CASA Welcome Overview Research Highlights Annual Report Staff Seminars
Conferences Publications Scientific Resources What's New Contact Us Internal Site

Thursday, December 7, 2006, 3:30 PM
ARC, Room 231/233

Photocathode Lifetime Measurements to 10 mA using the
New CEBAF 100 kV GaAs DC Photogun and Highlights of the
Polarized Electron Source Meeting in Kyoto,

Joe Grames

   A new 100 kV GaAs DC load locked photogun has been constructed and is run in the Test Lab for commissioning purposes and to study photocathodes producing up to 10 mA. The load locked design offers significant improvements compared with the two electron guns presently used for CEBAF operation and is planned for installation in 2007.  Improvements of photocathode handling, processing and operation in a high voltage, high vacuum environment will be described.

   A series of photocathode lifetime measurements were performed at DC beam current to 10 mA to benchmark operation of the new gun and for fundamental studies of the operation of GaAs photocathodes at high average current. Although difficult to gauge directly, we believe the new gun design has better vacuum conditions compared to the previous gun design, which is studied by means of photocathode lifetime.  In addition, lifetime measurements were performed using an activated photocathode coated with hydrogen.  These photocathodes begin with lower quantum efficiency, but exhibit increased yield when damaged, and consequently enhanced operational lifetime.  Finally, lifetime measurements were performed using a biased anode electrode, to investigate quantum efficiency decay associated with ion production outside the gun vacuum chamber.

   Finally, I will present some highlights of the Polarized Electron Source meeting in Kyoto, Japan, specifically discussion of  polarized electron and positron sources for the International Linear Collider.

Talk Slides: (Slides)

For more information, please contact Dr. Alex Bogacz, Chair of CASA Seminar Committee