Status report of the new Darmstadt polarized electron injector

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Status report of the new Darmstadt polarized
electron injector
Yuliya Poltoratska PESP2008, 1.10.2008

• S-DALINAC
• Polarized electron source
• Requirements
• Electron gun
• Characterization of the electron beam
• Implementation at the S-DALINAC

Supported by DFG through SFB 634 and GRK 410
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S-DALINAC
Experiment sites
Injector Photon scattering
Tagger Photon scattering
Experiment to determine nucleon polarizability
QClam spectrometer
High-resolution spectrometer
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S-DALINAC
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Planned experiments

• Polarized electron and photon scattering
• Parity-violation effects
• ? Polarized bremsstrahlung
• Measurement of the additional structure
  functions
• (polarized electron scattering)
• Low-q (lt 1 fm-1) experiments with polarized
  beams ? Completely unexplored field

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Polarized source requirements

• Polarization 80
• Average current gt 60 µA
• Repetition frequency 3 GHz
  cw
• Long lifetime
• Short maintenance period
• Compact form
• ?max. height including safety distance 2.3 m

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Test stand

• Cathode material GaAs
• Laser wavelength 830 nm

Preparation system
Electron gun
Alpha magnet
Chopper
Wien filter
Differential pumping stage
Laser system
Mott Polarimeter
Prebuncher
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Electrode

• EM Simulations
• Cathode surface E 0.85 MV/m
• Edges
• E 4 MV/m

• Fabrication
• Material 1.4429-ESU (316 LN)
• High polished surface

(CST EM StudioTM).
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Vacuum system

• Achieved vacuum pressure (after 12 days bake out
  _at_ 220 C )
• Cathode and preparation chambers
• lt 1.810-11 mbar (detection limit)
• HV beam line after DPS 6.010-9 mbar
• Cathode vacuum life-time (456 30)h

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Laser system
Single mode Laser diode Sanyo DL-8032-001
(Wavelength 830 nm) Semiconductor amplifier
Toptica TA 100 (optional)
Laser Lab
Optics assembly below the source

• 79 ps pulse length measured, limited by
  bandwidth of osciloscope

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Spin manipulation and polarimetry
Preparation system
Electron gun
Alpha magnet
Chopper
Differential pumping stage
Laser system
Prebuncher
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Degree of Polarization

• Elimination of the instrumental asymmetry by
  helicity switching
• Foil thickness extrapolation self supported
  gold foils 40 - 500 nm

Bulk GaAs
Bulk GaAs P (35.5
1.4) Strained superlattice P (86 3)
(830 nm) P (76 2) (808 nm)
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Beam characteristics
Bulk GaAs (?830 nm) en,x (0.146 0.037) mm
mrad en,y (0.197 0.089) mm mrad
Electron gun
Preparation system
Alpha magnet
Alpha magnet
Alpha magnet
Alpha magnet
Chopper
Wien fliter
Differential pumping stage
Laser system
Mott polarimeter
Prebuncher
Fluorescent screen
Wire scanner
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S-DALINAC Polarized Injector (SPIN)
100 keV Polarized Electron Gun
200 keV Thermionic Electron Gun
250 keV Thermionic Electron Gun
Experimental Area
10 MeV Injector
To Experimental Hall
40 MeV Linac
1st Recirculation
2nd Recirculation
Optical Fiber From Optics Lab
5 m
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SPIN at S-DALINAC
Transport for 100 keV polarized and 200 keV
unpolarized beams
Preparation system
Polarized electron gun
Injector cryostat
Prebuncher system
Wien filter
Chopper
Mott polarimeter
Differential pumping stages
1 m
Optical fiber from laser lab
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Polarimeters
A
i
Source
ii
Source of Polarized Electrons
Laser Systems
Polarimeters
100 keV Mott Polarimeter
Møller Polarimeter
10 MeV Mott Polarimeter
Compton Transmission Polarimeter
Experiments with polarized electrons/photons
(Christian Eckardt, Poster Session)
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Summary

• Test stand set up and put into operation
  successfully
• Required vacuum pressure in the electron source
  achieved
• Beam parameters
• Energy
  100 keV
• Duty cycle
  3 GHz cw
• Normalized Transverse Emittance (x) (0.146
  0.037) mm mrad
• (y) (0.197
  0.089) mm mrad
• Degree of polarization
• Bulk
  (35.4 1.4)
• Strained-Superlattice
  (86 3)

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Outlook

• Intensity stabilization
• Further improvement of cathode lifetime
• Chopper-Prebuncher system
• Titanium-Sapphire laser for pulsed operation of
  SPIN
• Installation at the S-DALINAC starting 2009
• Installation comissioning of polarimeters for
  experiments
• Experiments middle09

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Collaboration
Institut für Kernphysik, TU Darmstadt R. Barday,
U. Bonnes, M. Brunken, C. Eckardt, R.
Eichhorn, J. Enders, C. Heßler, C. Ingenhaag, M.
Platz, M. Roth, M. Wagner Institut für Theorie
Elektromagnetischer Felder, TU Darmstadt W.
Ackermann, W. F. O. Müller, B. Steiner, T.
Weiland Institut für Kernphysik, Universität
Mainz K. Aulenbacher
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Electron energy

• 100 keV injection energy to the superconducting
  Linac
• 2-cell capture structure necessary

V-Code simulations
Injection energy Thermionic gun 200
keV Polarized gun 100 keV
V-Code M. Krassilnikov, A. Novokhatski, T.
Weiland, W. Koch, P. Castro, ICAP2000, Darmstadt
(2000)
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100 keV Mott and Wien filter