1. Atomic Beam Polarization Measurement of the RHIC Polarized H-Jet Target
A. Nass, M. Chapman, D. Graham, W. Haeberli,
S. Kokhanovski, A. Kponou, G. Mahler,
Y. Makdisi, W. Meng, J. Ritter, T. Wise,
A. Zelenski, V. Zubets

2. Outline Setup of the JET
Design of the High Frequency Transitions (HFT)
Accuracy of Breit-Rabi-polarimeter (BRP) measurement
Efficiencies of the HFT’s and atomic polarization
Depolarizing effects
Velocity at the Interaction Point and target density
Summary
Alexander Nass, Brookhaven National Laboratory SPIN 2004, Oct

3. Setup of the JET
Atomic beam produced by expansion of a dissociated H beam through a cold nozzle into vacuum chamber
Nuclear polarization achieved by HFT’s (SFT, WFT) after focusing with sextupole magnets
After passing RHIC beam BRP sextupoles focus the atomic beam into the detector
Determination of the efficiencies of these HFT’s and the polarization of the beam by comparing the detector signals while running different HFT’s, e.g.:
ABS SFT
ABS WFT
ABS SFT + ABS WFT
BRP HFT’s for calibration

4. High Frequency Transitions
HFT’s located in a shielding box to reduce large z-field of main target magnet and avoid non adiabatic regions
Water cooling to reduce resonance drifting effects of cavity due to thermal expansion
Possible creation of short-lived (up to 10s) plasma inside the SFT cavity due to reduced pumping due to shielding box which slows down the turn on but didn’t affect polarization

5. Solving the problem
Creation of plasma depends on surrounding magnetic field, gas density and RF-power
Not convenient to change magnetic fields and necessary RF-power.
Solution: Pulsing of dissociator power to reduce density for a short period (~10 ms)

6. Accuracy of the BRP measurement
1/3 of the full jet beam analyzed in BRP
2 beam blockers to remove atoms in states |3> and |4> and molecules from beam
Chopped beam signal to subtract background
High signal to noise ratio due to improved signal processing (noise reduction, signal amplification, proper grounding)
Determination of HFT efficiencies to a relative error of DS/S < 0.1% in t < 1 min

7. Efficiencies and nuclear polarization
Due to beam blockers only atoms in state |1> and |2> reaching the BRP detector
Using 4 HFT’s in ABS and BRP to create and analyze the nuclear polarization
Parameters are the efficiencies (1- e1-3), (1-e2-4), (1-e’1-3), (1-e’2-4) and the transmission ratio N2/N1 of state |2> to |1> through sextupoles
Polarization: (q=arctan BC/BJET, BC=50.7 mT, BJET=120 mT)

8. Efficiencies and nuclear polarization
Stable behavior over the whole 2004 run, mean values for nuclear polarization of the atoms:
P+ = 0.957±0.001 and Pˉ = ±0.001

9. Stability of nuclear polarization

10. Depolarizing effects
Majorana depolarization if change of direction of magnetic fields in rest frame of the atoms along atomic beam path is too rapid
No depolarization if field changes are adiabatic, i.e. slow compared to Larmor time tL ~ 1/B

11. Depolarizing Effects Toms theoretical values to be added
Beam induced depolarization due to bunched structure of p-beam  transient magnetic fields transverse to the beam direction
Closely spaced depolarizing resonances in the usable range of the surrounding target holding field
High uniformity of the target holding field necessary
Required at JET:
DB/B=6ּ10-3
achieved 5ּ10-3
No depolarization
with 60 bunches in
RHIC
Toms theoretical values to be added

12. Velocity at the IP with RHIC
Measurements done using a fast chopper and a QMA
TOF signal influenced by opening function of the chopper window
Influence decreases as speed of chopper increases  Measurements at different chopper speeds
Result: v=1562±20 m/s
Variation in dissociator parameters showed only small (±50 m/s) variations in velocity spectrum since it is almost fixed by the transmission of the sextupole magnets

13. Areal density of the Jet
FWHM of the JET (comp. tube measurement): 5.5mm
Measured intensity: (12.4±0.2)ּ1016 atoms/s
Using measured velocity: rz=(7.94±0.13)ּ1010 atoms/mm
Assuming Gaussian distribution:
Density for RHIC interaction (square of 1 mm2):
= (1.33 ± 0.02) 1012 atoms/cm2

14. Velocity distribution at the BRP
Measurement done using the ABS-SFT and a QMA in BRP chamber
TOF spectrum measured using SFT pickup amplitude as trigger
Spectrum shows transmission peaks of the combined ABS and BRP sextupole system

15. Summary Highly efficient and stable polarization (P=0.958±0.001)
Very accurate measurement with BRP (DP/P < 0.1% )
No bunch field depolarization detectable with 60 bunches
Next run probably with 120 bunches, but uniformity of the target holding field assumed to be sufficient for a working point with no depolarization
Target density of (1.10 ± 0.02)ּ1012 atoms/cm2
Looking forward to run 2005 (120 bunches)
Alexander Nass, Brookhaven National Laboratory SPIN 2004, Oct