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Outline RHIC polarized proton set-up RHIC polarized proton performance plan for RHIC polarized proton summery. RHIC Polarized Proton Operation M. Bai, C-A Dept, BNL. Spin dynamics in a circular accelerator. Spin vector in particle’s rest frame. - PowerPoint PPT Presentation
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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
Spin dynamics in a circular accelerator
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,
SBGBGm
eS
dt
Sd
])1([ //
Spin vector in particle’s rest frame
GγQs
Challenge of Accelerating Polarized Beams
o Imperfection resonance Source: dipole errors,
quadrupole mis-alignments
Resonance location:
G = k k is an integer
o Intrinsic resonance Source: horizontal
focusing field from betatron oscillation
Resonance location:
G = kP±Qy, P is the periodicity of the
accelerator, Qy is the vertical betatron tune
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
• For protons, imperfection spin resonances are spaced by 523 MeV
• The higher the energy, the stronger the depolarizing resonance
RHIC Complex Layout
PHENIX (p)
AGS
LINACBOOSTER
Pol. H- Source
Solenoid Partial Siberian Snake
200 MeV Polarimeter
Helical Partial Siberian Snake
Spin Rotators(longitudinal polarization)
Siberian Snakes
Spin Rotators(longitudinal polarization)
Strong AGS Snake
RHIC pC PolarimetersAbsolute Polarimeter (H jet)
STAR (p)
BRAHMS(p)
AGS Polarimeters
Booster Polarized Proton Setup
Booster
Kinetic Energy: 200 MeV(G=2.2)~1.4 GeV(G=4.5)
Machine optics: vertical tune = 4.85
A total of 3 imperfection resonances. They are fully overcome by the harmonic correction of the vertical closed orbit
AGS Polarized Proton Setup
AGS (Alternating Gradient Synchrotron) Energy: 2.3 GeV ~ 23.8 GeV
A total of 41 imperfection resonances, 7 strong intrinsic resonances and 82 horizontal resonances Imperfection and intrinsic resonances: one 5.9%
partial snake plus one 10~15% partial snake and setting vertical tune inside the spin tune gap
Horizontal resonances: no correction. A total of ~10% polarization loss with current available beam size
2
ψsin
2
ψsin
3cosGγ
2
ψcos
2
ψcoscosGγcosπ cwcw sQ
Achieved polarization at extraction: 65% w. 1.5x1011 bunch intensity 60% w. 2.0x1011 bunch intensity
1
Spin tune gap
RHIC polarized proton setup
GiiGii
eeeeM 2
1)cos(sin
22
1)cossin(
2 21112212
Dual full snakes separated by half of the ring. Each snake rotates spin vector 180 degrees around an axis in the horizontal plane
9’clk
Snake 1
Snake 2
1
2
3’clk
Beam direction
Vertical stable spin direction of the whole ring
For two snakes with the axis perpendicular to each other, spin tune is ½.
)21(
3
i
e
Depolarizing mechanism in the presence of snakes
Snake resonance Conditions: mQy=Qs+k
Even order resonance Non-exist with dual snake setup
Odd order resonance Imperfection of snake, non-zero imperfection spin resonance
RHIC ramp working point
RHIC store working point
RHIC pp acceleration strategy
GQQQ sss )
2
1(0,
Keep Spin tune close to ½ as possible
Keep the betatron tune in the snake resonance free area
Contribution of spin tune
Spin tune error
=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
RHIC pp acceleration setup
Optimizing Snake Setting Snake current scan with both tunes
close to 0.75, snake resonance Qy=3/4
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 Qx=0.73, Qy=0.72 and
store working point at Qx=0.69, Qy=0.68 to avoid snake resonances at 0.75, 0.7 and 0.714
Achieved ~ 0.005 tune variation during the ramp
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
RHIC pp luminosity L delivered to PHENIX
0.01
0.1
1
10
100
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009
Calendar year
pp
lum
ino
sit
y L
[p
b-1
]
Last update: 10 March 2008
RHIC luminosity performance
Courtesy of W. Fischer
RUN08 is a short run (4 weeks physics) focusing on luminosity
RHIC polarization performance
Courtesy of W. FischerRHIC pp Polarization
0
10
20
30
40
50
60
70
2000 2001 2002 2003 2004 2005 2006 2007 2008
Calendar year
Po
lari
zati
on
Last update: 10 March 2008
RHIC polarization transmission efficiency
250 GeV Development
250 GeV
injectionPolarization at injection
Polarization at 250 GeV
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 polarization ramp measurement
0
0.002
0.004
0.006
0.008
0.01
0.012
20 40 60 80 100 120 140 160 180 200 220 240
Beam Energy [GeV]
Asy
mm
etry
d
Resonance around 136 GeV
Possible reason for polarization loss
G=
260
250
Ge
V,
*=2
m
G=
381
G=
422
Coupling snake resonance at 0.7
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
Plan for FY2009
Luminosity: 23x1030 —>40x1030[cm-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%
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
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 40x1030[cm-2s-1] for Run 2009
Backup slides
RHIC 100 GeV Ramp
G=
63
G=
98
G=
104
G=
179
100
Ge
V,
*=2
m• 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
Beta squeeze from 2m to 1m
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