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CEBAF Polarized Electron Guns

CEBAF Polarized Electron Guns. Marcy L. Stutzman for the Jefferson Lab Polarized Source Group. Status of the Gun 2001. Horizontal polarized guns Strained layer GaAs photocathode material (70% polarization) Homemade Ti:Sap lasers or diodes Vacuum not well understood

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CEBAF Polarized Electron Guns

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  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 Ti:Sap 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 Ti:Sap or low power diode lasers 2002: Transition to commercial Ti:Sap 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. ~10-10 Torr Full Scale Discharge event in beamline 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?

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