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A proposal for a polarized 3 He ++ ion source with the EBIS ionizer for RHIC.

A proposal for a polarized 3 He ++ ion source with the EBIS ionizer for RHIC. A.Zelenski, J,Alessi, E.Beebe, A.Pikin BNL M.Farkhondeh, W.Franklin, A. Kocoloski, R.Milner, C. Tschalaer, E.Tsentalovich MIT-Bates E.Hughes Caltech SPIN 2004, Trieste. Motivation.

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A proposal for a polarized 3 He ++ ion source with the EBIS ionizer for RHIC.

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  1. A proposal for a polarized 3He++ ion source with the EBIS ionizer for RHIC. A.Zelenski, J,Alessi, E.Beebe, A.PikinBNL M.Farkhondeh, W.Franklin, A. Kocoloski, R.Milner, C. Tschalaer, E.TsentalovichMIT-Bates E.HughesCaltech SPIN 2004, Trieste

  2. Motivation • Polarized 3He ~ polarized neutron => compatible with existing spin manipulation capability in RHIC • In all previous experimental study of the spin structure of the nucleon, measurements on the neutron have been essential • For eRHIC, polarized neutron as well as polarized proton allows tests of the fundamental Bjorken Sum Rule

  3. 3He - basic properties. • 3He magnetic moment - 2.13 μN • Critical fields to break hyperfine interaction: • 3He(1S0) - B = 10 G-holding field • 3He(23S1) - Bc = 2.407 kG • 3He+(1S) - Bc= 3.087kG • 3He+(2S) - Bc= 0.386 kG

  4. Polarized 3He sources. Status 1984. No new operational 3He ion sources were built.A number of new ideas were proposed and tested (not successfully). Spin-exchange and “metastability-exchange” techniques for 3He atoms polarization were greatly improved due to laser development and demanding applications.

  5. State of the art performance from Mainz group using new fiber lasers 50 bar liters/day = 1.3 x 1020 atoms/sec

  6. Rise/Texas A&M polarized 3He+ source. The source was operated at Texas A&M cyclotron during the 1976-78.

  7. Monte-Carlo simulations for 3He++ polarization in ECR ionizer. Excitation cross-section is an order of magnitude larger than ionization to He++. There will be a polarization loss in excited states in <10 kG field ECR source. Polarization 10-20%. ECR-ionizer for the 3He++ ions. RCNP, Osaka. 3He polarizer ECR ionizer

  8. EBIS ionizer for polarized 3He gas (proposal). • Polarized 3He gas is produced by a “metastability exchange” technique. P ~ 70-80% (pressure ~ 1 torr). • 3He gas is injected in the EBIS ionizer. • The ionization in EBIS is produced in a 50 kG field. • This field will greatly suppress the depolarization in the intermediate He+ single charge state, Bc(He+) = 3.1 kG • The charge ratio He++/He+>> 1. • The number of He++ ions is limited to the maximum charge which can be confined in EBIS (about 2.5 ·1011 of 3He++/store). • It is sufficient to obtain ~1011 He++/bunch in RHIC.

  9. EBIS ionizer for polarized 3He gas (proposal). He-3 metastability-exchange polarized cell. 2.5·1011 He++/pulse He(2S) RFQ EBIS-ionizer, B~ 50 kG Pumping laser 1083 nm. He-transfer line. ~50·1011 , 3He/pulse. P=70-80%.

  10. Polarized 3He gas injection into the EBIS-ionizer. • Polarized 3He gas can be transported without depolarization through glass and coated metal tubes. • There is a limitation due to the magnetic field gradient from the strong EBIS field in the transport line. Calculations show that there is no significant depolarization with the real magnetic field of the EBIS superconducting solenoid. A. Kocoloski (MIT)

  11. Direct optical pumping of the “fast” 3He(2S) beam (proposal). He(2S) He++ • After Cs-neutralizer cell almost 100% of He-atoms are in (23S1) state. Energy defect-0.38 ev. • Direct optical pumping can produce near 100% nuclear polarization in He(2S) states. P( He++) ~80-90%. He(2S) EBIS ionizer He+ source Cs-vapor cell 100 mA of a 1.0 keV energy He+ ion beam 4He-gas Ionizer cell He++ EBIS ionizer Optical pumping at 1083 nm He+ ~3 kG field

  12. 3He++ nuclear polarization measurements. • After acceleration to 300 keV/amu in RFQ a nuclear reaction like 3He +D p + 4He + 18.35 MeV. • Lamb-shift polarimeter technique can be used after He++ conversion to He+(2S) in the alkali-vapor cell. This polarimeter operates at the source energy of a 10-20 keV.

  13. Summary. • There exist several possible techniques to produce a required polarized 3He beam pulse intensity of about 2·1011 He++/pulse. • We propose a feasibility study of a polarized 3He++ source using the operational BNL EBIS ionizer and a metastability –exchange polarized 3He gas cell. • The expected beam intensity is about 2.5·1011 3He++/pulse with nuclear polarization: P >70 %.

  14. Birmingham Lamb-shift polarized 3He ion source,1974. This source was operated at the cyclotron in 1970-80 s .

  15. Double charge-exchange polarized 3He++ ion source INR, Moscow (proposal). 1015 3He/cm2, P ~ 70-80% Cross-section: σ (4He++ +3He →4He + 3He++) = 4·10-16 cm2 at 50 eV beam energy. Estimated current 100 uA polarized 3He++.

  16. Ionization rates for He+ and 3He++ by electron bombardment

  17. SPIN-EXCHANGE POLARIZATION IN PROTON-Rb COLLISIONS. Laser-795 nm Optical pumping Rb: NL(Rb) ~1014 cm-2 Stripper at 150kev, or EBIS Rb+ Rb0 He+ He+ source He+ He+ Sona transition Ionizer cell He++ 1.5 kG field Supperconducting solenoid 25 кГс Spin-exchange collisions:~0.6·10-14 cm2 Electron to proton polarization transfer Laser beam is a primary source of angular momentum: 10 W (795 nm) 4•1019 h/sec

  18. Spin-exchange polarization.

  19. Spin-exchange polarization cross-sections. Spin-exchange cross-sections lower than expected? Higher Rb thickness is required (~1015 at./cm2) to obtain high polarization.

  20. M.Tanaka’s conclusions. Very high Rb thickness is required!

  21. 3He++ production in spin-exchange source

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