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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 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 • Leaks in load-locked gun prototype
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
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?
~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
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?