SONA Transition Optimization in the Brookhaven OPPIS

1. SONA Transition Optimization in the Brookhaven OPPIS A. Kponou, A. Zelenski, S. Kokhanovski, V. Zubets & T. Lehn B. N. L.

2. Abstract In Optically Pumped Polarized Ion Sources (OPPIS), the atomic beam is first electron polarized, and this polarization is then transferred to the nucleus by a perturbing magnetic field. In the BNL OPPIS, the electron polarized atomic beam experiences the perturbing field when it traverses a region where the axial magnetic field reverses direction in a controlled manner – strength and gradient. This is the so-called Sona Transition region. In studying how the field in the Sona region affected beam polarization (nuclear), we observed unexpected reproducible, periodic variations of the polarization. We report on studies to understand this behavior.

3. Outline • Brief description of OPPIS • The electron polarization of Ho • Outline of the SONA transition • Conditions for same • View of the transition region • Magnetic field measurements & simulations (TRAK) • Optimizing • Scans • Analyses of scans

4. SCHEMATIC LAYOUT OF THE RHIC OPPIS. Cryopumps SCS solenoid Rb cell Pumping laser Probe laser Correction coil 29.2 GHz ECR proton source Na-jet Ionizer cell

5. Rubidium Optical Pumping (n=5)

6. mJ=1/2 mJ=-1/2 ... [Ho atoms] enter a region where B is decreasing in value…if this decrease is slow enough (adiabatic), each state follows the corresponding energy line….P. G. Sona energia nucleare, 14, No.5, 1967.

7. Br Bz Off-axis behavior Bz z

8. Conditions for the SONA Transition The transverse magnetic field. The precession rate about the transverse field. e & m are the electron charge and mass. r is the distance from the axis. To a particle traveling with velocity v parallel to the axis & r from it, the magnetic field appears to rotate at the rate: . . G. G. Ohlsen LA - 3949

9. SONA Transition conditions (cont’d) A “sudden” zero-field crossing requires: For r = 1 cm: For 3 keV Ho, v = 7 x 107 cm/s:

10. Sona Transition Region

15. Sona-transition.

18. A Recent Polarization Scan @ 200 MeV

20. Tom Clegg’s visit in the Fall of ’06. The oscillations in polarization when we scan the CC are due to π(minima) and 2π(maxima) spin flips about the off-axis radial fields due to the longitudinal gradient. (For atoms in state 1: mj=1/2, mI=1/2. Atoms in state 2, which has an admixture of state 4 which is large near the zero crossing point), adiabatically follow the reversing field.) Because Br varies with r, spin flip conditions also depend on r. The size of the polarization variation will vary with Sona configurations – shield diameter, position.. 15 to 50% observed. (cont’d)

21. At the higher zero-crossing gradients, outside the sona shield, Br increases rapidly with r. This reduces the polarization, because the spin flipping is less coherent. Collimating the beam to diameters of 12 mm, 16 mm, 20 mm, did not affect the optimized polarization. The i.d. of the Sona shield is ~ 46 mm. We can conclude that the Sona scheme is at maximum efficiency. We have applied these concepts to a CC scan. Results are shown in the next slide.

22. (For 4/4/07 scan.)

23. Polarization @200 MeV vs CC and Ionizer Currents(Before the present configuration.)

24. We invite anyone who is a good FORTRAN programmer, or has access to one, to do the necessary debugging to get Ohlsen’s program working again!