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Polarized Proton at RHIC: Status and Future Plan

Polarized Proton at RHIC: Status and Future Plan. Mei Bai Collider Accelerator Dept. BNL. Outline. Introduction RHIC polarized proton setup Achieved performance Polarization Luminosity Plans for improvement Summary. Spin flipper. BRAHMS(p). Absolute Polarimeter (H jet).

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Polarized Proton at RHIC: Status and Future Plan

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  1. Polarized Proton at RHIC: Status and Future Plan Mei Bai Collider Accelerator Dept. BNL A Special Beam Physics Symposium in Honor of Yaroslav Derbenev's 70th Birthday

  2. Outline • Introduction • RHIC polarized proton setup • Achieved performance • Polarization • Luminosity • Plans for improvement • Summary A Special Beam Physics Symposium in Honor of Yaroslav Derbenev's 70th Birthday

  3. 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

  4. RHIC Polarized Proton Setup • 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. A Special Beam Physics Symposium in Honor of Yaroslav Derbenev's 70th Birthday

  5. RHIC Polarized Proton Setup • 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 A Special Beam Physics Symposium in Honor of Yaroslav Derbenev's 70th Birthday

  6. Snake depolarization resonance in RHIC • Location • In the presence of two snakes, with zero closed orbit distortion • The stronger the intrinsic spin resonance, the stronger the snake resonance 11/16 Py old working point current working point 7/10 3/4

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

  8. How to avoid a snake resonance • Keep 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 A Special Beam Physics Symposium in Honor of Yaroslav Derbenev's 70th Birthday

  9. How to avoid a snake resonance • Keep spin tune as close to 0.5 as possible • Snake current setting • Control the angle between the horizontal orbits at the two snakes

  10. How to avoid a snake resonance • Precise control of the vertical closed orbit • Minimize the vertical closed orbit distortion to reduce the strength of even order snake resonances • Precise optics control • Proper working point at a location with no or negligible snake resonances • Minimize the linear coupling to avoid the resonance due to horizontal betatron oscillation • Minimize tune spread • Chromatic effect • Non-linear effects A Special Beam Physics Symposium in Honor of Yaroslav Derbenev's 70th Birthday

  11. Polarization Performance: 100 GeV • Polarization transmission efficiency • negligible polarization loss during acceleration RUN 06 RUN 08 RUN 09

  12. Polarization Performance: 100 GeV • Polarization lifetime during store • No deterioration during store w/w.o spin rotator

  13. Polarization Performance: 250 GeV • Polarization loss between 100 GeV and 250 GeV • Measured with CNI polarimeter

  14. Polarization Tune Scan: 250 GeV acceleration 11/16 resonance 7/10 resonance 3/4 resonance Working pt for 250 GeV run

  15. Polarization Profile Fill 10486, Yellow2 Fill 10753, Yellow2 Courtesy of A. Bazilevsky Sharper polarization profile for 250 GeV than for 100 GeV A Special Beam Physics Symposium in Honor of Yaroslav Derbenev's 70th Birthday

  16. How to Improve Polarization at 250 GeV? • RHIC: • accelerate close to 0.675 between 100 GeV and 250 GeV • Tighter control of optics and orbit • Dispersion slope at the two snakes • Local orbit at rotators • CNI polarimeter improvement • AGS: • Horizontal tune jump quad to avoid polarization losses at horizontal resonances • Source: • Upgrade to achieve ~90% polarization A Special Beam Physics Symposium in Honor of Yaroslav Derbenev's 70th Birthday

  17. Luminosity Performance Courtesy of W. Fischer Polarization as measured by H Jet target, average of the entire beam distribution. For 250 GeV, sharper polarization profile was observed and hence, effective polarization is ~ 20 % higher

  18. Luminosity Improvement: 9MHz • Dedicated 9MHz for acceleration: Mike Brenann and Blaskiewicz • Provide better longitudinal match at injection to avoid the longitudinal emittance blowup • Longer bunch length during acceleration to reduce the peak bunch intensity. Hence, minimize the electron cloud effect to avoid transverse beam size blowup • Adiabatic switch to existing 28MHz cavity results in a shorter bunch length. For a 1 ev-s beam, expected the bunch length rms ~ 1ns. A Special Beam Physics Symposium in Honor of Yaroslav Derbenev's 70th Birthday

  19. Luminosity Improvement: ELens • Electron lens: W. Fischer, Y. Luo and et al • Low energy electron beam to provide a focusing len to compensate the beam-beam induced tune spread • Allows higher bunch intensity • Simulation by Y. Luo and et al

  20. Luminosity Improvement: ELens • RHIC Electron lens: W. Fischer, Y. Luo and et al • One 2.5m long 6 T super-conducting solenoid with field lines straight within ~ 0.2σ • Electron gun of current intensity 14A/cm^2 • Received $4 million ARRA fund • Expect a factor of 2 gain in luminosity • Expect to commission in RUN 2012 A Special Beam Physics Symposium in Honor of Yaroslav Derbenev's 70th Birthday

  21. Luminosity Improvement for 250 GeV • Increase bunch intensity • From 1.1x10^11 to 2.0x10^11 bunch intensity • reducing beta* at 250 GeV • Run 09 shows 0.7 m beta* is the limit at 100 GeV. This is equivalent to a beta* of ~0.3 m at 250 GeV A Special Beam Physics Symposium in Honor of Yaroslav Derbenev's 70th Birthday

  22. Summary of Achieved Performance and Projection A Special Beam Physics Symposium in Honor of Yaroslav Derbenev's 70th Birthday

  23. Summary • The successful story of RHIC as the world’s first/only high energy polarized proton collider proved the genius invention of Siberian snake works! • Continuous efforts at RHIC to keep improving its performance to achieve its design goal for both polarization as well as luminosity • H tune jump quads in the AGS • Source upgrade to yield 90% polarization • Accelerating pp with Qy close to 0.67 from 100 GeV to 250 GeV • 9MHz accelerating cavity, Elens and etc to increase luminosity A Special Beam Physics Symposium in Honor of Yaroslav Derbenev's 70th Birthday

  24. Happy 70th Birthday, Prof. Derbenev, and many more to come!

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