Slide 1

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 Slide 2 Motivation Polarized 3 He ~ 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 Slide 3 3 He - basic properties. 3 He magnetic moment - 2.13 N Critical fields to break hyperfine interaction: 3 He( 1 S 0 ) - B = 10 G-holding field 3 He(2 3 S 1 ) - B c = 2.407 kG 3 He + (1S) - B c = 3.087kG 3 He + (2S) - B c = 0.386 kG Slide 4 Polarized 3 He sources. Status 1984. No new operational 3 He ion sources were built. A number of new ideas were proposed and tested (not successfully). Spin-exchange and metastability-exchange techniques for 3 He atoms polarization were greatly improved due to laser development and demanding applications. Slide 5 State of the art performance from Mainz group using new fiber lasers 50 bar liters/day = 1.3 x 10 20 atoms/sec Slide 6 Rise/Texas A&M polarized 3 He + source. The source was operated at Texas A&M cyclotron during the 1976-78. Slide 7 Monte-Carlo simulations for 3 He ++ 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 EBIS ionizer for polarized 3 He gas (proposal). Polarized 3 He gas is produced by a metastability exchange technique. P ~ 70-80% (pressure ~ 1 torr). 3 He 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, B c (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 10 11 of 3 He ++ /store). It is sufficient to obtain ~10 11 He ++ /bunch in RHIC. Slide 9 EBIS ionizer for polarized 3 He gas (proposal). He(2S) He-3 metastability- exchange polarized cell. Pumping laser 1083 nm. EBIS-ionizer, B~ 50 kG EBIS-ionizer, B~ 50 kG RFQ He-transfer line. ~5010 11, 3 He/pulse. P=70-80%. 2.510 11 He ++ /pulse Slide 10 Polarized 3 He gas injection into the EBIS-ionizer. Polarized 3 He 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) Slide 11 Direct optical pumping of the fast 3 He(2S) beam (proposal). After Cs-neutralizer cell almost 100% of He-atoms are in (2 3 S 1 ) state. Energy defect-0.38 ev. Direct optical pumping can produce near 100% nuclear polarization in He(2S) states. P( He ++ ) ~80-90%. He + source Cs-vapor cell He(2S) EBIS ionizer EBIS ionizer 4 He-gas Ionizer cell He + He ++ 100 mA of a 1.0 keV energy He + ion beam Optical pumping at 1083 nm ~3 kG field He(2S) Slide 12 3 He ++ nuclear polarization measurements. After acceleration to 300 keV/amu in RFQ a nuclear reaction like 3 He +D p + 4 He + 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. Slide 13 Summary. There exist several possible techniques to produce a required polarized 3 He beam pulse intensity of about 210 11 He ++ /pulse. We propose a feasibility study of a polarized 3 He ++ source using the operational BNL EBIS ionizer and a metastability exchange polarized 3 He gas cell. The expected beam intensity is about 2.510 11 3 He ++ /pulse with nuclear polarization: P >70 %. Slide 14 Birmingham Lamb-shift polarized 3 He ion source,1974. This source was operated at the cyclotron in 1970-80 s. Slide 15 Double charge-exchange polarized 3 He ++ ion source INR, Moscow (proposal). Cross-section: ( 4 He ++ + 3 He 4 He + 3 He ++ ) = 410 -16 cm 2 at 50 eV beam energy. Estimated current 100 uA polarized 3 He ++. 10 15 3 He/cm 2, P ~ 70-80% Slide 16 Ionization rates for He + and 3 He ++ by electron bombardment Slide 17 SPIN-EXCHANGE POLARIZATION IN PROTON-Rb COLLISIONS. Rb 0 He + He + source Laser-795 nm Optical pumping Rb: NL(Rb) ~10 14 cm -2 Sona transition Sona transition Ionizer cell Ionizer cell He ++ Laser beam is a primary source of angular momentum: 10 W (795 nm) 410 19 h /sec Supperconducting solenoid 25 1.5 kG field Spin-exchange collisions: ~0.610 -14 cm 2 Stripper at 150kev, or EBIS Electron to proton polarization transfer Rb + He+ Slide 18 Spin-exchange polarization. Slide 19 Spin-exchange polarization cross-sections. Spin-exchange cross-sections lower than expected? Higher Rb thickness is required (~10 15 at./cm 2 ) to obtain high polarization. Slide 20 M.Tanakas conclusions. Very high Rb thickness is required! Slide 21 3 He ++ production in spin-exchange source