Download He-3 - SPIN2004

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
•
3He
- basic properties.
magnetic moment
- 2.13 μN
• Critical fields to break hyperfine interaction:
•
•
•
•
3He(1S )
0
3He(23S )
1
3He+(1S)
3He+(2S) -
B = 10 G-holding field
Bc = 2.407 kG
Bc= 3.087kG
Bc= 0.386 kG
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.
State of the art performance from
Mainz group using new fiber lasers
Performance of the Mainz 3He Polariser and Compressor
with old ( LNA-laser 8 W ) and new ( IRP-fibre laser 25 W )
laser system
80
P [%] = 86 - 0.339 * Flux
Polarisation [%]
70
60
50
40
30
20
10
0
0
20
40
60
80
100
120
Flux [bar liters / day]
50 bar liters/day = 1.3 x 1020 atoms/sec
140
160
Rise/Texas A&M polarized 3He+ source.
The source was operated at Texas A&M cyclotron during
the 1976-78.
ECR-ionizer for the 3He++ ions. RCNP, Osaka.
3He
polarizer
ECR
ionizer
Monte-Carlo simulations for 3He++ polarization in ECR ionizer. Excitation crosssection 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 1020%.
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).
He-3
metastabilityexchange
polarized cell.
2.5·1011
He++/pulse
Pumping laser
1083 nm.
He(2S)
EBIS-ionizer,
B~ 50 kG
He-transfer line.
~50·1011 , 3He/pulse.
P=70-80%.
RFQ
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).
He+
source
Cs-vapor
cell
He(2S)
100 mA of a 1.0 keV
energy He+ ion beam
He(2S)
EBIS
He++
ionizer
4He-gas
Ionizer cell
EBIS
Optical pumping
He+
at 1083 nm
He++
ionizer
~3 kG field
• 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%.
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 alkalivapor cell. This polarimeter operates at the
source energy of a 10-20 keV.
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.
This source was operated at the cyclotron in 1970-80 s .
Double charge-exchange polarized 3He++ ion
source INR, Moscow (proposal).
1015 3He/cm2,
P ~ 70-80%
Cross-section: σ (4He++ +3He →
beam energy.
4He
+ 3He++) = 4·10-16 cm2 at 50 eV
Estimated current 100 uA polarized 3He++.
Ionization rates for He+ and 3He++ by electron
bombardment
SPIN-EXCHANGE POLARIZATION IN PROTON-Rb COLLISIONS.
Laser-795 nm
Optical pumping
Rb: NL(Rb) ~1014 cm-2
Rb0
He+ source
He+
Stripper at 150kev,
or EBIS
Rb+
He+
He+
Sona
transition
Ionizer
cell
He++
1.5 kG field
Supperconducting
solenoid 25 кГс
Spin-exchange
collisions: ~0.6·10-14 cm2
Laser beam is a primary source of angular momentum:
10 W (795 nm)
4•1019 h/sec
Electron to proton
polarization transfer
Spin-exchange polarization.
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.
Very high Rb thickness is required!
3He++
production in spin-exchange source