Transcript Polarization dilution by H2+ in the FABS.

Polarization optimization studying
in the RHIC OPPIS
G. Atoiana*, V. Klenovb, J. Rittera, D. Steskia, A. Zelenskia, V. Zubetsb
aBrookhaven
National Laboratory, Upton, NY 11973, USA
bInstitute of Nuclear Researches, Moscow, Russia
September 12, 2013
PSTP 2013
In Run-13 the upgraded polarized proton source was used
OPPIS (Optically Pumped Polarized Ion Source) H- ion source had
been upgraded to a higher intensity and polarization.
Up until Run-13 a ECR-type source was used for primary proton beam
generation. The source was originally developed for DC operation and placed
inside of the super conductive solenoid (SCS).
A tenfold intensity increase was demonstrated in pulsed operation by using a
high-brightness Fast Atomic Beam Source (FABS) instead of the ECR proton
source.
FABS was developed at Budker Institute of Nuclear Physics (BINP), Novosibirsk
to improve the source parameters such as beam current density, angular
divergence, and stability.
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Polarization transfer technique
Polarized
light
Polarized
electron
Polarized proton
(Quarks? Gluons ? Sea quarks?
Production of circular polarized tunable
wavelength (~795nm) laser beam
Polarization transfer from laser beam to electron in
Rb atoms by optical pumping technique
Production of electron spin polarized hydrogen atoms
when protons capture polarized electrons from Rb atoms
Polarization transfer from electron to proton by “Sonatransition” technique
Ionization of hydrogen atoms by capture of second
electron in Na-jet for acceleration
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OPPIS with FABS-injector layout (Run-13)
 OPPIS produces 3-5mA polarized H- ion pulse current
 Polarization at 200MeV polarimeter ~81-84 %
TMP2
TMP1
4-grids
extractor
(6-8keV)
CP3
CP1
CP4
Beam
SCS
Plasmatron
H-injector
H+
Neutralizer
H-cell
H-cell
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H0
He-cell
Ionizer &
decelerator
He-cell
Pump
-laser
CP2
Rb-cell
H+
4
Sonashield
Rb-cell
Na-jet
Ionizer
H0
Extractor
to 35KeV
Na-jet
5-10mA
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Low Energy Beam Transport line
The entire LEBT line has been modified for:
• an additional space for the new source (more then 1.5m);
• to transport more intense beam;
• energy separation of polarized component of the beam.
EL-tandem
Is “off”.
“off”
RFG
Laser Room
Moveable
optic prism
New FC
EL2-replaced with
Quad triplet
Pump-laser
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The LEBT is tuned
for 35keV beam
Energy transport.
transformation of the
longitudinal to the
transverse polarization
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LINAC
Add Vert. and
Horiz. steering
Variable collimators
to improvement of
energy separation
Polarization dilution due H0 in the new source
In FABS-source
H+ >90%
7keV
Neutralize
H0
7keV
Ionize
40%
H0
7keV
H+
7keV
Decelerate, ΔE=4.0keV
0.72%
HNa-jet 7keV Extr. 39keV
Ionize
Accelerate
32keV
2%
H-
H+
3keV
H0
3keV
Neutralize
Dilution of polarization (0.72/3 =0.24) can
be reduced by the energy separation of the
H- beam (~25-30 times) to 0.24/25~ 0.01
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Ionizer & Extractor
Inside of the SCS
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Ionize
H3keV
Accelerate
32keV
3%
H35keV
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He-ionizer cell with three-grid energy separation system
Two functions of the new He-cell with pulsed valve:
• Ionization of the injected neutral beam
• Deceleration of the ionized part of the beam to separate from the no-ionized part
He-valve
 Operating in high
magnetic field ~1-3T
He-cell
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He-pulsed
valve
3-grid beam
Deceleration system
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Energy separation a residual un-polarized H0 component
Only a portion of the beam is ionized in the He-cell (~60%) can be further polarized.
H0 + He → H+ + He + eIonization
in He-cell
Deceleration
by 3-grids system
Neutralization
in Rb-cell
He-cell
H0(7keV)
-4.1 kV
Rb -cell
H+(60%)
H+(3keV)
H0(3keV)
H0(40%)
H0(7keV)
H0(7keV)
-4.0 kV
-3.9 kV
-2.4 kV
+0.1 kV
Polarized part of the beam separates from un-polarized by the bending magnet and
collimators. Energy separation is better than 25-30 times.
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Depolarization factors
P = EH2 ∙ PRb∙ S ∙ BRG∙ ELS∙ EES ∙ ESona∙ Eion ~ 85-90%
Depol. factor
Process
Estimate
1
EH2
Dilution due H2+ in the new source (LEBT)
0.99 - 0.99
2
PRb
Rb-optical pumping (Laser system)
0.99 - 0.99
3
S
Rb polarization spatial distribution (Collimators)
0.97 - 0.98
4
BRG
Proton neutralization in residual gas (Vacuum)
0.98 - 0.99
5
ELS
Depolarization due to spin-orbital interaction
0.98 - 0.98
6
EES
Dilution due to incomplete energy separation not
polarized component of the beam (LEBT)
0.98 - 0.99
7
ESona
Sona-transition efficiency (Adjustment)
0.96 - 0.98
8
Eion
Incomplete hyperfine interaction breaking in the
ionizer magnetic field
0.98 - 0.99
Total: 0.85 - 0.90
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1
Dilution due H2+ in the new source (LEBT)
EH2
In FABS-source
0.99 - 0.99
Ionizer & Extractor
Inside of the SCS
H2+ <10% x 0.2=2% (Attenuate due to larger angular divergence ~ 0.2)
7keV
0.03%
8%
20%
H0
HHH0
Neutralize
3.5keV Na-jet 3.5keV Extr.
35.5keV
3.5keV
Ionize
Accelerate
32keV
Ionize
H+
3.5keV
Decelerate (ΔE=4.0keV)  Rejected
Ionize
Dilution of polarization due
H2+ component- 0.03/3 ~ 0.01
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Accelerate
32keV
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H- 0%
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2
PRb
Rb-optical pumping (Laser system)
0.99 - 0.99
Polarization strongly depends on the power, frequency, and the line width of the pumping laser.
After upgrade a laser system we:
• adjust of power, frequency, and line width of pumping laser;
• monitor and control frequency, and line width with new wave-meter.
Control the laser parameters
Before
By quality of the probe-laser pulse
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Now
By measured frequency and line width of pump-laser
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2
PRb
Rb-optical pumping (Laser system)
0.99 - 0.99
We can create a time-chart of frequency and line width and store data for analyzing.
Time-chart of frequency of the laser
Time-chart of line width
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3
S
Rb polarization spatial distribution (Collimators)
Beam profile out of Linac
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0.97 - 0.98
Polarization profile out of Linac
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3
S
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Rb polarization spatial distribution (Collimators)
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0.97 - 0.98
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4
BRG
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Proton neutralization in residual gas (Vacuum)
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0.98 - 0.99
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4
BRG
Proton neutralization in residual gas (Vacuum)
P~1/AN*[(IL-0.5iRG)-(IR- 0.5iRG)] / [(IL-0.5iRG)+(IR- 0.5iRG)]
P= 1/AN*(IL- IR)/(IL+ IR +iRG)
IM=IL+IR+iRG , if IR= a*IL
P= 1/AN* (IM-iRG)(1-a) / IM*(1+a)  iRG~3.7mkA
0.98 - 0.99
Dilution of polarization due
residual gas at Rb thickness
~5*1013 atoms/cm2 (~350mkA)
is 3.7/350 < 1.5%
iRG~3.7mkA; IL/IR ~0.315
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5
ELS
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Depolarization due to spin-orbital interaction
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0.98 - 0.98
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EES
Dilution due to incomplete energy separation not
polarized component of the beam (LEBT)
0.98 - 0.99
Ratio: 3000/30 ~100
3.5
H- ion beam current,
mA
6
3
31.5 + (7.5 – 4.0) = 35keV
He-valve ‘OFF’
2.5
2
1.5
He-valve ‘ON’
27.5 +7.5 =35keV
1
0.5
0
20
22
24
26
28
30
32
34
36
Acceleration voltage, kV
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7
ESona
Sona-transition efficiency (Adjustment)
0.96 - 0.98
2 corr. coils between SCS and Sona-shield
H0
He-cell
Na-jet
&
Solenoid
Rb-cell
SC-solenoid
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H-
Sona-transition with 3 corr. coils in it
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7
ESona
Sona-transition efficiency (Adjustment)
0.96 - 0.98
5 correction coils (LCC, SCC, ICC1, ICC2 and ICC3) used for
optimized magnetic field in Sona-shield to achieve maximum
polarization.
Sona
transition
region
No adiabatic
passage to weak
field region
Spin rotator
region
ICC-1
ICC-3
ICC-2
Sona shield
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ESona
Sona-transition efficiency (Adjustment)
0.96 - 0.98
For maximum polarization must be accurate selection of settings all correction coils. Any change
in the magnetic field of coils, SCS or ionizer as well as their position requires a new settings.
LCC fine scan
LCC scan
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Eion
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Incomplete hyperfine interaction breaking in the
ionizer magnetic field
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0.98 - 0.99
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Beam performance during RHIC fill #17472 (May 7, 2013)
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T(Rb)=81C, I(T9)=295mkA (4.9*10^11)
84.2+/-0.5%
15 min
83.9+/0.7%
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Summary
Polarization is an average about 2-3% higher than ECRbased source. It is expected that polarization can be further
improved to 85%. Higher polarization is expected due to reduce
depolarization factors:
• Rb polarization spatial distribution;
• reduce residual gas;
• Sona-transition efficiency;
• incomplete energy separation and
• Incomplete hyperfine interaction breaking in the ionizer
magnetic field.
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