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

3He - basic properties.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

Polarized 3He sources. Status 1984.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.

0 20 40 60 80 100 120 140 1600

10

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50

60

70

80

P [%] = 86 - 0.339 * Flux

Performance of the Mainz 3He Polariser and Compressorwith old ( LNA-laser 8 W ) and new ( IRP-fibre laser 25 W )laser system

P

ola

risa

tion

[%

]

Flux [bar liters / day]

State of the art performance from Mainz group using new fiber lasers

50 bar liters/day = 1.3 x 1020 atoms/sec

Rise/Texas A&M polarized 3He+ source.Rise/Texas A&M polarized 3He+ source.

The source was operated at Texas A&M cyclotron during the 1976-78.

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.ECR-ionizer for the 3He++ ions. RCNP, Osaka.

3He polarizer

3He polarizer

ECR

ionizer

ECR

ionizer

EBIS ionizer for polarized 3He gas (proposal).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.

EBIS ionizer for polarized 3He gas (proposal).EBIS ionizer for polarized 3He gas (proposal).

He(2S)He(2S)

He-3 metastability-exchange polarized cell.

Pumping laser 1083 nm.

Pumping laser 1083 nm.

EBIS-ionizer,

B~ 50 kG

EBIS-ionizer,

B~ 50 kG

RFQRFQ

He-transfer line.

~50·1011 , 3He/pulse. P=70-80%.

2.5·1011 He++/pulse

Polarized 3He gas injection into the EBIS-ionizer.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)

Direct optical pumping of the “fast” 3He(2S) beam (proposal).

Direct optical pumping of the “fast” 3He(2S) beam (proposal).

• 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+ source

Cs-vapor cell

He(2S)EBIS

ionizer

EBIS

ionizer

4He-gas

Ionizer cell

He+

He++

He++

100 mA of a 1.0 keV energy He+ ion beam

Optical pumping

at 1083 nm

~3 kG field

He(2S)

3He++ nuclear polarization measurements.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.

Summary.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 %.

Birmingham Lamb-shift polarized 3He ion source,1974.Birmingham Lamb-shift polarized 3He ion source,1974.

This source was operated at the cyclotron in 1970-80 s .

Double charge-exchange polarized 3He++ ion source INR, Moscow (proposal).

Double charge-exchange polarized 3He++ ion source INR, Moscow (proposal).

Cross-section: σ (4He++ +3He → 4He + 3He++) = 4·10-16 cm2 at 50 eV beam energy.

Estimated current 100 uA polarized 3He++.

1015 3He/cm2,

P ~ 70-80%

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

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

SPIN-EXCHANGE POLARIZATION IN PROTON-Rb COLLISIONS.SPIN-EXCHANGE POLARIZATION IN PROTON-Rb COLLISIONS.

Rb0

He+ He+He+ sourceHe+ source

Laser-795 nmOptical pumpingRb: NL(Rb) ~1014 cm-2

Sonatransition

Sonatransition

Ionizercell

Ionizercell

He++

Laser beam is a primary source of angular momentum:

10 W (795 nm) 4•1019 h/sec

Supperconducting solenoid 25 кГс

1.5 kG field

Spin-exchange collisions:

~0.6·10-14 cm2

Stripper at 150kev,

or EBIS

Electron to proton polarization transfer

Rb+

He+

Spin-exchange polarization.Spin-exchange polarization.

Spin-exchange polarization cross-sections.Spin-exchange polarization cross-sections.

Spin-exchange cross-sections lower than expected?

Higher Rb thickness is required (~1015 at./cm2) to obtain high polarization.

M.Tanaka’s conclusions.M.Tanaka’s conclusions.

Very high Rb thickness is required!

3He++ production in spin-exchange source