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Polarization in MeRHIC and eRHIC

Polarization in MeRHIC and eRHIC. M. Bai for Polarization and Source Group Collider Accelerator Department, BNL. Outline. Design goals of polarization Electron polarization issues for MeRHIC and eRHIC Bunch to bunch spin direction spread Achieve longitudinal polarization at IP

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Polarization in MeRHIC and eRHIC

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  1. Polarization in MeRHIC and eRHIC M. Bai for Polarization and Source Group Collider Accelerator Department, BNL EIC Meeting at SUNY

  2. Outline • Design goals of polarization • Electron polarization issues for MeRHIC and eRHIC • Bunch to bunch spin direction spread • Achieve longitudinal polarization at IP • Ion polarization issues • Proton • Achieved polarized proton performance • He-3 • Polarimetry EIC Meeting at SUNY

  3. Design Goals of Polarization EIC Meeting at SUNY

  4. Electron Polarization Issues • Spin direction alignment • deviation of spin direction from bunch to bunch after combiner • Electric field: for 200 keV electron beam this corresponds to a polarization reduction of ~1.2% • Magnetic field: • Spin precession is negligible, hence bunch to bunch spin direction deviation is none. Combiner 244cm 31cm 60cm EIC Meeting at SUNY

  5. Spin Transparent Gatling Gun Dogleg is Spin transparent • Vladimir: Combiner EIC Meeting at SUNY

  6. Spin Direction at IP Pre-accelerator 90 MeV ERL • Goal: longitudinal polarization at detector Electron gun Linac 1 0.1 GeV arc2 arc1 Main ERLs; 6 cryomodules x 6 cavities x 18 Mev/cav = 0.65 GeV per linac 0.75, 2.05, 3.35 GeV 0.1, 1.4, 2.7 GeV Linac 2 4 GeV • Longitudinal polarization at the entrance of LINAC 1 and remain the same direction after LINAC1 • Spin direction is the same at the end of arc1 as at IP • Spin precesses around vertical direction by after the first pass EIC Meeting at SUNY

  7. Spin direction at IP contd Pre-accelerator 90 MeV ERL Electron gun Linac 1 0.1 GeV Main ERLs; 6 cryomodules x 6 cavities x 18 Mev/cav = 0.65 GeV per linac 0.75, 2.05, 3.35 GeV 0.1, 1.4, 2.7 GeV Linac 2 • Total amount of spin precession at the nth pass is • For current MeRHIC parameter, i.e. injection energy 0.1 GeV, or γi=195.7, energy gain at each LINAC 0.65 GeV, or Δγ=1272.0156, #of passes to achieve 4GeV=3, 19080.234 • Spin rotates 23.26π in the horizontal plane 4 GeV EIC Meeting at SUNY

  8. Spin direction at IP contd Pre-accelerator 90 MeV ERL Electron gun Linac 1 0.1 GeV Main ERLs; 6 cryomodules x 6 cavities x 18 Mev/cav = 0.65 GeV per linac 0.75, 2.05, 3.35 GeV 0.1, 1.4, 2.7 GeV Linac 2 • To have longitudinal spin direction at IP • and • For n=3, a longitudinal polarization can be achieved at IP with either 3.95GeV or 4.13GeV electron beam • For 4 GeV, longitudinal polarization can be achieved by rotating spin vector(using wien filter) out of source by 47 degrees away from longitudinal 4 GeV EIC Meeting at SUNY

  9. Electron Spin Direction Spread at IP • Spin direction spread due to momentum spread • For current MeRHIC parameters and momentum spread of 5x10^-4 • ~ 2 degrees EIC Meeting at SUNY

  10. eRHIC Layout 2 x 200 m SRF linac 4 (5) GeV per pass 5 (4) passes eRHIC detector Coherent e-cooler MeRHIC detector PHENIX 4 to 5 vertically separated recirculating passes STAR

  11. Spin direction at IP12 • Total amount of spin precession at the nth pass is • First pass, • and • For current eRHIC parameter, • injection energy 0.1 GeV, or γi=195.69, • energy gain at initial LINAC 1.95 GeV, or Δγ0=3718.20, • Energy gain of each ERL LINAC Δγ=3913.89 • Electron energy 20 GeV, or n=5 • Spin rotates 322.25π in the horizontal plane • To obtain a longitudinal spin direction, inject electron beam with spin at -45 degrees away from longitudinal EIC Meeting at SUNY

  12. Electron Spin Direction Spread at IP • Spin direction spread due to momentum spread • For current eRHIC parameters, • Electron energy 20 GeV or n=5 • momentum spread 0.0001 • ~ 8.25 degrees • For larger momentum spread, local spin rotators at IP maybe needed to provide longitudinal spin direction to minimize the spread of the spin directions of the beam EIC Meeting at SUNY

  13. Achieved Polarization Performance at RHIC • At 100 GeV • Average polarization: 55% • Polarization direction: longitudinal and transverse • At 250 GeV, polarization • Average polarization: 35% • Polarization direction: longitudinal and transverse RUN 06 RUN 08 RUN 09 EIC Meeting at SUNY

  14. Remaining Polarization Issues for Protons • polarization were lost beyond 100 GeV to 250 GeV • Average polarization transmission efficiency: ~80% • Best polarization achieved w.o. rotator: ~54% MeRHIC Cost Review – Pre Run

  15. Plans for Reaching 70% Polarization Protons • Accelerating protons from 100 GeV to 250 GeV with vertical tune at 0.675 • 90% or higher polarization transmission efficiency with this working point was measured during pp 2009 run • Plan to test during the current Au run • Horizontal jump quads in the AGS to minimize ~10% polarization loss at all the horizontal intrinsic resonance • To be commissioned during current Au run • Upgrade ofpolarized H- source to achieve 90% or higher polarization • Explore other alternative in RHIC • Different working point • others EIC Meeting at SUNY

  16. Longitudinal Polarization • For eRHIC, use existing RHIC spin rotators • For MeRHIC • need additional pair of current RHIC type rotators EIC Meeting At SUNY

  17. Polarization Issues for He3 • G=-4.184, Resonances are stronger and closer(218MeV/u). Needs more precise orbit and optics controls EIC Meeting at SUNY

  18. Polarization Issues for He3 • G=-4.184, Required snake strength is about 64% of what’s for proton. Same factor apply to spin rotators [E. Courant’s Tech Note] • Needs more precise orbit and optics controls for avoiding depolarization • Alternative is to add two more pair of snakes EIC Meeting at SUNY

  19. High Precision Electron Polarimetry • Mott polarimeter • To measure the polarization at lower energy. • Both radial and longitudinal component • Compton polarimeter • Monitor polarization at energy from 4 GeV to 20 GeV • 1% or better systematic uncertainty • Bunch by bunch • Detailed design and location need to be integrated with MeRHIC lattice design • Will be discussed by Wouter Deconinck and Dave Gaskell EIC Meeting at SUNY

  20. Hadron Polarimetry • Proton • CNI polarimeter • Currently located in the warm section of IP12 • Operational for now • Needs upgrade for MeRHIC and eRHIC to achieve • 3% or better systematic error uncertainty • Bunch by bunch if necessary • Absolute polarimeter using H jet: calibrate CNI polarimeter • Currently located at IP12 • Operational • He3 • Require high precision • Need R&D to explore and develop theoretical and experimental aspects of He3 polarimeter EIC Meeting at SUNY

  21. Summary • Electron polarization • Gatling gun is spin transparent • MeRHIC • No issues • eRHIC • No Issues • Longitudinal polarization direction at IP is realized by setting the spin direction at injection using a Wien Filter in the injector • Hadron polarization • Planned studies of He3 depolarizing effects in the injectors and in RHIC • Require high precision and low systematic errors • Need R&D to identify He3 polarimeter EIC Meeting at SUNY

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