# Presentation: 035490

## Towards 100% polarization in the Optically-Pumped Polarized Ion Source at RHIC. 

- The OPPIS polarization technique.
- Polarization losses in a multi-step spin- transfer process.
- OPPIS performance in 2006-07 Runs.
- Polarized Sources,Targets and Polarimeters
-    Workshop PST-2007 at BNL.

- Anatoli Zelenski, BNL

-      RSC, August 30, 2007

## Optically-Pumped Polarized H- Ion Source at RHIC.

- RHIC OPPIS produces
- reliably 0.5-1.0mA
- (maximum 1.6 mA)
- polarized H- ion current.
- Pulse duration 400 us.
- Polarization at 200 MeV
- P = 85-90 %.
- Beam intensity (ion/pulse)
- routine operation:
- Source         - 1012 H-/pulse
- Linac (200MeV)   - 5∙1011
- Booster              - 2∙1011,
- (50% - scraping).
- AGS                  - 1.7∙1011
- RHIC                 - 1.5∙1011
-                                     (p/bunch).

- The RHIC OPPIS was developed in collaboration
-  with TRIUMF and INR, Moscow.

## SCHEMATIC LAYOUT OF THE RHIC OPPIS.

- 29.2 GHz ECR
-  proton source

- SCS solenoid

- Probe
- laser

- Na-jet
- Ionizer
- cell

- Pumping
- laser

- Cryopumps

- Correction coil

- Sona-shield

- Rb-cell

- SCS -solenoid

## Depolarization factors in the OPPIS.

| Depol. 
Factor | Process | Estimate |
| --- | --- | --- |
|    PRb | Rb polarization | 0.98 - 0.99 |
|    S | Rb polarization spatial distribution | 0.97 - 0.98 |
|     BH2 | Proton neutralization in residual gas. | 0.94 - 0.97 |
|    ELS | Depolarization due to spin-orbital interaction. | 0.98 - 0.98 |
|    ES | Sona-transition efficiency | 0.96 - 0.99 |
|    E ioniz. | Incomplete hyperfine interaction breaking in the ionizer magnetic field.  | 0.95 - 0.98 |
|    M | Polarization dilution by molecular hydrogen ions in the ECR source. | 1.00 –1.00 |

- Total:   0.82 - 0.90

- (0.9/0.8)4 ~1.6

- P = PRb∙ S ∙ BH2∙ ELS∙ ESona∙ Eion∙ M ~ 85-90%

## Polarized beams in RHIC.

- OPPIS

- LINAC

- Booster

- AGS

- RHIC

- 1.5-1.7 p/bunch, P ~65-70%

- 10∙1011(maximum 40∙1011) polarized H- /pulse, P =85%

- 5∙1011  polarized H- /pulse at 200 MeV, P=85%

- 2∙1011  polarized protons /pulse at 2.3 GeV

- Maximum RHIC bunch intensity ~1.5 1011 p/bunch
- Polarization -65%

## Proton polarization vs. Rb vapor thickness.

- Long Rb cell

- A new short Rb cell

- Rb cell upgrades:
- A new vacuum chamber.
- A new cooling system.
- A new  deflecting plates.

## Optical pumping of Rb charge-exchange vapor cell.

- Rb

- h

- Proton beam.

- 28 mm

- Optical pumping by σ+:   ΔmJ=1
- Spontaneous radiation: ΔmJ=0, 1.

- mJ          -1/2                    +1/2

- Rb pol.
- Profile.

- Rb vapor cell.

- 795 nm

## Sodium-jet ionizer cell.

- Reservoir– operational temperature. Tres. ~500 оС.
- Nozzle – Tn ~500 оС.
- Collector- Na-vapor condensation: Tcoll.~120оС
- Trap- return line. T ~ 120 – 180 оС.

- Transversal vapor flow in the  N-jet cell.
- Reduces sodium vapor losses for 3-4 orders
- of magnitude, which allow the cell aperture
-  increase up to 3.0 cm .

- Nozzle
- 500deg.C

- Collector
- ~150 deg.C

- Reservoir
- ~500 deg.C

- NL ~2·1015 atoms/cm2
- L ~ 2-3 cm

## Proton polarization vs. Rb vapor thickness.

- Long Rb cell

- A new short Rb cell

- Rb cell upgrades:
- A new vacuum chamber.
- A new cooling system.
- A new  deflecting plates.

- H+ + Rb       H0  - polarized
-            H2        H0 - unpolarized

## SONA-TRANSITION. Polarization transfer from electrons to protons.

- Sona-transition

- ECR-zone

- Correction coil

- Steel plate

## Bz-field component in the Sona-transition region.

- Sona-shield
- Soft steel cylinder
- Mu-metal incert.

- Na-jet

- -

- dBz/dZ<< 0.2 G/cm

- Correction Coil

## Polarization vs. Correction Coil current with a new Sona-shield in Run-2007.

- 86.7%

- 86.4%

- 200 μA 400 μs pulse at 200 MeV
- ~ 4.8∙1011 H-/pulse

- Polarization measurement in 200 MeV polarimeter.

## Polarization oscillations vs. Correction Coil current.

## Polarization in the Lamb-shift polarimeter.

## Calculated magnetic field profiles in the Sona transition region. 

- Sona - shield

- Correction coil currents correspond to polarization oscillation peaks.

- Br = r/2 ∙dBz/dZ,  **ω****L**∙B∙t= 2π∙28∙109 Br∙t ~ 2**π**

**π**-flip

## Polarization oscillations in the Sona-transition, Run - 07.

- 85%

- Polarization at 200 MeV vs. Correction Coil current

- 50 A

- After Sona-transition upgrade, Run 07
- Simulations and field measurements.
- A new diam. 4.0” Sona-shield
- A new Correction Coil
- Optimized positions for shield and CC

- 85%

-   Polarization measurements in 200 MeV polarimeter.

## Correction coil scan.

- 12 mm collimator
- Ionizer -250 A, 1.8 kG

## Polarization vs. ionizer solenoid current with the 12mm collimator.

- Maximum polarization from the correction coil scans, collim. -12 mm.
- 160 A ↔1.16 kG,     81.6%    (95.9%)
- 200 A ↔1.45 kG,     84.9%    (97.0%)
- 250 A ↔1.81 kG ,    88.1%    (98.1%)

- Theoretical
-     limit

- 23 mm collimator.
- 200 A ↔1.45 kG,    82.5%    (97.0%)
- 250 A ↔1.81 kG ,   84.5%    (98.1%)
- A new ionizer solenoid:
- 250 A ↔1.98 kG ,   90.0%    (98.4%)

- Theoretical
-     limit

## Depolarization caused by incomplete hyperfine coupling breakdown in the ionizer magnetic field (Eioniz).

- P = P0 (1 + x /√1 +x2)/2
- X = B / Bc,  Bc = 507 G – critical field.

|    x | 1 | 2 | 3 | 4 | 5 |
| --- | --- | --- | --- | --- | --- |
|  B, G | 508 | 1016 | 1523 | 2030 | 2538 |
|  P, % | 85.4 | 94.7 | 97.4 | 98.5 | 99.0 |
| ΔEn, 
π∙mm∙mrad | 0.8
0.29 | 1.6
0.58 | 2.4
0.87 | 3.2
1.15 | 4.0
1.44 |

- R=1.0 cm

- R=0.6 cm

- ΔEn –normalized emittance growth associated with charge exchange
- in the magnetic field.

- 91.2+/-1.5%

## Polarization measurements at 200 MeV.

- 90%

## BNL OPPIS  reliably delivered polarized H- ion beam 
    (P= 82-86%)   in the 2006 run for the RHIC spin program.

A beam intensity greatly exceeds RHIC bunch intensity limit, which allowed strong beam collimation in the Booster, to reduce longitudinal and transverse beam emittances. 

85-90% polarization was achieved at further Sona-transition optimization and ionizer magnetic field increase to 1.98 kG in Run 07.

-     (P= 82-86%)   in the 2006 run for the RHIC spin program.
- A beam intensity greatly exceeds RHIC bunch intensity limit, which allowed strong beam collimation in the Booster, to reduce longitudinal and transverse beam emittances.
- 85-90% polarization was achieved at further Sona-transition optimization and ionizer magnetic field increase to 1.98 kG in Run 07.

- OPPIS operation in Runs 2006-07

-  Further improvements:
*A higher brightness primary proton beam is required for high intensity*
*source with the **smaller diameter collimated beam in Sona-transition and ionizer*
*(which is necessary for high polarization). *

## Proton “cannon” of the atomic H injector.

- The source produced 3 A ! pulsed
- proton current at 5.0 keV.** **

- ~20-50 mA H- current. P=75-80%
- ~10 mA ,                       P  90%.
- ~ 300 mA unpolarized H- ion current.

- Ion Optical System with “geometrical focusing”.

## OPPIS with the “Fast Atomic Beam Source” layout.

- He –ionizer cell serves as a proton source in the high magnetic field.

- H0

- H2 neutralizer cell

- Rb cell

- Proton
- source

## OPPIS with the “Fast Atomic Hydrogen Source”(Towards 100% polarization in OPPIS).

-     Higher polarization is also expected with the fast atomic beam source due to:
-      *a) elimination of neutralization in residual hydrogen;*
*     **b) better Sona-transition efficiency for the smaller ~ 1.5 cm diameter beam;*
*     **c) use of higher ionizer field (up to 3.0 kG), while still keeping the beam emittance below 2.0 π mm∙mrad, because of the smaller beam – 1.5 cm diameter.*
- All these factors combined will further increase polarization in the pulsed OPPIS to:
-     *over 90% and the source intensity to over 10 mA.** *
*    **(*A new superconducting solenoid is required).
- The ECR-source replacement with an atomic hydrogen injector will provide the high intensity and high polarization beam for polarized RHIC luminosity upgrade and for future eRHIC facilities.

## Present LEBT & MEBT

- Optics
- box

- 750 keV

- 35 keV

## New Proposed LEBT/MEBT, 35-750 keV

- Spin-rotator

- Einzel lens

- OPPIS

## Slide 31