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High-Intensity Polarized H - Beam production in Charge-exchange Collisions A.Zelenski, BNL

High-Intensity Polarized H - Beam production in Charge-exchange Collisions A.Zelenski, BNL. PSTP 2011, September 14, St.Petersburg. RHIC: the “Polarized” Collider. Polarization facilities at RHIC. Design goal: P= 70 %, L max = 1.6  10 32 s -1 cm -2 50 < √ s < 500 GeV.

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High-Intensity Polarized H - Beam production in Charge-exchange Collisions A.Zelenski, BNL

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  1. High-Intensity Polarized H- Beam production in Charge-exchange CollisionsA.Zelenski, BNL PSTP 2011, September 14, St.Petersburg

  2. RHIC: the “Polarized” Collider Polarization facilities at RHIC. Design goal: P=70%, L max = 1.6  1032 s-1cm-2 50 < √s < 500 GeV RHIC pC “CNI” polarimeters Absolute H-jet polarimeter RHIC PHENIX STAR Siberian Snakes Spin Rotators 5% Snake Pol. H- ion source LINAC AGS, 24GeV AGS pC “CNI” polarimeter 200 MeV polarimeter 20% Snake BOOSTER, 2.5 GeV

  3. Operational Polarized H- Source at RHIC. RHIC OPPIS produces reliably 0.5-1.0mA polarized H- ion current. Polarization at 200 MeV: P = 80-85%. Beam intensity (ion/pulse) routine operation: Source - 1012 H-/pulse Linac - 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 .

  4. Polarized beams at RHIC. OPPIS 10∙1011(maximum 40∙1011) polarized H- /pulse. LINAC 5∙1011 polarized H- /pulse at 200 MeV, P=85-90% Booster 2∙1011 protons /pulse at 2.3 GeV AGS 1.7∙1011 p/bunch RHIC ~1.5∙1011 p/bunch, P~60-65% at 100 GeV P ~ 53% at 250 GeV

  5. SPIN -TRANSFER POLARIZATION IN PROTON-Rb COLLISIONS. Laser-795 nm Optical pumping Rb: NL(Rb) ~1014 cm-2 Na-jet ionizer cell: NL(Na)~ 3•1015 cm-2 Rb+ Rb+ Proton source H+ H+ Sona transition Ionizer cell H- 1.5 kG field Charge-exchange collisions:~10-14 cm2 Electron to proton polarization transfer ECR-29 GHz Н+source Supperconducting solenoid 25 кГс Laser beam is a primary source of angular momentum: 10 W (795 nm) 4•1019 h/sec 2 A, H0equivalent intensity.

  6. Schematic Layout of the RHIC OPPIS Cryopumps SCS solenoid SCS -solenoid Rb-cell Probe laser Pumping laser 29.2 GHz ECR proton source Na-jet Ionizer cell Sona-transition

  7. Pulsed OPPIS with the atomic hydrogen injector at INR, Moscow, 1982-1990. The First-Generation. Atomic H injector Helium ionizer cell ~80% ionization efficiency. Lamb-shift polarimeter H- current 0.4mA, P=65%, 1986

  8. Hydrogen atomic beam ionization efficiency in the He- cell. H0 + He → H+ + He + e 80% 10 keV

  9. 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+ H+ H- H0 H0 The source produces ~ 5.0 A ! (peak) proton current at 5.0 keV. ~ 10 mAH- current, P = 85-90%. ~ 300 mA (high-brightness) unpolarized H- ion current.

  10. 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.

  11. Pulsed OPPIS at TRIUMF, 1997-99. Atomic H Injector. A pulsed H- ion current of a 10 mA was obtained in 1999.

  12. 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

  13. 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.

  14. BINP design for the “Atomic Beam Injector”. Plasmatron 4-grid proton extraction system ~ 5.0A equivalent H0 beam H2 Neutralization cell

  15. Ratio of the target to the emitter current density vs spherical grids focal length. 5A, H+→ 200mA, H0→ 16 mA, H- Fig. 8. Ratio of the target current to the emitter current vs focal distance: 1 – without magnetic field, 2 – with magnetic field.

  16. Residual unpolarized H0 beam component suppression by the energy separation. Deceleration H0 + He → H+ + He + e Rb -cell He-ionizer cell H0(10keV) H+(60%) H0(3.0keV) H0(40%) H0(10.0keV) -7.1 kV -7.0 kV -7.0 kV -7.1 kV

  17. Polarization dilution in the FABS. H+ (10keV) H2-cell 0.8% 40% 2% 95% H0(10keV) H-(10keV) H-(42keV) H0 (10keV) He-cell 60% H+ (10keV) Deceleration, ΔE = - 7.0 keV ? H+ (3.0keV) 50% H0 (3.0keV) 8.5% H- (3.0keV) 0.8/2.7 =0.3- polarization dilution. 7.0 keV energy separation would allow dilution reduction to less than 0.1%. Acceleration, - 32 keV H- (35keV) 2.7%

  18. Polarization dilution by H2+ in the FABS. ~10% H+2(10keV) H2-cell 0.12% 20% 6% H0(5.0keV) H-(5.0keV) H-(37keV) H0 (5.0keV) He-cell 80% H+ (5.0keV) Deceleration, ΔE=7.0 keV Beam loss at deceleration? H+ (3.0keV) 50% H0 (3.0keV) 8.5% H- (3.0keV) 0.12/3.0 =0.04- polarization dilution. 2.0 keV energy separation reduces dilution to less than 0.4% H- (35.0keV) Acceleration, 32 keV 3%

  19. LEBT upgrades for the Run 2010-11. A new Spin Rotator Solenoid “Tandem” Einzel Lens New stirrers, Buncher, (Quads?)

  20. Molecular component suppression by the double Einzel lens in the LEBT. Deepak simulations.

  21. Molecular component suppression by the double Einzel lens in the LEBT. Tk 9, current, 200 MeV 32.2 +2.8 =35.0 keV ~10-15% beam intensity losses 1.4 kV 2.0 kV Extractor Voltage, kV

  22. 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.

  23. A new superconducting solenoid. • 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.

  24. Magnetic field maps for Oxford Instr. and Toshiba solenoids. Toshiba solenoid Oxford solenoid Correction coil Rb-cell RF-power input ECR-grids Z- Bz -field component at the solenoid axis. Sona-transition

  25. A new superconducting solenoid. ECR-mode. 30 kG Contract with Cryomagnetics, Tennesi. Delivery: May, 2011

  26. Depolarization caused by spin-orbital (LS) interaction in excited 2P states. ~92% at 20 kG –low limit Most of the H aoms are produced in excited n=2 states. A high magnetic field has to be Applied in the optically-pumped vapor cell to avoid depolarization due to spin-orbital interaction.

  27. H- yield vs beam energy ~ 8.4 % at 3.0 keV beam energy

  28. Sodium-jet ionizer cell • 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.

  29. Sodium-jet ionizer cell Reservoir– operational temperature. Tres. ~500оС. Nozzle – Tn ~500оС. Collector- Na-vapor condensation: Tcoll.~120оС Trap- return line. T ~120 – 180оС. Transversal vapor flow in the N-jet cell. Reduces sodium vapor losses for 3-4 orders of magnitude, which allow the cell aperture increase up to 3.0 cm . Nozzle 500deg.C Collector ~150 deg.C NL ~2·1015 atoms/cm2 L ~ 2-3 cm Reservoir ~500 deg.C

  30. H- beam acceleration to 35 keV at the exit of Na-jet ionizer cell H- 35 keV Na-jet cell is isolated and biased to – 32 keV. The H- beam is accelerated in a two-stage acceleration system. -32 kV -28 keV -15 keV

  31. H- beam acceleration to 35 keV at the exit of Na-jet ionizer cell H- 35 keV Na-jet cell is isolated and biased to – 32 keV. The H- beam is accelerated in a two-stage acceleration system. -32 kV -28 keV -15 keV

  32. 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.

  33. 97.5% x x x After Sona-transition upgrade, Run 07 Simulations and field measurements. A new diam. 4.0” Sona-shield A new Correction Coil Optimized positions for shield and CC x

  34. Polarization vs. ionizer solenoid current with the 12mm collimator. 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: 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%)

  35. 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.

  36. High- brighthess un-polarized H- ion beam production εn ~ 0.1πmm mrad H2 –gas neutralizer cell ~ 300 mA H- ion beam H+ 3.0 keV H0 ~ 4.0 A equivalent H0 current through 2.0 cm (Diameter) Na –jet cell. Na-jet ionizer cell

  37. A new FABS test bench. TMP for He pumping

  38. FABS operation Beam energy, 7.0 keV H- current, 12 mA Arc current, 650A

  39. H- ion beam current vs beam energy (within 25 mm ionizer acceptance). H0-intensity H- current, (× 10)

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

  41. Neutral hydrogen beam intensity profile at 250 cm distance from the source. 20 mm

  42. Depolarization factors in the OPPIS. Total: 0.81-0.95 (0.9/0.8)4 ~1.6

  43. OPPIS current and polarization vs. Rb –cell vapor thickness. Higher ~105 deg Rb cell temperature 5∙1013 X 1013 Rb-cell thickness, atoms/cm^2

  44. 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.

  45. 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

  46. LSP Polarization vs. ionizer current.

  47. Polarized beams in RHIC. OPPIS 6.3∙1011(maximum 40∙1011) polarized H- /pulse. LINAC 3.6∙1011 polarized H- /pulse at 200 MeV, P=80-82% 200 uA X300us Booster 2.5∙1011 protons /pulse at 2.3 GeV Scraping in Booster AGS 2.2∙1011 p/bunch, P ~65% RHIC ~1.7∙1011 p/bunch, P~60-65% at 100GeV P ~ 53% at 250 GeV

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