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Summary Session 9B

Summary Session 9B. Polarized electron (positron) sources. Session 9B : Polarized electron (positron) sources. Presentations oral : 15 poster : 6. 11 groups. JLAB, SLAC, Univ. of Mainz, Univ. of Bonn, CERN, DESY, St. Petersburg., KEK, Osaka Electro-Communication Univ.,

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Summary Session 9B

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  1. SummarySession 9B Polarized electron (positron) sources

  2. Session 9B : Polarized electron (positron) sources • Presentations • oral : 15 • poster : 6 11 groups JLAB, SLAC, Univ. of Mainz, Univ. of Bonn, CERN, DESY, St. Petersburg., KEK, Osaka Electro-Communication Univ., Rikkyo Univ., and Nagoya Univ.,

  3. Topics • Pol.e- source operation • High average current operation • High current density test • Photocathodes Development • strained super-lattice photocathode • gridded photocathode, pyramidal shape photocathode • Low Emittance Beam Production • Polarized electron source for SPLEEM • Pol.e±Source for ILC • Polarized electron beam injector • Polarized positron beam production

  4. Topics : Pol.e- source operation

  5. High average current test :JLAB pol.e- source Experimental Setup Faraday Cup Laser (1 W @ 532 nm) High Voltage (100 kV) NEG pipe Activation (Cs/NF3, 5 mm) Spot Size Adjustment 350 mm 1500 mm Load lock (GaAs on puck) J.Grames (JLAB)

  6. laser light IN electron beam OUT anode residual gas cathode Ionized residual gas strikes photocathode Ion damage distributed over larger area Can increasing the laser spot size improve charge lifetime? (Best Solution – Improve Vacuum, but this is not easy) Bigger laser spot, same # electrons, same # ions J.Grames (JLAB)

  7. 2 1500 Expectation: ≈ 18 350 High average current test :JLAB pol.e- source Tough to measure >1000 C lifetimes with 100-200 C runs! 5 15 J.Grames (JLAB)

  8. High average current test Mainz pol.e- source emitted area p*(1.05mm)2~3.5 mm2 hole concentration 2*1019 cm-3 Current density is presently limited to 1.6 A/cm2. 57 mA in 100 ms long pulses at 100 Hz repetition rate. Q=5.7 mC per Impulse K.Aulenbacher (Mainz)

  9. Non-linear effects 1: Cathode heating We are here at I=1mA (QE=20mA/W) Photocathode vacuum lifetime normalized to the vacuum lifetime at the laser power 23 mW (>300h) (no current drawn during ill.). K.Aulenbacher (Mainz)

  10. High current density test Nagoya pol.e- source M.Yamamoto (Nagoya) bunch charge : 3.3pC/bunch Laser Spot size : f~1.6mm(2s) bunch width : ~30ps (estimate) Peak current density (estimate) : ~240 mA/mm2 Bunch width (FWHM): 1.6ns Bunch charge : 8nC Laser spot size : f~20mm, Peak current density ~18 mA/mm2 No Charge Limit

  11. P = 80% @ 830 nm QE = 0.2 % Load-lock gun operation at Univ.Bonn M.Eberhardt and J.Wittschen (Bonn)

  12. New Load-Lock at Univ.Bonn M.Eberhardt and J.Wittschen (Bonn)

  13. Topics : Photocathodes Development

  14. MBE grown InAlGaAs/AlGaAs strained-well superlattice Eg=1.543eV, Valence band splitting Ehh1 - Elh1 = 60 meV, Pmax=92%, QE=0.6%. Y.Mamaev (St.Petersburg)

  15. SL In0.155Al 0.2Ga0.645As(5.1nm)/Al0.36Ga0.64As(2.3nm), 4 pairs polarization(max.) : 92%, Quantum efficiency : 0.6% The optimization of DBR – superlattice structures is underway. Y.Mamaev (St.Petersburg)

  16. Material specific depolarization • P0: Initial polarization • s : spin relaxation time • emit : photoemission time • PBBR: depolarization at BBR • emit= 3-5 ps (Mainz) • If s < 35 ps, the spin relaxation time has a significant effect on polarization. • D’yakonov-Perel (DP) mechanism is dominant in low doped SL. • DP mechanism comes from the spin-orbit interaction. • Find materials with a smaller spin-orbit interaction. GaN GaP GaAs GaSb SO (eV) 0.01 0.08 0.34 0.76 • Try GaAs/InGaP strained-superlattice T.Maruyama (SLAC)

  17. Spin relaxation rate based on D’yakonov-Perel mechanism •  : spin-orbit-induced spin splitting coefficient • E1e: confinement energy s ~ 2 ps s ~ 10 ps • Narrower well has a larger confinement energy. • Larger confinement energy  • Less vertical transport, thus lower QE • More scattering, thus lower polarization. T.Maruyama (SLAC)

  18. Superlattice structure affects dramatically 1.5 nm GaAs + 4 nm In0.65Ga0.35P 4 nm GaAs + 1.5 nm In0.65Ga0.35P QE ~ 0.002% Pol ~ 40% QE ~ 0.01% Pol ~ 68% T.Maruyama (SLAC)

  19. Structure of gridded cathode MBE grown high surface/low active doping gridded cathode Metal grid, Schottky contact Composition Thickness Doping GaAs surface region5-10nm 1- 5x1019cm-3 Be doped GaAs,AlGaAs, GaAsP/GaAs active region90nm 1014 - 1018 cm-3 Be doped Al.3Ga.7As buffer 5x1018cm-3 Be doped p- GaAs substrate, 5x1018cm-3 Zn doped 0.3um W film, Ohmic contact K.Ioakeimidi (SLAC)

  20. QE&Polarization - gridded samples Thin GaAs films with 4mm 2D grid and 48mm pitch 5x1016cm-3 • Monte Carlo simulations indicate that the QE-Polarization trade off can be broken by accelerating the electrons in the active region • Preliminary experimental results indicate a 1% increase in polarization K.Ioakeimidi (SLAC)

  21. Pol.e- extraction from Pyramid-shaped Photocathode • Extraction of polarized electrons by F.E. • Electrons extracted by F.E. have higher polarization than NEA’s. • long lifetime compared with NEA surface. M.Kuwahara (Nagoya)

  22. Topics : Low Emittance Beam Production

  23. Low Emittance Beam extraction from GaAs-GaAsP superlattice photocathode N.Yamamoto (Nagoya)

  24. Low Emittance Beam extraction from GaAs-GaAsP superlattice photocathode erms : 0.096±0.015 p.mm.mrad N.Yamamoto (Nagoya)

  25. Topics : Polarized electron source for SPLEEM

  26. SURFACE SENSITIVE LEEM (Low Energy Electron Microscopy) Low energy electrons: strong interaction with surfaces - relatively high reflectivity - small penetration depth Reflection Diffraction Electrons sample energy filter energy filter CCD camera e- source electron optics beam separator screen objective lens manipulator HV sample 20cm Yasue (Osaka Elec.Comuni.Univ)

  27. f=-90o f=-45o f=0o f=45o f=90o CONTRAST: P·M f M M M P SPLEEM IMAGE Spin Polarized LEEM (SPLEEM) Co/W(110) 3.8eV FOV=25mm in-plane P //M: maximum (minimum) P  M: 0 Yasue (Osaka Elec.Comuni.Univ)

  28. SPLEEM Contrast: HIGH POLARIZATION For higher magnification For much faster acquisition Exchange Asymmetry A REQUIREMENT FAST ACQUISITION OF SPLEEM IMAGE HIGH BRIGHTNESS (HIGH INTENSITY) SOURCE Yasue (Osaka Elec.Comuni.Univ)

  29. Concept of extracting high brightness beam focusing length ~ 4mm spot size ~ 3mm S.Okumi (Nagoya)

  30. S.Okumi (Nagoya)

  31. Topics : Pol.e±Source for ILC

  32. … … L-band buncher ILC e- injectorwith SLC gun and drift distance to SHB1 All units in cm 202 75 33 10 20 5 75 20 bend SHB1 SHB2 Two 5-cell L-band Two 50-cell NC L-band pre-acceleration DC gun 6.4 nC, 2 ns PARMELA results J.E.Clendenin (SLAC)

  33. SHB2 SHB1 Beam Simulation (Nagoya 200keV Gun) Solenoid erms ~ 9.7 pi.mm.mrad Solenoid 4.8nC, f16mm 200kV,1.0ns,4.8nC anode 0 0.15 0.5[m] 200keV,4.8nC,1.0ns 108MHz 433MHz 0 1.0 3.0 3.4[m] Similar geometry of TESLA 2001-22 (Aline Curtoni et al). M.Yamamoto (Nagoya)

  34. Schematic Layout A.Brachmann (SLAC)

  35. Low Energy Beam Line and Bunching System Simulations including Space Charge matching triplet 108MHz SHB Two 5-cell SW L-band 1st TW Structure 2nd TW Structure 433 MHz SHB A.Brachmann (SLAC)

  36. Svertical (Precession) Stransverse (Rotation) Pair of Solenoids (SC) DR Spin Rotation using Solenoids Slongitudonal ~ 7.5 m 5 GeV Depolarization in arc due to energy spread: Bend of n * 7.9312o Odd Integer Arc bending angle θ= 55.51o Spin precession angle  =(7/2) Energy spread Δ/ = ±0.02 GeV Depolarization (analytic) ΔP/P = 0.024 Particle tracking ΔP/P = 0.007 ILC design: n = 7  55.51o A.Brachmann (SLAC)

  37. Laser-Based Polarized e+ Source for ILC T.Omori (KEK)

  38. A = 0.90 ± 0.18 % Pol. = 73 % M. Fukuda et al., PRL 91(2003)164801 T.Omori (KEK)

  39. Re-use Concept laser pulse stacking cavities Compton ring positron stacking in main DR Electron storage ring to main linac T.Omori (KEK)

  40. The E166 Experiment P.Shuler (DESY)

  41. Pol.e+ (max.) : ~80% P.Shuler (DESY)

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