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RHIC Polarized Proton Operation M. Bai, C-A Dept, BNL

Outline RHIC polarized proton set-up RHIC polarized proton performance plan for RHIC polarized proton summery. RHIC Polarized Proton Operation M. Bai, C-A Dept, BNL. Spin dynamics in a circular accelerator. Spin vector in particle’s rest frame.

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RHIC Polarized Proton Operation M. Bai, C-A Dept, BNL

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  1. Outline RHIC polarized proton set-up RHIC polarized proton performance plan for RHIC polarized proton summery RHIC Polarized Proton OperationM. Bai, C-A Dept, BNL

  2. Spin dynamics in a circular accelerator Spin vector in particle’s rest frame • In a perfect accelerator, spin vector precesses around the bending dipole field direction: vertical • Spin tune Qs: number of precessions in one orbital revolution. In general,

  3. Challenge of Accelerating Polarized Beams • Spin depolarizing resonance : coherent build-up of perturbations on the spin vector when the spin vector gets kicked at the same frequency as its precession frequency • Intrinsic resonance • Source: horizontal focusing field from betatron oscillation • Resonance location: • G = kP±Qy, • P is the periodicity of the accelerator, Qy is the vertical betatron tune • Imperfection resonance • Source: dipole errors, quadrupole mis-alignments • Resonance location: G = k k is an integer • For protons, imperfection spin resonances are spaced by 523 MeV • The higher the energy, the stronger the depolarizing resonance

  4. RHIC Complex Layout BRAHMS(p) Absolute Polarimeter (H jet) RHIC pC Polarimeters Siberian Snakes 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

  5. Booster • Kinetic Energy: 200 MeV(G=2.2)~1.4 GeV(G=4.5) • Machine optics: vertical tune = 4.85 • A total of 3 imperfection resonances. They are fully overcome by the harmonic correction of the vertical closed orbit Booster Polarized Proton Setup

  6. AGS (Alternating Gradient Synchrotron) • Energy: 2.3 GeV ~ 23.8 GeV • A total of 41 imperfection resonances, 7 strong intrinsic resonances and 82 horizontal resonances • Imperfection and intrinsic resonances: one 5.9% partial snake plus one 10~15% partial snake and setting vertical tune inside the spin tune gap • Horizontal resonances: no correction. A total of ~10% polarization loss with current available beam size     AGS Polarized Proton Setup • Achieved polarization at extraction: 65% w. 1.5x1011 bunch intensity • 60% w.2.0x1011 bunch intensity 1 Spin tune gap

  7. Dual full snakes separated by half of the ring. Each snake rotates spin vector 180 degrees around an axis in the horizontal plane • Vertical stable spin direction of the whole ring • For two snakes with the axis perpendicular to each other, spin tune is ½. RHIC polarized proton setup Beam direction 1 Snake 1 9’clk 3’clk 2 Snake 2

  8. Snake resonance • Conditions: mQy=Qs+k • Even order resonance • Non-exist with dual snake setup • Odd order resonance • Imperfection of snake, non-zero imperfection spin resonance Depolarizing mechanism in the presence of snakes RHIC ramp working point RHIC store working point

  9. RHIC pp acceleration strategy • Keep Spin tune close to ½ as possible • Keep the betatron tune in the snake resonance free area Spin tune error Contribution of spin tune • =1+2 is a function of energy especially when beam is at relatively low energy. It becomes energy independent when beam gets relativistic. •  is the horizontal orbital angle between the two snakes, ~ 0.3mrad angle corresponds to about 0.019 spin tune change at 100 GeV

  10. RHIC pp acceleration setup • Optimizing Snake Setting • Snake current scan with both tunes close to 0.75, snake resonance Qy=3/4 • Control the orbital angle between the two snakes • Closed Orbit: • requires closed orbit distortion ≤ 0.5 mm for 100 GeV and ≤0.3 mm for 250 GeV • Achieved ~ 0.5 mm closed orbit distortion • Optics setup:working point in resonance free window • Ramp working point at Qx=0.73, Qy=0.72 and store working point at Qx=0.69, Qy=0.68 to avoid snake resonances at 0.75, 0.7 and 0.714 • Achieved ~ 0.005 tune variation during the ramp

  11. RHIC overall performance

  12. RHIC luminosity performance Courtesy of W. Fischer RUN08 is a short run (4 weeks physics) focusing on luminosity

  13. RHIC polarization performance Courtesy of W. Fischer

  14. RHIC polarization transmission efficiency

  15. 250 GeV Development • Significant polarization was measured at 250GeV. The polarization number at 250GeV is using the analyzing power at 100 GeV which is calibrated by the H Jet polarimeter • About 25% polarization losses during the 250 GeV ramp 250 GeV injection Polarization at 250 GeV Polarization at injection

  16. Resonance around 136 GeV 250 GeV polarization ramp measurement

  17. Possible reason for polarization loss G=422 G=381 G=260 Coupling snake resonance at 0.7 250GeV,*=2m

  18. Remaining issues • Luminosity: • Limited by beam-beam effect • Polarization • Polarization loss in the AGS due to horizontal spin resonances • Polarization intensity dependence from AGS • Polarization loss in RHIC between 100 GeV and 250 GeV

  19. Plan for FY2009 • Luminosity: 23x1030—>40x1030[cm-2s-1] • 9MHz cavity: shorter bunch length • Improve the longitudinal matching • Allow longer bunch length during acceleration to minimize the electron cloud • Non-linear chromaticity correction • Increase the effective tune space to accommodate larger beam-beam effect, i.e. higher bunch intensity • Beta squeeze • A further beta squeeze from 1m to 0.7m gives an increase of luminosity of 40%

  20. Plan for FY2009 • Polarization • Control the spin tune • Control the orbital angle between snakes • calibrate the snake current error on spin tune as function of energy • Optics control along the ramp to avoid snake resonances • RHIC tune/decoupling feedback • AGS improvement • Fast quad to jump across H resonances to minimize the polarization losses • Minimize beam emittance • LEBT/MEBT upgrade • Better optics matching between Booster to AGS

  21. Conclusion • RHIC has achieved 60% polarization at 100 GeV and 45% at 250 GeV • Expect to achieve 100% polarization transmission to 250GeV with better orbital and optics control • AGS plans on increase the polarization transmission efficiency and mitigate the polarization dependence on bunch intensity • Various efforts in RHIC aiming to improve the luminosity to 40x1030[cm-2s-1] for Run 2009

  22. Backup slides

  23. RHIC 100 GeV Ramp G=104 G=98 100GeV,*=2m Beta squeeze from 2m to 1m G=63 • kept the vertical rms closed orbit • distortion below 0.5mm at the four • intrinsic resonances • kept both betatron tunes away from • the snake resonance at 0.75 and at 0.7 G=179

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