GTS meeting 5 17 16

• Generated beam at 275kV[1]
  • No real limitation on voltage, we stopped there b/c we observed 'beam' on the viewer. Fearing it would be Field Emission from the multi-alkali photocathode, we stopped at this voltage.
  • Later on we realized it was real photoemission beam from ambient light being picked up through the gun laser input viewport!
  • This indicated right away that the multi-alkali photocathode has good QE, contrary to what we estimated in the cathode prep chamber, see discussion below
  • We ran with the least possible amount of laser power
  • 

• We need to fix the following:
  • Two viewer cameras (old, removed from FEL) have radiation damage, hard to see the image
  • Make a shade to prevent ambient room light reaching the photocathode
  • Carlos to coordinate with RadCon for Rad measurements during beam steering to get permission to run at full current.

• What we must do, it would be essential, and really cool!
  • Carlos to contact software to get Keithely Dump current in EPICS
  • Shukui and Carlos to work with software for re-commissioning cathode QE scanner. This will have to be done with the gun biased at ~1kV

• Measuring QE in the cathode prep chamber with the slope of I vs Laser Power to make sure we stay away from charge saturation
  • Media:Surface charge limit QE calculation GTS cathode May 12 2016.pdf

• Let's discuss beam measurements plans!