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

1
RHIC Polarized Proton OperationM. Bai, C-A
Dept, BNL

• Outline
• RHIC polarized proton set-up
• RHIC polarized proton performance
• plan for RHIC polarized proton
• summery

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Spin dynamics in a circular accelerator
Spin vector in particles 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,

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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? kPQy,
• 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

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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
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Booster Polarized Proton Setup
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AGS Polarized Proton Setup
Achieved polarization at extraction 65 w.
1.5x1011 bunch intensity
60 w. 2.0x1011
bunch intensity
1
Spin tune gap
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RHIC polarized proton setup
Beam direction
?1
Snake 1
9clk
3clk
?2
Snake 2
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Depolarizing mechanism in the presence of snakes
RHIC ramp working point
RHIC store working point
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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

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RHIC pp acceleration setup

• Optimizing Snake Setting
• Snake current scan with both tunes close to
  0.75, snake resonance Qy3/4

• 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 Qx0.73, Qy0.72 and store
  working point at Qx0.69, Qy0.68 to avoid snake
  resonances at 0.75, 0.7 and 0.714
• Achieved 0.005 tune variation during the ramp

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RHIC overall performance
Parameter unit 2002 2003 2004 2005 2006 2008
No. of bunches -- 55 55 56 106 111 111
Bunch intensity 1011 0.7 0.7 0.7 0.9 1.3 1.5
Store energy GeV 100 100 100 100 100 100
? m 3.0 1.0 1.0 1.0 1.0 1.0
Peak luminosity 1030cm-2s-1 2 6 6 10 28 35
Average luminosity 1030cm-2s-1 1 4 4 7 18 23
Collision points -- 4 4 3 3 2 2
Time in store 30 41 38 56 46 60
Average store polarization 15 35 46 47 58 45
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RHIC luminosity performance
Courtesy of W. Fischer
RUN08 is a short run (4 weeks physics) focusing
on luminosity
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RHIC polarization performance
Courtesy of W. Fischer
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RHIC polarization transmission efficiency
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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
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250 GeV polarization ramp measurement
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Possible reason for polarization loss
G?422
G?381
G?260
Coupling snake resonance at 0.7
250GeV,?2m
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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

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Plan for FY2009

• Luminosity 23x1030 gt40x1030cm-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

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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

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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 40x1030cm-2s-1 for Run 2009

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Backup slides
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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