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Polarization Experiments

Polarization Experiments. M. Bai C-A Department, BNL. Outline. RHIC pp experiments in FY2006 Spin de-coherence measurement Polarization dependence with beam intensity and source polarization Spin tune measurement using an ac dipole Snake resonance spectrum RHIC pp experiments for FY2007

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Polarization Experiments

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  1. Polarization Experiments M. Bai C-A Department, BNL

  2. Outline • RHIC pp experiments in FY2006 • Spin de-coherence measurement • Polarization dependence with beam intensity and source polarization • Spin tune measurement using an ac dipole • Snake resonance spectrum • RHIC pp experiments for FY2007 • Polarization dependence with beam intensity • Measure driven coherent spin precession • Spin echo

  3. Polazation vs. injection beam intensity H. Huang, A. Zelenski, W. MacKay, S. Bravar, J. Woods, S. Tepikian • Goal • to understand the correlation between beam polarization with beam intensity • No intensity dependence in this intensity range. This is very different from last year’s operation with ac dipole • to see if different polarization distribution would evolve differently through acceleration • No data was taken for this part

  4. Snake resonance spectrum experiment M. Bai, T. Roser, V. Pitisyn, S. Tepikian, A. Luccio, P. Cameron • Goal • Complete the 7/10 resonance spectrum • Study the behavior of snake resonance crossing

  5. Snake resonance spectrum • The 7/10 resonance is evident in both rings • The tune scan between 0.683 to 0.70 seems to suggest that the 7/10 resonance in Yellow ring is weaker than the resonance inBlue ring

  6. Snake resonance crossing: Yellow • No strong correlation between the amount of depolarization and slow factor. • Two data points show the maximum depolarization occurs when the tune gets ramped from 0.72 to 0.6816 with a slow factor  100

  7. Snake resonance crossing: Blue • Even though the depolarization seems to be evident when the resonance is crossed, the amount of depolarization is independent of the resonance crossing rate.

  8. Goal: Use the ac dipole to induce a coherent spin precession in the horizontal plane. The turn by turn asymmetry measured by CNI polarimeter can be transformed into the rotating frame to give the coherent precession amplitude in the horizontal plane y beam direction z x Spin Flipper M. Bai, T. Roser, A. Brava, G. Bunce, A. Luccio, R. Gill, P. Oddo Thanks for the help from: Itaru, Larry Hoff, Brian Oerter, Joe P

  9. Summary of the spin tune measurement experiment • Results • Took data at injection and store(100 GeV) • Observed effect of ac dipole on beam polarization. Beam was fully depolarized injection when the ac dipole tune was set to 0.498

  10. Summary of the spin tune measurement experiment

  11. Summary of the spin tune measurement experiment • Results • Took data at injection and store(100 GeV) • Observed effect of ac dipole on beam polarization. Beam was fully depolarized injection when the ac dipole tune was set to 0.498 • Encouraging data sets but not conclusive

  12. Summary of the spin tune measurement experiment

  13. Summary of the spin tune measurement experiment • Results • Took data at injection and store(100 GeV) • Observed effect of ac dipole on beam polarization. Beam was fully depolarized injection when the ac dipole tune was set to 0.498 • Encouraging data sets but not conclusive • Experienced a lot hardware problems • Power supply tripping off when the ac dipole frequency was set to be out of the bandwidth • Low level waveform generator (DDS) problem • Sudden phase jump • Kept driving the ac dipole with the same frequency even though the set frequency was changed

  14. RHIC pp experiments for FY 2007 • Snake resonance • Detailed theoretical and simulation studies to study the snake resonance crossing data from FY06. Would like to ask for 2 hour APEX beam time to explore the resonance crossing behavior based on simulation studies. • Measure driven coherent spin precession • Team: M. Bai, T. Roser, G. Bunce, A. Luccio, R. Gill, P. Oddo • Spin echo • Team: M. Bai, A. Chao, V. Ptitsyn, T. Roser, …

  15. Measure driven coherent spin precession • Goal: to measure the coherent driven spin precession as a function of the ac dipole tune • Benefit • The success of this will provide an effective way to measure the spin tune for injection as well as for store • This is also critical for the success of the future spin flipper for RHIC Py Px

  16. Measure driven coherent spin precession • Progress and status • low level waveform generator problem: fixed • Power amplifier tripping issue: fixed • an online ac dipole current/frequency readback data acquisition/logging: working progress Py Px 2Qacdipole • Plan • Take the turn by turn asymmetry data with the six Si CNI detectors • Bin the data with the ac dipole frequency. The advantage of this is to improve the statistics greatly • Beam time: dedicated. Prefer to take the data at store

  17. Spin flipper for RHIC -167.493o 208.03o 90oSpin rotator -45oSpin rotator • Specs: • Ac dipole: • field amplitude: 20 Gauss-m • frequency: • 90o Spin rotator: • magnet: a DC dipole with vertical field • integrated field strength: 2.7 Tesla-m • dipole deflection: • 100 GeV: 8.2 mrad • 250 GeV: 3.2mrad

  18. Spin Echo: A. Chao • What is spin echo? • Proposed by A. Chao, “Spin Echo in Synchrotrons”, SPIN2006, Kyoto, Japan, 2006 • Recurrence of coherent spin precession when a polarized proton beam with non-zero energy spread jumps across a spin resonance twice • The echo occurs at a time  after the 2nd jump.  is also the time between the two jumps. The echo also happen once. • The width of the spin echo is determined by the spin tune spread while any diffusion of spin tune affects how strong the echo is

  19. Two resonance crossing When =0, all terms mix together. Result is what was obtained for single particle.  Interference between two jumps (constructive example shown)  When ≠0, different terms separate. Each term acquires its own physical meaning. shock response to first jump shock response to second jump echo  Courtesy from A. Chao

  20. Spin Echo • Benefit of the experiment • A contribution understand the general spin dynamics • Can also help us to explore the spin tune diffusion mechanism at RHIC

  21. Spin Echo: A. Chao • What to do? • Part I: to measure the spin echo • Drive the ac dipole adiabatically at a tune near the spin precession tune(~1/2) • Cross the resonance by jumping the ac dipole tune • Wait a time of  and jump the ac dipole tune back to its start value • Measure the beam polarization right after the second crossing • Part II: to study the spin echo as a function of • Momentum spread • Bunch intensity • …

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