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