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Statistics: 34 participants from 16 different institutions 8 sessions, 24 talks Poster session

Summary Workshop Polarized Electron Sources and Polarimeters PESP-2004 October 7-9 2004 presented by Kurt Aulenbacher (IKP, Mainz). PESP-2004 Hosted by: Institut für Kernphysik der Universität Mainz Mainz, Germany Sponsored by: Institut für Kernphysik, University of Mainz,

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Statistics: 34 participants from 16 different institutions 8 sessions, 24 talks Poster session

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  1. SummaryWorkshop Polarized Electron Sources and Polarimeters PESP-2004October 7-9 2004presented by Kurt Aulenbacher (IKP, Mainz)

  2. PESP-2004 Hosted by: Institut für Kernphysik der Universität Mainz Mainz, Germany Sponsored by: Institut für Kernphysik, University of Mainz, Committee for Spin Physics Symposia, Deutsche Forschungsgemeinschaft Statistics: 34 participants from 16 different institutions 8 sessions, 24 talks Poster session Round table discussion: Polarized source requirements for the ILC

  3. Grouping together important subjects • Photocathode/Photoemission (basic) research (9 talks) • Source system performance (7 talks) • Subsystems (6 talks) • Future requirements (3 talks, round table)

  4. CB s+ Photoemission from semicoductors Basic idea: Polarisation by helicity transfer: Photabsorbtion withhin the bandstructure of suitable semiconductor 3-step procedure: Photoabsorbtion Transport to the surface Emission through NEA-surface: Problem: Find the best compromise Towards Polarization and QE: Best structure/lowest transport losses NEA-losses? VB

  5. Composition Thickness Doping As cover GaAs QW 60 A 11019 cm-3 Zn GaAs0.75P0.25 SL 40 A 41017 cm-3 Zn In0.16Al0.14Ga0.7As 40 A Al0.3Ga0.7As Buffer 0.5 mm 61018 cm-3 Zn p-GaAs substrate, Zn doped Parameters of strain-compensated SLs Gerchikov (Theory), Mamaev(exp)

  6. Fit to Data with Parameters VB-scattering/smearing...(Gerchikov, SPTU) Matrix elements, splitting,QSE:theory Probematic: transport/emission depol/surface-states GaAs0.83P0.17/Al0.1In0.18Ga0.72As (4x5nm)x20

  7. SL‘s with P > 80% ; 1% QE, low activation temperature! (MAMAEV, SPTU) (InAlGaAs, GaAs)

  8. Promising option: GaAs/GaAsP • Achieves high QE (1%), high P (86%) and low Anisotropy (<2%) (Maruyama, SLAC) • Experimental observation of P and QE Spectra gives tool to identifiy if structure is in agreement with predictions (Kuwahara, Nagoya) • Nagoya: P=92%+-6 observed at 0.3% QE • SLAC: Photovoltage effects are well under control: 10^12 electrons in 60ns (suitable for NLC). Charge relaxation time constant is of order <10ns (emittance ??) Polarimeter accuuracy is limiting factor in comparison of ‚record‘ polarisations!!!!

  9. Time resolved studies • Reveal: • not all superlattices • Have fast response with • low depolarisation • ‚first‘ electrons have highest • Polarisation P=91+-4.5% • (Mainz data)even higher P • Is possible • Emission from surface • States always contributes, • Can be taken as • ‚quality check‘ (Terekhov • Novosibirsk) • Theoretica understanding of • Cs-O covered NEA surface • Is under way, • but not yet complete • (Kulkova,Tomsk)

  10. c.w. regime: JLAB MAMI/Mainz Pulsed regime: SLAC MIT/Bates (Storage (BLAST)/LINAC(Sample)) ELSA/Bonn Operating sources for high energy exp.

  11. Highlights of c.w. operation: Very high reliability/availability Polarisation 80+ Average currents up to 200 Mikroamps (Poelker JLAB) Current stability on target DI/I<10^-3 HC-I- asymmetry <1ppm, Energy stability DE/E =10^-6, HC-E-asymmetry <3*10^-8 (Maas, IKP-Mainz), Present day PV-experiments are limited by statistics, rather than HC-systematic effects

  12. Pulsed operation (storage ring) M. Frakondeh, MIT-Bates • Highly automated ring fill and BLAST data taking based on EPICS controls system. 6-8 K Coulombs per day on tape

  13. Polarimeters • Compton backscattering polarimeter with 850 MeV beam integrated in lasercavity (J. Imai, Mainz) • Ultracompact spin analyzer for low energy electrons based on transmission of magnetic thin films (D. Lamine, EcolePolytechnique, Palaiseau) • High accuracy Mott-polarimeter at 3.5 MeV, with double focussing spectrometers (V. Tioukine, Mainz)

  14. Experimental techniques • Hydrogen cleaning: reduces activation temperature of photocathodes from typ. 580 to 450 °C (Maruyama, SLAC) • Very reliable q-switched lasers for pulsed operation (Brachmann, SLAC), • 31MHz and 499 Mhz rep-rate synchro-Lasers (Titanium-sapphire) with 70 pikosecond pulse length commercially available (Poelker, JLAB) • 2.5 GHz rep rate 40ps semiconductor synchro-laser with rms stability <10^-3 (Mainz) • Field emission ‚fundamental‘ studies at Nagoya: Very high static field gradients possible with Mo/Ti Kathode/Anode Combination; 170MV/m at 1nA (but low gap separation)

  15. Photocathode lifetime: • Lifetime well sufficient for present day accelerators.Extractable charges in one lifetime several hundert C. • ELIC-type accelerators could require extractable charges of 10^4 Coulomb (talk by M.Farkondeh), depending on accelerator design. • High c.w. current + low emittance + good lifetime + high polarization is problematic, the simultaneous tasks cause interacting problems BUT:It‘s worthwhile

  16. Test experiments with bulk-GaAs 200 keV (Yamamoto, Nagoya) Gun at Nagoya 350 keV (JLAB): Both are making good progress: low emittance, high current density Vacuum lifetime of photocathodes is considerably smaller than ‚standard‘ sources. Field emission? Vacuum problems? Ultracold GaAs source at Heidelberg: (talk by D. Orlov): transverse energy distribution <1meV Thermal conductivity optimized to 20deg/Watt: Would ‚thermally‘ allow to produce >7mA average current from SL-Kathode (high polarization) Mask activation (Grames, JLAB) offers reduction of transmission Losses, and ion backbombardment Large emittance beams (2mm dia at Cathode) can be transported with losses <10^-5 and high extractabe charge (i=1mA, C=200 Coulomb, Mainz), guns with extreme pumping speed (JLAB, Nagoya) and reduction of outgassing by NEG coating (Mainz) are in prepartion TEST OF ‚nonlinear‘ current induced lifetime effects necessary!

  17. ILC-round table • S-RF design: low frequency, large acceptance loosens restrictions towards emittance & bunch length: Conservative HV-design possible, but again: low emittance high gradient high potential, desirable but must not compromise availability • Long bunch train not yet demonstrated (should be no problem) • >90% beam polarization desirable: +1% in P +2% higher ‚statistical ROI‘ of collider investment. • International Photocathode research should be cordinated to find comparable testing conditions • Polarized positron sources are well under way, two approaches in cirular gamma ray production: Helical ondulator (Leihem, DESY) and Compton backscattering (Omori, KEK)

  18. Summary of Summary • Existing sources work well. • 90% Polarization barrier is about to be broken • Great potential of Photoemission source for higher c.w. currents. • may be necessary to realize it for future accelerators. • PESP-2004 proceedings will be published togehter with this conference.

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