High-Intensity Polarized H- Beam production in Charge-exchange Collisions

A.Zelenski, BNL

PSTP 2011, September 14, St.Petersburg

RHIC: the “Polarized” Collider

STARPHENIX

AGS, 24GeVLINAC

BOOSTER, 2.5 GeV

Pol. H- ion source

Spin Rotators

20% Snake

Siberian Snakes

200 MeV polarimeter

RHIC pC “CNI” polarimeters

RHIC

Absolute H-jetpolarimeter

Design goal: P=70%, L max = 1.6 1032 s-1cm-2 50 < √s < 500 GeV

AGS pC “CNI” polarimeter

5% Snake

Polarization facilities at RHIC.Polarization facilities at RHIC.

Operational Polarized H- Source at RHIC. Operational Polarized H- Source at RHIC.

RHIC OPPIS produces reliably 0.5-1.0mApolarized H- ion current.Polarization at 200 MeV: P = 80-85%.Beam intensity (ion/pulse)routine operation:Source - 1012 H-/pulseLinac - 5∙1011

AGS - 1.5-2.0 ∙ 1011

RHIC - 1.5∙1011

(protons/bunch).

A 29.2 GHz ECR-type source is used for primary proton beam generation.The source was originally developed for dc operation. A ten-fold intensity increase was demonstrated in a pulsed operation by using a very high-brightness Fast Atomic Beam Source instead of the ECR proton source .

Polarized beams at RHIC.Polarized beams at RHIC.

OPPIS

LINAC

Booster

AGS

RHIC

1.7 10∙ 11 p/bunch

10 10∙ 11(maximum 40 10∙ 11) polarized H- /pulse.

5 10∙ 11 polarized H- /pulse at 200 MeV, P=85-90%

2 10∙ 11 protons /pulse at 2.3 GeV

~1.5∙1011 p/bunch, P~60-65% at 100 GeV P ~ 53% at 250 GeV

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

Rb+

H+ H+Proton source

Proton source

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

Sonatransition

Sonatransition

Ionizercell

Ionizercell

H-

Laser beam is a primary source of angular momentum:

10 W (795 nm) 4•1019 h/sec 2 A, H0 equivalent intensity.

Supperconducting solenoid 25 кГс

1.5 kG field

Charge-exchange

collisions: ~10-14 cm2

Na-jet ionizer cell:

NL(Na)~ 3•1015 cm-2

Electron to proton polarization transfer

ECR-29 GHz Н+ source

Rb+

Schematic Layout of the RHIC OPPISSchematic Layout of the RHIC OPPIS

29.2 GHz ECR proton source29.2 GHz ECR proton source

SCS solenoidSCS solenoid

Probelaser

Na-jetIonizer

cell

Na-jetIonizer

cell

Pumpinglaser

CryopumpsCryopumps

Sona-transition

Rb-cellSCS -solenoid

Pulsed OPPIS with the atomic hydrogen injector

at INR, Moscow, 1982-1990. The First-Generation.

Atomic H injector

Helium ionizer cell~80% ionizationefficiency. Lamb-shift

polarimeter

H- current 0.4mA, P=65%, 1986

Hydrogen atomic beam ionization efficiency in the He- cell.

Hydrogen atomic beam ionization efficiency in the He- cell.

10 keV

80%

H0 + He → H+ + He + e

OPPIS upgrade with the Fast Atomic Beam Source (FABS). The Third- Generation.

OPPIS upgrade with the Fast Atomic Beam Source (FABS). The Third- Generation.

He – ionizer cell serves as a proton source in the high magnetic field.

H+H0 H-

H0

H+

The source produces ~ 5.0 A ! (peak) proton current at 5.0 keV.

~ 10 mA H- current, P = 85-90%.~ 300 mA (high-brightness) unpolarized H- ion current.

Feasibility studies with Atomic Beam Injector at TRIUMF, 1997-99.

The Second Generation.

Feasibility studies with Atomic Beam Injector at TRIUMF, 1997-99.

The Second Generation.

A pulsed H- ion current of a 10 mA was obtained in 1999.

Pulsed OPPIS at TRIUMF, 1997-99.Pulsed OPPIS at TRIUMF, 1997-99.

A pulsed H- ion current of a 10 mA was obtained in 1999.

Atomic H

Injector.

Small diameter beam in the FABS.

• Atomic H0 injector produces an order of magnitude higher brightness beam. A 5-10 mA H- ion current can be obtained with the smaller, (about 15 mm in diameter) beam.

• Higher Sona-transition efficiency for the smaller beam radius.

• Smaller beam emittance : εn ~ B × R 2

The Atomic Hydrogen Injector

Collaboration agreement with BINP, Novosibirsk

on polarized source upgrade. • Contract with BINP, Novosibirsk. Delivery: May, 2011.• Two sets of sources and power supplies, local control

system.• 4- sets of spherical extraction grids (focal length

~150 cm) for polarized source.• 2- sets of shorter focal length (~ 50cm) grids for

studies of basic limitation of high-brightness H- ion beam production in the charge-exchange process.

BINP design for the “Atomic Beam Injector”.

Plasmatron 4-grid protonextraction system

H2 Neutralization cell

~ 5.0AequivalentH0 beam

Ratio of the target to the emitter current density vs spherical grids focal length.

Fig. 8. Ratio of the target current to the emitter current vs focal distance: 1 – without magnetic field, 2 – with magnetic field.

5A, H+ → 200mA, H0→ 16 mA, H-

Residual unpolarized H0 beam component suppression by the energy separation.

H+(60%)H0(10keV) H0(3.0keV)

-7.0 kV-7.1 kV

-7.1 kV

-7.0 kV

H0(10.0keV)

He-ionizer cell Rb -cell

H0(40%)

DecelerationH0 + He → H+ + He + e

Polarization dilution in the FABS.

H0 (10keV)

H+ (10keV)

H+ (3.0keV)

H0 (3.0keV)

H- (3.0keV)

H- (35keV)

He-cell60%

?

50%

8.5%

2.7%

H0(10keV) H-(10keV) H-(42keV)40% 2% 0.8%

H+ (10keV)

H2-cell

0.8/2.7 =0.3- polarization dilution.7.0 keV energy separation would allow dilution reduction to less than 0.1%.

Deceleration, ΔE = - 7.0 keV

Acceleration, - 32 keV

95%

Polarization dilution by H2+ in the FABS.

H0 (5.0keV)

H+ (5.0keV)

H+ (3.0keV)

H0 (3.0keV)

H- (3.0keV)

H- (35.0keV)

He-cell80%

Beam loss at deceleration ?

50%

8.5%

3%

H0(5.0keV) H-(5.0keV) H-(37keV)20% 6% 0.12%

H+2(10ke

V) H2-cell

Deceleration, ΔE=7.0 keV

Acceleration, 32 keV

~10%

0.12/3.0 =0.04- polarization dilution.2.0 keV energy separation reduces dilution to less than 0.4%

LEBT upgrades for the Run 2010-11.

“Tandem” Einzel Lens

A new Spin Rotator Solenoid

New stirrers, Buncher, (Quads?)

Molecular component suppression by the double Einzel lens in the LEBT.

Deepak simulations.

Molecular component suppression by the double Einzel lens in the LEBT.

Extractor Voltage, kV

1.4 kV

~10-15% beam intensity losses

32.2 +2.8 =35.0 keV

Tk 9, current, 200 MeV

2.0 kV

Primary proton beam energy (~ 10.0 keV) choice.

• Higher energy gives higher beam intensity.• Lower ionization efficiency in the He-cell (~60%).• Larger deceleration (~7.0 keV) after the He-cell is

required.• H- yield reduction for 10 keV residual unpolarized

H0.

• Higher energy increases the energy separation efficiency.

• At least 10 keV energy is required for molecular H2+

beam component suppression.

Contract with Cryomagnetics, Tennesi. Delivery: December, 2011. Higher 30 kG field. Better field shape. Cold iron yoke. He- re-condenser, low maintenance cost. Two mode of operations. Atomic beam mode –long flattop. ECR- mode provides field shape for the conventional

ECR-mode operation.

A new superconducting solenoid.

Magnetic field maps for Oxford Instr. and Toshiba

solenoids. Magnetic field maps for Oxford Instr. and Toshiba

solenoids.

0

5

10

15

20

25

30

0 10 20 30 40 50 60 70 80 90 100 110 120

Position, cm

Mag

net

ic f

ield

, kG

Toshiba solenoid

Oxford solenoid

Bz -field component at the solenoid axis.

Z-

RF-power input

Rb-cell

ECR-grids

Sona-transition

Correction coil

0

5000

10000

15000

20000

25000

30000

35000

-30.0 -20.0 -10.0 0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0 110.0 120.0

z (cm)

B (

Ga

uss

)

Atomic Mode (G)

OPPIS Mode (G)

Flat_Xiaofeng

ERC_Xiaofeng

A new superconducting solenoid. ECR-mode.

Contract with Cryomagnetics, Tennesi. Delivery: May, 2011

30 kG

Depolarization caused by spin-orbital (LS) interaction in excited 2P states.

Depolarization caused by spin-orbital (LS) interaction in excited 2P states.

~92% at 20 kG –low limit

Most of the H aoms are producedin excited n=2 states.

A high magnetic field has to beApplied in the optically-pumpedvapor cell to avoid depolarizationdue to spin-orbital interaction.

H- yield vs beam energy

0

1

2

3

4

5

6

7

8

9

10

0 2 4 6 8 10 12

Beam energy, keV

H-

ion

yie

ld,

%

~ 8.4 % at 3.0 keV beam energy

• An application of conventional “hot-pipe” sodium vapor cell for high-intensity H- ion beam production in charge-exchange collisions is limited by the fast increase of the sodium losses, which are proportional: ~ n3 / L ,

where n is vapor density and L- is the cell length.

The solution is the Jet-ionizer cell.

Sodium-jet ionizer cellSodium-jet ionizer cell

Sodium-jet ionizer cellSodium-jet ionizer cell

Reservoir– operational temperature. Tres. ~500 оС.Nozzle – Tn ~500 оС.Collector- Na-vapor condensation: Tcoll.~120оСTrap- return line. T ~ 120 – 180 оС.

Transversal vapor flow in the N-jet cell.Reduces sodium vapor losses for 3-4 ordersof magnitude, which allow the cell aperture increase up to 3.0 cm .

Transversal vapor flow in the N-jet cell.Reduces sodium vapor losses for 3-4 ordersof magnitude, which allow the cell aperture increase up to 3.0 cm .

Nozzle500deg.C

Collector~150 deg.C

Reservoir~500 deg.C

NL ~2·1015 atoms/cm2

L ~ 2-3 cm

H- beam acceleration to 35 keV at the exit of Na-jet ionizer cell

H- beam acceleration to 35 keV at the exit of Na-jet ionizer cell

Na-jet cell is isolated and biased to – 32 keV. The H- beam is accelerated in a two-stage acceleration system.

-32 kV

H-

35 keV

-28 keV -15 keV

H- beam acceleration to 35 keV at the exit of Na-jet ionizer cell

H- beam acceleration to 35 keV at the exit of Na-jet ionizer cell

Na-jet cell is isolated and biased to – 32 keV. The H- beam is accelerated in a two-stage acceleration system.

-32 kV

H-

35 keV

-28 keV -15 keV

Small diameter beam in the FABS.

• Atomic H injector produces an order of magnitude higher brightness beam. A 5-10 mA H- ion current can be obtained with the smaller, (about 15 mm in diameter) beam.

• Higher Sona-transition efficiency for the smaller beam radius.

• Smaller beam emittance : ε ~ B × R 2

• High-brightness source (FABS) will deliver at least 10 times more beam intensity then ECR-proton source

within the small ionizer aperture.

200 MeV Polarization CC Scan on 4/4/07

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

Correction Coil Current (x25 = Amps)

Pol

ariz

atio

n at

200

MeV

200 MeV Polarization

11 mm radius

5 mm radius

After Sona-transition upgrade, Run 07Simulations and field measurements.A new diam. 4.0” Sona-shieldA new Correction CoilOptimized positions for shield and CC

97.5%

x x x

x

Polarization vs. ionizer solenoid current with the 12mm collimator.

80

81

82

83

84

85

86

87

88

89

90

150 160 170 180 190 200 210 220 230 240 250 260

Ionizer solenoid current, A

Po

lari

zatio

n a

t 2

00

Me

V,

%

Maximum polarization from the correction coil scans, collim. -12 mm.

160 A ↔1.16 kG, 81.6%, (95.9%)

200 A ↔1.45 kG, 84.9%, (97.0%)

250 A ↔1.81 kG , 88.1%, (98.1%) Expected:

Maximum polarization from the correction coil scans, collim. -12 mm.

160 A ↔1.16 kG, 81.6%, (95.9%)

200 A ↔1.45 kG, 84.9%, (97.0%)

250 A ↔1.81 kG , 88.1%, (98.1%) Expected:

23 mm collimator.

200 A ↔1.45 kG, 82.5% (97.0%)

250 A ↔1.81 kG , 84.5% (98.1%) A new ionizer solenoid:250 A ↔1.98 kG , 90.0% (98.4%)

23 mm collimator.

200 A ↔1.45 kG, 82.5% (97.0%)

250 A ↔1.81 kG , 84.5% (98.1%) A new ionizer solenoid:250 A ↔1.98 kG , 90.0% (98.4%)

Expected

Basic limitation on the intensity of H- beam production in the Na-jet cell.

• According to paper: A.I.Krylov, V.V.Kuznetsov. Fizika Plasmy, 11, p.1508 (1985), influence of secondary plasma on a Na-jet stable operation is determined by parameter :

α = Jσion / ev0

where: J - beam current (per cm) of jet-target length; σion – cross-section of ionization of atoms of a target, v0 – atoms velocity in the Jet.

Critical value (Jet instability) of α is ~ 0.06.• The cross section of charge exchange of protons on sodium atom has

value of: 1.2·10-14 cm2.• The electron capture cross section for hydrogen atoms in Na-jet is of: 5·10-16 cm2.

The separation of neutralization and H- production cells should allow current density increase to: J ~1.5 A/cm2,

without impact on the Na-jet operation.

High- brighthess un-polarized H- ion beam production

~ 300 mAH- ion beamH+

3.0 keV

H2 –gas neutralizer cell

H0

Na-jet ionizer cell

~ 4.0 A equivalent H0 currentthrough 2.0 cm (Diameter)Na –jet cell.

εn ~ 0.1π mm mrad

A new FABS test bench.

TMP for He pumping

FABS operation

H- current, 12 mA

Arc current, 650A

Beam energy, 7.0 keV

H- ion beam current vs beam energy (within 25 mm ionizer acceptance).

0

50

100

150

200

250

300

0 2 4 6 8

Beam energy, keV

Be

am

cu

rre

nt,

mA

H- current, (× 10)

H0-intensity

A new BINP neutral H-injector installed at the test-bench

Neutral hydrogen beam intensity profile at 250 cm distance from the

source.

20 mm

Depolarization factors in the OPPIS.Depolarization factors in the OPPIS.Depol. Factor

Process Estimate

PRb Rb polarization 0.99

S Rb polarization spatial distribution 0.97-0.99

BH2 Proton neutralization in residual gas. 0.95-0.99

+ ELS Depolarization due to spin-orbital

interaction.0.95-0.99 +

ES Sona-transition efficiency 0.98-1.00 +

E ioniz. Incomplete hyperfine interaction breaking in the ionizer magnetic field.

0.95-0.99 +

X Polarization dilution by molecular hydrogen ions in the ECR source.

X

Total: 0.81-0.95(0.9/0.8)4 ~1.6

OPPIS current and polarization vs. Rb –cell vapor thickness.

5∙1013

Rb-cell thickness, atoms/cm^2

X 1013

Higher ~105 deg Rb cell temperature

Summary I

• Atomic H injector produces an order of magnitude higher brightness beam than present ECR source.

• A 5-10 mA polarized H- ion current (50-100 mA proton current) can be obtained for the smaller (higher brightness) beam.

• The basic limitation on the production of the high-intensity (~300 mA) , high-brightness unpolarized H- ion beam in charge – exchange collisions will be also studied.

• Higher polarization is expected with the fast atomic beam source due to:

a) elimination of neutralization in residual hydrogen;

b) better Sona-transition efficiency for the smaller diameter beam;

c) use of higher ionizer field (up to 3.0 kG), while still keeping the beam emittance below 2.0 π mm∙mrad, due to the smaller beam diameter.

• All these factors combined will further increase polarization in the pulsed OPPIS to over 85%.

Summary II

LSP Polarization vs. ionizer current.

Polarized beams in RHIC.Polarized beams in RHIC.

OPPIS

LINAC

Booster

AGS

RHIC

2.2 10∙ 11 p/bunch, P ~65%

6.3 10∙ 11(maximum 40 10∙ 11) polarized H- /pulse.

3.6 10∙ 11 polarized H- /pulse at 200 MeV, P=80-82%

2.5 10∙ 11 protons /pulse at 2.3 GeV

~1.7∙1011 p/bunch, P~60-65% at 100GeV P ~ 53% at 250 GeV

200 uA X300us

Scraping in Booster