Summary Session 9B Polarized electron (positron) sources

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

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

Topics : Pol.e- source operation

Load lock (GaAs on puck) NEG pipe Laser (1 532 nm) Faraday Cup High Voltage (100 kV) Activation (Cs/NF3, 5 mm) Experimental Setup 350  m1500  m Spot Size Adjustment High average current test : JLAB pol.e- source J.Grames (JLAB)

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

Tough to measure >1000 C lifetimes with C runs! ≈ 18 Expectation: High average current test : JLAB pol.e- source J.Grames (JLAB)

High average current test Mainz pol.e- source Current density is presently limited to 1.6 A/cm mA in 100  s long pulses at 100 Hz repetition rate. Q=5.7  C per Impulse emitted area  *(1.05mm) 2 ~3.5 mm 2 hole concentration 2*10 19 cm -3 Power, W 15 Wavelength, nm 808 (fixed) Pulse length, ms Frequency, Hz 100 Beam divergence, N.A K.Aulenbacher (Mainz)

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

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

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

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

Topics : Photocathodes Development

CompositionThicknessDoping As cap GaAs QW60 A 7  cm -3 Be Al 0.36 Ga 0.64 As SL 23 A 3  cm -3 Be In Al 0.2 Ga As 51 A Al 0.4 Ga 0.6 AsBuffer 0.3  m6  cm -3 Be p-GaAs substrate MBE grown InAlGaAs/AlGaAs strained-well superlattice E g =1.543eV, Valence band splitting E hh1 - E lh1 = 60 meV, P max =92%, QE=0.6%. Y.Mamaev (St.Petersburg)

SL In Al 0.2 Ga As(5.1nm)/Al 0.36 Ga 0.64 As(2.3nm), 4 pairs Y.Mamaev (St.Petersburg) The optimization of DBR – superlattice structures is underway. polarization(max.) : 92%, Quantum efficiency : 0.6%

Material specific depolarization  emit = 3-5 ps (Mainz)  emit = 3-5 ps (Mainz) If  s < 35 ps, the spin relaxation time has a significant effect on polarization. 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. D’yakonov-Perel (DP) mechanism is dominant in low doped SL. DP mechanism comes from the spin-orbit interaction. DP mechanism comes from the spin-orbit interaction. Find materials with a smaller spin-orbit interaction. Find materials with a smaller spin-orbit interaction. GaN GaP GaAs GaSb GaN GaP GaAs GaSb  SO (eV)  SO (eV) Try GaAs/InGaP strained-superlattice Try GaAs/InGaP strained-superlattice P 0 : Initial polarization P 0 : Initial polarization  s : spin relaxation time  s : spin relaxation time  emit : photoemission time  emit : photoemission time P BBR : depolarization at BBR P BBR : depolarization at BBR T.Maruyama (SLAC)

Spin relaxation rate based on D’yakonov-Perel mechanism  : spin-orbit-induced spin splitting coefficient  : spin-orbit-induced spin splitting coefficient E 1e : confinement energy E 1e : confinement energy Narrower well has a larger confinement energy. Narrower well has a larger confinement energy. Larger confinement energy  Larger confinement energy  Less vertical transport, thus lower QE Less vertical transport, thus lower QE More scattering, thus lower polarization. More scattering, thus lower polarization.  s ~ 10 ps  s ~ 2 ps T.Maruyama (SLAC)

Superlattice structure affects dramatically 1.5 nm GaAs + 4 nm In 0.65 Ga 0.35 P4 nm GaAs nm In 0.65 Ga 0.35 P QE ~ 0.002% Pol ~ 40% QE ~ 0.01% Pol ~ 68% T.Maruyama (SLAC)

Structure of gridded cathode CompositionThicknessDoping p- GaAs substrate, 5x10 18 cm -3 Zn doped Al.3 Ga.7 As buffer 5x10 18 cm -3 Be doped GaAs,AlGaAs, GaAsP/GaAs active region 90nm cm -3 Be doped GaAs surface region 5-10nm 1- 5x10 19 cm -3 Be doped MBE grown high surface/low active doping gridded cathode 0.3um W film, Ohmic contact Metal grid, Schottky contact K.Ioakeimidi (SLAC)

Thin GaAs films with 4mm 2D grid and 48mm pitch QE&Polarization - gridded samples 5x10 16 cm -3 K.Ioakeimidi (SLAC) 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

M.Kuwahara (Nagoya) 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.

Topics : Low Emittance Beam Production

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

Low Emittance Beam extraction from GaAs-GaAsP superlattice photocathode  rms : 0.096±0.015 .mm.mrad N.Yamamoto (Nagoya)

Topics : Polarized electron source for SPLEEM

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

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

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

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

S.Okumi (Nagoya)

Topics : Pol.e ± Source for ILC

L- band bunc her 6.4 nC, 2 ns ILC e- injector with SLC gun and drift distance to SHB  bend DC gun SHB1SHB2 Two 5-cell L-band Two 50-cell NC L-band pre-acceleration All units in cm …… J.E.Clendenin (SLAC)ParameterUnitsAt gun exit After bunchers*ChargenC Bunch length (FWHM) ps Deg. L- band Energy/Energy spread MeV /0.09 (0.95%) Normalized rms emittance m n/a43 PARMELA results

M.Yamamoto (Nagoya) Solenoid 4.8nC,  16mm [m] anode Solenoid 200kV,1.0ns,4.8nC SHB1SHB [m] 108MHz433MHz 200keV,4.8nC,1.0ns Similar geometry of TESLA (Aline Curtoni et al).  rms ~ 9.7 pi.mm.mrad Beam Simulation (Nagoya 200keV Gun)

A.Brachmann (SLAC) Schematic Layout

A.Brachmann (SLAC) Two 5-cell SW L-band108MHz SHB 433 MHz SHB 1 st TW Structure2 nd TW Structure matching triplet Low Energy Beam Line and Bunching System Simulations including Space Charge

Spin Rotation using Solenoids 5 GeV Bend of n * o Odd Integer S longitudonal ~ 7.5 m DR Pair of Solenoids (SC) S vertical (Precession) S transverse (Rotation) ILC design: n = 7  o Depolarization in arc due to energy spread: Arc bending angleθ = o Spin precession angle  =(7/2)  Energy spreadΔ  /  = ±0.02 GeV Depolarization (analytic)ΔP/P = Particle trackingΔP/P = A.Brachmann (SLAC)

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

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

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

P.Shuler (DESY) The E166 Experiment

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