo, F. Pilat, W. W. MacKay, Y. Makdisi A. Marusic, M. Minty, C. Montag, V. Ptitsyn, T. Roser T. Satogata, S. Tepikian, D. Trbojevic, N. Tsoupas, A. Zelensk K. Zeno and S. Y. Zhang Brookhaven National Lab., Upton, NY I. G. Alekseev, D. Svirida Institute of Theoretical and Experimental Physics, Moscow, Russia Oct. 1, 2010 Spin 2010, Julich, Germany

  2. Outline • Introduction • Snake resonance: depolarizing mechanism in the presence of Siberian snakes • RHIC polarized proton setup • Experimental observations • How to preserve polarization at RHIC • Depolarization observed at RHIC • Snake resonance observed • Summary

  3. Snake Resonances • Depolarizing in the presence of snakes • Driven by intrinsic resonances • Location • Odd order resonance: m is odd integer • Driven by the intrinsic resonance • Even order resonance: m is even integer • Disappears for dual snake setup if no closed orbit distortion. • Will re-appear if intrinsic resonance overlaps with an imperfection resonance

  4. Snake Resonances Two-snake case with no imperfection resonance current working point old working point 7/10 3/4 Two-snake case with imperfection resonance

  5. Spin flipper BRAHMS(p) Absolute Polarimeter (H jet) RHIC pC Polarimeters Siberian Snakes PHENIX (p) STAR (p) Spin Rotators (longitudinal polarization) Spin Rotators (longitudinal polarization) LINAC BOOSTER Helical Partial Siberian Snake Pol. H- Source AGS 200 MeV Polarimeter AGS Polarimeters Strong AGS Snake SpinFest, August 7, 2008

  6. How to preserve polarization in the presence of snake resonances? • Avoid snake resonances • Keep the spin tune as close to 0.5 as possible • Sources of spin tune deviation • Angles between the spin precession axes of the two snakes • Horizontal orbital angle between the two snakes • Make sure that betatron tune to be in the snake resonance free region • Minimize spin tune spread

  7. Proper Snake Setup • Snake Current Scan • 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

  8. Minimize spin tune shift • Control the angle between the horizontal orbits at the two snakes

  9. Achieved beam control: betatron tune Relativistic gamma Betatron tune

  10. Achieved beam control: closed orbit distortion Yellow X Yellow Y Relativistic gamma Closed orbit distortion [mm] Blue Y Blue X

  11. Achieved beam control: H snake angle Relativistic gamma Horizontal Angle between two snakes [urad]

  12. Depolarization Observed in RHIC

  13. Depolarization from 100 GeV to 250 GeV • 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 SpinFest, August 7, 2008

  14. Snake Resonance from 100 GeV and 250 GeV 11/16 resonance 7/10 resonance 3/4 resonance Working pt for 250 GeV run

  15. Snake Resonance from 100 GeV and 250 GeV • even order resonance at • 7/10 resonance was unexpected wide • bad closed orbit due to reversal of • bpm offsets • spin tune spread • momentum spread: ~0.001 • For coming run • bpm offset problem was fixed • minimize D’ slope between two snakes Working pt for coming RUN 11 250 GeV run

  16. 2nd Order Snake Resonance at 2Qy=Qs ¼ snake resonance Maximum vertical tune V. H. Ranjbar, et al, Observation of Higher-Order Snake Resonances in Polarized Proton Acceleration in RHIC, Phys. Rev. Lett. 91, 034801 (2003) – Published July 15, 2003

  17. High Order Snake Resonance due to Coupling Coupled 3/14 snake resonance |Horizontal tune – 3/14| V. H. Ranjbar, et al, Observation of Higher-Order Snake Resonances in Polarized Proton Acceleration in RHIC, Phys. Rev. Lett. 91, 034801 (2003) – Published July 15, 2003

  18. 5th order snake resonance at 5Qy=Qs+3 accelerated with vertical tune at 0.685 7/10 snake resonance accelerated with vertical tune at 0.73 accelerated to an energy of G=63, a location of a strong intrinsic spin resonance

  19. Conclusion • Snake resonances observed at RHIC • Both odd order and even order • 2nd order resonance was used at injection to set the snake current • The snake resonance at 5Qy=Qs+1 was unexpected wide between 100 GeV and 250 GeV • Bad closed orbit due to wrong bpm offsets • Significant spin tune spread • To preserve polarization to 250 GeV • Accelerate at working point 0.675 • Minimize spin tune spread

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