Presentation on theme: "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,"— Presentation transcript:
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 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
3 He - basic properties. 3 He magnetic moment μ 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 = kG 3 He + (1S) - B c = 3.087kG 3 He + (2S) - B c = kG
Polarized 3 He sources. Status 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.
State of the art performance from Mainz group using new fiber lasers 50 bar liters/day = 1.3 x atoms/sec
Rise/Texas A&M polarized 3 He + source. The source was operated at Texas A&M cyclotron during the
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 <10 kG field ECR source. Polarization %. ECR-ionizer for the 3 He ++ ions. RCNP, Osaka. 3 He polarizer ECR ionizer ECR ionizer
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.
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. ~50·10 11, 3 He/pulse. P=70-80%. 2.5·10 11 He ++ /pulse
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)
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 mA of a 1.0 keV energy He + ion beam Optical pumping at 1083 nm ~3 kG field He(2S)
3 He ++ nuclear polarization measurements. After acceleration to 300 keV/amu in RFQ a nuclear reaction like 3 He +D p + 4 He 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 keV.
Summary. There exist several possible techniques to produce a required polarized 3 He beam pulse intensity of about 2·10 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 2.5· He ++ /pulse with nuclear polarization: P >70 %.
Birmingham Lamb-shift polarized 3 He ion source,1974. This source was operated at the cyclotron in s.
Double charge-exchange polarized 3 He ++ ion source INR, Moscow (proposal). Cross-section: σ ( 4 He He → 4 He + 3 He ++ ) = 4· cm 2 at 50 eV beam energy. Estimated current 100 uA polarized 3 He He/cm 2, P ~ 70-80%
Ionization rates for He + and 3 He ++ by electron bombardment
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) h /sec Supperconducting solenoid 25 кГс 1.5 kG field Spin-exchange collisions: ~0.6· cm 2 Stripper at 150kev, or EBIS Electron to proton polarization transfer Rb + He+
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.
M.Tanaka’s conclusions. Very high Rb thickness is required!