# Presentation: 118589

## Polarized Proton Operations in AGS and RHIC

- Mei Bai
- Brookhaven National Laboratory

## Outline

- Layout of polarized proton acceleration complex
- Milestones of RHIC polarized proton program
- Spin Dynamics
- Spin depolarization resonances
- Status
- AGS capability
- RHIC capability
- Challenges and Future Plans
- Machine developments for the future

## Polarized Proton Acceleration Complex Layout

## Milestones of RHIC Spin Program

|  | Milestone |
| --- | --- |
| FY00 | New polarized proton source (OPPIS) commissioned
One snake was installed in the sector 9 in Blue ring

CNI polarimeter in Blue installed and commissioned |
| FY02 | All snakes for both rings installed and commissioned
CNI polarimeter in Yellow installed and commissioned |
| FY03 | Spin rotators installed and commissioned

 |
| FY04 | RHIC new working point commissioned  
RHIC absolute polarimeter using Hydrogen Jet target installed 
and commissioned
AGS 5% helical warm snake installed and commissioned |

- By slowly turning on this snake after the pp was injected, a radial
- polarization was measured and demonstrated that the snake was
- working as expected

- provided longitudinal polarizations at STAR and PHENIX for
- physics data taking

## Goal for the Polarized Proton in RHIC

-  Polarization
-  70% beam polarization at RHIC store energy 250 GeV/c
-  Luminosity
-  bunch intensity: 2x1011 protons per bunch
-  112 bunch per ring
-  with a normalized beam emittance of 20 mm-mrad, a luminosity of
-  60x1030 cm-2s-1 is expected at 100 GeV/c
-  150x1030 cm-2s-1 is expected at 250 GeV/c

## Spin Dynamics

- Spin precession in a planar circular accelerator [in the lab frame]
- Spin tune

- In the frame which moves with the particle

-  Orbital motion

## Spin Depolarization resonances

- First order spin depolarization resonance
- Imperfection resonance
- Due to the additional kick on the spin vector by the dipole field from the correctors or magnet misalignments
- Intrinsic resonance
- Due to the additional kicks from the quadrupole
-       fields particle experiences during the betatron oscillation
- For a machine with P super-periodicity

## Overcome Spin Depolarization resonances

- Siberian Snake:
- Rotates spin vector by 180o
- Partial Snake
- AC dipole
- Provide large coherent oscillation at a intrinsic spin resonance to achieve a full spin flip at normal acceleration speed.

- Imperfection resonance

- Rotation angle of the spin vector
- from the partial snake

- Intrinsic resonance

## Current AGS Setup

- Machine parameters
- Lattice
- 12 fold superperiodicity, 5 FODO cells per  super-period
- Energy:
- Injection: 2.2 GeV
- Extraction: 24.3 GeV
- Spin depolarization resonances
- Imperfection spin resonance
- A total of 42 resonances at G = integer
- Overcome by helical 5% partial snake
- Intrinsic spin resonance
- A total of 7 significant intrinsic resonances
- 4 strong ones at G = 0+Qy, 12+Qy and 36±Qy are overcome by the AC dipole
- 3 weak ones at G = 24±Qy and 48-Qy are crossed without any corrections

## AGS Current Capability

- routinely provide a beam of 0.7x1011 bunch intensity with 50% polarization at RHIC injection energy
- Demonstrated the capability of providing 1.0x1011 bunch intensity with 50% polarization at RHIC injection energy

## Challenges of reaching > 70% at the AGS extraction

-  Polarization losses due to weak intrinsic resonance
-  polarization losses due to coupling resonance

- 36+Qy

- 48-Qy

## Other Challenges of Improving AGS Performance

-  Beam polarization dependance on the bunch intensity

## Solution I: a strong partial snake

-  AGS strong cold snake, funded by DOE,  is expected to yield 100% polarization transmission efficiency from AGS injection energy to extraction energy. The expected absolute polarization is 70%.

- desired vertical
- betatron tune to
- avoid depolarization

- partial snake resonance

- 30% s.c. helical snake build at SMD (AIP)

## Solution II: two snakes

- 
- 

- 
- 

- Vertical component of stable spin direction
- Spin tune

- Injection

- First intrinsic resonance (0+Qy)

## AGS Plan for Run 5

-  operational: warm helical partial snake + AC dipole (the same
-     setup as RHIC pp FY04 Run)
-  commission the two snake solution (cold helical snake at
-     2.5Tesla field + warm helical snake at 1.5 Tesla field)

## RHIC pp Setup

| Energy at injection | 24.3 | GeV/u |
| --- | --- | --- |
| Energy at Store | 100.2 | GeV/c |
| Interaction points | 6    8  10 12  2   4 | clock |
| * at injection | 10 10 10 10 10 10 | m |
| * at store | 1    1  10  10  10  10 | m |
| Working points | Inj & ramp: (28.73, 28.72)
Store: (28.69, 29.68) |  |
| Snakes current | DC |  |
| Spin rotator current | Ramp up after store |  |
| Experimental magnets | STAR, PHENIX: on DC from inj. to top |  |
| RF accelerating cavities | At injection: 100 kV
ramp: 300 kV
At store: 300 kV |  |
| RF storage cavities | No rebucketing |  |

- Two full Siberian snakes per ring. The two snakes are located 180o apart with their precession axes perpendicular to each other

## RHIC Achieved Performance

|  | bunch intensity
[1011] | # of bunch | £peak
[1030]
cm-2s-1 | £store average
[1030]
cm-2s-1 | £per week
[pb-1] | polarization at store |
| --- | --- | --- | --- | --- | --- | --- |
| FY04 | 0.70 | 56 | 5.4 | 4.0 | 1.0 | 40-45%  |
| FY04
Unpolarized proton | 1.70 | 28 | 10.0 | -- | -- | -- |

## A typical store

## Challenges in RHIC

- Improve the luminosity performance
- Goal:
- 60x1030 cm-2s-1 is expected at 100 GeV/c
-  150x1030 cm-2s-1 is expected at 250 GeV/c
- Achieve > 70% beam polarization at 100 GeV/c as well as 250 GeV/c

## Challenges in RHIC -- Luminosity

- Beam-beam effect on the luminosity lifetime
- Beam emittance blowup
- beam lifetime dominated by the beam-beam driven resonances
- Total beam intensity limit due to the dynamic pressure rise

- Treatment: proper working point

- Treatment: NEG coating the warm beam pipes

## Polarization challenges in RHIC: snake resonances

-  Snake resonance
-  even order resonance: m is even, driven by overlapping imperfection and intrinsic resonance. The stronger the two resonances, the stronger the snake resonance
-  odd order resonance: m is odd, driven by intrinsic resonance

- K, m are integers

- See V. Ptitsyn’s talk

- RHIC working point

## RHIC Intrinsic spin resonance spectrum

-  p=217 GeV
- This gives the same Brho
- as Cu and one can avoid
- an additional DX magnet
- training

- Intrinsic spin resonance
- Qx=28.73, Qy=29.72, emit= 10

- achieved

## Solution I: precise orbit control

- golden orbit using the latest survey

- Flat orbit:
-     Sum of kicks on the spin vector
-     from quads as well as the dipole
-     correctors = 0

- Orbit through the center of bpms

- Goal: rms orbit distortion < 0.25mm

- Details in V. Ptitsyn’s talk

## Solution 2: precise tune control

- The tune feedback
- system has been
- demonstrated
- during the RHIC PP
- FY04 Run

## RHIC Plan for Reaching the Machine Goal

- During the summer shut-down
- Resurvey and re-alignment of IP12
- BPM system upgrade
- Plan for Machine development
- Polarimeter development: H. Huang’s talks
- Spin tune measurement: H. Huang’s talks
- This will allow us to check the snake current settings at top energy
**Explore pp acceleration beyond 100 GeV towards 250 GeV**
- Spin flipping commissioning
- Establish injection with both snake and spin rotators on at full field
- This will allow us to save ~7 minutes per store.

- If time permits

## Summary

| FY05 |  survey and realignment IP12
 BPM(Beam Position Monitor) system uprade
 AGS cold snake commissioning
 NEG coating 250m warm beam pipes
 acceleration beyond 100 GeV
 better solenoid for the polarized proton source OPPIS |
| --- | --- |
| FY06 |  realignment more areas
AGS cold snake operational
 more NEG coating
 more luminosity improvement |

-  Source performance: measured at the end of LINAC
-  Achieved: Average polarization 80% with 3~5x1011 bunch intensity
-  Expect: Average polarization 85% with >5x1011 bunch intensity
-  AGS performance: 50% polarization with 0.7~1.0x1011 bunch intensity
-  RHIC performance: 40~45% polarization with average 1 pb-1/week luminosity

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