1. 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

2. 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

3. Vacuum Improvements Chamber material Al, 304SS, 316L SS Coatings
TiN, SiO2, Getter
Pump Speed measurements at UHV

4. 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

5. Gun 2 after bakeout, 15 September 20037 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