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Hydrogen and Ultra-High Vacuum
Jefferson Lab Photo-Electron Gun Baked Stainless chamber Base pressure ~1e-11 Torr Pumped with Ion and NEG pumps Hydrogen dominates residual gas
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Photocathode Lifetime
Thomas Jefferson National Accelerator Facility Marcy Stutzman 26 September 2003 Photocathode Lifetime ~2.5E-11 Torr ~5.0E-11 Torr >15.0E-11 Torr J. Grames, Jefferson Lab Cathode Degradation Lifetime vs. Pressure
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Vacuum Improvements Chamber material Al, 304SS, 316L SS Coatings
TiN, SiO2, Getter Pump Speed measurements at UHV
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Conclusions Vacuum quality directly affects photocathode lifetime
Hydrogen is the primary residual gas in UHV/XHV systems We are researching diffusion barriers and pumping for UHV
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Gun 2 after bakeout, 15 September 2003
7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 -13 1.0x10 -12 -11 -10 Atomic Mass Units Torr Gun 2 after bakeout, 15 September 2003
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