Summary Workshop Polarized Electron Sources and Polarimeters PESP2004 October 79 2004 presented by K

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SummaryWorkshop Polarized Electron Sources
and Polarimeters PESP-2004October 7-9
2004presented by Kurt Aulenbacher (IKP, Mainz)
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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
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Grouping together important subjects

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

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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 Proble
m Find the best compromise Towards Polarization
and QE Best structure/lowest transport
losses NEA-losses?
VB
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Parameters of strain-compensated SLs Gerchikov
(Theory), Mamaev(exp)
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Fit to Data with Parameters VB-scattering/smearin
g...(Gerchikov, SPTU) Matrix elements,
splitting,QSEtheory Probematic
transport/emission depol/surface-states
GaAs0.83P0.17/Al0.1In0.18Ga0.72As (4x5nm)x20
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SLs with P gt 80 1 QE, low activation
temperature! (MAMAEV, SPTU) (InAlGaAs, GaAs)
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Promising option GaAs/GaAsP

• Achieves high QE (1), high P (86) and low
  Anisotropy (lt2) (Maruyama, SLAC)
• Experimental observation of P and QE Spectra
  gives tool to identifiy if structure is in
  agreement with predictions (Kuwahara, Nagoya)
• Nagoya P92-6 observed at 0.3 QE
• SLAC Photovoltage effects are well under
  control 1012 electrons in 60ns (suitable for
  NLC). Charge relaxation time constant is of order
  lt10ns (emittance ??)

Polarimeter accuuracy is limiting factor in
comparison of record polarisations!!!!
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• Time resolved studies
• Reveal
• not all superlattices
• Have fast response with
• low depolarisation
• first electrons have highest
• Polarisation P91-4.5
• (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,

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Operating sources for high energy exp.

• c.w. regime
• JLAB
• MAMI/Mainz

• Pulsed regime
• SLAC
• MIT/Bates (Storage (BLAST)/LINAC(Sample))
• ELSA/Bonn

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Highlights of c.w. operation
Very high reliability/availability Polarisation
80 Average currents up to 200 Mikroamps (Poelker
JLAB) Current stability on target DI/Ilt10-3
HC-I- asymmetry lt1ppm, Energy stability DE/E
10-6, HC-E-asymmetry lt310-8 (Maas,
IKP-Mainz), Present day PV-experiments are
limited by statistics, rather than HC-systematic
effects
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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
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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)

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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 lt10-3 (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)

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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 104 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

BUTIts worthwhile
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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 lt1meV Thermal conductivity optimized
to 20deg/Watt Would thermally allow to produce
gt7mA 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
lt10-5 and high extractabe charge (i1mA, C200
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!
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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)
• gt90 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)

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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.