CEBAF Polarized Electron Guns

1
CEBAF Polarized Electron Guns

• Marcy L. Stutzman
• for the
• Jefferson Lab
• Polarized Source Group

2
Status of the Gun 2001

• Horizontal polarized guns
• Strained layer GaAs photocathode material
  (70 polarization)
• Homemade TiSap lasers or diodes
• Vacuum not well understood
• Leaks in load-locked gun prototype

3
Photocathode Improvements

• Strained layer
• relaxation limits polarization to 70
• Superlattice material
• SLAC Small Business Innovation Research (SBIR)
  collaboration
• 85 polarization routinely
• Higher QE, 780 nm lasers
• Delicate no hydrogen cleaning
• New anodization procedure developed
• Beam from superlattice photocathodes since summer
  2005

4
Laser Improvements

• 2000 High maintenance, high power TiSap or low
  power diode lasers
• 2002 Transition to commercial TiSap lasers
  starting with G0 experiment for 32 MHz repetition
  rate, same vendor for 499 MHz regular running
• 2004 Clean room installed
• 2006 Gain-switched fiber-coupled diode laser and
  ErYb-doped fiber amplifier
• More power
• Better reliability
• Compatible with superlattice
• Final solution for CEBAF lasers?

5
Vacuum Improvements

• Better vacuum leads to longer lifetime
• Real time UHV monitoring
• Outgassing rate studies showed benefit of EP,
  vacuum fire
• Pump speed measurements quantified improvement
  with activation
• NEG coating characterization
• XHV pressure measurement?

• New load-locked gun July 2007
• Best vacuum practices
• No chemicals in HV chamber
• No Cs on electrodes
• Multiple photocathodes
• No anodization required

6
Future

• Always looking for next 100 polarization
  cathode
• Developing a micro-Mott polarimeter to
  characterize photocathodes (collaboration with
  Tim Gay, U. Nebraska)
• 100/500 kV Mott polarimeter for injector
  segmented mode
• CrO2 photocathode? half metal developed for
  spintronics
• Need to continue GaAs photocathode research -
  SBIR
• Load locked gun utilizing vacuum improvements
  will be installed in tunnel no more need for
  anodization
• We have the final last perfect laser?