Polarization Experiments

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Polarization Experiments

• M. Bai
• C-A Department, BNL

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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

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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 years operation
  with ac dipole
• to see if different polarization distribution
  would evolve differently through acceleration
• No data was taken for this part

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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

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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 in Blue ring

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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

Q before Qafter slowfactor of crossing Polarization error
0.6816 0.6816 0 0 46.75 1.5
0.6816 0.6816 1 4 41.98 1.5
0.6816 0.6816 10 4 39.44 1.5
0.6816 0.6816 100 2 25.17 1.5
0.6816 0.7189 300 1 23.31 1.5
0.7189 0.7189 0 0 25.22 1.5
0.7189 0.6816 1 1 17.07 1.5
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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.

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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

• 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

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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

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Summary of the spin tune measurement experiment
Run Drive tune Pi Pf events million mode bunches Energy GeV
7834.106 0.499 63.6-1.4 55.2-1.4 35 Fix(V) 56 inj
7834.107 0.499 51.3-1.5 30 Fix(V) 56 inj
7834.108 0.499 48.2-1.6 Fix(V) inj
7834.110 0.506 61.1-2 61.3-1.3 42 Fix(V) inj
7834.111 0.493 56.21.1 54 inj
7834.112 0.496 57.7-1.2
7858.008 0.495 61.22-0.8 55.54-0.8 fix)(V) inj
7858.009 0.495 48.4-0.8 fix)(V) inj
7951.003 0.496 62.0-2.7 57.0-2 50 Profile(H) 120 100
7951.004 0.496 54.9-1 200 profile 120 100
7954.007 0.497 56.8-2.1 54.1-1 200 fix 120 100
7954.008 0.497 50.7-1 200 fix 120 100
7957.008 0.498 59.9-3.1 58.7-1 200 fix 120 100
7957.009 0.499 57.0-1 200 fix 120 100
7957.010 0.495 54.4-1 200 fix 120 100
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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

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Summary of the spin tune measurement experiment
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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

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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,

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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
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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

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Spin flipper for RHIC
-167.493o
208.03o
90o Spin rotator
-45o Spin 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

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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

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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
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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

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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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